train_cmd.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#include "stdafx.h"
#include "error.h"
#include "articulated_vehicles.h"
#include "command_func.h"
#include "error_func.h"
#include "pathfinder/yapf/yapf.hpp"
#include "news_func.h"
#include "company_func.h"
#include "newgrf_sound.h"
#include "newgrf_text.h"
#include "strings_func.h"
#include "viewport_func.h"
#include "vehicle_func.h"
#include "sound_func.h"
#include "ai/ai.hpp"
#include "game/game.hpp"
#include "newgrf_station.h"
#include "effectvehicle_func.h"
#include "network/network.h"
#include "core/random_func.hpp"
#include "company_base.h"
#include "newgrf.h"
#include "order_backup.h"
#include "zoom_func.h"
#include "newgrf_debug.h"
#include "framerate_type.h"
#include "train_cmd.h"
#include "misc_cmd.h"
#include "timer/timer_game_calendar.h"
#include "timer/timer_game_economy.h"
 
#include "table/strings.h"
#include "table/train_sprites.h"
 
#include "safeguards.h"
 
static Track ChooseTrainTrack(Train *v, TileIndex tile, DiagDirection enterdir, TrackBits tracks, bool force_res, bool *got_reservation, bool mark_stuck);
static bool TrainCheckIfLineEnds(Train *v, bool reverse = true);
bool TrainController(Train *v, Vehicle *nomove, bool reverse = true); // Also used in vehicle_sl.cpp.
static TileIndex TrainApproachingCrossingTile(const Train *v);
static void CheckIfTrainNeedsService(Train *v);
static void CheckNextTrainTile(Train *v);
 
static const uint8_t _vehicle_initial_x_fract[4] = {10, 8, 4,  8};
static const uint8_t _vehicle_initial_y_fract[4] = { 8, 4, 8, 10};

template <>
bool IsValidImageIndex<VEH_TRAIN>(uint8_t image_index)
{
  return image_index < lengthof(_engine_sprite_base);
}
 

uint8_t FreightWagonMult(CargoType cargo)
{
  if (!CargoSpec::Get(cargo)->is_freight) return 1;
  return _settings_game.vehicle.freight_trains;
}

void CheckTrainsLengths()
{
  bool first = true;
 
  for (const Train *v : Train::Iterate()) {
    if (v->First() == v && !v->vehstatus.Test(VehState::Crashed)) {
      for (const Train *u = v->GetMovingFront(), *w = v->GetMovingNext(); w != nullptr; u = w, w = w->GetMovingNext()) {
        if (u->track != TRACK_BIT_DEPOT) {
          if ((w->track != TRACK_BIT_DEPOT &&
              std::max(abs(u->x_pos - w->x_pos), abs(u->y_pos - w->y_pos)) != u->CalcNextVehicleOffset()) ||
              (w->track == TRACK_BIT_DEPOT && TicksToLeaveDepot(u) <= 0)) {
            ShowErrorMessage(GetEncodedString(STR_BROKEN_VEHICLE_LENGTH, v->index, v->owner), {}, WL_CRITICAL);
 
            if (!_networking && first) {
              first = false;
              Command<Commands::Pause>::Post(PauseMode::Error, true);
            }
            /* Break so we warn only once for each train. */
            break;
          }
        }
      }
    }
  }
}

void Train::ConsistChanged(ConsistChangeFlags allowed_changes)
{
  uint16_t max_speed = UINT16_MAX;
 
  assert(this->IsFrontEngine() || this->IsFreeWagon());
 
  const RailVehicleInfo *rvi_v = RailVehInfo(this->engine_type);
  EngineID first_engine = this->IsFrontEngine() ? this->engine_type : EngineID::Invalid();
  this->gcache.cached_total_length = 0;
  this->compatible_railtypes = {};
 
  bool train_can_tilt = true;
  int16_t min_curve_speed_mod = INT16_MAX;
 
  for (Train *u = this; u != nullptr; u = u->Next()) {
    const RailVehicleInfo *rvi_u = RailVehInfo(u->engine_type);
 
    /* Check the this->first cache. */
    assert(u->First() == this);
 
    /* update the 'first engine' */
    u->gcache.first_engine = this == u ? EngineID::Invalid() : first_engine;
    u->railtypes = rvi_u->railtypes;
 
    if (u->IsEngine()) first_engine = u->engine_type;
 
    /* Set user defined data to its default value */
    u->tcache.user_def_data = rvi_u->user_def_data;
    this->InvalidateNewGRFCache();
    u->InvalidateNewGRFCache();
  }
 
  for (Train *u = this; u != nullptr; u = u->Next()) {
    /* Update user defined data (must be done before other properties) */
    u->tcache.user_def_data = GetVehicleProperty(u, PROP_TRAIN_USER_DATA, u->tcache.user_def_data);
    this->InvalidateNewGRFCache();
    u->InvalidateNewGRFCache();
  }
 
  for (Train *u = this; u != nullptr; u = u->Next()) {
    const Engine *e_u = u->GetEngine();
    const RailVehicleInfo *rvi_u = &e_u->VehInfo<RailVehicleInfo>();
 
    if (!e_u->info.misc_flags.Test(EngineMiscFlag::RailTilts)) train_can_tilt = false;
    min_curve_speed_mod = std::min(min_curve_speed_mod, u->GetCurveSpeedModifier());
 
    /* Cache wagon override sprite group. nullptr is returned if there is none */
    u->tcache.cached_override = GetWagonOverrideSpriteSet(u->engine_type, u->cargo_type, u->gcache.first_engine);
 
    /* Reset colour map */
    u->colourmap = PAL_NONE;
 
    /* Update powered-wagon-status and visual effect */
    u->UpdateVisualEffect(true);
 
    if (rvi_v->pow_wag_power != 0 && rvi_u->railveh_type == RAILVEH_WAGON &&
        UsesWagonOverride(u) && !HasBit(u->vcache.cached_vis_effect, VE_DISABLE_WAGON_POWER)) {
      /* wagon is powered */
      u->flags.Set(VehicleRailFlag::PoweredWagon); // cache 'powered' status
    } else {
      u->flags.Reset(VehicleRailFlag::PoweredWagon);
    }
 
    if (!u->IsArticulatedPart()) {
      /* Do not count powered wagons for the compatible railtypes, as wagons always
         have railtype normal */
      if (rvi_u->power > 0) {
        this->compatible_railtypes.Set(GetAllPoweredRailTypes(u->railtypes));
      }
 
      /* Some electric engines can be allowed to run on normal rail. It happens to all
       * existing electric engines when elrails are disabled and then re-enabled */
      if (u->flags.Test(VehicleRailFlag::AllowedOnNormalRail)) {
        u->railtypes.Set(RAILTYPE_RAIL);
        u->compatible_railtypes.Set(RAILTYPE_RAIL);
      }
 
      /* max speed is the minimum of the speed limits of all vehicles in the consist */
      if ((rvi_u->railveh_type != RAILVEH_WAGON || _settings_game.vehicle.wagon_speed_limits) && !UsesWagonOverride(u)) {
        uint16_t speed = GetVehicleProperty(u, PROP_TRAIN_SPEED, rvi_u->max_speed);
        if (speed != 0) max_speed = std::min(speed, max_speed);
      }
    }
 
    uint16_t new_cap = e_u->DetermineCapacity(u);
    if (allowed_changes.Test(ConsistChangeFlag::Capacity)) {
      /* Update vehicle capacity. */
      if (u->cargo_cap > new_cap) u->cargo.Truncate(new_cap);
      u->refit_cap = std::min(new_cap, u->refit_cap);
      u->cargo_cap = new_cap;
    } else {
      /* Verify capacity hasn't changed. */
      if (new_cap != u->cargo_cap) ShowNewGrfVehicleError(u->engine_type, STR_NEWGRF_BROKEN, STR_NEWGRF_BROKEN_CAPACITY, GRFBug::VehCapacity, true);
    }
    u->vcache.cached_cargo_age_period = GetVehicleProperty(u, PROP_TRAIN_CARGO_AGE_PERIOD, e_u->info.cargo_age_period);
 
    /* check the vehicle length (callback) */
    uint16_t veh_len = CALLBACK_FAILED;
    if (e_u->GetGRF() != nullptr && e_u->GetGRF()->grf_version >= 8) {
      /* Use callback 36 */
      veh_len = GetVehicleProperty(u, PROP_TRAIN_SHORTEN_FACTOR, CALLBACK_FAILED);
 
      if (veh_len != CALLBACK_FAILED && veh_len >= VEHICLE_LENGTH) {
        ErrorUnknownCallbackResult(e_u->GetGRFID(), CBID_VEHICLE_LENGTH, veh_len);
      }
    } else if (e_u->info.callback_mask.Test(VehicleCallbackMask::Length)) {
      /* Use callback 11 */
      veh_len = GetVehicleCallback(CBID_VEHICLE_LENGTH, 0, 0, u->engine_type, u);
    }
    if (veh_len == CALLBACK_FAILED) veh_len = rvi_u->shorten_factor;
    veh_len = VEHICLE_LENGTH - Clamp(veh_len, 0, VEHICLE_LENGTH - 1);
 
    if (allowed_changes.Test(ConsistChangeFlag::Length)) {
      /* Update vehicle length. */
      u->gcache.cached_veh_length = veh_len;
    } else {
      /* Verify length hasn't changed. */
      if (veh_len != u->gcache.cached_veh_length) VehicleLengthChanged(u);
    }
 
    this->gcache.cached_total_length += u->gcache.cached_veh_length;
    this->InvalidateNewGRFCache();
    u->InvalidateNewGRFCache();
  }
 
  /* store consist weight/max speed in cache */
  this->vcache.cached_max_speed = max_speed;
  this->tcache.cached_tilt = train_can_tilt;
  this->tcache.cached_curve_speed_mod = min_curve_speed_mod;
  this->tcache.cached_max_curve_speed = this->GetCurveSpeedLimit();
 
  /* recalculate cached weights and power too (we do this *after* the rest, so it is known which wagons are powered and need extra weight added) */
  this->CargoChanged();
 
  if (this->IsFrontEngine()) {
    this->UpdateAcceleration();
    SetWindowDirty(WC_VEHICLE_DETAILS, this->index);
    InvalidateWindowData(WC_VEHICLE_REFIT, this->index, VIWD_CONSIST_CHANGED);
    InvalidateWindowData(WC_VEHICLE_ORDERS, this->index, VIWD_CONSIST_CHANGED);
    InvalidateNewGRFInspectWindow(GrfSpecFeature::Trains, this->index);
 
    /* If the consist is changed while in a depot, the vehicle view window must be invalidated to update the availability of refitting. */
    InvalidateWindowData(WC_VEHICLE_VIEW, this->index, VIWD_CONSIST_CHANGED);
  }
}

int GetTrainStopLocation(StationID station_id, TileIndex tile, const Train *moving_front, int *station_ahead, int *station_length)
{
  const Train *consist = moving_front->First();
  const Station *st = Station::Get(station_id);
  *station_ahead  = st->GetPlatformLength(tile, DirToDiagDir(moving_front->GetMovingDirection())) * TILE_SIZE;
  *station_length = st->GetPlatformLength(tile) * TILE_SIZE;
 
  /* Default to the middle of the station for stations stops that are not in
   * the order list like intermediate stations when non-stop is disabled */
  OrderStopLocation osl = OrderStopLocation::Middle;
  if (consist->gcache.cached_total_length >= *station_length) {
    /* The train is longer than the station, make it stop at the far end of the platform */
    osl = OrderStopLocation::FarEnd;
  } else if (consist->current_order.IsType(OT_GOTO_STATION) && consist->current_order.GetDestination() == station_id) {
    osl = consist->current_order.GetStopLocation();
  }
 
  /* The stop location of the FRONT! of the train */
  int stop;
  switch (osl) {
    default: NOT_REACHED();
 
    case OrderStopLocation::NearEnd:
      stop = consist->gcache.cached_total_length;
      break;
 
    case OrderStopLocation::Middle:
      stop = *station_length - (*station_length - consist->gcache.cached_total_length) / 2;
      break;
 
    case OrderStopLocation::FarEnd:
      stop = *station_length;
      break;
  }
 
  /* Subtract half the front vehicle length of the train so we get the real
   * stop location of the train. */
  uint8_t rounding = consist->IsDrivingBackwards() ? 2 : 1;
  return stop - (consist->gcache.cached_veh_length + rounding) / 2;
}
 

uint16_t Train::GetCurveSpeedLimit() const
{
  assert(this->First() == this);
 
  static const int absolute_max_speed = UINT16_MAX;
  int max_speed = absolute_max_speed;
 
  if (_settings_game.vehicle.train_acceleration_model == AM_ORIGINAL) return max_speed;
 
  int curvecount[2] = {0, 0};
 
  /* first find the curve speed limit */
  int numcurve = 0;
  int sum = 0;
  int pos = 0;
  int lastpos = -1;
  for (const Train *u = this; u->Next() != nullptr; u = u->Next(), pos += u->gcache.cached_veh_length) {
    Direction this_dir = u->direction;
    Direction next_dir = u->Next()->direction;
 
    DirDiff dirdiff = DirDifference(this_dir, next_dir);
    if (dirdiff == DIRDIFF_SAME) continue;
 
    if (dirdiff == DIRDIFF_45LEFT) curvecount[0]++;
    if (dirdiff == DIRDIFF_45RIGHT) curvecount[1]++;
    if (dirdiff == DIRDIFF_45LEFT || dirdiff == DIRDIFF_45RIGHT) {
      if (lastpos != -1) {
        numcurve++;
        sum += pos - lastpos;
        if (pos - lastpos <= static_cast<int>(VEHICLE_LENGTH) && max_speed > 88) {
          max_speed = 88;
        }
      }
      lastpos = pos;
    }
 
    /* if we have a 90 degree turn, fix the speed limit to 60 */
    if (dirdiff == DIRDIFF_90LEFT || dirdiff == DIRDIFF_90RIGHT) {
      max_speed = 61;
    }
  }
 
  if (numcurve > 0 && max_speed > 88) {
    if (curvecount[0] == 1 && curvecount[1] == 1) {
      max_speed = absolute_max_speed;
    } else {
      sum = CeilDiv(sum, VEHICLE_LENGTH);
      sum /= numcurve;
      max_speed = 232 - (13 - Clamp(sum, 1, 12)) * (13 - Clamp(sum, 1, 12));
    }
  }
 
  if (max_speed != absolute_max_speed) {
    /* Apply the current railtype's curve speed advantage */
    const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(this->tile));
    max_speed += (max_speed / 2) * rti->curve_speed;
 
    if (this->tcache.cached_tilt) {
      /* Apply max_speed bonus of 20% for a tilting train */
      max_speed += max_speed / 5;
    }
 
    /* Apply max_speed modifier (cached value is fixed-point binary with 8 fractional bits)
     * and clamp the result to an acceptable range. */
    max_speed += (max_speed * this->tcache.cached_curve_speed_mod) / 256;
    max_speed = Clamp(max_speed, 2, absolute_max_speed);
  }
 
  return static_cast<uint16_t>(max_speed);
}

int Train::GetCurrentMaxSpeed() const
{
  const Train *moving_front = this->GetMovingFront();
  int max_speed = _settings_game.vehicle.train_acceleration_model == AM_ORIGINAL ?
      this->gcache.cached_max_track_speed :
      this->tcache.cached_max_curve_speed;
 
  if (_settings_game.vehicle.train_acceleration_model == AM_REALISTIC && IsRailStationTile(moving_front->tile)) {
    StationID sid = GetStationIndex(moving_front->tile);
    if (this->current_order.ShouldStopAtStation(this, sid)) {
      int station_ahead;
      int station_length;
      int stop_at = GetTrainStopLocation(sid, moving_front->tile, moving_front, &station_ahead, &station_length);
 
      /* The distance to go is whatever is still ahead of the train minus the
       * distance from the train's stop location to the end of the platform */
      int distance_to_go = station_ahead / TILE_SIZE - (station_length - stop_at) / TILE_SIZE;
 
      if (distance_to_go > 0) {
        int st_max_speed = 120;
 
        int delta_v = this->cur_speed / (distance_to_go + 1);
        if (max_speed > (this->cur_speed - delta_v)) {
          st_max_speed = this->cur_speed - (delta_v / 10);
        }
 
        st_max_speed = std::max(st_max_speed, 25 * distance_to_go);
        max_speed = std::min(max_speed, st_max_speed);
      }
    }
  }
 
  for (const Train *u = this; u != nullptr; u = u->Next()) {
    if (_settings_game.vehicle.train_acceleration_model == AM_REALISTIC && u->track == TRACK_BIT_DEPOT) {
      constexpr int DEPOT_SPEED_LIMIT = 61;
      max_speed = std::min(max_speed, DEPOT_SPEED_LIMIT);
      break;
    }
 
    /* Vehicle is on the middle part of a bridge. */
    if (u->track == TRACK_BIT_WORMHOLE && !u->vehstatus.Test(VehState::Hidden)) {
      max_speed = std::min<int>(max_speed, GetBridgeSpec(GetBridgeType(u->tile))->speed);
    }
  }
 
  max_speed = std::min<int>(max_speed, this->current_order.GetMaxSpeed());
 
  /* If the train is going backwards, without a leading cab, restrict its speed. */
  if (!moving_front->CanLeadTrain()) {
    constexpr int BACKWARDS_NO_CAB_SPEED_LIMIT = 32;
    max_speed = std::min<int>(max_speed, BACKWARDS_NO_CAB_SPEED_LIMIT);
  }
 
  return std::min<int>(max_speed, this->gcache.cached_max_track_speed);
}

void Train::UpdateAcceleration()
{
  assert(this->IsFrontEngine() || this->IsFreeWagon());
 
  uint power = this->gcache.cached_power;
  uint weight = this->gcache.cached_weight;
  assert(weight != 0);
  this->acceleration = Clamp(power / weight * 4, 1, 255);
}

int Train::GetCursorImageOffset() const
{
  if (this->gcache.cached_veh_length != 8 && this->flags.Test(VehicleRailFlag::Flipped) && !EngInfo(this->engine_type)->misc_flags.Test(EngineMiscFlag::RailFlips)) {
    int reference_width = TRAININFO_DEFAULT_VEHICLE_WIDTH;
 
    const Engine *e = this->GetEngine();
    if (e->GetGRF() != nullptr && IsCustomVehicleSpriteNum(e->VehInfo<RailVehicleInfo>().image_index)) {
      reference_width = e->GetGRF()->traininfo_vehicle_width;
    }
 
    return ScaleSpriteTrad((this->gcache.cached_veh_length - (int)VEHICLE_LENGTH) * reference_width / (int)VEHICLE_LENGTH);
  }
  return 0;
}

int Train::GetDisplayImageWidth(Point *offset) const
{
  int reference_width = TRAININFO_DEFAULT_VEHICLE_WIDTH;
  int vehicle_pitch = 0;
 
  const Engine *e = this->GetEngine();
  if (e->GetGRF() != nullptr && IsCustomVehicleSpriteNum(e->VehInfo<RailVehicleInfo>().image_index)) {
    reference_width = e->GetGRF()->traininfo_vehicle_width;
    vehicle_pitch = e->GetGRF()->traininfo_vehicle_pitch;
  }
 
  if (offset != nullptr) {
    if (this->flags.Test(VehicleRailFlag::Flipped) && !EngInfo(this->engine_type)->misc_flags.Test(EngineMiscFlag::RailFlips)) {
      offset->x = ScaleSpriteTrad(((int)this->gcache.cached_veh_length - (int)VEHICLE_LENGTH / 2) * reference_width / (int)VEHICLE_LENGTH);
    } else {
      offset->x = ScaleSpriteTrad(reference_width) / 2;
    }
    offset->y = ScaleSpriteTrad(vehicle_pitch);
  }
  return ScaleSpriteTrad(this->gcache.cached_veh_length * reference_width / VEHICLE_LENGTH);
}
 
static SpriteID GetDefaultTrainSprite(uint8_t spritenum, Direction direction)
{
  assert(IsValidImageIndex<VEH_TRAIN>(spritenum));
  return ((direction + _engine_sprite_add[spritenum]) & _engine_sprite_and[spritenum]) + _engine_sprite_base[spritenum];
}

void Train::GetImage(Direction direction, EngineImageType image_type, VehicleSpriteSeq *result) const
{
  uint8_t spritenum = this->spritenum;
 
  if (this->flags.Test(VehicleRailFlag::Flipped)) direction = ReverseDir(direction);
 
  if (IsCustomVehicleSpriteNum(spritenum)) {
    if (spritenum == CUSTOM_VEHICLE_SPRITENUM_REVERSED) direction = ReverseDir(direction);
    GetCustomVehicleSprite(this, direction, image_type, result);
    if (result->IsValid()) return;
 
    spritenum = this->GetEngine()->original_image_index;
  }
 
  assert(IsValidImageIndex<VEH_TRAIN>(spritenum));
  SpriteID sprite = GetDefaultTrainSprite(spritenum, direction);
 
  if (this->cargo.StoredCount() >= this->cargo_cap / 2U) sprite += _wagon_full_adder[spritenum];
 
  result->Set(sprite);
}
 
static void GetRailIcon(EngineID engine, bool rear_head, int &y, EngineImageType image_type, VehicleSpriteSeq *result)
{
  const Engine *e = Engine::Get(engine);
  Direction dir = rear_head ? DIR_E : DIR_W;
  uint8_t spritenum = e->VehInfo<RailVehicleInfo>().image_index;
 
  if (IsCustomVehicleSpriteNum(spritenum)) {
    GetCustomVehicleIcon(engine, dir, image_type, result);
    if (result->IsValid()) {
      if (e->GetGRF() != nullptr) {
        y += ScaleSpriteTrad(e->GetGRF()->traininfo_vehicle_pitch);
      }
      return;
    }
 
    spritenum = Engine::Get(engine)->original_image_index;
  }
 
  if (rear_head) spritenum++;
 
  result->Set(GetDefaultTrainSprite(spritenum, DIR_W));
}
 
void DrawTrainEngine(int left, int right, int preferred_x, int y, EngineID engine, PaletteID pal, EngineImageType image_type)
{
  if (RailVehInfo(engine)->railveh_type == RAILVEH_MULTIHEAD) {
    int yf = y;
    int yr = y;
 
    VehicleSpriteSeq seqf, seqr;
    GetRailIcon(engine, false, yf, image_type, &seqf);
    GetRailIcon(engine, true, yr, image_type, &seqr);
 
    Rect rectf, rectr;
    seqf.GetBounds(&rectf);
    seqr.GetBounds(&rectr);
 
    preferred_x = Clamp(preferred_x,
        left - UnScaleGUI(rectf.left) + ScaleSpriteTrad(14),
        right - UnScaleGUI(rectr.right) - ScaleSpriteTrad(15));
 
    seqf.Draw(preferred_x - ScaleSpriteTrad(14), yf, pal, pal == PALETTE_CRASH);
    seqr.Draw(preferred_x + ScaleSpriteTrad(15), yr, pal, pal == PALETTE_CRASH);
  } else {
    VehicleSpriteSeq seq;
    GetRailIcon(engine, false, y, image_type, &seq);
 
    Rect rect;
    seq.GetBounds(&rect);
    preferred_x = Clamp(preferred_x,
        left - UnScaleGUI(rect.left),
        right - UnScaleGUI(rect.right));
 
    seq.Draw(preferred_x, y, pal, pal == PALETTE_CRASH);
  }
}

void GetTrainSpriteSize(EngineID engine, uint &width, uint &height, int &xoffs, int &yoffs, EngineImageType image_type)
{
  int y = 0;
 
  VehicleSpriteSeq seq;
  GetRailIcon(engine, false, y, image_type, &seq);
 
  Rect rect;
  seq.GetBounds(&rect);
 
  width  = UnScaleGUI(rect.Width());
  height = UnScaleGUI(rect.Height());
  xoffs  = UnScaleGUI(rect.left);
  yoffs  = UnScaleGUI(rect.top);
 
  if (RailVehInfo(engine)->railveh_type == RAILVEH_MULTIHEAD) {
    GetRailIcon(engine, true, y, image_type, &seq);
    seq.GetBounds(&rect);
 
    /* Calculate values relative to an imaginary center between the two sprites. */
    width = ScaleSpriteTrad(TRAININFO_DEFAULT_VEHICLE_WIDTH) + UnScaleGUI(rect.right) - xoffs;
    height = std::max<uint>(height, UnScaleGUI(rect.Height()));
    xoffs  = xoffs - ScaleSpriteTrad(TRAININFO_DEFAULT_VEHICLE_WIDTH) / 2;
    yoffs  = std::min(yoffs, UnScaleGUI(rect.top));
  }
}

static std::vector<VehicleID> GetFreeWagonsInDepot(TileIndex tile)
{
  std::vector<VehicleID> free_wagons;
 
  for (Vehicle *v : VehiclesOnTile(tile)) {
    if (v->type != VEH_TRAIN) continue;
    if (v->vehstatus.Test(VehState::Crashed)) continue;
    if (!Train::From(v)->IsFreeWagon()) continue;
 
    free_wagons.push_back(v->index);
  }
 
  /* Sort by vehicle index for consistency across clients. */
  std::ranges::sort(free_wagons);
  return free_wagons;
}

static CommandCost CmdBuildRailWagon(DoCommandFlags flags, TileIndex tile, const Engine *e, Vehicle **ret)
{
  const RailVehicleInfo *rvi = &e->VehInfo<RailVehicleInfo>();
 
  /* Check that the wagon can drive on the track in question */
  if (!IsCompatibleRail(rvi->railtypes, GetRailType(tile))) return CMD_ERROR;
 
  if (flags.Test(DoCommandFlag::Execute)) {
    Train *v = Train::Create();
    *ret = v;
    v->spritenum = rvi->image_index;
 
    v->engine_type = e->index;
    v->gcache.first_engine = EngineID::Invalid(); // needs to be set before first callback
 
    DiagDirection dir = GetRailDepotDirection(tile);
 
    v->direction = DiagDirToDir(dir);
    v->tile = tile;
 
    int x = TileX(tile) * TILE_SIZE | _vehicle_initial_x_fract[dir];
    int y = TileY(tile) * TILE_SIZE | _vehicle_initial_y_fract[dir];
 
    v->x_pos = x;
    v->y_pos = y;
    v->z_pos = GetSlopePixelZ(x, y, true);
    v->owner = _current_company;
    v->track = TRACK_BIT_DEPOT;
    v->vehstatus = {VehState::Hidden, VehState::DefaultPalette};
 
    v->SetWagon();
 
    v->SetFreeWagon();
    InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
 
    v->cargo_type = e->GetDefaultCargoType();
    assert(IsValidCargoType(v->cargo_type));
    v->cargo_cap = rvi->capacity;
    v->refit_cap = 0;
 
    v->railtypes = rvi->railtypes;
 
    v->date_of_last_service = TimerGameEconomy::date;
    v->date_of_last_service_newgrf = TimerGameCalendar::date;
    v->build_year = TimerGameCalendar::year;
    v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
    v->random_bits = Random();
 
    v->group_id = DEFAULT_GROUP;
 
    auto prob = TestVehicleBuildProbability(v, BuildProbabilityType::Reversed);
    if (prob.has_value()) v->flags.Set(VehicleRailFlag::Flipped, prob.value());
    AddArticulatedParts(v);
 
    v->UpdatePosition();
    v->First()->ConsistChanged(CCF_ARRANGE);
    UpdateTrainGroupID(v->First());
 
    CheckConsistencyOfArticulatedVehicle(v);
 
    /* Try to connect the vehicle to one of free chains of wagons. */
    for (VehicleID vehicle : GetFreeWagonsInDepot(tile)) {
      if (vehicle == v->index) continue;
 
      const Train *w = Train::Get(vehicle);
      if (w->engine_type != v->engine_type) continue; 
      if (w->First() == v) continue; 
 
      if (Command<Commands::MoveRailVehicle>::Do(DoCommandFlag::Execute, v->index, w->Last()->index, true).Succeeded()) {
        break;
      }
    }
  }
 
  return CommandCost();
}

void NormalizeTrainVehInDepot(const Train *u)
{
  assert(u->IsEngine());
  for (VehicleID vehicle : GetFreeWagonsInDepot(u->tile)) {
    if (Command<Commands::MoveRailVehicle>::Do(DoCommandFlag::Execute, vehicle, u->index, true).Failed()) {
      break;
    }
  }
}
 
static void AddRearEngineToMultiheadedTrain(Train *v)
{
  Train *u = Train::Create();
  v->value >>= 1;
  u->value = v->value;
  u->direction = v->direction;
  u->owner = v->owner;
  u->tile = v->tile;
  u->x_pos = v->x_pos;
  u->y_pos = v->y_pos;
  u->z_pos = v->z_pos;
  u->track = TRACK_BIT_DEPOT;
  u->vehstatus = v->vehstatus;
  u->vehstatus.Reset(VehState::Stopped);
  u->spritenum = v->spritenum + 1;
  u->cargo_type = v->cargo_type;
  u->cargo_subtype = v->cargo_subtype;
  u->cargo_cap = v->cargo_cap;
  u->refit_cap = v->refit_cap;
  u->railtypes = v->railtypes;
  u->engine_type = v->engine_type;
  u->date_of_last_service = v->date_of_last_service;
  u->date_of_last_service_newgrf = v->date_of_last_service_newgrf;
  u->build_year = v->build_year;
  u->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
  u->random_bits = Random();
  v->SetMultiheaded();
  u->SetMultiheaded();
  v->SetNext(u);
  auto prob = TestVehicleBuildProbability(u, BuildProbabilityType::Reversed);
  if (prob.has_value()) u->flags.Set(VehicleRailFlag::Flipped, prob.value());
  u->UpdatePosition();
 
  /* Now we need to link the front and rear engines together */
  v->other_multiheaded_part = u;
  u->other_multiheaded_part = v;
}

CommandCost CmdBuildRailVehicle(DoCommandFlags flags, TileIndex tile, const Engine *e, Vehicle **ret)
{
  const RailVehicleInfo *rvi = &e->VehInfo<RailVehicleInfo>();
 
  if (rvi->railveh_type == RAILVEH_WAGON) return CmdBuildRailWagon(flags, tile, e, ret);
 
  /* Check if depot and new engine uses the same kind of tracks *
   * We need to see if the engine got power on the tile to avoid electric engines in non-electric depots */
  if (!HasPowerOnRail(rvi->railtypes, GetRailType(tile))) return CMD_ERROR;
 
  if (flags.Test(DoCommandFlag::Execute)) {
    DiagDirection dir = GetRailDepotDirection(tile);
    int x = TileX(tile) * TILE_SIZE + _vehicle_initial_x_fract[dir];
    int y = TileY(tile) * TILE_SIZE + _vehicle_initial_y_fract[dir];
 
    Train *v = Train::Create();
    *ret = v;
    v->direction = DiagDirToDir(dir);
    v->tile = tile;
    v->owner = _current_company;
    v->x_pos = x;
    v->y_pos = y;
    v->z_pos = GetSlopePixelZ(x, y, true);
    v->track = TRACK_BIT_DEPOT;
    v->vehstatus = {VehState::Hidden, VehState::Stopped, VehState::DefaultPalette};
    v->spritenum = rvi->image_index;
    v->cargo_type = e->GetDefaultCargoType();
    assert(IsValidCargoType(v->cargo_type));
    v->cargo_cap = rvi->capacity;
    v->refit_cap = 0;
    v->last_station_visited = StationID::Invalid();
    v->last_loading_station = StationID::Invalid();
 
    v->engine_type = e->index;
    v->gcache.first_engine = EngineID::Invalid(); // needs to be set before first callback
 
    v->reliability = e->reliability;
    v->reliability_spd_dec = e->reliability_spd_dec;
    v->max_age = e->GetLifeLengthInDays();
 
    v->railtypes = rvi->railtypes;
 
    v->SetServiceInterval(Company::Get(_current_company)->settings.vehicle.servint_trains);
    v->date_of_last_service = TimerGameEconomy::date;
    v->date_of_last_service_newgrf = TimerGameCalendar::date;
    v->build_year = TimerGameCalendar::year;
    v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
    v->random_bits = Random();
 
    if (e->flags.Test(EngineFlag::ExclusivePreview)) v->vehicle_flags.Set(VehicleFlag::BuiltAsPrototype);
    v->SetServiceIntervalIsPercent(Company::Get(_current_company)->settings.vehicle.servint_ispercent);
 
    v->group_id = DEFAULT_GROUP;
 
    v->SetFrontEngine();
    v->SetEngine();
 
    auto prob = TestVehicleBuildProbability(v, BuildProbabilityType::Reversed);
    if (prob.has_value()) v->flags.Set(VehicleRailFlag::Flipped, prob.value());
    v->UpdatePosition();
 
    if (rvi->railveh_type == RAILVEH_MULTIHEAD) {
      AddRearEngineToMultiheadedTrain(v);
    } else {
      AddArticulatedParts(v);
    }
 
    v->ConsistChanged(CCF_ARRANGE);
    UpdateTrainGroupID(v);
 
    CheckConsistencyOfArticulatedVehicle(v);
  }
 
  return CommandCost();
}
 
static Train *FindGoodVehiclePos(const Train *src)
{
  EngineID eng = src->engine_type;
 
  for (VehicleID vehicle : GetFreeWagonsInDepot(src->tile)) {
    Train *dst = Train::Get(vehicle);
 
    /* check so all vehicles in the line have the same engine. */
    Train *t = dst;
    while (t->engine_type == eng) {
      t = t->Next();
      if (t == nullptr) return dst;
    }
  }
 
  return nullptr;
}

typedef std::vector<Train *> TrainList;

static void MakeTrainBackup(TrainList &list, Train *t)
{
  for (; t != nullptr; t = t->Next()) list.push_back(t);
}

static void RestoreTrainBackup(TrainList &list)
{
  /* No train, nothing to do. */
  if (list.empty()) return;
 
  Train *prev = nullptr;
  /* Iterate over the list and rebuild it. */
  for (Train *t : list) {
    if (prev != nullptr) {
      prev->SetNext(t);
    } else if (t->Previous() != nullptr) {
      /* Make sure the head of the train is always the first in the chain. */
      t->Previous()->SetNext(nullptr);
    }
    prev = t;
  }
}

static void RemoveFromConsist(Train *part, bool chain = false)
{
  Train *tail;
 
  if (chain) {
    /* We're moving several vehicles, find the last one in the chain. */
    tail = part;
    while (tail->Next() != nullptr) tail = tail->Next();
  } else {
    /* We're just moving one vehicle, but make sure we get all the articulated parts. */
    tail = part->GetLastEnginePart();
  }
 
  /* Unlink at the front, but make it point to the next
   * vehicle after the to be remove part. */
  if (part->Previous() != nullptr) part->Previous()->SetNext(tail->Next());
 
  /* Unlink at the back */
  tail->SetNext(nullptr);
}

static void InsertInConsist(Train *dst, Train *chain)
{
  /* We do not want to add something in the middle of an articulated part. */
  assert(dst != nullptr && (dst->Next() == nullptr || !dst->Next()->IsArticulatedPart()));
 
  chain->Last()->SetNext(dst->Next());
  dst->SetNext(chain);
}

static void NormaliseDualHeads(Train *t)
{
  for (; t != nullptr; t = t->GetNextVehicle()) {
    if (!t->IsMultiheaded() || !t->IsEngine()) continue;
 
    /* Make sure that there are no free cars before next engine */
    Train *u;
    for (u = t; u->Next() != nullptr && !u->Next()->IsEngine(); u = u->Next()) {}
 
    if (u == t->other_multiheaded_part) continue;
 
    /* Remove the part from the 'wrong' train */
    RemoveFromConsist(t->other_multiheaded_part);
    /* And add it to the 'right' train */
    InsertInConsist(u, t->other_multiheaded_part);
  }
}

static void NormaliseSubtypes(Train *chain)
{
  /* Nothing to do */
  if (chain == nullptr) return;
 
  /* We must be the first in the chain. */
  assert(chain->Previous() == nullptr);
 
  /* Set the appropriate bits for the first in the chain. */
  if (chain->IsWagon()) {
    chain->SetFreeWagon();
  } else {
    assert(chain->IsEngine());
    chain->SetFrontEngine();
  }
 
  /* Now clear the bits for the rest of the chain */
  for (Train *t = chain->Next(); t != nullptr; t = t->Next()) {
    t->ClearFreeWagon();
    t->ClearFrontEngine();
  }
}

static CommandCost CheckNewTrain(Train *original_dst, Train *dst, Train *original_src, Train *src)
{
  /* Just add 'new' engines and subtract the original ones.
   * If that's less than or equal to 0 we can be sure we did
   * not add any engines (read: trains) along the way. */
  if ((src          != nullptr && src->IsEngine()          ? 1 : 0) +
      (dst          != nullptr && dst->IsEngine()          ? 1 : 0) -
      (original_src != nullptr && original_src->IsEngine() ? 1 : 0) -
      (original_dst != nullptr && original_dst->IsEngine() ? 1 : 0) <= 0) {
    return CommandCost();
  }
 
  /* Get a free unit number and check whether it's within the bounds.
   * There will always be a maximum of one new train. */
  if (GetFreeUnitNumber(VEH_TRAIN) <= _settings_game.vehicle.max_trains) return CommandCost();
 
  return CommandCost(STR_ERROR_TOO_MANY_VEHICLES_IN_GAME);
}

static CommandCost CheckTrainAttachment(Train *t)
{
  /* No multi-part train, no need to check. */
  if (t == nullptr || t->Next() == nullptr) return CommandCost();
 
  /* The maximum length for a train. For each part we decrease this by one
   * and if the result is negative the train is simply too long. */
  int allowed_len = _settings_game.vehicle.max_train_length * TILE_SIZE - t->gcache.cached_veh_length;
 
  /* For free-wagon chains, check if they are within the max_train_length limit. */
  if (!t->IsEngine()) {
    t = t->Next();
    while (t != nullptr) {
      allowed_len -= t->gcache.cached_veh_length;
 
      t = t->Next();
    }
 
    if (allowed_len < 0) return CommandCost(STR_ERROR_TRAIN_TOO_LONG);
    return CommandCost();
  }
 
  Train *head = t;
  Train *prev = t;
 
  /* Break the prev -> t link so it always holds within the loop. */
  t = t->Next();
  prev->SetNext(nullptr);
 
  /* Make sure the cache is cleared. */
  head->InvalidateNewGRFCache();
 
  while (t != nullptr) {
    allowed_len -= t->gcache.cached_veh_length;
 
    Train *next = t->Next();
 
    /* Unlink the to-be-added piece; it is already unlinked from the previous
     * part due to the fact that the prev -> t link is broken. */
    t->SetNext(nullptr);
 
    /* Don't check callback for articulated or rear dual headed parts */
    if (!t->IsArticulatedPart() && !t->IsRearDualheaded()) {
      /* Back up and clear the first_engine data to avoid using wagon override group */
      EngineID first_engine = t->gcache.first_engine;
      t->gcache.first_engine = EngineID::Invalid();
 
      /* We don't want the cache to interfere. head's cache is cleared before
       * the loop and after each callback does not need to be cleared here. */
      t->InvalidateNewGRFCache();
 
      std::array<int32_t, 1> regs100;
      uint16_t callback = GetVehicleCallbackParent(CBID_TRAIN_ALLOW_WAGON_ATTACH, 0, 0, head->engine_type, t, head, regs100);
 
      /* Restore original first_engine data */
      t->gcache.first_engine = first_engine;
 
      /* We do not want to remember any cached variables from the test run */
      t->InvalidateNewGRFCache();
      head->InvalidateNewGRFCache();
 
      if (callback != CALLBACK_FAILED) {
        /* A failing callback means everything is okay */
        StringID error = STR_NULL;
 
        if (head->GetGRF()->grf_version < 8) {
          if (callback == 0xFD) error = STR_ERROR_INCOMPATIBLE_RAIL_TYPES;
          if (callback  < 0xFD) error = GetGRFStringID(head->GetGRFID(), GRFSTR_MISC_GRF_TEXT + callback);
          if (callback >= 0x100) ErrorUnknownCallbackResult(head->GetGRFID(), CBID_TRAIN_ALLOW_WAGON_ATTACH, callback);
        } else {
          if (callback < 0x400) {
            error = GetGRFStringID(head->GetGRFID(), GRFSTR_MISC_GRF_TEXT + callback);
          } else {
            switch (callback) {
              case 0x400: // allow if railtypes match (always the case for OpenTTD)
              case 0x401: // allow
                break;
 
              case 0x40F:
                error = GetGRFStringID(head->GetGRFID(), static_cast<GRFStringID>(regs100[0]));
                break;
 
              default:    // unknown reason -> disallow
              case 0x402: // disallow attaching
                error = STR_ERROR_INCOMPATIBLE_RAIL_TYPES;
                break;
            }
          }
        }
 
        if (error != STR_NULL) return CommandCost(error);
      }
    }
 
    /* And link it to the new part. */
    prev->SetNext(t);
    prev = t;
    t = next;
  }
 
  if (allowed_len < 0) return CommandCost(STR_ERROR_TRAIN_TOO_LONG);
  return CommandCost();
}

static CommandCost ValidateTrains(Train *original_dst, Train *dst, Train *original_src, Train *src, bool check_limit)
{
  /* Check whether we may actually construct the trains. */
  CommandCost ret = CheckTrainAttachment(src);
  if (ret.Failed()) return ret;
  ret = CheckTrainAttachment(dst);
  if (ret.Failed()) return ret;
 
  /* Check whether we need to build a new train. */
  return check_limit ? CheckNewTrain(original_dst, dst, original_src, src) : CommandCost();
}

static void ArrangeTrains(Train **dst_head, Train *dst, Train **src_head, Train *src, bool move_chain)
{
  /* First determine the front of the two resulting trains */
  if (*src_head == *dst_head) {
    /* If we aren't moving part(s) to a new train, we are just moving the
     * front back and there is not destination head. */
    *dst_head = nullptr;
  } else if (*dst_head == nullptr) {
    /* If we are moving to a new train the head of the move train would become
     * the head of the new vehicle. */
    *dst_head = src;
  }
 
  if (src == *src_head) {
    /* If we are moving the front of a train then we are, in effect, creating
     * a new head for the train. Point to that. Unless we are moving the whole
     * train in which case there is not 'source' train anymore.
     * In case we are a multiheaded part we want the complete thing to come
     * with us, so src->GetNextUnit(), however... when we are e.g. a wagon
     * that is followed by a rear multihead we do not want to include that. */
    *src_head = move_chain ? nullptr :
        (src->IsMultiheaded() ? src->GetNextUnit() : src->GetNextVehicle());
  }
 
  /* Now it's just simply removing the part that we are going to move from the
   * source train and *if* the destination is a not a new train add the chain
   * at the destination location. */
  RemoveFromConsist(src, move_chain);
  if (*dst_head != src) InsertInConsist(dst, src);
 
  /* Now normalise the dual heads, that is move the dual heads around in such
   * a way that the head and rear of a dual head are in the same train */
  NormaliseDualHeads(*src_head);
  NormaliseDualHeads(*dst_head);
}

static void NormaliseTrainHead(Train *head)
{
  /* Not much to do! */
  if (head == nullptr) return;
 
  /* Tell the 'world' the train changed. */
  head->ConsistChanged(CCF_ARRANGE);
  UpdateTrainGroupID(head);
 
  /* Not a front engine, i.e. a free wagon chain. No need to do more. */
  if (!head->IsFrontEngine()) return;
 
  /* Update the refit button and window */
  InvalidateWindowData(WC_VEHICLE_REFIT, head->index, VIWD_CONSIST_CHANGED);
  SetWindowWidgetDirty(WC_VEHICLE_VIEW, head->index, WID_VV_REFIT);
 
  /* If we don't have a unit number yet, set one. */
  if (head->unitnumber != 0) return;
  head->unitnumber = Company::Get(head->owner)->freeunits[head->type].UseID(GetFreeUnitNumber(VEH_TRAIN));
}

CommandCost CmdMoveRailVehicle(DoCommandFlags flags, VehicleID src_veh, VehicleID dest_veh, bool move_chain)
{
  Train *src = Train::GetIfValid(src_veh);
  if (src == nullptr) return CMD_ERROR;
 
  CommandCost ret = CheckOwnership(src->owner);
  if (ret.Failed()) return ret;
 
  /* Do not allow moving crashed vehicles inside the depot, it is likely to cause asserts later */
  if (src->vehstatus.Test(VehState::Crashed)) return CMD_ERROR;
 
  /* if nothing is selected as destination, try and find a matching vehicle to drag to. */
  Train *dst;
  if (dest_veh == VehicleID::Invalid()) {
    dst = (src->IsEngine() || flags.Test(DoCommandFlag::AutoReplace)) ? nullptr : FindGoodVehiclePos(src);
  } else {
    dst = Train::GetIfValid(dest_veh);
    if (dst == nullptr) return CMD_ERROR;
 
    ret = CheckOwnership(dst->owner);
    if (ret.Failed()) return ret;
 
    /* Do not allow appending to crashed vehicles, too */
    if (dst->vehstatus.Test(VehState::Crashed)) return CMD_ERROR;
  }
 
  /* if an articulated part is being handled, deal with its parent vehicle */
  src = src->GetFirstEnginePart();
  if (dst != nullptr) {
    dst = dst->GetFirstEnginePart();
  }
 
  /* don't move the same vehicle.. */
  if (src == dst) return CommandCost();
 
  /* locate the head of the two chains */
  Train *src_head = src->First();
  Train *dst_head;
  if (dst != nullptr) {
    dst_head = dst->First();
    if (dst_head->tile != src_head->tile) return CMD_ERROR;
    /* Now deal with articulated part of destination wagon */
    dst = dst->GetLastEnginePart();
  } else {
    dst_head = nullptr;
  }
 
  if (src->IsRearDualheaded()) return CommandCost(STR_ERROR_REAR_ENGINE_FOLLOW_FRONT);
 
  /* When moving all wagons, we can't have the same src_head and dst_head */
  if (move_chain && src_head == dst_head) return CommandCost();
 
  /* When moving a multiheaded part to be place after itself, bail out. */
  if (!move_chain && dst != nullptr && dst->IsRearDualheaded() && src == dst->other_multiheaded_part) return CommandCost();
 
  /* Check if all vehicles in the source train are stopped inside a depot. */
  if (!src_head->IsStoppedInDepot()) return CommandCost(STR_ERROR_TRAINS_CAN_ONLY_BE_ALTERED_INSIDE_A_DEPOT);
 
  /* Check if all vehicles in the destination train are stopped inside a depot. */
  if (dst_head != nullptr && !dst_head->IsStoppedInDepot()) return CommandCost(STR_ERROR_TRAINS_CAN_ONLY_BE_ALTERED_INSIDE_A_DEPOT);
 
  /* First make a backup of the order of the trains. That way we can do
   * whatever we want with the order and later on easily revert. */
  TrainList original_src;
  TrainList original_dst;
 
  MakeTrainBackup(original_src, src_head);
  MakeTrainBackup(original_dst, dst_head);
 
  /* Also make backup of the original heads as ArrangeTrains can change them.
   * For the destination head we do not care if it is the same as the source
   * head because in that case it's just a copy. */
  Train *original_src_head = src_head;
  Train *original_dst_head = (dst_head == src_head ? nullptr : dst_head);
 
  /* We want this information from before the rearrangement, but execute this after the validation.
   * original_src_head can't be nullptr; src is by definition != nullptr, so src_head can't be nullptr as
   * src->GetFirst() always yields non-nullptr, so eventually original_src_head != nullptr as well. */
  bool original_src_head_front_engine = original_src_head->IsFrontEngine();
  bool original_dst_head_front_engine = original_dst_head != nullptr && original_dst_head->IsFrontEngine();
 
  /* (Re)arrange the trains in the wanted arrangement. */
  ArrangeTrains(&dst_head, dst, &src_head, src, move_chain);
 
  if (!flags.Test(DoCommandFlag::AutoReplace)) {
    /* If the autoreplace flag is set we do not need to test for the validity
     * because we are going to revert the train to its original state. As we
     * assume the original state was correct autoreplace can skip this. */
    ret = ValidateTrains(original_dst_head, dst_head, original_src_head, src_head, true);
    if (ret.Failed()) {
      /* Restore the train we had. */
      RestoreTrainBackup(original_src);
      RestoreTrainBackup(original_dst);
      return ret;
    }
  }
 
  /* do it? */
  if (flags.Test(DoCommandFlag::Execute)) {
    /* Remove old heads from the statistics */
    if (original_src_head_front_engine) GroupStatistics::CountVehicle(original_src_head, -1);
    if (original_dst_head_front_engine) GroupStatistics::CountVehicle(original_dst_head, -1);
 
    /* First normalise the sub types of the chains. */
    NormaliseSubtypes(src_head);
    NormaliseSubtypes(dst_head);
 
    /* There are 14 different cases:
     *  1) front engine gets moved to a new train, it stays a front engine.
     *     a) the 'next' part is a wagon that becomes a free wagon chain.
     *     b) the 'next' part is an engine that becomes a front engine.
     *     c) there is no 'next' part, nothing else happens
     *  2) front engine gets moved to another train, it is not a front engine anymore
     *     a) the 'next' part is a wagon that becomes a free wagon chain.
     *     b) the 'next' part is an engine that becomes a front engine.
     *     c) there is no 'next' part, nothing else happens
     *  3) front engine gets moved to later in the current train, it is not a front engine anymore.
     *     a) the 'next' part is a wagon that becomes a free wagon chain.
     *     b) the 'next' part is an engine that becomes a front engine.
     *  4) free wagon gets moved
     *     a) the 'next' part is a wagon that becomes a free wagon chain.
     *     b) the 'next' part is an engine that becomes a front engine.
     *     c) there is no 'next' part, nothing else happens
     *  5) non front engine gets moved and becomes a new train, nothing else happens
     *  6) non front engine gets moved within a train / to another train, nothing happens
     *  7) wagon gets moved, nothing happens
     */
    if (src == original_src_head && src->IsEngine() && !src->IsFrontEngine()) {
      /* Cases #2 and #3: the front engine gets trashed. */
      CloseWindowById(WC_VEHICLE_VIEW, src->index);
      CloseWindowById(WC_VEHICLE_ORDERS, src->index);
      CloseWindowById(WC_VEHICLE_REFIT, src->index);
      CloseWindowById(WC_VEHICLE_DETAILS, src->index);
      CloseWindowById(WC_VEHICLE_TIMETABLE, src->index);
      DeleteNewGRFInspectWindow(GrfSpecFeature::Trains, src->index);
      SetWindowDirty(WC_COMPANY, _current_company);
 
      if (src_head != nullptr && src_head->IsFrontEngine()) {
        /* Cases #?b: Transfer order, unit number and other stuff
         * to the new front engine. */
        src_head->orders = src->orders;
        if (src_head->orders != nullptr) src_head->AddToShared(src);
        src_head->CopyVehicleConfigAndStatistics(src);
      }
      /* Remove stuff not valid anymore for non-front engines. */
      DeleteVehicleOrders(src);
      src->ReleaseUnitNumber();
      src->name.clear();
    }
 
    /* We weren't a front engine but are becoming one. So
     * we should be put in the default group. */
    if (original_src_head != src && dst_head == src) {
      SetTrainGroupID(src, DEFAULT_GROUP);
      SetWindowDirty(WC_COMPANY, _current_company);
    }
 
    /* Handle 'new engine' part of cases #1b, #2b, #3b, #4b and #5 in NormaliseTrainHead. */
    NormaliseTrainHead(src_head);
    NormaliseTrainHead(dst_head);
 
    /* Add new heads to statistics.
     * This should be done after NormaliseTrainHead due to engine total limit checks in GetFreeUnitNumber. */
    if (src_head != nullptr && src_head->IsFrontEngine()) GroupStatistics::CountVehicle(src_head, 1);
    if (dst_head != nullptr && dst_head->IsFrontEngine()) GroupStatistics::CountVehicle(dst_head, 1);
 
    if (!flags.Test(DoCommandFlag::NoCargoCapacityCheck)) {
      CheckCargoCapacity(src_head);
      CheckCargoCapacity(dst_head);
    }
 
    if (src_head != nullptr) src_head->First()->MarkDirty();
    if (dst_head != nullptr) dst_head->First()->MarkDirty();
 
    /* We are undoubtedly changing something in the depot and train list. */
    InvalidateWindowData(WC_VEHICLE_DEPOT, src->tile);
    InvalidateWindowClassesData(WC_TRAINS_LIST, 0);
  } else {
    /* We don't want to execute what we're just tried. */
    RestoreTrainBackup(original_src);
    RestoreTrainBackup(original_dst);
  }
 
  return CommandCost();
}

CommandCost CmdSellRailWagon(DoCommandFlags flags, Vehicle *t, bool sell_chain, bool backup_order, ClientID user)
{
  Train *v = Train::From(t)->GetFirstEnginePart();
  Train *first = v->First();
 
  if (v->IsRearDualheaded()) return CommandCost(STR_ERROR_REAR_ENGINE_FOLLOW_FRONT);
 
  /* First make a backup of the order of the train. That way we can do
   * whatever we want with the order and later on easily revert. */
  TrainList original;
  MakeTrainBackup(original, first);
 
  /* We need to keep track of the new head and the head of what we're going to sell. */
  Train *new_head = first;
  Train *sell_head = nullptr;
 
  /* Split the train in the wanted way. */
  ArrangeTrains(&sell_head, nullptr, &new_head, v, sell_chain);
 
  /* We don't need to validate the second train; it's going to be sold. */
  CommandCost ret = ValidateTrains(nullptr, nullptr, first, new_head, !flags.Test(DoCommandFlag::AutoReplace));
  if (ret.Failed()) {
    /* Restore the train we had. */
    RestoreTrainBackup(original);
    return ret;
  }
 
  if (first->orders == nullptr && !OrderList::CanAllocateItem()) {
    /* Restore the train we had. */
    RestoreTrainBackup(original);
    return CommandCost(STR_ERROR_NO_MORE_SPACE_FOR_ORDERS);
  }
 
  CommandCost cost(EXPENSES_NEW_VEHICLES);
  for (Train *part = sell_head; part != nullptr; part = part->Next()) cost.AddCost(-part->value);
 
  /* do it? */
  if (flags.Test(DoCommandFlag::Execute)) {
    /* First normalise the sub types of the chain. */
    NormaliseSubtypes(new_head);
 
    if (v == first && !sell_chain && new_head != nullptr && new_head->IsFrontEngine()) {
      if (v->IsEngine()) {
        /* We are selling the front engine. In this case we want to
         * 'give' the order, unit number and such to the new head. */
        new_head->orders = first->orders;
        new_head->AddToShared(first);
        DeleteVehicleOrders(first);
 
        /* Copy other important data from the front engine */
        new_head->CopyVehicleConfigAndStatistics(first);
      }
      GroupStatistics::CountVehicle(new_head, 1); // after copying over the profit, if required
    } else if (v->IsPrimaryVehicle() && backup_order) {
      OrderBackup::Backup(v, user);
    }
 
    /* We need to update the information about the train. */
    NormaliseTrainHead(new_head);
 
    /* We are undoubtedly changing something in the depot and train list. */
    InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
    InvalidateWindowClassesData(WC_TRAINS_LIST, 0);
 
    /* Actually delete the sold 'goods' */
    delete sell_head;
  } else {
    /* We don't want to execute what we're just tried. */
    RestoreTrainBackup(original);
  }
 
  return cost;
}
 
void Train::UpdateDeltaXY()
{
  /* Set common defaults. */
  this->bounds = {{-1, -1, 0}, {3, 3, 6}, {}};
 
  /* Set if flipped and engine is NOT flagged with custom flip handling. */
  int flipped = this->flags.Test(VehicleRailFlag::Flipped) && !EngInfo(this->engine_type)->misc_flags.Test(EngineMiscFlag::RailFlips);
  /* If flipped and vehicle length is odd, we need to adjust the bounding box offset slightly. */
  int flip_offs = flipped && (this->gcache.cached_veh_length & 1);
 
  Direction dir = this->direction;
  if (flipped) dir = ReverseDir(dir);
 
  if (!IsDiagonalDirection(dir)) {
    static const Point _sign_table[] = {
      /* x, y */
      {-1, -1}, // DIR_N
      {-1,  1}, // DIR_E
      { 1,  1}, // DIR_S
      { 1, -1}, // DIR_W
    };
 
    int half_shorten = (VEHICLE_LENGTH - this->gcache.cached_veh_length + flipped) / 2;
 
    /* For all straight directions, move the bound box to the centre of the vehicle, but keep the size. */
    this->bounds.offset.x -= half_shorten * _sign_table[DirToDiagDir(dir)].x;
    this->bounds.offset.y -= half_shorten * _sign_table[DirToDiagDir(dir)].y;
  } else {
    switch (dir) {
        /* Shorten southern corner of the bounding box according the vehicle length
         * and center the bounding box on the vehicle. */
      case DIR_NE:
        this->bounds.origin.x = -(this->gcache.cached_veh_length + 1) / 2 + flip_offs;
        this->bounds.extent.x = this->gcache.cached_veh_length;
        this->bounds.offset.x = 1;
        break;
 
      case DIR_NW:
        this->bounds.origin.y = -(this->gcache.cached_veh_length + 1) / 2 + flip_offs;
        this->bounds.extent.y = this->gcache.cached_veh_length;
        this->bounds.offset.y = 1;
        break;
 
        /* Move northern corner of the bounding box down according to vehicle length
         * and center the bounding box on the vehicle. */
      case DIR_SW:
        this->bounds.origin.x = -(this->gcache.cached_veh_length) / 2 - flip_offs;
        this->bounds.extent.x = this->gcache.cached_veh_length;
        this->bounds.offset.x = 1 - (VEHICLE_LENGTH - this->gcache.cached_veh_length);
        break;
 
      case DIR_SE:
        this->bounds.origin.y = -(this->gcache.cached_veh_length) / 2 - flip_offs;
        this->bounds.extent.y = this->gcache.cached_veh_length;
        this->bounds.offset.y = 1 - (VEHICLE_LENGTH - this->gcache.cached_veh_length);
        break;
 
      default:
        NOT_REACHED();
    }
  }
}

static void MarkTrainAsStuck(Train *consist)
{
  if (!consist->flags.Test(VehicleRailFlag::Stuck)) {
    /* It is the first time the problem occurred, set the "train stuck" flag. */
    consist->flags.Set(VehicleRailFlag::Stuck);
 
    consist->wait_counter = 0;
 
    /* Stop train */
    consist->cur_speed = 0;
    consist->subspeed = 0;
    consist->SetLastSpeed();
 
    SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
  }
}

static void SwapTrainFlags(uint16_t *swap_flag1, uint16_t *swap_flag2)
{
  uint16_t flag1 = *swap_flag1;
  uint16_t flag2 = *swap_flag2;
 
  /* Clear the flags */
  ClrBit(*swap_flag1, GVF_GOINGUP_BIT);
  ClrBit(*swap_flag1, GVF_GOINGDOWN_BIT);
  ClrBit(*swap_flag2, GVF_GOINGUP_BIT);
  ClrBit(*swap_flag2, GVF_GOINGDOWN_BIT);
 
  /* Reverse the rail-flags (if needed) */
  if (HasBit(flag1, GVF_GOINGUP_BIT)) {
    SetBit(*swap_flag2, GVF_GOINGDOWN_BIT);
  } else if (HasBit(flag1, GVF_GOINGDOWN_BIT)) {
    SetBit(*swap_flag2, GVF_GOINGUP_BIT);
  }
  if (HasBit(flag2, GVF_GOINGUP_BIT)) {
    SetBit(*swap_flag1, GVF_GOINGDOWN_BIT);
  } else if (HasBit(flag2, GVF_GOINGDOWN_BIT)) {
    SetBit(*swap_flag1, GVF_GOINGUP_BIT);
  }
}

static void UpdateStatusAfterSwap(Train *v, bool reverse = true)
{
  /* Maybe reverse the direction. */
  if (reverse) v->direction = ReverseDir(v->direction);
 
  /* Call the proper EnterTile function unless we are in a wormhole. */
  if (v->track != TRACK_BIT_WORMHOLE) {
    VehicleEnterTile(v, v->tile, v->x_pos, v->y_pos);
  } else {
    /* VehicleEnterTile_TunnelBridge() sets TRACK_BIT_WORMHOLE when the vehicle
     * is on the last bit of the bridge head (frame == TILE_SIZE - 1).
     * If we were swapped with such a vehicle, we have set TRACK_BIT_WORMHOLE,
     * when we shouldn't have. Check if this is the case. */
    TileIndex vt = TileVirtXY(v->x_pos, v->y_pos);
    if (IsTileType(vt, TileType::TunnelBridge)) {
      VehicleEnterTile(v, vt, v->x_pos, v->y_pos);
      if (v->track != TRACK_BIT_WORMHOLE && IsBridgeTile(v->tile)) {
        /* We have just left the wormhole, possibly set the
         * "goingdown" bit. UpdateInclination() can be used
         * because we are at the border of the tile. */
        v->UpdatePosition();
        v->UpdateInclination(true, true);
        return;
      }
    }
  }
 
  v->UpdatePosition();
  v->UpdateViewport(true, true);
}

void ReverseTrainSwapVeh(Train *v, int l, int r)
{
  Train *a, *b;
 
  /* locate vehicles to swap */
  for (a = v; l != 0; l--) a = a->Next();
  for (b = v; r != 0; r--) b = b->Next();
 
  if (a != b) {
    /* swap the hidden bits */
    {
      bool a_hidden = a->vehstatus.Test(VehState::Hidden);
      bool b_hidden = b->vehstatus.Test(VehState::Hidden);
      b->vehstatus.Set(VehState::Hidden, a_hidden);
      a->vehstatus.Set(VehState::Hidden, b_hidden);
    }
 
    std::swap(a->track, b->track);
    std::swap(a->direction, b->direction);
    std::swap(a->x_pos, b->x_pos);
    std::swap(a->y_pos, b->y_pos);
    std::swap(a->tile,  b->tile);
    std::swap(a->z_pos, b->z_pos);
 
    SwapTrainFlags(&a->gv_flags, &b->gv_flags);
 
    UpdateStatusAfterSwap(a);
    UpdateStatusAfterSwap(b);
  } else {
    /* Swap GVF_GOINGUP_BIT/GVF_GOINGDOWN_BIT.
     * This is a little bit redundant way, a->gv_flags will
     * be (re)set twice, but it reduces code duplication */
    SwapTrainFlags(&a->gv_flags, &a->gv_flags);
    UpdateStatusAfterSwap(a);
  }
}

static bool IsTrain(const Vehicle *v)
{
  return v->type == VEH_TRAIN;
}

bool TrainOnCrossing(TileIndex tile)
{
  assert(IsLevelCrossingTile(tile));
 
  return HasVehicleOnTile(tile, IsTrain);
}

static bool TrainApproachingCrossingEnum(const Vehicle *v, TileIndex tile)
{
  if (v->type != VEH_TRAIN || v->vehstatus.Test(VehState::Crashed)) return false;
 
  const Train *t = Train::From(v);
  if (!t->IsMovingFront()) return false;
 
  return TrainApproachingCrossingTile(t) == tile;
}
 

static bool TrainApproachingCrossing(TileIndex tile)
{
  assert(IsLevelCrossingTile(tile));
 
  DiagDirection dir = AxisToDiagDir(GetCrossingRailAxis(tile));
  TileIndex tile_from = tile + TileOffsByDiagDir(dir);
 
  if (HasVehicleOnTile(tile_from, [&](const Vehicle *v) {
      return TrainApproachingCrossingEnum(v, tile);
    })) return true;
 
  dir = ReverseDiagDir(dir);
  tile_from = tile + TileOffsByDiagDir(dir);
 
  return HasVehicleOnTile(tile_from, [&](const Vehicle *v) {
    return TrainApproachingCrossingEnum(v, tile);
  });
}

static inline bool CheckLevelCrossing(TileIndex tile)
{
  /* reserved || train on crossing || train approaching crossing */
  return HasCrossingReservation(tile) || TrainOnCrossing(tile) || TrainApproachingCrossing(tile);
}

static void UpdateLevelCrossingTile(TileIndex tile, bool sound, bool force_barred)
{
  assert(IsLevelCrossingTile(tile));
  bool set_barred;
 
  /* We force the crossing to be barred when an adjacent crossing is barred, otherwise let it decide for itself. */
  set_barred = force_barred || CheckLevelCrossing(tile);
 
  /* The state has changed */
  if (set_barred != IsCrossingBarred(tile)) {
    if (set_barred && sound && _settings_client.sound.ambient) SndPlayTileFx(SND_0E_LEVEL_CROSSING, tile);
    SetCrossingBarred(tile, set_barred);
    MarkTileDirtyByTile(tile);
  }
}

void UpdateLevelCrossing(TileIndex tile, bool sound, bool force_bar)
{
  if (!IsLevelCrossingTile(tile)) return;
 
  bool forced_state = force_bar;
 
  const Axis axis = GetCrossingRoadAxis(tile);
  const DiagDirection dir1 = AxisToDiagDir(axis);
  const DiagDirection dir2 = ReverseDiagDir(dir1);
 
  /* Check if an adjacent crossing is barred. */
  for (DiagDirection dir : { dir1, dir2 }) {
    for (TileIndex t = tile; !forced_state && t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == axis; t = TileAddByDiagDir(t, dir)) {
      forced_state |= CheckLevelCrossing(t);
    }
  }
 
  /* Now that we know whether all tiles in this crossing should be barred or open,
   * we need to update those tiles. We start with the tile itself, then look along the road axis. */
  UpdateLevelCrossingTile(tile, sound, forced_state);
  for (DiagDirection dir : { dir1, dir2 }) {
    for (TileIndex t = TileAddByDiagDir(tile, dir); t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == axis; t = TileAddByDiagDir(t, dir)) {
      UpdateLevelCrossingTile(t, sound, forced_state);
    }
  }
}

void MarkDirtyAdjacentLevelCrossingTiles(TileIndex tile, Axis road_axis)
{
  const DiagDirection dir1 = AxisToDiagDir(road_axis);
  const DiagDirection dir2 = ReverseDiagDir(dir1);
  for (DiagDirection dir : { dir1, dir2 }) {
    const TileIndex t = TileAddByDiagDir(tile, dir);
    if (t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis) {
      MarkTileDirtyByTile(t);
    }
  }
}

void UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(TileIndex tile, Axis road_axis)
{
  const DiagDirection dir1 = AxisToDiagDir(road_axis);
  const DiagDirection dir2 = ReverseDiagDir(dir1);
  for (DiagDirection dir : { dir1, dir2 }) {
    const TileIndexDiff diff = TileOffsByDiagDir(dir);
    bool occupied = false;
    for (TileIndex t = tile + diff; t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
      occupied |= CheckLevelCrossing(t);
    }
    if (occupied) {
      /* Mark the immediately adjacent tile dirty */
      const TileIndex t = tile + diff;
      if (t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis) {
        MarkTileDirtyByTile(t);
      }
    } else {
      /* Unbar the crossing tiles in this direction as necessary */
      for (TileIndex t = tile + diff; t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
        if (IsCrossingBarred(t)) {
          /* The crossing tile is barred, unbar it and continue to check the next tile */
          SetCrossingBarred(t, false);
          MarkTileDirtyByTile(t);
        } else {
          /* The crossing tile is already unbarred, mark the tile dirty and stop checking */
          MarkTileDirtyByTile(t);
          break;
        }
      }
    }
  }
}

static inline void MaybeBarCrossingWithSound(TileIndex tile)
{
  if (!IsCrossingBarred(tile)) {
    SetCrossingReservation(tile, true);
    UpdateLevelCrossing(tile, true);
  }
}
 

static void AdvanceWagonsBeforeSwap(Train *moving_front)
{
  Train *base = moving_front;
  Train *first = base; // first vehicle to move
  Train *last = moving_front->GetMovingBack(); // last vehicle to move
  uint length = CountVehiclesInChain(moving_front->First());
 
  while (length > 2) {
    last = last->GetMovingPrev();
    first = first->GetMovingNext();
 
    int differential = base->CalcNextVehicleOffset() - last->CalcNextVehicleOffset();
 
    /* do not update images now
     * negative differential will be handled in AdvanceWagonsAfterSwap() */
    for (int i = 0; i < differential; i++) TrainController(first, last->GetMovingNext());
 
    base = first; // == base->GetMovingNext()
    length -= 2;
  }
}
 

static void AdvanceWagonsAfterSwap(Train *moving_front)
{
  /* first of all, fix the situation when the train was entering a depot */
  Train *dep = moving_front; // last vehicle in front of just left depot
  while (dep->GetMovingNext() != nullptr && (dep->track == TRACK_BIT_DEPOT || dep->GetMovingNext()->track != TRACK_BIT_DEPOT)) {
    dep = dep->GetMovingNext(); // find first vehicle outside of a depot, with next vehicle inside a depot
  }
 
  Train *leave = dep->GetMovingNext(); // first vehicle in a depot we are leaving now
 
  if (leave != nullptr) {
    /* 'pull' next wagon out of the depot, so we won't miss it (it could stay in depot forever) */
    int d = TicksToLeaveDepot(dep);
 
    if (d <= 0) {
      leave->vehstatus.Reset(VehState::Hidden); // move it out of the depot
      leave->track = TrackToTrackBits(GetRailDepotTrack(leave->tile));
      for (int i = 0; i >= d; i--) TrainController(leave, nullptr); // maybe move it, and maybe let another wagon leave
    }
  } else {
    dep = nullptr; // no vehicle in a depot, so no vehicle leaving a depot
  }
 
  Train *base = moving_front;
  Train *first = base; // first vehicle to move
  Train *last = moving_front->GetMovingBack(); // last vehicle to move
  uint length = CountVehiclesInChain(moving_front->First());
 
  /* We have to make sure all wagons that leave a depot because of train reversing are moved correctly
   * they have already correct spacing, so we have to make sure they are moved how they should */
  bool nomove = (dep == nullptr); // If there is no vehicle leaving a depot, limit the number of wagons moved immediately.
 
  while (length > 2) {
    /* we reached vehicle (originally) in front of a depot, stop now
     * (we would move wagons that are already moved with new wagon length). */
    if (base == dep) break;
 
    /* the last wagon was that one leaving a depot, so do not move it anymore */
    if (last == dep) nomove = true;
 
    last = last->GetMovingPrev();
    first = first->GetMovingNext();
 
    int differential = last->CalcNextVehicleOffset() - base->CalcNextVehicleOffset();
 
    /* do not update images now */
    for (int i = 0; i < differential; i++) TrainController(first, (nomove ? last->GetMovingNext() : nullptr));
 
    base = first; // == base->GetMovingNext()
    length -= 2;
  }
}
 
static bool IsWholeTrainInsideDepot(const Train *v)
{
  for (const Train *u = v; u != nullptr; u = u->Next()) {
    if (u->track != TRACK_BIT_DEPOT || u->tile != v->tile) return false;
  }
  return true;
}

static void ReverseTrainDirection(Train *consist)
{
  Train *moving_front = consist->GetMovingFront();
  if (IsRailDepotTile(moving_front->tile)) {
    if (IsWholeTrainInsideDepot(consist)) return;
    InvalidateWindowData(WC_VEHICLE_DEPOT, moving_front->tile);
  }
 
  /* Clear path reservation in front if train is not stuck. */
  if (!consist->flags.Test(VehicleRailFlag::Stuck)) FreeTrainTrackReservation(consist);
 
  /* Check if we were approaching a rail/road-crossing */
  TileIndex crossing = TrainApproachingCrossingTile(moving_front);
 
  /* Check if we should back up or flip the train. */
  if (consist->vehicle_flags.Test(VehicleFlag::DrivingBackwards) || _settings_game.difficulty.train_flip_reverse_allowed == TrainFlipReversingAllowed::None || consist->Last()->CanLeadTrain()) {
    /* The train will back up. */
    consist->vehicle_flags.Flip(VehicleFlag::DrivingBackwards);
 
    for (Train *u = consist; u != nullptr; u = u->Next()) {
      /* Invert going up/down */
      if (HasBit(u->gv_flags, GVF_GOINGUP_BIT) || HasBit(u->gv_flags, GVF_GOINGDOWN_BIT)) {
        ToggleBit(u->gv_flags, GVF_GOINGDOWN_BIT);
        ToggleBit(u->gv_flags, GVF_GOINGUP_BIT);
      }
      UpdateStatusAfterSwap(u, false);
    }
    /* We may have entered a depot and stopped driving backwards. */
    moving_front = consist->GetMovingFront();
  } else {
    /* The train will flip. */
    int r = CountVehiclesInChain(consist) - 1;  // number of vehicles - 1
 
    AdvanceWagonsBeforeSwap(moving_front);
 
    /* swap start<>end, start+1<>end-1, ... */
    int l = 0;
    do {
      ReverseTrainSwapVeh(consist, l++, r--);
    } while (l <= r);
 
    AdvanceWagonsAfterSwap(moving_front);
  }
 
  if (IsRailDepotTile(moving_front->tile)) {
    InvalidateWindowData(WC_VEHICLE_DEPOT, moving_front->tile);
  }
 
  consist->flags.Flip(VehicleRailFlag::Reversed);
  consist->flags.Reset(VehicleRailFlag::Reversing);
 
  /* recalculate cached data */
  consist->ConsistChanged(CCF_TRACK);
 
  /* update all images */
  for (Train *u = consist; u != nullptr; u = u->Next()) u->UpdateViewport(false, false);
 
  /* update crossing we were approaching */
  if (crossing != INVALID_TILE) UpdateLevelCrossing(crossing);
 
  /* maybe we are approaching crossing now, after reversal */
  crossing = TrainApproachingCrossingTile(moving_front);
  if (crossing != INVALID_TILE) MaybeBarCrossingWithSound(crossing);
 
  /* If we are inside a depot after reversing, don't bother with path reserving. */
  if (moving_front->track == TRACK_BIT_DEPOT) {
    /* Can't be stuck here as inside a depot is always a safe tile. */
    if (consist->flags.Test(VehicleRailFlag::Stuck)) SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
    consist->flags.Reset(VehicleRailFlag::Stuck);
    return;
  }
 
  /* VehicleExitDir does not always produce the desired dir for depots and
   * tunnels/bridges that is needed for UpdateSignalsOnSegment. */
  DiagDirection dir = VehicleExitDir(moving_front->GetMovingDirection(), moving_front->track);
  if (IsRailDepotTile(moving_front->tile) || IsTileType(moving_front->tile, TileType::TunnelBridge)) dir = INVALID_DIAGDIR;
 
  if (UpdateSignalsOnSegment(moving_front->tile, dir, consist->owner) == SIGSEG_PBS || _settings_game.pf.reserve_paths) {
    /* If we are currently on a tile with conventional signals, we can't treat the
     * current tile as a safe tile or we would enter a PBS block without a reservation. */
    bool first_tile_okay = !(IsTileType(moving_front->tile, TileType::Railway) &&
      HasSignalOnTrackdir(moving_front->tile, moving_front->GetVehicleTrackdir()) &&
      !IsPbsSignal(GetSignalType(moving_front->tile, FindFirstTrack(moving_front->track))));
 
    /* If we are on a depot tile facing outwards, do not treat the current tile as safe. */
    if (IsRailDepotTile(moving_front->tile) && TrackdirToExitdir(moving_front->GetVehicleTrackdir()) == GetRailDepotDirection(moving_front->tile)) first_tile_okay = false;
 
    if (IsRailStationTile(moving_front->tile)) SetRailStationPlatformReservation(moving_front->tile, TrackdirToExitdir(moving_front->GetVehicleTrackdir()), true);
    if (TryPathReserve(consist, false, first_tile_okay)) {
      /* Do a look-ahead now in case our current tile was already a safe tile. */
      CheckNextTrainTile(consist);
    } else if (consist->current_order.GetType() != OT_LOADING) {
      /* Do not wait for a way out when we're still loading */
      MarkTrainAsStuck(consist);
    }
  } else if (consist->flags.Test(VehicleRailFlag::Stuck)) {
    /* A train not inside a PBS block can't be stuck. */
    consist->flags.Reset(VehicleRailFlag::Stuck);
    consist->wait_counter = 0;
  }
}

CommandCost CmdReverseTrainDirection(DoCommandFlags flags, VehicleID veh_id, bool reverse_single_veh)
{
  Train *v = Train::GetIfValid(veh_id);
  if (v == nullptr) return CMD_ERROR;
 
  CommandCost ret = CheckOwnership(v->owner);
  if (ret.Failed()) return ret;
 
  if (reverse_single_veh) {
    /* turn a single unit around */
 
    if (v->IsMultiheaded() || EngInfo(v->engine_type)->callback_mask.Test(VehicleCallbackMask::ArticEngine)) {
      return CommandCost(STR_ERROR_CAN_T_REVERSE_DIRECTION_RAIL_VEHICLE_MULTIPLE_UNITS);
    }
 
    Train *front = v->First();
    /* make sure the vehicle is stopped in the depot */
    if (!front->IsStoppedInDepot()) {
      return CommandCost(STR_ERROR_TRAINS_CAN_ONLY_BE_ALTERED_INSIDE_A_DEPOT);
    }
 
    if (flags.Test(DoCommandFlag::Execute)) {
      v->flags.Flip(VehicleRailFlag::Flipped);
 
      front->ConsistChanged(CCF_ARRANGE);
      SetWindowDirty(WC_VEHICLE_DEPOT, front->tile);
      SetWindowDirty(WC_VEHICLE_DETAILS, front->index);
      InvalidateWindowData(WC_VEHICLE_VIEW, front->index);
      SetWindowClassesDirty(WC_TRAINS_LIST);
    }
  } else {
    /* turn the whole train around */
    if (!v->IsPrimaryVehicle()) return CMD_ERROR;
    if (v->vehstatus.Test(VehState::Crashed) || v->breakdown_ctr != 0) return CMD_ERROR;
 
    if (flags.Test(DoCommandFlag::Execute)) {
      /* Properly leave the station if we are loading and won't be loading anymore */
      if (v->current_order.IsType(OT_LOADING)) {
        const Vehicle *moving_back = v->GetMovingBack();
 
        /* not a station || different station --> leave the station */
        if (!IsTileType(moving_back->tile, TileType::Station) || GetStationIndex(moving_back->tile) != GetStationIndex(v->GetMovingFront()->tile)) {
          v->LeaveStation();
        }
      }
 
      /* We cancel any 'skip signal at dangers' here */
      v->force_proceed = TFP_NONE;
      InvalidateWindowData(WC_VEHICLE_VIEW, v->index);
 
      if (_settings_game.vehicle.train_acceleration_model != AM_ORIGINAL && v->cur_speed != 0) {
        v->flags.Flip(VehicleRailFlag::Reversing);
      } else {
        v->cur_speed = 0;
        v->SetLastSpeed();
        HideFillingPercent(&v->fill_percent_te_id);
        ReverseTrainDirection(v);
      }
 
      /* Unbunching data is no longer valid. */
      v->ResetDepotUnbunching();
    }
  }
  return CommandCost();
}

static TrainForceProceeding DetermineNextTrainForceProceeding(const Train *t)
{
  if (t->vehstatus.Test(VehState::Crashed) || t->force_proceed == TFP_SIGNAL) return TFP_NONE;
  if (!t->flags.Test(VehicleRailFlag::Stuck)) return t->IsChainInDepot() ? TFP_STUCK : TFP_SIGNAL;
 
  const Train *moving_front = t->GetMovingFront();
  TileIndex next_tile = TileAddByDiagDir(moving_front->tile, TrackdirToExitdir(moving_front->GetVehicleTrackdir()));
  if (next_tile == INVALID_TILE || !IsTileType(next_tile, TileType::Railway) || !HasSignals(next_tile)) return TFP_STUCK;
  TrackBits new_tracks = DiagdirReachesTracks(TrackdirToExitdir(moving_front->GetVehicleTrackdir())) & GetTrackBits(next_tile);
  return new_tracks != TRACK_BIT_NONE && HasSignalOnTrack(next_tile, FindFirstTrack(new_tracks)) ? TFP_SIGNAL : TFP_STUCK;
}

CommandCost CmdForceTrainProceed(DoCommandFlags flags, VehicleID veh_id)
{
  Train *t = Train::GetIfValid(veh_id);
  if (t == nullptr) return CMD_ERROR;
 
  if (!t->IsPrimaryVehicle()) return CMD_ERROR;
 
  CommandCost ret = CheckOwnership(t->owner);
  if (ret.Failed()) return ret;
 
 
  if (flags.Test(DoCommandFlag::Execute)) {
    t->force_proceed = DetermineNextTrainForceProceeding(t);
    InvalidateWindowData(WC_VEHICLE_VIEW, t->index);
 
    /* Unbunching data is no longer valid. */
    t->ResetDepotUnbunching();
  }
 
  return CommandCost();
}

static FindDepotData FindClosestTrainDepot(Train *v, int max_distance)
{
  assert(!v->vehstatus.Test(VehState::Crashed));
 
  return YapfTrainFindNearestDepot(v->GetMovingFront(), max_distance);
}
 
ClosestDepot Train::FindClosestDepot()
{
  FindDepotData tfdd = FindClosestTrainDepot(this, 0);
  if (tfdd.best_length == UINT_MAX) return ClosestDepot();
 
  return ClosestDepot(tfdd.tile, GetDepotIndex(tfdd.tile), tfdd.reverse);
}
 
void Train::PlayLeaveStationSound(bool force) const
{
  static const SoundFx sfx[] = {
    SND_04_DEPARTURE_STEAM,
    SND_0A_DEPARTURE_TRAIN,
    SND_0A_DEPARTURE_TRAIN,
    SND_47_DEPARTURE_MONORAIL,
    SND_41_DEPARTURE_MAGLEV
  };
 
  if (PlayVehicleSound(this, VSE_START, force)) return;
 
  SndPlayVehicleFx(sfx[RailVehInfo(this->engine_type)->engclass], this);
}

static void CheckNextTrainTile(Train *consist)
{
  /* Don't do any look-ahead if path_backoff_interval is 255. */
  if (_settings_game.pf.path_backoff_interval == 255) return;
 
  const Train *moving_front = consist->GetMovingFront();
 
  /* Exit if we are inside a depot. */
  if (moving_front->track == TRACK_BIT_DEPOT) return;
 
  switch (consist->current_order.GetType()) {
    /* Exit if we reached our destination depot. */
    case OT_GOTO_DEPOT:
      if (moving_front->tile == consist->dest_tile) return;
      break;
 
    case OT_GOTO_WAYPOINT:
      /* If we reached our waypoint, make sure we see that. */
      if (IsRailWaypointTile(moving_front->tile) && GetStationIndex(moving_front->tile) == consist->current_order.GetDestination()) ProcessOrders(consist);
      break;
 
    case OT_NOTHING:
    case OT_LEAVESTATION:
    case OT_LOADING:
      /* Exit if the current order doesn't have a destination, but the train has orders. */
      if (consist->GetNumOrders() > 0) return;
      break;
 
    default:
      break;
  }
  /* Exit if we are on a station tile and are going to stop. */
  if (IsRailStationTile(moving_front->tile) && consist->current_order.ShouldStopAtStation(consist, GetStationIndex(moving_front->tile))) return;
 
  Trackdir td = moving_front->GetVehicleTrackdir();
 
  /* On a tile with a red non-pbs signal, don't look ahead. */
  if (IsTileType(moving_front->tile, TileType::Railway) && HasSignalOnTrackdir(moving_front->tile, td) &&
      !IsPbsSignal(GetSignalType(moving_front->tile, TrackdirToTrack(td))) &&
      GetSignalStateByTrackdir(moving_front->tile, td) == SIGNAL_STATE_RED) return;
 
  CFollowTrackRail ft(consist);
  if (!ft.Follow(moving_front->tile, td)) return;
 
  if (!HasReservedTracks(ft.new_tile, TrackdirBitsToTrackBits(ft.new_td_bits))) {
    /* Next tile is not reserved. */
    if (KillFirstBit(ft.new_td_bits) == TRACKDIR_BIT_NONE) {
      if (HasPbsSignalOnTrackdir(ft.new_tile, FindFirstTrackdir(ft.new_td_bits))) {
        /* If the next tile is a PBS signal, try to make a reservation. */
        TrackBits tracks = TrackdirBitsToTrackBits(ft.new_td_bits);
        if (Rail90DegTurnDisallowed(GetTileRailType(ft.old_tile), GetTileRailType(ft.new_tile))) {
          tracks &= ~TrackCrossesTracks(TrackdirToTrack(ft.old_td));
        }
        ChooseTrainTrack(consist, ft.new_tile, ft.exitdir, tracks, false, nullptr, false);
      }
    }
  }
}

static bool CheckTrainStayInDepot(Train *v)
{
  /* bail out if not all wagons are in the same depot or not in a depot at all */
  for (const Train *u = v; u != nullptr; u = u->Next()) {
    if (u->track != TRACK_BIT_DEPOT || u->tile != v->tile) return false;
  }
 
  /* if the train got no power, then keep it in the depot */
  if (v->gcache.cached_power == 0) {
    v->vehstatus.Set(VehState::Stopped);
    SetWindowDirty(WC_VEHICLE_DEPOT, v->tile);
    return true;
  }
 
  /* Check if we should wait here for unbunching. */
  if (v->IsWaitingForUnbunching()) return true;
 
  SigSegState seg_state;
 
  if (v->force_proceed == TFP_NONE) {
    /* force proceed was not pressed */
    if (++v->wait_counter < 37) {
      SetWindowClassesDirty(WC_TRAINS_LIST);
      return true;
    }
 
    v->wait_counter = 0;
 
    seg_state = _settings_game.pf.reserve_paths ? SIGSEG_PBS : UpdateSignalsOnSegment(v->tile, INVALID_DIAGDIR, v->owner);
    if (seg_state == SIGSEG_FULL || HasDepotReservation(v->tile)) {
      /* Full and no PBS signal in block or depot reserved, can't exit. */
      SetWindowClassesDirty(WC_TRAINS_LIST);
      return true;
    }
  } else {
    seg_state = _settings_game.pf.reserve_paths ? SIGSEG_PBS : UpdateSignalsOnSegment(v->tile, INVALID_DIAGDIR, v->owner);
  }
 
  /* We are leaving a depot, but have to go to the exact same one; re-enter. */
  if (v->current_order.IsType(OT_GOTO_DEPOT) && v->tile == v->dest_tile) {
    /* Service when depot has no reservation. */
    if (!HasDepotReservation(v->tile)) VehicleEnterDepot(v);
    return true;
  }
 
  /* Only leave when we can reserve a path to our destination. */
  if (seg_state == SIGSEG_PBS && !TryPathReserve(v) && v->force_proceed == TFP_NONE) {
    /* No path and no force proceed. */
    SetWindowClassesDirty(WC_TRAINS_LIST);
    MarkTrainAsStuck(v);
    return true;
  }
 
  SetDepotReservation(v->tile, true);
  if (_settings_client.gui.show_track_reservation) MarkTileDirtyByTile(v->tile);
 
  VehicleServiceInDepot(v);
  v->LeaveUnbunchingDepot();
  v->PlayLeaveStationSound();
  SetWindowClassesDirty(WC_TRAINS_LIST);
 
  v->track = TRACK_BIT_X;
  if (v->direction & 2) v->track = TRACK_BIT_Y;
 
  v->vehstatus.Reset(VehState::Hidden);
  v->cur_speed = 0;
 
  v->UpdateViewport(true, true);
  v->UpdatePosition();
  UpdateSignalsOnSegment(v->tile, INVALID_DIAGDIR, v->owner);
  v->UpdateAcceleration();
  InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
 
  return false;
}

static void ClearPathReservation(const Train *v, TileIndex tile, Trackdir track_dir)
{
  DiagDirection dir = TrackdirToExitdir(track_dir);
 
  if (IsTileType(tile, TileType::TunnelBridge)) {
    /* Are we just leaving a tunnel/bridge? */
    if (GetTunnelBridgeDirection(tile) == ReverseDiagDir(dir)) {
      TileIndex end = GetOtherTunnelBridgeEnd(tile);
 
      if (TunnelBridgeIsFree(tile, end, v).Succeeded()) {
        /* Free the reservation only if no other train is on the tiles. */
        SetTunnelBridgeReservation(tile, false);
        SetTunnelBridgeReservation(end, false);
 
        if (_settings_client.gui.show_track_reservation) {
          if (IsBridge(tile)) {
            MarkBridgeDirty(tile);
          } else {
            MarkTileDirtyByTile(tile);
            MarkTileDirtyByTile(end);
          }
        }
      }
    }
  } else if (IsRailStationTile(tile)) {
    TileIndex new_tile = TileAddByDiagDir(tile, dir);
    /* If the new tile is not a further tile of the same station, we
     * clear the reservation for the whole platform. */
    if (!IsCompatibleTrainStationTile(new_tile, tile)) {
      SetRailStationPlatformReservation(tile, ReverseDiagDir(dir), false);
    }
  } else {
    /* Any other tile */
    UnreserveRailTrack(tile, TrackdirToTrack(track_dir));
  }
}

void FreeTrainTrackReservation(const Train *consist)
{
  assert(consist->IsFrontEngine());
 
  const Train *moving_front = consist->GetMovingFront();
  TileIndex tile = moving_front->tile;
  Trackdir td = moving_front->GetVehicleTrackdir();
  bool free_tile = tile != moving_front->tile || !(IsRailStationTile(moving_front->tile) || IsTileType(moving_front->tile, TileType::TunnelBridge));
  StationID station_id = IsRailStationTile(moving_front->tile) ? GetStationIndex(moving_front->tile) : StationID::Invalid();
 
  /* Can't be holding a reservation if we enter a depot. */
  if (IsRailDepotTile(tile) && TrackdirToExitdir(td) != GetRailDepotDirection(tile)) return;
  if (moving_front->track == TRACK_BIT_DEPOT) {
    /* Front engine is in a depot. We enter if some part is not in the depot. */
    for (const Train *u = consist; u != nullptr; u = u->Next()) {
      if (u->track != TRACK_BIT_DEPOT || u->tile != consist->tile) return;
    }
  }
  /* Don't free reservation if it's not ours. */
  if (TracksOverlap(GetReservedTrackbits(tile) | TrackToTrackBits(TrackdirToTrack(td)))) return;
 
  CFollowTrackRail ft(consist, GetAllCompatibleRailTypes(consist->railtypes));
  while (ft.Follow(tile, td)) {
    tile = ft.new_tile;
    TrackdirBits bits = ft.new_td_bits & TrackBitsToTrackdirBits(GetReservedTrackbits(tile));
    td = RemoveFirstTrackdir(&bits);
    assert(bits == TRACKDIR_BIT_NONE);
 
    if (!IsValidTrackdir(td)) break;
 
    if (IsTileType(tile, TileType::Railway)) {
      if (HasSignalOnTrackdir(tile, td) && !IsPbsSignal(GetSignalType(tile, TrackdirToTrack(td)))) {
        /* Conventional signal along trackdir: remove reservation and stop. */
        UnreserveRailTrack(tile, TrackdirToTrack(td));
        break;
      }
      if (HasPbsSignalOnTrackdir(tile, td)) {
        if (GetSignalStateByTrackdir(tile, td) == SIGNAL_STATE_RED) {
          /* Red PBS signal? Can't be our reservation, would be green then. */
          break;
        } else {
          /* Turn the signal back to red. */
          SetSignalStateByTrackdir(tile, td, SIGNAL_STATE_RED);
          MarkTileDirtyByTile(tile);
        }
      } else if (HasPbsSignalOnTrackdir(tile, ReverseTrackdir(td))) {
        /* Reservation passes an opposing path signal. Mark signal for update to re-establish the proper default state. */
        AddSideToSignalBuffer(tile, TrackdirToExitdir(ReverseTrackdir(td)), consist->owner);
      } else if (HasSignalOnTrackdir(tile, ReverseTrackdir(td)) && IsOnewaySignal(tile, TrackdirToTrack(td))) {
        break;
      }
    }
 
    /* Don't free first station/bridge/tunnel if we are on it. */
    if (free_tile || (!(ft.is_station && GetStationIndex(ft.new_tile) == station_id) && !ft.is_tunnel && !ft.is_bridge)) ClearPathReservation(consist, tile, td);
 
    free_tile = true;
  }
 
  UpdateSignalsInBuffer();
}
 
static const uint8_t _initial_tile_subcoord[6][4][3] = {
{{ 15, 8, 1 }, { 0, 0, 0 }, { 0, 8, 5 }, { 0,  0, 0 }},
{{  0, 0, 0 }, { 8, 0, 3 }, { 0, 0, 0 }, { 8, 15, 7 }},
{{  0, 0, 0 }, { 7, 0, 2 }, { 0, 7, 6 }, { 0,  0, 0 }},
{{ 15, 8, 2 }, { 0, 0, 0 }, { 0, 0, 0 }, { 8, 15, 6 }},
{{ 15, 7, 0 }, { 8, 0, 4 }, { 0, 0, 0 }, { 0,  0, 0 }},
{{  0, 0, 0 }, { 0, 0, 0 }, { 0, 8, 4 }, { 7, 15, 0 }},
};

static Track DoTrainPathfind(const Train *v, TileIndex tile, DiagDirection enterdir, TrackBits tracks, bool &path_found, bool do_track_reservation, PBSTileInfo *dest, TileIndex *final_dest)
{
  if (final_dest != nullptr) *final_dest = INVALID_TILE;
  return YapfTrainChooseTrack(v, tile, enterdir, tracks, path_found, do_track_reservation, dest, final_dest);
}

static PBSTileInfo ExtendTrainReservation(const Train *v, TrackBits *new_tracks, DiagDirection *enterdir)
{
  PBSTileInfo origin = FollowTrainReservation(v);
 
  CFollowTrackRail ft(v);
 
  std::vector<std::pair<TileIndex, Trackdir>> signals_set_to_red;
 
  TileIndex tile = origin.tile;
  Trackdir  cur_td = origin.trackdir;
  while (ft.Follow(tile, cur_td)) {
    if (KillFirstBit(ft.new_td_bits) == TRACKDIR_BIT_NONE) {
      /* Possible signal tile. */
      if (HasOnewaySignalBlockingTrackdir(ft.new_tile, FindFirstTrackdir(ft.new_td_bits))) break;
    }
 
    if (Rail90DegTurnDisallowed(GetTileRailType(ft.old_tile), GetTileRailType(ft.new_tile))) {
      ft.new_td_bits &= ~TrackdirCrossesTrackdirs(ft.old_td);
      if (ft.new_td_bits == TRACKDIR_BIT_NONE) break;
    }
 
    /* Station, depot or waypoint are a possible target. */
    bool target_seen = ft.is_station || (IsTileType(ft.new_tile, TileType::Railway) && !IsPlainRail(ft.new_tile));
    if (target_seen || KillFirstBit(ft.new_td_bits) != TRACKDIR_BIT_NONE) {
      /* Choice found or possible target encountered.
       * On finding a possible target, we need to stop and let the pathfinder handle the
       * remaining path. This is because we don't know if this target is in one of our
       * orders, so we might cause pathfinding to fail later on if we find a choice.
       * This failure would cause a bogous call to TryReserveSafePath which might reserve
       * a wrong path not leading to our next destination. */
      if (HasReservedTracks(ft.new_tile, TrackdirBitsToTrackBits(TrackdirReachesTrackdirs(ft.old_td)))) break;
 
      /* If we did skip some tiles, backtrack to the first skipped tile so the pathfinder
       * actually starts its search at the first unreserved tile. */
      if (ft.tiles_skipped != 0) ft.new_tile -= TileOffsByDiagDir(ft.exitdir) * ft.tiles_skipped;
 
      /* Choice found, path valid but not okay. Save info about the choice tile as well. */
      if (new_tracks != nullptr) *new_tracks = TrackdirBitsToTrackBits(ft.new_td_bits);
      if (enterdir != nullptr) *enterdir = ft.exitdir;
      return PBSTileInfo(ft.new_tile, ft.old_td, false);
    }
 
    tile = ft.new_tile;
    cur_td = FindFirstTrackdir(ft.new_td_bits);
 
    Trackdir rev_td = ReverseTrackdir(cur_td);
    if (IsSafeWaitingPosition(v, tile, cur_td, true, _settings_game.pf.forbid_90_deg)) {
      bool wp_free = IsWaitingPositionFree(v, tile, cur_td, _settings_game.pf.forbid_90_deg);
      if (!(wp_free && TryReserveRailTrack(tile, TrackdirToTrack(cur_td)))) break;
      /* Green path signal opposing the path? Turn to red. */
      if (HasPbsSignalOnTrackdir(tile, rev_td) && GetSignalStateByTrackdir(tile, rev_td) == SIGNAL_STATE_GREEN) {
        signals_set_to_red.emplace_back(tile, rev_td);
        SetSignalStateByTrackdir(tile, rev_td, SIGNAL_STATE_RED);
        MarkTileDirtyByTile(tile);
      }
      /* Safe position is all good, path valid and okay. */
      return PBSTileInfo(tile, cur_td, true);
    }
 
    if (!TryReserveRailTrack(tile, TrackdirToTrack(cur_td))) break;
 
    /* Green path signal opposing the path? Turn to red. */
    if (HasPbsSignalOnTrackdir(tile, rev_td) && GetSignalStateByTrackdir(tile, rev_td) == SIGNAL_STATE_GREEN) {
      signals_set_to_red.emplace_back(tile, rev_td);
      SetSignalStateByTrackdir(tile, rev_td, SIGNAL_STATE_RED);
      MarkTileDirtyByTile(tile);
    }
  }
 
  if (ft.err == CFollowTrackRail::EC_OWNER || ft.err == CFollowTrackRail::EC_NO_WAY) {
    /* End of line, path valid and okay. */
    return PBSTileInfo(ft.old_tile, ft.old_td, true);
  }
 
  /* Sorry, can't reserve path, back out. */
  tile = origin.tile;
  cur_td = origin.trackdir;
  TileIndex stopped = ft.old_tile;
  Trackdir  stopped_td = ft.old_td;
  while (tile != stopped || cur_td != stopped_td) {
    if (!ft.Follow(tile, cur_td)) break;
 
    if (Rail90DegTurnDisallowed(GetTileRailType(ft.old_tile), GetTileRailType(ft.new_tile))) {
      ft.new_td_bits &= ~TrackdirCrossesTrackdirs(ft.old_td);
      assert(ft.new_td_bits != TRACKDIR_BIT_NONE);
    }
    assert(KillFirstBit(ft.new_td_bits) == TRACKDIR_BIT_NONE);
 
    tile = ft.new_tile;
    cur_td = FindFirstTrackdir(ft.new_td_bits);
 
    UnreserveRailTrack(tile, TrackdirToTrack(cur_td));
  }
 
  /* Re-instate green signals we turned to red. */
  for (auto [sig_tile, td] : signals_set_to_red) {
    SetSignalStateByTrackdir(sig_tile, td, SIGNAL_STATE_GREEN);
  }
 
  /* Path invalid. */
  return PBSTileInfo();
}

static bool TryReserveSafeTrack(const Train *v, TileIndex tile, Trackdir td, bool override_railtype)
{
  return YapfTrainFindNearestSafeTile(v, tile, td, override_railtype);
}

class VehicleOrderSaver {
private:
  Train          *v;
  Order          old_order;
  TileIndex      old_dest_tile;
  StationID      old_last_station_visited;
  VehicleOrderID index;
  bool           suppress_implicit_orders;
  bool           restored;
 
public:
  VehicleOrderSaver(Train *_v) :
    v(_v),
    old_order(_v->current_order),
    old_dest_tile(_v->dest_tile),
    old_last_station_visited(_v->last_station_visited),
    index(_v->cur_real_order_index),
    suppress_implicit_orders(HasBit(_v->gv_flags, GVF_SUPPRESS_IMPLICIT_ORDERS)),
    restored(false)
  {
  }

  void Restore()
  {
    this->v->current_order = this->old_order;
    this->v->dest_tile = this->old_dest_tile;
    this->v->last_station_visited = this->old_last_station_visited;
    AssignBit(this->v->gv_flags, GVF_SUPPRESS_IMPLICIT_ORDERS, suppress_implicit_orders);
    this->restored = true;
  }

  ~VehicleOrderSaver()
  {
    if (!this->restored) this->Restore();
  }

  bool SwitchToNextOrder(bool skip_first)
  {
    if (this->v->GetNumOrders() == 0) return false;
 
    if (skip_first) ++this->index;
 
    int depth = 0;
 
    do {
      /* Wrap around. */
      if (this->index >= this->v->GetNumOrders()) this->index = 0;
 
      Order *order = this->v->GetOrder(this->index);
      assert(order != nullptr);
 
      switch (order->GetType()) {
        case OT_GOTO_DEPOT:
          /* Skip service in depot orders when the train doesn't need service. */
          if (order->GetDepotOrderType().Test(OrderDepotTypeFlag::Service) && !this->v->NeedsServicing()) break;
          [[fallthrough]];
        case OT_GOTO_STATION:
        case OT_GOTO_WAYPOINT:
          this->v->current_order = *order;
          return UpdateOrderDest(this->v, order, 0, true);
        case OT_CONDITIONAL: {
          VehicleOrderID next = ProcessConditionalOrder(order, this->v);
          if (next != INVALID_VEH_ORDER_ID) {
            depth++;
            this->index = next;
            /* Don't increment next, so no break here. */
            continue;
          }
          break;
        }
        default:
          break;
      }
      /* Don't increment inside the while because otherwise conditional
       * orders can lead to an infinite loop. */
      ++this->index;
      depth++;
    } while (this->index != this->v->cur_real_order_index && depth < this->v->GetNumOrders());
 
    return false;
  }
};
 
/* choose a track */
static Track ChooseTrainTrack(Train *consist, TileIndex tile, DiagDirection enterdir, TrackBits tracks, bool force_res, bool *got_reservation, bool mark_stuck)
{
  Track best_track = INVALID_TRACK;
  bool do_track_reservation = _settings_game.pf.reserve_paths || force_res;
  bool changed_signal = false;
  TileIndex final_dest = INVALID_TILE;
 
  assert((tracks & ~TRACK_BIT_MASK) == 0);
 
  if (got_reservation != nullptr) *got_reservation = false;
 
  /* Don't use tracks here as the setting to forbid 90 deg turns might have been switched between reservation and now. */
  TrackBits res_tracks = (TrackBits)(GetReservedTrackbits(tile) & DiagdirReachesTracks(enterdir));
  /* Do we have a suitable reserved track? */
  if (res_tracks != TRACK_BIT_NONE) return FindFirstTrack(res_tracks);
 
  /* Quick return in case only one possible track is available */
  if (KillFirstBit(tracks) == TRACK_BIT_NONE) {
    Track track = FindFirstTrack(tracks);
    /* We need to check for signals only here, as a junction tile can't have signals. */
    if (track != INVALID_TRACK && HasPbsSignalOnTrackdir(tile, TrackEnterdirToTrackdir(track, enterdir))) {
      do_track_reservation = true;
      changed_signal = true;
      SetSignalStateByTrackdir(tile, TrackEnterdirToTrackdir(track, enterdir), SIGNAL_STATE_GREEN);
    } else if (!do_track_reservation) {
      return track;
    }
    best_track = track;
  }
 
  const Train *moving_front = consist->GetMovingFront();
 
  PBSTileInfo   res_dest(tile, INVALID_TRACKDIR, false);
  DiagDirection dest_enterdir = enterdir;
  if (do_track_reservation) {
    res_dest = ExtendTrainReservation(consist, &tracks, &dest_enterdir);
    if (res_dest.tile == INVALID_TILE) {
      /* Reservation failed? */
      if (mark_stuck) MarkTrainAsStuck(consist);
      if (changed_signal) SetSignalStateByTrackdir(tile, TrackEnterdirToTrackdir(best_track, enterdir), SIGNAL_STATE_RED);
      return FindFirstTrack(tracks);
    }
    if (res_dest.okay) {
      /* Got a valid reservation that ends at a safe target, quick exit. */
      if (got_reservation != nullptr) *got_reservation = true;
      if (changed_signal) MarkTileDirtyByTile(tile);
      TryReserveRailTrack(moving_front->tile, TrackdirToTrack(moving_front->GetVehicleTrackdir()));
      return best_track;
    }
 
    /* Check if the train needs service here, so it has a chance to always find a depot.
     * Also check if the current order is a service order so we don't reserve a path to
     * the destination but instead to the next one if service isn't needed. */
    CheckIfTrainNeedsService(consist);
    if (consist->current_order.IsType(OT_DUMMY) || consist->current_order.IsType(OT_CONDITIONAL) || consist->current_order.IsType(OT_GOTO_DEPOT)) ProcessOrders(consist);
  }
 
  /* Save the current train order. The destructor will restore the old order on function exit. */
  VehicleOrderSaver orders(consist);
 
  /* If the current tile is the destination of the current order and
   * a reservation was requested, advance to the next order.
   * Don't advance on a depot order as depots are always safe end points
   * for a path and no look-ahead is necessary. This also avoids a
   * problem with depot orders not part of the order list when the
   * order list itself is empty. */
  if (consist->current_order.IsType(OT_LEAVESTATION)) {
    orders.SwitchToNextOrder(false);
  } else if (consist->current_order.IsType(OT_LOADING) || (!consist->current_order.IsType(OT_GOTO_DEPOT) && (
      consist->current_order.IsType(OT_GOTO_STATION) ?
      IsRailStationTile(moving_front->tile) && consist->current_order.GetDestination() == GetStationIndex(moving_front->tile) :
      moving_front->tile == consist->dest_tile))) {
    orders.SwitchToNextOrder(true);
  }
 
  if (res_dest.tile != INVALID_TILE && !res_dest.okay) {
    /* Pathfinders are able to tell that route was only 'guessed'. */
    bool      path_found = true;
    TileIndex new_tile = res_dest.tile;
 
    Track next_track = DoTrainPathfind(consist, new_tile, dest_enterdir, tracks, path_found, do_track_reservation, &res_dest, &final_dest);
    if (new_tile == tile) best_track = next_track;
    consist->HandlePathfindingResult(path_found);
  }
 
  /* No track reservation requested -> finished. */
  if (!do_track_reservation) return best_track;
 
  /* A path was found, but could not be reserved. */
  if (res_dest.tile != INVALID_TILE && !res_dest.okay) {
    if (mark_stuck) MarkTrainAsStuck(consist);
    FreeTrainTrackReservation(consist);
    return best_track;
  }
 
  /* No possible reservation target found, we are probably lost. */
  if (res_dest.tile == INVALID_TILE) {
    /* Try to find any safe destination. */
    PBSTileInfo origin = FollowTrainReservation(consist);
    if (TryReserveSafeTrack(consist, origin.tile, origin.trackdir, false)) {
      TrackBits res = GetReservedTrackbits(tile) & DiagdirReachesTracks(enterdir);
      best_track = FindFirstTrack(res);
      TryReserveRailTrack(moving_front->tile, TrackdirToTrack(moving_front->GetVehicleTrackdir()));
      if (got_reservation != nullptr) *got_reservation = true;
      if (changed_signal) MarkTileDirtyByTile(tile);
    } else {
      FreeTrainTrackReservation(consist);
      if (mark_stuck) MarkTrainAsStuck(consist);
    }
    return best_track;
  }
 
  if (got_reservation != nullptr) *got_reservation = true;
 
  /* Reservation target found and free, check if it is safe. */
  while (!IsSafeWaitingPosition(consist, res_dest.tile, res_dest.trackdir, true, _settings_game.pf.forbid_90_deg)) {
    /* Extend reservation until we have found a safe position. */
    DiagDirection exitdir = TrackdirToExitdir(res_dest.trackdir);
    TileIndex     next_tile = TileAddByDiagDir(res_dest.tile, exitdir);
    TrackBits     reachable = TrackdirBitsToTrackBits((TrackdirBits)(GetTileTrackStatus(next_tile, TRANSPORT_RAIL, RoadTramType::Invalid))) & DiagdirReachesTracks(exitdir);
    if (Rail90DegTurnDisallowed(GetTileRailType(res_dest.tile), GetTileRailType(next_tile))) {
      reachable &= ~TrackCrossesTracks(TrackdirToTrack(res_dest.trackdir));
    }
 
    /* Get next order with destination. */
    if (orders.SwitchToNextOrder(true)) {
      PBSTileInfo cur_dest;
      bool path_found;
      DoTrainPathfind(consist, next_tile, exitdir, reachable, path_found, true, &cur_dest, nullptr);
      if (cur_dest.tile != INVALID_TILE) {
        res_dest = cur_dest;
        if (res_dest.okay) continue;
        /* Path found, but could not be reserved. */
        FreeTrainTrackReservation(consist);
        if (mark_stuck) MarkTrainAsStuck(consist);
        if (got_reservation != nullptr) *got_reservation = false;
        changed_signal = false;
        break;
      }
    }
    /* No order or no safe position found, try any position. */
    if (!TryReserveSafeTrack(consist, res_dest.tile, res_dest.trackdir, true)) {
      FreeTrainTrackReservation(consist);
      if (mark_stuck) MarkTrainAsStuck(consist);
      if (got_reservation != nullptr) *got_reservation = false;
      changed_signal = false;
    }
    break;
  }
 
  TryReserveRailTrack(moving_front->tile, TrackdirToTrack(moving_front->GetVehicleTrackdir()));
 
  if (changed_signal) MarkTileDirtyByTile(tile);
 
  orders.Restore();
  if (consist->current_order.IsType(OT_GOTO_DEPOT) &&
      consist->current_order.GetDepotActionType().Test(OrderDepotActionFlag::NearestDepot) &&
      final_dest != INVALID_TILE && IsRailDepotTile(final_dest)) {
    consist->current_order.SetDestination(GetDepotIndex(final_dest));
    consist->dest_tile = final_dest;
    SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
  }
 
  return best_track;
}

bool TryPathReserve(Train *consist, bool mark_as_stuck, bool first_tile_okay)
{
  assert(consist->IsFrontEngine());
 
  const Train *moving_front = consist->GetMovingFront();
 
  /* We have to handle depots specially as the track follower won't look
   * at the depot tile itself but starts from the next tile. If we are still
   * inside the depot, a depot reservation can never be ours. */
  if (moving_front->track == TRACK_BIT_DEPOT) {
    if (HasDepotReservation(moving_front->tile)) {
      if (mark_as_stuck) MarkTrainAsStuck(consist);
      return false;
    } else {
      /* Depot not reserved, but the next tile might be. */
      TileIndex next_tile = TileAddByDiagDir(moving_front->tile, GetRailDepotDirection(moving_front->tile));
      if (HasReservedTracks(next_tile, DiagdirReachesTracks(GetRailDepotDirection(moving_front->tile)))) return false;
    }
  }
 
  Vehicle *other_train = nullptr;
  PBSTileInfo origin = FollowTrainReservation(consist, &other_train);
  /* The path we are driving on is already blocked by some other train.
   * This can only happen in certain situations when mixing path and
   * block signals or when changing tracks and/or signals.
   * Exit here as doing any further reservations will probably just
   * make matters worse. */
  if (other_train != nullptr && other_train->index != consist->index) {
    if (mark_as_stuck) MarkTrainAsStuck(consist);
    return false;
  }
  /* If we have a reserved path and the path ends at a safe tile, we are finished already. */
  if (origin.okay && (moving_front->tile != origin.tile || first_tile_okay)) {
    /* Can't be stuck then. */
    if (consist->flags.Test(VehicleRailFlag::Stuck)) SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
    consist->flags.Reset(VehicleRailFlag::Stuck);
    return true;
  }
 
  /* If we are in a depot, tentatively reserve the depot. */
  if (moving_front->track == TRACK_BIT_DEPOT) {
    SetDepotReservation(moving_front->tile, true);
    if (_settings_client.gui.show_track_reservation) MarkTileDirtyByTile(moving_front->tile);
  }
 
  DiagDirection exitdir = TrackdirToExitdir(origin.trackdir);
  TileIndex     new_tile = TileAddByDiagDir(origin.tile, exitdir);
  TrackBits     reachable = TrackdirBitsToTrackBits(TrackStatusToTrackdirBits(GetTileTrackStatus(new_tile, TRANSPORT_RAIL, RoadTramType::Invalid)) & DiagdirReachesTrackdirs(exitdir));
 
  if (Rail90DegTurnDisallowed(GetTileRailType(origin.tile), GetTileRailType(new_tile))) reachable &= ~TrackCrossesTracks(TrackdirToTrack(origin.trackdir));
 
  bool res_made = false;
  ChooseTrainTrack(consist, new_tile, exitdir, reachable, true, &res_made, mark_as_stuck);
 
  if (!res_made) {
    /* Free the depot reservation as well. */
    if (moving_front->track == TRACK_BIT_DEPOT) SetDepotReservation(moving_front->tile, false);
    return false;
  }
 
  if (consist->flags.Test(VehicleRailFlag::Stuck)) {
    consist->wait_counter = 0;
    SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
  }
  consist->flags.Reset(VehicleRailFlag::Stuck);
  return true;
}

static bool CheckReverseTrain(const Train *consist)
{
  const Train *moving_front = consist->GetMovingFront();
  if (_settings_game.difficulty.train_flip_reverse_allowed == TrainFlipReversingAllowed::EndOfLineOnly ||
      moving_front->track == TRACK_BIT_DEPOT || moving_front->track == TRACK_BIT_WORMHOLE ||
      !(moving_front->GetMovingDirection() & 1)) {
    return false;
  }
 
  assert(moving_front->track != TRACK_BIT_NONE);
 
  return YapfTrainCheckReverse(consist);
}

TileIndex Train::GetOrderStationLocation(StationID station)
{
  if (station == this->last_station_visited) this->last_station_visited = StationID::Invalid();
 
  const Station *st = Station::Get(station);
  if (!st->facilities.Test(StationFacility::Train)) {
    /* The destination station has no trainstation tiles. */
    this->IncrementRealOrderIndex();
    return TileIndex{};
  }
 
  return st->xy;
}

void Train::MarkDirty()
{
  Train *v = this;
  do {
    v->colourmap = PAL_NONE;
    v->UpdateViewport(true, false);
  } while ((v = v->Next()) != nullptr);
 
  /* need to update acceleration and cached values since the goods on the train changed. */
  this->CargoChanged();
  this->UpdateAcceleration();
}

int Train::UpdateSpeed()
{
  switch (_settings_game.vehicle.train_acceleration_model) {
    default: NOT_REACHED();
    case AM_ORIGINAL:
      return this->DoUpdateSpeed(this->acceleration * (this->GetAccelerationStatus() == AS_BRAKE ? -4 : 2), 0, this->GetCurrentMaxSpeed());
 
    case AM_REALISTIC:
      return this->DoUpdateSpeed(this->GetAcceleration(), this->GetAccelerationStatus() == AS_BRAKE ? 0 : 2, this->GetCurrentMaxSpeed());
  }
}

static void TrainEnterStation(Train *consist, StationID station)
{
  consist->last_station_visited = station;
 
  /* check if a train ever visited this station before */
  Station *st = Station::Get(station);
  if (!(st->had_vehicle_of_type & HVOT_TRAIN)) {
    st->had_vehicle_of_type |= HVOT_TRAIN;
    AddVehicleNewsItem(
      GetEncodedString(STR_NEWS_FIRST_TRAIN_ARRIVAL, st->index),
      consist->owner == _local_company ? NewsType::ArrivalCompany : NewsType::ArrivalOther,
      consist->index,
      st->index
    );
    AI::NewEvent(consist->owner, new ScriptEventStationFirstVehicle(st->index, consist->index));
    Game::NewEvent(new ScriptEventStationFirstVehicle(st->index, consist->index));
  }
 
  consist->force_proceed = TFP_NONE;
  InvalidateWindowData(WC_VEHICLE_VIEW, consist->index);
 
  consist->BeginLoading();
 
  TileIndex tile = consist->GetMovingFront()->tile;
  TriggerStationRandomisation(st, tile, StationRandomTrigger::VehicleArrives);
  TriggerStationAnimation(st, tile, StationAnimationTrigger::VehicleArrives);
}

static inline bool CheckCompatibleRail(const Train *v, TileIndex tile, bool check_railtype)
{
  return IsTileOwner(tile, v->owner) &&
      (!check_railtype || !v->IsFrontEngine() || v->compatible_railtypes.Test(GetRailType(tile)));
}

struct AccelerationSlowdownParams {
  uint8_t small_turn; 
  uint8_t large_turn; 
  uint8_t z_up;       
  uint8_t z_down;     
};

static const AccelerationSlowdownParams _accel_slowdown[] = {
  /* normal accel */
  {256 / 4, 256 / 2, 256 / 4, 2}, 
  {256 / 4, 256 / 2, 256 / 4, 2}, 
  {0,       256 / 2, 256 / 4, 2}, 
};

static inline void AffectSpeedByZChange(Train *consist, int z_diff)
{
  if (z_diff == 0 || _settings_game.vehicle.train_acceleration_model != AM_ORIGINAL) return;
 
  const AccelerationSlowdownParams *asp = &_accel_slowdown[static_cast<int>(consist->GetAccelerationType())];
 
  if (z_diff > 0) {
    consist->cur_speed -= (consist->cur_speed * asp->z_up >> 8);
  } else {
    uint16_t spd = consist->cur_speed + asp->z_down;
    if (spd <= consist->gcache.cached_max_track_speed) consist->cur_speed = spd;
  }
}
 
static bool TrainMovedChangeSignals(TileIndex tile, DiagDirection dir)
{
  if (IsTileType(tile, TileType::Railway) &&
      GetRailTileType(tile) == RailTileType::Signals) {
    TrackdirBits tracks = TrackBitsToTrackdirBits(GetTrackBits(tile)) & DiagdirReachesTrackdirs(dir);
    Trackdir trackdir = FindFirstTrackdir(tracks);
    if (UpdateSignalsOnSegment(tile,  TrackdirToExitdir(trackdir), GetTileOwner(tile)) == SIGSEG_PBS && HasSignalOnTrackdir(tile, trackdir)) {
      /* A PBS block with a non-PBS signal facing us? */
      if (!IsPbsSignal(GetSignalType(tile, TrackdirToTrack(trackdir)))) return true;
    }
  }
  return false;
}

void Train::ReserveTrackUnderConsist() const
{
  for (const Train *u = this; u != nullptr; u = u->Next()) {
    switch (u->track) {
      case TRACK_BIT_WORMHOLE:
        TryReserveRailTrack(u->tile, DiagDirToDiagTrack(GetTunnelBridgeDirection(u->tile)));
        break;
      case TRACK_BIT_DEPOT:
        break;
      default:
        TryReserveRailTrack(u->tile, TrackBitsToTrack(u->track));
        break;
    }
  }
}

uint Train::Crash(bool flooded)
{
  uint victims = 0;
  if (this->IsFrontEngine()) {
    victims += 2; // driver
 
    /* Remove the reserved path in front of the train if it is not stuck.
     * Also clear all reserved tracks the train is currently on. */
    if (!this->flags.Test(VehicleRailFlag::Stuck)) FreeTrainTrackReservation(this);
    for (const Train *v = this; v != nullptr; v = v->Next()) {
      ClearPathReservation(v, v->tile, v->GetVehicleTrackdir());
      if (IsTileType(v->tile, TileType::TunnelBridge)) {
        /* ClearPathReservation will not free the wormhole exit
         * if the train has just entered the wormhole. */
        SetTunnelBridgeReservation(GetOtherTunnelBridgeEnd(v->tile), false);
      }
    }
 
    /* we may need to update crossing we were approaching,
     * but must be updated after the train has been marked crashed */
    TileIndex crossing = TrainApproachingCrossingTile(this->GetMovingFront());
    if (crossing != INVALID_TILE) UpdateLevelCrossing(crossing);
 
    /* Remove the loading indicators (if any) */
    HideFillingPercent(&this->fill_percent_te_id);
  }
 
  victims += this->GroundVehicleBase::Crash(flooded);
 
  this->crash_anim_pos = flooded ? 4000 : 1; // max 4440, disappear pretty fast when flooded
  return victims;
}

static uint TrainCrashed(Train *v)
{
  uint victims = 0;
 
  /* do not crash train twice */
  if (!v->vehstatus.Test(VehState::Crashed)) {
    victims = v->Crash();
    TileIndex tile = v->GetMovingFront()->tile;
    AI::NewEvent(v->owner, new ScriptEventVehicleCrashed(v->index, tile, ScriptEventVehicleCrashed::CRASH_TRAIN, victims, v->owner));
    Game::NewEvent(new ScriptEventVehicleCrashed(v->index, tile, ScriptEventVehicleCrashed::CRASH_TRAIN, victims, v->owner));
  }
 
  /* Try to re-reserve track under already crashed train too.
   * Crash() clears the reservation! */
  v->ReserveTrackUnderConsist();
 
  return victims;
}

static uint CheckTrainCollision(Vehicle *v, Train *moving_front)
{
  /* Make sure we are a train, and are not in a depot. */
  if (v->type != VEH_TRAIN) return 0;
 
  /* We can't crash into trains in a depot. */
  if (Train::From(v)->track == TRACK_BIT_DEPOT) return 0;
 
  /* Do not crash into trains of another company. */
  if (v->owner != moving_front->First()->owner) return 0;
 
  /* Do not collide with our own wagons */
  if (v->First() == moving_front->First()) return 0;
 
  int x_diff = v->x_pos - moving_front->x_pos;
  int y_diff = v->y_pos - moving_front->y_pos;
 
  /* Do fast calculation to check whether trains are not in close vicinity
   * and quickly reject trains distant enough for any collision.
   * Differences are shifted by 7, mapping range [-7 .. 8] into [0 .. 15]
   * Differences are then ORed and then we check for any higher bits */
  uint hash = (y_diff + 7) | (x_diff + 7);
  if (hash & ~15) return 0;
 
  /* Slower check using multiplication */
  int min_diff = (Train::From(v)->gcache.cached_veh_length + 1) / 2 + (moving_front->gcache.cached_veh_length + 1) / 2 - 1;
  if (x_diff * x_diff + y_diff * y_diff > min_diff * min_diff) return 0;
 
  /* Happens when there is a train under bridge next to bridge head */
  if (abs(v->z_pos - moving_front->z_pos) > 5) return 0;
 
  /* Crash both trains. Two statements required to guarantee execution
   * order because RandomRange() is involved. */
  uint num_victims = TrainCrashed(moving_front->First());
  return num_victims + TrainCrashed(Train::From(v)->First());
}

static bool CheckTrainCollision(Train *moving_front)
{
  /* can't collide in depot */
  if (moving_front->track == TRACK_BIT_DEPOT) return false;
 
  assert(moving_front->track == TRACK_BIT_WORMHOLE || TileVirtXY(moving_front->x_pos, moving_front->y_pos) == moving_front->tile);
 
  uint num_victims = 0;
 
  /* find colliding vehicles */
  if (moving_front->track == TRACK_BIT_WORMHOLE) {
    for (Vehicle *u : VehiclesOnTile(moving_front->tile)) {
      num_victims += CheckTrainCollision(u, moving_front);
    }
    for (Vehicle *u : VehiclesOnTile(GetOtherTunnelBridgeEnd(moving_front->tile))) {
      num_victims += CheckTrainCollision(u, moving_front);
    }
  } else {
    for (Vehicle *u : VehiclesNearTileXY(moving_front->x_pos, moving_front->y_pos, 7)) {
      num_victims += CheckTrainCollision(u, moving_front);
    }
  }
 
  /* any dead -> no crash */
  if (num_victims == 0) return false;
 
  AddTileNewsItem(GetEncodedString(STR_NEWS_TRAIN_CRASH, num_victims), NewsType::Accident, moving_front->tile);
 
  ModifyStationRatingAround(moving_front->tile, moving_front->First()->owner, -160, 30);
  if (_settings_client.sound.disaster) SndPlayVehicleFx(SND_13_TRAIN_COLLISION, moving_front);
  return true;
}

bool TrainController(Train *v, Vehicle *nomove, bool reverse)
{
  Train *first = v->First();
  Train *prev;
  bool direction_changed = false; // has direction of any part changed?
 
  /* For every vehicle after and including the given vehicle */
  for (prev = v->GetMovingPrev(); v != nomove; prev = v, v = v->GetMovingNext()) {
    DiagDirection enterdir = DIAGDIR_BEGIN;
    bool update_signals_crossing = false; // will we update signals or crossing state?
 
    GetNewVehiclePosResult gp = GetNewVehiclePos(v);
    if (v->track != TRACK_BIT_WORMHOLE) {
      /* Not inside tunnel */
      if (gp.old_tile == gp.new_tile) {
        /* Staying in the old tile */
        if (v->track == TRACK_BIT_DEPOT) {
          /* Inside depot */
          gp.x = v->x_pos;
          gp.y = v->y_pos;
        } else {
          /* Not inside depot */
 
          /* Reverse when we are at the end of the track already, do not move to the new position */
          if (v->IsMovingFront() && !TrainCheckIfLineEnds(v, reverse)) return false;
 
          auto vets = VehicleEnterTile(v, gp.new_tile, gp.x, gp.y);
          if (vets.Test(VehicleEnterTileState::CannotEnter)) {
            goto invalid_rail;
          }
          if (vets.Test(VehicleEnterTileState::EnteredStation)) {
            /* The new position is the end of the platform */
            TrainEnterStation(first, GetStationIndex(gp.new_tile));
          }
        }
      } else {
        /* A new tile is about to be entered. */
 
        /* Determine what direction we're entering the new tile from */
        enterdir = DiagdirBetweenTiles(gp.old_tile, gp.new_tile);
        assert(IsValidDiagDirection(enterdir));
 
        /* Get the status of the tracks in the new tile and mask
         * away the bits that aren't reachable. */
        TrackStatus ts = GetTileTrackStatus(gp.new_tile, TRANSPORT_RAIL, RoadTramType::Invalid, ReverseDiagDir(enterdir));
        TrackdirBits reachable_trackdirs = DiagdirReachesTrackdirs(enterdir);
 
        TrackdirBits trackdirbits = TrackStatusToTrackdirBits(ts) & reachable_trackdirs;
        TrackBits red_signals = TrackdirBitsToTrackBits(TrackStatusToRedSignals(ts) & reachable_trackdirs);
 
        TrackBits bits = TrackdirBitsToTrackBits(trackdirbits);
        if (Rail90DegTurnDisallowed(GetTileRailType(gp.old_tile), GetTileRailType(gp.new_tile)) && prev == nullptr) {
          /* We allow wagons to make 90 deg turns, because forbid_90_deg
           * can be switched on halfway a turn */
          bits &= ~TrackCrossesTracks(FindFirstTrack(v->track));
        }
 
        if (bits == TRACK_BIT_NONE) goto invalid_rail;
 
        /* Check if the new tile constrains tracks that are compatible
         * with the current train, if not, bail out. */
        if (!CheckCompatibleRail(v->First(), gp.new_tile, v->IsMovingFront())) goto invalid_rail;
 
        TrackBits chosen_track;
        if (v->IsMovingFront()) {
          /* Currently the locomotive is active. Determine which one of the
           * available tracks to choose */
          chosen_track = TrackToTrackBits(ChooseTrainTrack(first, gp.new_tile, enterdir, bits, false, nullptr, true));
          assert(chosen_track & (bits | GetReservedTrackbits(gp.new_tile)));
 
          if (first->force_proceed != TFP_NONE && IsPlainRailTile(gp.new_tile) && HasSignals(gp.new_tile)) {
            /* For each signal we find decrease the counter by one.
             * We start at two, so the first signal we pass decreases
             * this to one, then if we reach the next signal it is
             * decreased to zero and we won't pass that new signal. */
            Trackdir dir = FindFirstTrackdir(trackdirbits);
            if (HasSignalOnTrackdir(gp.new_tile, dir) ||
                (HasSignalOnTrackdir(gp.new_tile, ReverseTrackdir(dir)) &&
                GetSignalType(gp.new_tile, TrackdirToTrack(dir)) != SIGTYPE_PBS)) {
              /* However, we do not want to be stopped by PBS signals
               * entered via the back. */
              first->force_proceed = (first->force_proceed == TFP_SIGNAL) ? TFP_STUCK : TFP_NONE;
              InvalidateWindowData(WC_VEHICLE_VIEW, first->index);
            }
          }
 
          /* Check if it's a red signal and that force proceed is not clicked. */
          if ((red_signals & chosen_track) && first->force_proceed == TFP_NONE) {
            /* In front of a red signal */
            Trackdir i = FindFirstTrackdir(trackdirbits);
 
            /* Don't handle stuck trains here. */
            if (first->flags.Test(VehicleRailFlag::Stuck)) return false;
 
            if (!HasSignalOnTrackdir(gp.new_tile, ReverseTrackdir(i))) {
              first->cur_speed = 0;
              first->subspeed = 0;
              first->progress = 255; // make sure that every bit of acceleration will hit the signal again, so speed stays 0.
              if (!_settings_game.pf.reverse_at_signals || ++first->wait_counter < _settings_game.pf.wait_oneway_signal * Ticks::DAY_TICKS * 2) return false;
            } else if (HasSignalOnTrackdir(gp.new_tile, i)) {
              first->cur_speed = 0;
              first->subspeed = 0;
              first->progress = 255; // make sure that every bit of acceleration will hit the signal again, so speed stays 0.
              if (!_settings_game.pf.reverse_at_signals || ++first->wait_counter < _settings_game.pf.wait_twoway_signal * Ticks::DAY_TICKS * 2) {
                DiagDirection exitdir = TrackdirToExitdir(i);
                TileIndex o_tile = TileAddByDiagDir(gp.new_tile, exitdir);
 
                exitdir = ReverseDiagDir(exitdir);
 
                /* check if a train is waiting on the other side */
                if (!HasVehicleOnTile(o_tile, [&exitdir](const Vehicle *u) {
                    if (u->type != VEH_TRAIN || u->vehstatus.Test(VehState::Crashed)) return false;
                    const Train *t = Train::From(u);
 
                    /* not front engine of a train, inside wormhole or depot, crashed */
                    if (!t->IsFrontEngine() || !(t->track & TRACK_BIT_MASK)) return false;
 
                    if (t->cur_speed > 5 || VehicleExitDir(t->direction, t->track) != exitdir) return false;
 
                    return true;
                  })) return false;
              }
            }
 
            /* If we would reverse but are currently in a PBS block and
             * reversing of stuck trains is disabled, don't reverse.
             * This does not apply if the reason for reversing is a one-way
             * signal blocking us, because a train would then be stuck forever. */
            if (!_settings_game.pf.reverse_at_signals && !HasOnewaySignalBlockingTrackdir(gp.new_tile, i) &&
                UpdateSignalsOnSegment(v->tile, enterdir, v->owner) == SIGSEG_PBS) {
              first->wait_counter = 0;
              return false;
            }
            goto reverse_train_direction;
          } else {
            TryReserveRailTrack(gp.new_tile, TrackBitsToTrack(chosen_track), false);
          }
        } else {
          /* The wagon is active, simply follow the prev vehicle. */
          if (prev->tile == gp.new_tile) {
            /* Choose the same track as prev */
            if (prev->track == TRACK_BIT_WORMHOLE) {
              /* Vehicles entering tunnels enter the wormhole earlier than for bridges.
               * However, just choose the track into the wormhole. */
              assert(IsTunnel(prev->tile));
              chosen_track = bits;
            } else {
              chosen_track = prev->track;
            }
          } else {
            /* Choose the track that leads to the tile where prev is.
             * This case is active if 'prev' is already on the second next tile, when 'v' just enters the next tile.
             * I.e. when the tile between them has only space for a single vehicle like
             *  1) horizontal/vertical track tiles and
             *  2) some orientations of tunnel entries, where the vehicle is already inside the wormhole at 8/16 from the tile edge.
             *     Is also the train just reversing, the wagon inside the tunnel is 'on' the tile of the opposite tunnel entry.
             */
            static const TrackBits _connecting_track[DIAGDIR_END][DIAGDIR_END] = {
              {TRACK_BIT_X,     TRACK_BIT_LOWER, TRACK_BIT_NONE,  TRACK_BIT_LEFT },
              {TRACK_BIT_UPPER, TRACK_BIT_Y,     TRACK_BIT_LEFT,  TRACK_BIT_NONE },
              {TRACK_BIT_NONE,  TRACK_BIT_RIGHT, TRACK_BIT_X,     TRACK_BIT_UPPER},
              {TRACK_BIT_RIGHT, TRACK_BIT_NONE,  TRACK_BIT_LOWER, TRACK_BIT_Y    }
            };
            DiagDirection exitdir = DiagdirBetweenTiles(gp.new_tile, prev->tile);
            assert(IsValidDiagDirection(exitdir));
            chosen_track = _connecting_track[enterdir][exitdir];
          }
          chosen_track &= bits;
        }
 
        /* Make sure chosen track is a valid track */
        assert(
            chosen_track == TRACK_BIT_X     || chosen_track == TRACK_BIT_Y ||
            chosen_track == TRACK_BIT_UPPER || chosen_track == TRACK_BIT_LOWER ||
            chosen_track == TRACK_BIT_LEFT  || chosen_track == TRACK_BIT_RIGHT);
 
        /* Update XY to reflect the entrance to the new tile, and select the direction to use */
        const uint8_t *b = _initial_tile_subcoord[FindFirstBit(chosen_track)][enterdir];
        gp.x = (gp.x & ~0xF) | b[0];
        gp.y = (gp.y & ~0xF) | b[1];
        Direction chosen_dir = (Direction)b[2];
 
        /* Call the landscape function and tell it that the vehicle entered the tile */
        auto vets = VehicleEnterTile(v, gp.new_tile, gp.x, gp.y);
        if (vets.Test(VehicleEnterTileState::CannotEnter)) {
          goto invalid_rail;
        }
 
        if (!vets.Test(VehicleEnterTileState::EnteredWormhole)) {
          Track track = FindFirstTrack(chosen_track);
          Trackdir tdir = TrackDirectionToTrackdir(track, chosen_dir);
          if (v->IsMovingFront() && HasPbsSignalOnTrackdir(gp.new_tile, tdir)) {
            SetSignalStateByTrackdir(gp.new_tile, tdir, SIGNAL_STATE_RED);
            MarkTileDirtyByTile(gp.new_tile);
          }
 
          /* Clear any track reservation when the last vehicle leaves the tile */
          if (v->GetMovingNext() == nullptr) ClearPathReservation(v, v->tile, v->GetVehicleTrackdir());
 
          v->tile = gp.new_tile;
 
          if (GetTileRailType(gp.new_tile) != GetTileRailType(gp.old_tile)) {
            first->ConsistChanged(CCF_TRACK);
          }
 
          v->track = chosen_track;
          assert(v->track);
        }
 
        /* We need to update signal status, but after the vehicle position hash
         * has been updated by UpdateInclination() */
        update_signals_crossing = true;
 
        if (chosen_dir != v->GetMovingDirection()) {
          if (prev == nullptr && _settings_game.vehicle.train_acceleration_model == AM_ORIGINAL) {
            const AccelerationSlowdownParams *asp = &_accel_slowdown[static_cast<int>(v->GetAccelerationType())];
            DirDiff diff = DirDifference(v->direction, chosen_dir);
            v->cur_speed -= (diff == DIRDIFF_45RIGHT || diff == DIRDIFF_45LEFT ? asp->small_turn : asp->large_turn) * v->cur_speed >> 8;
          }
          direction_changed = true;
          v->SetMovingDirection(chosen_dir);
        }
 
        if (v->IsMovingFront()) {
          first->wait_counter = 0;
 
          /* If we are approaching a crossing that is reserved, play the sound now. */
          TileIndex crossing = TrainApproachingCrossingTile(v); // We know we are the moving front, so we can check v.
          if (crossing != INVALID_TILE && HasCrossingReservation(crossing) && _settings_client.sound.ambient) SndPlayTileFx(SND_0E_LEVEL_CROSSING, crossing);
 
          /* Always try to extend the reservation when entering a tile. */
          CheckNextTrainTile(first);
        }
 
        if (vets.Test(VehicleEnterTileState::EnteredStation)) {
          /* The new position is the location where we want to stop */
          TrainEnterStation(first, GetStationIndex(gp.new_tile));
        }
      }
    } else {
      if (IsTileType(gp.new_tile, TileType::TunnelBridge) && VehicleEnterTile(v, gp.new_tile, gp.x, gp.y).Test(VehicleEnterTileState::EnteredWormhole)) {
        /* Perform look-ahead on tunnel exit. */
        if (v->IsMovingFront()) {
          TryReserveRailTrack(gp.new_tile, DiagDirToDiagTrack(GetTunnelBridgeDirection(gp.new_tile)));
          CheckNextTrainTile(first);
        }
        /* Prevent v->UpdateInclination() being called with wrong parameters.
         * This could happen if the train was reversed inside the tunnel/bridge. */
        if (gp.old_tile == gp.new_tile) {
          gp.old_tile = GetOtherTunnelBridgeEnd(gp.old_tile);
        }
      } else {
        v->x_pos = gp.x;
        v->y_pos = gp.y;
        v->UpdatePosition();
        if (!v->vehstatus.Test(VehState::Hidden)) v->Vehicle::UpdateViewport(true);
        continue;
      }
    }
 
    /* update image of train, as well as delta XY */
    v->UpdateDeltaXY();
 
    v->x_pos = gp.x;
    v->y_pos = gp.y;
    v->UpdatePosition();
 
    /* update the Z position of the vehicle */
    int old_z = v->UpdateInclination(gp.new_tile != gp.old_tile, false);
 
    if (prev == nullptr) {
      /* This is the first vehicle in the train */
      AffectSpeedByZChange(first, v->z_pos - old_z);
    }
 
    if (update_signals_crossing) {
      if (v->IsMovingFront()) {
        if (TrainMovedChangeSignals(gp.new_tile, enterdir)) {
          /* We are entering a block with PBS signals right now, but
           * not through a PBS signal. This means we don't have a
           * reservation right now. As a conventional signal will only
           * ever be green if no other train is in the block, getting
           * a path should always be possible. If the player built
           * such a strange network that it is not possible, the train
           * will be marked as stuck and the player has to deal with
           * the problem. */
          if ((!HasReservedTracks(gp.new_tile, v->track) &&
              !TryReserveRailTrack(gp.new_tile, FindFirstTrack(v->track))) ||
              !TryPathReserve(first)) {
            MarkTrainAsStuck(first);
          }
        }
      }
 
      /* Signals can only change when the first
       * (above) or the last vehicle moves. */
      if (v->GetMovingNext() == nullptr) {
        TrainMovedChangeSignals(gp.old_tile, ReverseDiagDir(enterdir));
        if (IsLevelCrossingTile(gp.old_tile)) UpdateLevelCrossing(gp.old_tile);
      }
    }
 
    /* Do not check on every tick to save some computing time. */
    if (v->IsMovingFront() && first->tick_counter % _settings_game.pf.path_backoff_interval == 0) CheckNextTrainTile(first);
  }
 
  if (direction_changed) first->tcache.cached_max_curve_speed = first->GetCurveSpeedLimit();
 
  return true;
 
invalid_rail:
  /* We've reached end of line?? */
  if (prev != nullptr) FatalError("Disconnecting train");
 
reverse_train_direction:
  if (reverse) {
    first->wait_counter = 0;
    first->cur_speed = 0;
    first->subspeed = 0;
    ReverseTrainDirection(first);
  }
 
  return false;
}
 
static bool IsRailStationPlatformOccupied(TileIndex tile)
{
  TileIndexDiff delta = TileOffsByAxis(GetRailStationAxis(tile));
 
  for (TileIndex t = tile; IsCompatibleTrainStationTile(t, tile); t -= delta) {
    if (HasVehicleOnTile(t, IsTrain)) return true;
  }
  for (TileIndex t = tile + delta; IsCompatibleTrainStationTile(t, tile); t += delta) {
    if (HasVehicleOnTile(t, IsTrain)) return true;
  }
 
  return false;
}

static void DeleteLastWagon(Train *v)
{
  Train *first = v->First();
 
  /* Go to the last wagon and delete the link pointing there
   * new_last is then the one-before-last wagon, and v the last
   * one which will physically be removed */
  Train *new_last = v;
  for (; v->Next() != nullptr; v = v->Next()) new_last = v;
  new_last->SetNext(nullptr);
 
  if (first != v) {
    /* Recalculate cached train properties */
    first->ConsistChanged(CCF_ARRANGE);
    /* Update the depot window in case a part of the consist is in a depot. */
    SetWindowDirty(WC_VEHICLE_DEPOT, first->tile);
    SetWindowDirty(WC_VEHICLE_DEPOT, v->tile);
  }
 
  /* 'v' shouldn't be accessed after it has been deleted */
  TrackBits trackbits = v->track;
  TileIndex tile = v->tile;
  Owner owner = v->owner;
 
  delete v;
  v = nullptr; // make sure nobody will try to read 'v' anymore
 
  if (trackbits == TRACK_BIT_WORMHOLE) {
    /* Vehicle is inside a wormhole, v->track contains no useful value then. */
    trackbits = DiagDirToDiagTrackBits(GetTunnelBridgeDirection(tile));
  }
 
  Track track = TrackBitsToTrack(trackbits);
  if (HasReservedTracks(tile, trackbits)) {
    UnreserveRailTrack(tile, track);
 
    /* If there are still crashed vehicles on the tile, give the track reservation to them */
    TrackBits remaining_trackbits = TRACK_BIT_NONE;
    for (const Vehicle *u : VehiclesOnTile(tile)) {
      if (u->type != VEH_TRAIN || !u->vehstatus.Test(VehState::Crashed)) continue;
      TrackBits train_tbits = Train::From(u)->track;
      if (train_tbits == TRACK_BIT_WORMHOLE) {
        /* Vehicle is inside a wormhole, u->track contains no useful value then. */
        remaining_trackbits |= DiagDirToDiagTrackBits(GetTunnelBridgeDirection(u->tile));
      } else if (train_tbits != TRACK_BIT_DEPOT) {
        remaining_trackbits |= train_tbits;
      }
    }
 
    /* It is important that these two are the first in the loop, as reservation cannot deal with every trackbit combination */
    assert(TRACK_BEGIN == TRACK_X && TRACK_Y == TRACK_BEGIN + 1);
    for (Track t : SetTrackBitIterator(remaining_trackbits)) TryReserveRailTrack(tile, t);
  }
 
  /* check if the wagon was on a road/rail-crossing */
  if (IsLevelCrossingTile(tile)) UpdateLevelCrossing(tile);
 
  if (IsRailStationTile(tile)) {
    bool occupied = IsRailStationPlatformOccupied(tile);
    DiagDirection dir = AxisToDiagDir(GetRailStationAxis(tile));
    SetRailStationPlatformReservation(tile, dir, occupied);
    SetRailStationPlatformReservation(tile, ReverseDiagDir(dir), occupied);
  }
 
  /* Update signals */
  if (IsTileType(tile, TileType::TunnelBridge) || IsRailDepotTile(tile)) {
    UpdateSignalsOnSegment(tile, INVALID_DIAGDIR, owner);
  } else {
    SetSignalsOnBothDir(tile, track, owner);
  }
}

static void ChangeTrainDirRandomly(Train *v)
{
  static const DirDiff delta[] = {
    DIRDIFF_45LEFT, DIRDIFF_SAME, DIRDIFF_SAME, DIRDIFF_45RIGHT
  };
 
  do {
    /* We don't need to twist around vehicles if they're not visible */
    if (!v->vehstatus.Test(VehState::Hidden)) {
      v->direction = ChangeDir(v->direction, delta[GB(Random(), 0, 2)]);
      /* Refrain from updating the z position of the vehicle when on
       * a bridge, because UpdateInclination() will put the vehicle under
       * the bridge in that case */
      if (v->track != TRACK_BIT_WORMHOLE) {
        v->UpdatePosition();
        v->UpdateInclination(false, true);
      } else {
        v->UpdateViewport(false, true);
      }
    }
  } while ((v = v->Next()) != nullptr);
}

static bool HandleCrashedTrain(Train *v)
{
  int state = ++v->crash_anim_pos;
 
  if (state == 4 && !v->vehstatus.Test(VehState::Hidden)) {
    CreateEffectVehicleRel(v, 4, 4, 8, EV_EXPLOSION_LARGE);
  }
 
  uint32_t r;
  if (state <= 200 && Chance16R(1, 7, r)) {
    int index = (r * 10 >> 16);
 
    Vehicle *u = v;
    do {
      if (--index < 0) {
        r = Random();
 
        CreateEffectVehicleRel(u,
          GB(r,  8, 3) + 2,
          GB(r, 16, 3) + 2,
          GB(r,  0, 3) + 5,
          EV_EXPLOSION_SMALL);
        break;
      }
    } while ((u = u->Next()) != nullptr);
  }
 
  if (state <= 240 && !(v->tick_counter & 3)) ChangeTrainDirRandomly(v);
 
  if (state >= 4440 && !(v->tick_counter & 0x1F)) {
    bool ret = v->Next() != nullptr;
    DeleteLastWagon(v);
    return ret;
  }
 
  return true;
}

static const uint16_t _breakdown_speeds[16] = {
  225, 210, 195, 180, 165, 150, 135, 120, 105, 90, 75, 60, 45, 30, 15, 15
};
 

static bool TrainApproachingLineEnd(Train *moving_front, bool signal, bool reverse)
{
  /* Calc position within the current tile */
  uint x = moving_front->x_pos & 0xF;
  uint y = moving_front->y_pos & 0xF;
 
  Direction vdir = moving_front->GetMovingDirection();
 
  /* for diagonal directions, 'x' will be 0..15 -
   * for other directions, it will be 1, 3, 5, ..., 15 */
  switch (vdir) {
    case DIR_N : x = ~x + ~y + 25; break;
    case DIR_NW: x = y;            [[fallthrough]];
    case DIR_NE: x = ~x + 16;      break;
    case DIR_E : x = ~x + y + 9;   break;
    case DIR_SE: x = y;            break;
    case DIR_S : x = x + y - 7;    break;
    case DIR_W : x = ~y + x + 9;   break;
    default: break;
  }
 
  Train *consist = moving_front->First();
 
  /* Do not reverse when approaching red signal. Make sure the vehicle's front
   * does not cross the tile boundary when we do reverse, but as the vehicle's
   * location is based on their center, use half a vehicle's length as offset.
   * Multiply the half-length by two for straight directions to compensate that
   * we only get odd x offsets there. */
  uint8_t rounding = moving_front->IsDrivingBackwards() ? 0 : 1;
  if (!signal && x + (moving_front->gcache.cached_veh_length + rounding) / 2 * (IsDiagonalDirection(vdir) ? 1 : 2) >= TILE_SIZE) {
    /* we are too near the tile end, reverse now */
    consist->cur_speed = 0;
    if (reverse) ReverseTrainDirection(consist);
    return false;
  }
 
  /* slow down */
  consist->vehstatus.Set(VehState::TrainSlowing);
  uint16_t break_speed = _breakdown_speeds[x & 0xF];
  if (break_speed < consist->cur_speed) consist->cur_speed = break_speed;
 
  return true;
}
 

static bool TrainCanLeaveTile(const Train *moving_front)
{
  /* Exit if inside a tunnel/bridge or a depot */
  if (moving_front->track == TRACK_BIT_WORMHOLE || moving_front->track == TRACK_BIT_DEPOT) return false;
 
  TileIndex tile = moving_front->tile;
 
  /* entering a tunnel/bridge? */
  if (IsTileType(tile, TileType::TunnelBridge)) {
    DiagDirection dir = GetTunnelBridgeDirection(tile);
    if (DiagDirToDir(dir) == moving_front->GetMovingDirection()) return false;
  }
 
  /* entering a depot? */
  if (IsRailDepotTile(tile)) {
    DiagDirection dir = ReverseDiagDir(GetRailDepotDirection(tile));
    if (DiagDirToDir(dir) == moving_front->GetMovingDirection()) return false;
  }
 
  return true;
}
 

static TileIndex TrainApproachingCrossingTile(const Train *moving_front)
{
  assert(moving_front->IsMovingFront());
  assert(!moving_front->First()->vehstatus.Test(VehState::Crashed));
 
  if (!TrainCanLeaveTile(moving_front)) return INVALID_TILE;
 
  DiagDirection dir = VehicleExitDir(moving_front->GetMovingDirection(), moving_front->track);
  TileIndex tile = moving_front->tile + TileOffsByDiagDir(dir);
 
  /* not a crossing || wrong axis || unusable rail (wrong type or owner) */
  if (!IsLevelCrossingTile(tile) || DiagDirToAxis(dir) == GetCrossingRoadAxis(tile) ||
      !CheckCompatibleRail(moving_front->First(), tile, true)) {
    return INVALID_TILE;
  }
 
  return tile;
}
 

static bool TrainCheckIfLineEnds(Train *moving_front, bool reverse)
{
  /* First, handle broken down train */
 
  Train *consist = moving_front->First();
  int t = consist->breakdown_ctr;
  if (t > 1) {
    consist->vehstatus.Set(VehState::TrainSlowing);
 
    uint16_t break_speed = _breakdown_speeds[GB(~t, 4, 4)];
    if (break_speed < consist->cur_speed) consist->cur_speed = break_speed;
  } else {
    consist->vehstatus.Reset(VehState::TrainSlowing);
  }
 
  if (!TrainCanLeaveTile(moving_front)) return true;
 
  /* Determine the non-diagonal direction in which we will exit this tile */
  DiagDirection dir = VehicleExitDir(moving_front->GetMovingDirection(), moving_front->track);
  /* Calculate next tile */
  TileIndex tile = moving_front->tile + TileOffsByDiagDir(dir);
 
  /* Determine the track status on the next tile */
  TrackStatus ts = GetTileTrackStatus(tile, TRANSPORT_RAIL, RoadTramType::Invalid, ReverseDiagDir(dir));
  TrackdirBits reachable_trackdirs = DiagdirReachesTrackdirs(dir);
 
  TrackdirBits trackdirbits = TrackStatusToTrackdirBits(ts) & reachable_trackdirs;
  TrackdirBits red_signals = TrackStatusToRedSignals(ts) & reachable_trackdirs;
 
  /* We are sure the train is not entering a depot, it is detected above */
 
  /* mask unreachable track bits if we are forbidden to do 90deg turns */
  TrackBits bits = TrackdirBitsToTrackBits(trackdirbits);
  if (Rail90DegTurnDisallowed(GetTileRailType(moving_front->tile), GetTileRailType(tile))) {
    bits &= ~TrackCrossesTracks(FindFirstTrack(moving_front->track));
  }
 
  /* no suitable trackbits at all || unusable rail (wrong type or owner) */
  if (bits == TRACK_BIT_NONE || !CheckCompatibleRail(consist, tile, true)) {
    return TrainApproachingLineEnd(moving_front, false, reverse);
  }
 
  /* approaching red signal */
  if ((trackdirbits & red_signals) != 0) return TrainApproachingLineEnd(moving_front, true, reverse);
 
  /* approaching a rail/road crossing? then make it red */
  if (IsLevelCrossingTile(tile)) MaybeBarCrossingWithSound(tile);
 
  return true;
}

static bool TrainLocoHandler(Train *consist, bool mode)
{
  /* train has crashed? */
  if (consist->vehstatus.Test(VehState::Crashed)) {
    return mode ? true : HandleCrashedTrain(consist); // 'this' can be deleted here
  }
 
  if (consist->force_proceed != TFP_NONE) {
    consist->flags.Reset(VehicleRailFlag::Stuck);
    SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
  }
 
  /* train is broken down? */
  if (consist->HandleBreakdown()) return true;
 
  if (consist->flags.Test(VehicleRailFlag::Reversing) && consist->cur_speed == 0) {
    ReverseTrainDirection(consist);
  }
 
  /* exit if train is stopped */
  if (consist->vehstatus.Test(VehState::Stopped) && consist->cur_speed == 0) return true;
 
  bool valid_order = !consist->current_order.IsType(OT_NOTHING) && consist->current_order.GetType() != OT_CONDITIONAL;
  if (ProcessOrders(consist) && CheckReverseTrain(consist)) {
    consist->wait_counter = 0;
    consist->cur_speed = 0;
    consist->subspeed = 0;
    consist->flags.Reset(VehicleRailFlag::LeavingStation);
    ReverseTrainDirection(consist);
    return true;
  } else if (consist->flags.Test(VehicleRailFlag::LeavingStation)) {
    /* Try to reserve a path when leaving the station as we
     * might not be marked as wanting a reservation, e.g.
     * when an overlength train gets turned around in a station. */
    const Train *moving_front = consist->GetMovingFront();
    DiagDirection dir = VehicleExitDir(moving_front->GetMovingDirection(), moving_front->track);
    if (IsRailDepotTile(moving_front->tile) || IsTileType(moving_front->tile, TileType::TunnelBridge)) dir = INVALID_DIAGDIR;
 
    if (UpdateSignalsOnSegment(moving_front->tile, dir, consist->owner) == SIGSEG_PBS || _settings_game.pf.reserve_paths) {
      TryPathReserve(consist, true, true);
    }
    consist->flags.Reset(VehicleRailFlag::LeavingStation);
  }
 
  consist->HandleLoading(mode);
 
  if (consist->current_order.IsType(OT_LOADING)) return true;
 
  if (CheckTrainStayInDepot(consist)) return true;
 
  if (!mode) consist->ShowVisualEffect();
 
  /* We had no order but have an order now, do look ahead. */
  if (!valid_order && !consist->current_order.IsType(OT_NOTHING)) {
    CheckNextTrainTile(consist);
  }
 
  /* Handle stuck trains. */
  if (!mode && consist->flags.Test(VehicleRailFlag::Stuck)) {
    ++consist->wait_counter;
 
    /* Should we try reversing this tick if still stuck? */
    bool turn_around = consist->wait_counter % (_settings_game.pf.wait_for_pbs_path * Ticks::DAY_TICKS) == 0 && _settings_game.pf.reverse_at_signals;
 
    if (!turn_around && consist->wait_counter % _settings_game.pf.path_backoff_interval != 0 && consist->force_proceed == TFP_NONE) return true;
    if (!TryPathReserve(consist)) {
      /* Still stuck. */
      if (turn_around) ReverseTrainDirection(consist);
 
      if (consist->flags.Test(VehicleRailFlag::Stuck) && consist->wait_counter > 2 * _settings_game.pf.wait_for_pbs_path * Ticks::DAY_TICKS) {
        /* Show message to player. */
        if (_settings_client.gui.lost_vehicle_warn && consist->owner == _local_company) {
          AddVehicleAdviceNewsItem(AdviceType::TrainStuck, GetEncodedString(STR_NEWS_TRAIN_IS_STUCK, consist->index), consist->index);
        }
        consist->wait_counter = 0;
      }
      /* Exit if force proceed not pressed, else reset stuck flag anyway. */
      if (consist->force_proceed == TFP_NONE) return true;
      consist->flags.Reset(VehicleRailFlag::Stuck);
      consist->wait_counter = 0;
      SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
    }
  }
 
  if (consist->current_order.IsType(OT_LEAVESTATION)) {
    consist->current_order.Free();
    SetWindowWidgetDirty(WC_VEHICLE_VIEW, consist->index, WID_VV_START_STOP);
    return true;
  }
 
  int j = consist->UpdateSpeed();
 
  /* we need to invalidate the widget if we are stopping from 'Stopping 0 km/h' to 'Stopped' */
  if (consist->cur_speed == 0 && consist->vehstatus.Test(VehState::Stopped)) {
    /* If we manually stopped, we're not force-proceeding anymore. */
    consist->force_proceed = TFP_NONE;
    InvalidateWindowData(WC_VEHICLE_VIEW, consist->index);
  }
 
  Train* moving_front = consist->GetMovingFront();
  int adv_spd = moving_front->GetAdvanceDistance();
  if (j < adv_spd) {
    /* if the vehicle has speed 0, update the last_speed field. */
    if (consist->cur_speed == 0) consist->SetLastSpeed();
  } else {
    TrainCheckIfLineEnds(moving_front);
    moving_front = moving_front->GetMovingFront();
    /* Loop until the train has finished moving. */
    for (;;) {
      j -= adv_spd;
      TrainController(moving_front, nullptr);
      moving_front = moving_front->GetMovingFront();
      /* Don't continue to move if the train crashed. */
      if (CheckTrainCollision(moving_front)) break;
      /* Determine distance to next map position */
      adv_spd = moving_front->GetAdvanceDistance();
 
      /* No more moving this tick */
      if (j < adv_spd || consist->cur_speed == 0) break;
 
      OrderType order_type = consist->current_order.GetType();
      /* Do not skip waypoints (incl. 'via' stations) when passing through at full speed. */
      if ((order_type == OT_GOTO_WAYPOINT || order_type == OT_GOTO_STATION) &&
            consist->current_order.GetNonStopType().Test(OrderNonStopFlag::GoVia) &&
            IsTileType(moving_front->tile, TileType::Station) &&
            consist->current_order.GetDestination() == GetStationIndex(moving_front->tile)) {
        ProcessOrders(consist);
      }
    }
    consist->SetLastSpeed();
  }
 
  for (Train *u = consist; u != nullptr; u = u->Next()) {
    if (u->vehstatus.Test(VehState::Hidden)) continue;
 
    u->UpdateViewport(false, false);
  }
 
  if (consist->progress == 0) consist->progress = j; // Save unused spd for next time, if TrainController didn't set progress
 
  return true;
}

Money Train::GetRunningCost() const
{
  Money cost = 0;
  const Train *v = this;
 
  do {
    const Engine *e = v->GetEngine();
    if (e->VehInfo<RailVehicleInfo>().running_cost_class == Price::Invalid) continue;
 
    uint cost_factor = GetVehicleProperty(v, PROP_TRAIN_RUNNING_COST_FACTOR, e->VehInfo<RailVehicleInfo>().running_cost);
    if (cost_factor == 0) continue;
 
    /* Halve running cost for multiheaded parts */
    if (v->IsMultiheaded()) cost_factor /= 2;
 
    cost += GetPrice(e->VehInfo<RailVehicleInfo>().running_cost_class, cost_factor, e->GetGRF());
  } while ((v = v->GetNextVehicle()) != nullptr);
 
  return cost;
}

bool Train::Tick()
{
  this->tick_counter++;
 
  if (this->IsFrontEngine()) {
    PerformanceAccumulator framerate(PFE_GL_TRAINS);
 
    if (!this->vehstatus.Test(VehState::Stopped) || this->cur_speed > 0) this->running_ticks++;
 
    this->current_order_time++;
 
    if (!TrainLocoHandler(this, false)) return false;
 
    return TrainLocoHandler(this, true);
  } else if (this->IsFreeWagon() && this->vehstatus.Test(VehState::Crashed)) {
    /* Delete flooded standalone wagon chain */
    if (++this->crash_anim_pos >= 4400) {
      delete this;
      return false;
    }
  }
 
  return true;
}

static void CheckIfTrainNeedsService(Train *v)
{
  if (Company::Get(v->owner)->settings.vehicle.servint_trains == 0 || !v->NeedsAutomaticServicing()) return;
  if (v->IsChainInDepot()) {
    VehicleServiceInDepot(v);
    return;
  }
 
  uint max_penalty = _settings_game.pf.yapf.maximum_go_to_depot_penalty;
 
  FindDepotData tfdd = FindClosestTrainDepot(v, max_penalty);
  /* Only go to the depot if it is not too far out of our way. */
  if (tfdd.best_length == UINT_MAX || tfdd.best_length > max_penalty) {
    if (v->current_order.IsType(OT_GOTO_DEPOT)) {
      /* If we were already heading for a depot but it has
       * suddenly moved farther away, we continue our normal
       * schedule? */
      v->current_order.MakeDummy();
      SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
    }
    return;
  }
 
  DepotID depot = GetDepotIndex(tfdd.tile);
 
  if (v->current_order.IsType(OT_GOTO_DEPOT) &&
      v->current_order.GetDestination() != depot &&
      !Chance16(3, 16)) {
    return;
  }
 
  SetBit(v->gv_flags, GVF_SUPPRESS_IMPLICIT_ORDERS);
  v->current_order.MakeGoToDepot(depot, OrderDepotTypeFlag::Service, OrderNonStopFlag::NonStop, OrderDepotActionFlag::NearestDepot);
  v->dest_tile = tfdd.tile;
  SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
}

void Train::OnNewCalendarDay()
{
  AgeVehicle(this);
}

void Train::OnNewEconomyDay()
{
  EconomyAgeVehicle(this);
 
  if ((++this->day_counter & 7) == 0) DecreaseVehicleValue(this);
 
  if (this->IsFrontEngine()) {
    CheckVehicleBreakdown(this);
 
    CheckIfTrainNeedsService(this);
 
    CheckOrders(this);
 
    /* update destination */
    if (this->current_order.IsType(OT_GOTO_STATION)) {
      TileIndex tile = Station::Get(this->current_order.GetDestination().ToStationID())->train_station.tile;
      if (tile != INVALID_TILE) this->dest_tile = tile;
    }
 
    if (this->running_ticks != 0) {
      /* running costs */
      CommandCost cost(EXPENSES_TRAIN_RUN, this->GetRunningCost() * this->running_ticks / (CalendarTime::DAYS_IN_YEAR  * Ticks::DAY_TICKS));
 
      this->profit_this_year -= cost.GetCost();
      this->running_ticks = 0;
 
      SubtractMoneyFromCompanyFract(this->owner, cost);
 
      SetWindowDirty(WC_VEHICLE_DETAILS, this->index);
      SetWindowClassesDirty(WC_TRAINS_LIST);
    }
  }
}

Trackdir Train::GetVehicleTrackdir() const
{
  if (this->vehstatus.Test(VehState::Crashed)) return INVALID_TRACKDIR;
 
  if (this->track == TRACK_BIT_DEPOT) {
    /* We'll assume the train is facing outwards */
    return DiagDirToDiagTrackdir(GetRailDepotDirection(this->tile)); // Train in depot
  }
 
  if (this->track == TRACK_BIT_WORMHOLE) {
    /* train in tunnel or on bridge, so just use its direction and assume a diagonal track */
    return DiagDirToDiagTrackdir(DirToDiagDir(this->GetMovingDirection()));
  }
 
  return TrackDirectionToTrackdir(FindFirstTrack(this->track), this->GetMovingDirection());
}
 
uint16_t Train::GetMaxWeight() const
{
  uint16_t weight = CargoSpec::Get(this->cargo_type)->WeightOfNUnitsInTrain(this->GetEngine()->DetermineCapacity(this));
 
  /* Vehicle weight is not added for articulated parts. */
  if (!this->IsArticulatedPart()) {
    weight += GetVehicleProperty(this, PROP_TRAIN_WEIGHT, RailVehInfo(this->engine_type)->weight);
  }
 
  /* Powered wagons have extra weight added. */
  if (this->flags.Test(VehicleRailFlag::PoweredWagon)) {
    weight += RailVehInfo(this->gcache.first_engine)->pow_wag_weight;
  }
 
  return weight;
}