autoreplace_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 <http://www.gnu.org/licenses/>.
 */
 
#include "stdafx.h"
#include "company_func.h"
#include "train.h"
#include "command_func.h"
#include "engine_func.h"
#include "vehicle_func.h"
#include "autoreplace_func.h"
#include "autoreplace_gui.h"
#include "articulated_vehicles.h"
#include "core/bitmath_func.hpp"
#include "core/random_func.hpp"
#include "vehiclelist.h"
#include "road.h"
#include "ai/ai.hpp"
#include "news_func.h"
#include "strings_func.h"
#include "autoreplace_cmd.h"
#include "group_cmd.h"
#include "order_cmd.h"
#include "train_cmd.h"
#include "vehicle_cmd.h"
 
#include "table/strings.h"
 
#include "safeguards.h"
 
extern void ChangeVehicleViewports(VehicleID from_index, VehicleID to_index);
extern void ChangeVehicleNews(VehicleID from_index, VehicleID to_index);
extern void ChangeVehicleViewWindow(VehicleID from_index, VehicleID to_index);
 
static bool EnginesHaveCargoInCommon(EngineID engine_a, EngineID engine_b)
{
  CargoTypes available_cargoes_a = GetUnionOfArticulatedRefitMasks(engine_a, true);
  CargoTypes available_cargoes_b = GetUnionOfArticulatedRefitMasks(engine_b, true);
  return (available_cargoes_a == 0 || available_cargoes_b == 0 || (available_cargoes_a & available_cargoes_b) != 0);
}
 
bool CheckAutoreplaceValidity(EngineID from, EngineID to, CompanyID company)
{
  assert(Engine::IsValidID(from) && Engine::IsValidID(to));
 
  const Engine *e_from = Engine::Get(from);
  const Engine *e_to = Engine::Get(to);
  VehicleType type = e_from->type;
 
  /* check that the new vehicle type is available to the company and its type is the same as the original one */
  if (!IsEngineBuildable(to, type, company)) return false;
 
  switch (type) {
    case VEH_TRAIN: {
      /* make sure the railtypes are compatible */
      if ((GetRailTypeInfo(e_from->u.rail.railtype)->compatible_railtypes & GetRailTypeInfo(e_to->u.rail.railtype)->compatible_railtypes) == 0) return false;
 
      /* make sure we do not replace wagons with engines or vice versa */
      if ((e_from->u.rail.railveh_type == RAILVEH_WAGON) != (e_to->u.rail.railveh_type == RAILVEH_WAGON)) return false;
      break;
    }
 
    case VEH_ROAD:
      /* make sure the roadtypes are compatible */
      if ((GetRoadTypeInfo(e_from->u.road.roadtype)->powered_roadtypes & GetRoadTypeInfo(e_to->u.road.roadtype)->powered_roadtypes) == ROADTYPES_NONE) return false;
 
      /* make sure that we do not replace a tram with a normal road vehicles or vice versa */
      if (HasBit(e_from->info.misc_flags, EF_ROAD_TRAM) != HasBit(e_to->info.misc_flags, EF_ROAD_TRAM)) return false;
      break;
 
    case VEH_AIRCRAFT:
      /* make sure that we do not replace a plane with a helicopter or vice versa */
      if ((e_from->u.air.subtype & AIR_CTOL) != (e_to->u.air.subtype & AIR_CTOL)) return false;
      break;
 
    default: break;
  }
 
  /* the engines needs to be able to carry the same cargo */
  return EnginesHaveCargoInCommon(from, to);
}
 
void CheckCargoCapacity(Vehicle *v)
{
  assert(v == nullptr || v->First() == v);
 
  for (Vehicle *src = v; src != nullptr; src = src->Next()) {
    assert(src->cargo.TotalCount() == src->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
 
    /* Do we need to more cargo away? */
    if (src->cargo.TotalCount() <= src->cargo_cap) continue;
 
    /* We need to move a particular amount. Try that on the other vehicles. */
    uint to_spread = src->cargo.TotalCount() - src->cargo_cap;
    for (Vehicle *dest = v; dest != nullptr && to_spread != 0; dest = dest->Next()) {
      assert(dest->cargo.TotalCount() == dest->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
      if (dest->cargo.TotalCount() >= dest->cargo_cap || dest->cargo_type != src->cargo_type) continue;
 
      uint amount = std::min(to_spread, dest->cargo_cap - dest->cargo.TotalCount());
      src->cargo.Shift(amount, &dest->cargo);
      to_spread -= amount;
    }
 
    /* Any left-overs will be thrown away, but not their feeder share. */
    if (src->cargo_cap < src->cargo.TotalCount()) src->cargo.Truncate(src->cargo.TotalCount() - src->cargo_cap);
  }
}
 
static void TransferCargo(Vehicle *old_veh, Vehicle *new_head, bool part_of_chain)
{
  assert(!part_of_chain || new_head->IsPrimaryVehicle());
  /* Loop through source parts */
  for (Vehicle *src = old_veh; src != nullptr; src = src->Next()) {
    assert(src->cargo.TotalCount() == src->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
    if (!part_of_chain && src->type == VEH_TRAIN && src != old_veh && src != Train::From(old_veh)->other_multiheaded_part && !src->IsArticulatedPart()) {
      /* Skip vehicles, which do not belong to old_veh */
      src = src->GetLastEnginePart();
      continue;
    }
    if (src->cargo_type >= NUM_CARGO || src->cargo.TotalCount() == 0) continue;
 
    /* Find free space in the new chain */
    for (Vehicle *dest = new_head; dest != nullptr && src->cargo.TotalCount() > 0; dest = dest->Next()) {
      assert(dest->cargo.TotalCount() == dest->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
      if (!part_of_chain && dest->type == VEH_TRAIN && dest != new_head && dest != Train::From(new_head)->other_multiheaded_part && !dest->IsArticulatedPart()) {
        /* Skip vehicles, which do not belong to new_head */
        dest = dest->GetLastEnginePart();
        continue;
      }
      if (dest->cargo_type != src->cargo_type) continue;
 
      uint amount = std::min(src->cargo.TotalCount(), dest->cargo_cap - dest->cargo.TotalCount());
      if (amount <= 0) continue;
 
      src->cargo.Shift(amount, &dest->cargo);
    }
  }
 
  /* Update train weight etc., the old vehicle will be sold anyway */
  if (part_of_chain && new_head->type == VEH_TRAIN) Train::From(new_head)->ConsistChanged(CCF_LOADUNLOAD);
}
 
static bool VerifyAutoreplaceRefitForOrders(const Vehicle *v, EngineID engine_type)
{
  CargoTypes union_refit_mask_a = GetUnionOfArticulatedRefitMasks(v->engine_type, false);
  CargoTypes union_refit_mask_b = GetUnionOfArticulatedRefitMasks(engine_type, false);
 
  const Vehicle *u = (v->type == VEH_TRAIN) ? v->First() : v;
  for (const Order *o : u->Orders()) {
    if (!o->IsRefit() || o->IsAutoRefit()) continue;
    CargoID cargo_type = o->GetRefitCargo();
 
    if (!HasBit(union_refit_mask_a, cargo_type)) continue;
    if (!HasBit(union_refit_mask_b, cargo_type)) return false;
  }
 
  return true;
}
 
static int GetIncompatibleRefitOrderIdForAutoreplace(const Vehicle *v, EngineID engine_type)
{
  CargoTypes union_refit_mask = GetUnionOfArticulatedRefitMasks(engine_type, false);
 
  const Order *o;
  const Vehicle *u = (v->type == VEH_TRAIN) ? v->First() : v;
 
  const OrderList *orders = u->orders;
  if (orders == nullptr) return -1;
  for (VehicleOrderID i = 0; i < orders->GetNumOrders(); i++) {
    o = orders->GetOrderAt(i);
    if (!o->IsRefit()) continue;
    if (!HasBit(union_refit_mask, o->GetRefitCargo())) return i;
  }
 
  return -1;
}
 
static CargoID GetNewCargoTypeForReplace(Vehicle *v, EngineID engine_type, bool part_of_chain)
{
  CargoTypes available_cargo_types, union_mask;
  GetArticulatedRefitMasks(engine_type, true, &union_mask, &available_cargo_types);
 
  if (union_mask == 0) return CARGO_NO_REFIT; // Don't try to refit an engine with no cargo capacity
 
  CargoID cargo_type;
  CargoTypes cargo_mask = GetCargoTypesOfArticulatedVehicle(v, &cargo_type);
  if (!HasAtMostOneBit(cargo_mask)) {
    CargoTypes new_engine_default_cargoes = GetCargoTypesOfArticulatedParts(engine_type);
    if ((cargo_mask & new_engine_default_cargoes) == cargo_mask) {
      return CARGO_NO_REFIT; // engine_type is already a mixed cargo type which matches the incoming vehicle by default, no refit required
    }
 
    return INVALID_CARGO; // We cannot refit to mixed cargoes in an automated way
  }
 
  if (!IsValidCargoID(cargo_type)) {
    if (v->type != VEH_TRAIN) return CARGO_NO_REFIT; // If the vehicle does not carry anything at all, every replacement is fine.
 
    if (!part_of_chain) return CARGO_NO_REFIT;
 
    /* the old engine didn't have cargo capacity, but the new one does
     * now we will figure out what cargo the train is carrying and refit to fit this */
 
    for (v = v->First(); v != nullptr; v = v->Next()) {
      if (!v->GetEngine()->CanCarryCargo()) continue;
      /* Now we found a cargo type being carried on the train and we will see if it is possible to carry to this one */
      if (HasBit(available_cargo_types, v->cargo_type)) return v->cargo_type;
    }
 
    return CARGO_NO_REFIT; // We failed to find a cargo type on the old vehicle and we will not refit the new one
  } else {
    if (!HasBit(available_cargo_types, cargo_type)) return INVALID_CARGO; // We can't refit the vehicle to carry the cargo we want
 
    if (part_of_chain && !VerifyAutoreplaceRefitForOrders(v, engine_type)) return INVALID_CARGO; // Some refit orders lose their effect
 
    return cargo_type;
  }
}
 
static CommandCost GetNewEngineType(const Vehicle *v, const Company *c, bool always_replace, EngineID &e)
{
  assert(v->type != VEH_TRAIN || !v->IsArticulatedPart());
 
  e = INVALID_ENGINE;
 
  if (v->type == VEH_TRAIN && Train::From(v)->IsRearDualheaded()) {
    /* we build the rear ends of multiheaded trains with the front ones */
    return CommandCost();
  }
 
  bool replace_when_old;
  e = EngineReplacementForCompany(c, v->engine_type, v->group_id, &replace_when_old);
  if (!always_replace && replace_when_old && !v->NeedsAutorenewing(c, false)) e = INVALID_ENGINE;
 
  /* Autoreplace, if engine is available */
  if (e != INVALID_ENGINE && IsEngineBuildable(e, v->type, _current_company)) {
    return CommandCost();
  }
 
  /* Autorenew if needed */
  if (v->NeedsAutorenewing(c)) e = v->engine_type;
 
  /* Nothing to do or all is fine? */
  if (e == INVALID_ENGINE || IsEngineBuildable(e, v->type, _current_company)) return CommandCost();
 
  /* The engine we need is not available. Report error to user */
  return CommandCost(STR_ERROR_RAIL_VEHICLE_NOT_AVAILABLE + v->type);
}
 
static CommandCost BuildReplacementVehicle(Vehicle *old_veh, Vehicle **new_vehicle, bool part_of_chain, DoCommandFlag flags)
{
  *new_vehicle = nullptr;
 
  /* Shall the vehicle be replaced? */
  const Company *c = Company::Get(_current_company);
  EngineID e;
  CommandCost cost = GetNewEngineType(old_veh, c, true, e);
  if (cost.Failed()) return cost;
  if (e == INVALID_ENGINE) return CommandCost(); // neither autoreplace is set, nor autorenew is triggered
 
  /* Does it need to be refitted */
  CargoID refit_cargo = GetNewCargoTypeForReplace(old_veh, e, part_of_chain);
  if (!IsValidCargoID(refit_cargo)) {
    if (!IsLocalCompany() || (flags & DC_EXEC) == 0) return CommandCost();
 
    VehicleID old_veh_id = (old_veh->type == VEH_TRAIN) ? Train::From(old_veh)->First()->index : old_veh->index;
    SetDParam(0, old_veh_id);
 
    int order_id = GetIncompatibleRefitOrderIdForAutoreplace(old_veh, e);
    if (order_id != -1) {
      /* Orders contained a refit order that is incompatible with the new vehicle. */
      SetDParam(1, STR_ERROR_AUTOREPLACE_INCOMPATIBLE_REFIT);
      SetDParam(2, order_id + 1); // 1-based indexing for display
    } else {
      /* Current cargo is incompatible with the new vehicle. */
      SetDParam(1, STR_ERROR_AUTOREPLACE_INCOMPATIBLE_CARGO);
      SetDParam(2, CargoSpec::Get(old_veh->cargo_type)->name);
    }
 
    AddVehicleAdviceNewsItem(STR_NEWS_VEHICLE_AUTORENEW_FAILED, old_veh_id);
    return CommandCost();
  }
 
  /* Build the new vehicle */
  VehicleID new_veh_id;
  std::tie(cost, new_veh_id, std::ignore, std::ignore, std::ignore) = Command<CMD_BUILD_VEHICLE>::Do(DC_EXEC | DC_AUTOREPLACE, old_veh->tile, e, true, INVALID_CARGO, INVALID_CLIENT_ID);
  if (cost.Failed()) return cost;
 
  Vehicle *new_veh = Vehicle::Get(new_veh_id);
  *new_vehicle = new_veh;
 
  /* Refit the vehicle if needed */
  if (refit_cargo != CARGO_NO_REFIT) {
    uint8_t subtype = GetBestFittingSubType(old_veh, new_veh, refit_cargo);
 
    cost.AddCost(std::get<0>(Command<CMD_REFIT_VEHICLE>::Do(DC_EXEC, new_veh->index, refit_cargo, subtype, false, false, 0)));
    assert(cost.Succeeded()); // This should be ensured by GetNewCargoTypeForReplace()
  }
 
  /* Try to reverse the vehicle, but do not care if it fails as the new type might not be reversible */
  if (new_veh->type == VEH_TRAIN && HasBit(Train::From(old_veh)->flags, VRF_REVERSE_DIRECTION)) {
    Command<CMD_REVERSE_TRAIN_DIRECTION>::Do(DC_EXEC, new_veh->index, true);
  }
 
  return cost;
}
 
static inline CommandCost DoCmdStartStopVehicle(const Vehicle *v, bool evaluate_callback)
{
  return Command<CMD_START_STOP_VEHICLE>::Do(DC_EXEC | DC_AUTOREPLACE, v->index, evaluate_callback);
}
 
static inline CommandCost CmdMoveVehicle(const Vehicle *v, const Vehicle *after, DoCommandFlag flags, bool whole_chain)
{
  return Command<CMD_MOVE_RAIL_VEHICLE>::Do(flags | DC_NO_CARGO_CAP_CHECK, v->index, after != nullptr ? after->index : INVALID_VEHICLE, whole_chain);
}
 
static CommandCost CopyHeadSpecificThings(Vehicle *old_head, Vehicle *new_head, DoCommandFlag flags)
{
  CommandCost cost = CommandCost();
 
  /* Share orders */
  if (cost.Succeeded() && old_head != new_head) cost.AddCost(Command<CMD_CLONE_ORDER>::Do(DC_EXEC, CO_SHARE, new_head->index, old_head->index));
 
  /* Copy group membership */
  if (cost.Succeeded() && old_head != new_head) cost.AddCost(std::get<0>(Command<CMD_ADD_VEHICLE_GROUP>::Do(DC_EXEC, old_head->group_id, new_head->index, false, VehicleListIdentifier{})));
 
  /* Perform start/stop check whether the new vehicle suits newgrf restrictions etc. */
  if (cost.Succeeded()) {
    /* Start the vehicle, might be denied by certain things */
    assert((new_head->vehstatus & VS_STOPPED) != 0);
    cost.AddCost(DoCmdStartStopVehicle(new_head, true));
 
    /* Stop the vehicle again, but do not care about evil newgrfs allowing starting but not stopping :p */
    if (cost.Succeeded()) cost.AddCost(DoCmdStartStopVehicle(new_head, false));
  }
 
  /* Last do those things which do never fail (resp. we do not care about), but which are not undo-able */
  if (cost.Succeeded() && old_head != new_head && (flags & DC_EXEC) != 0) {
    /* Copy other things which cannot be copied by a command and which shall not stay resetted from the build vehicle command */
    new_head->CopyVehicleConfigAndStatistics(old_head);
    GroupStatistics::AddProfitLastYear(new_head);
 
    /* Switch vehicle windows/news to the new vehicle, so they are not closed/deleted when the old vehicle is sold */
    ChangeVehicleViewports(old_head->index, new_head->index);
    ChangeVehicleViewWindow(old_head->index, new_head->index);
    ChangeVehicleNews(old_head->index, new_head->index);
  }
 
  return cost;
}
 
static CommandCost ReplaceFreeUnit(Vehicle **single_unit, DoCommandFlag flags, bool *nothing_to_do)
{
  Train *old_v = Train::From(*single_unit);
  assert(!old_v->IsArticulatedPart() && !old_v->IsRearDualheaded());
 
  CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);
 
  /* Build and refit replacement vehicle */
  Vehicle *new_v = nullptr;
  cost.AddCost(BuildReplacementVehicle(old_v, &new_v, false, flags));
 
  /* Was a new vehicle constructed? */
  if (cost.Succeeded() && new_v != nullptr) {
    *nothing_to_do = false;
 
    if ((flags & DC_EXEC) != 0) {
      /* Move the new vehicle behind the old */
      CmdMoveVehicle(new_v, old_v, DC_EXEC, false);
 
      /* Take over cargo
       * Note: We do only transfer cargo from the old to the new vehicle.
       *       I.e. we do not transfer remaining cargo to other vehicles.
       *       Else you would also need to consider moving cargo to other free chains,
       *       or doing the same in ReplaceChain(), which would be quite troublesome.
       */
      TransferCargo(old_v, new_v, false);
 
      *single_unit = new_v;
 
      AI::NewEvent(old_v->owner, new ScriptEventVehicleAutoReplaced(old_v->index, new_v->index));
    }
 
    /* Sell the old vehicle */
    cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags, old_v->index, false, false, INVALID_CLIENT_ID));
 
    /* If we are not in DC_EXEC undo everything */
    if ((flags & DC_EXEC) == 0) {
      Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, new_v->index, false, false, INVALID_CLIENT_ID);
    }
  }
 
  return cost;
}
 
struct ReplaceChainItem {
  Vehicle *old_veh; 
  Vehicle *new_veh; 
  Money cost; 
 
  ReplaceChainItem(Vehicle *old_veh, Vehicle *new_veh, Money cost) : old_veh(old_veh), new_veh(new_veh), cost(cost) { }
 
  Vehicle *GetVehicle() const { return new_veh == nullptr ? old_veh : new_veh; }
};
 
static CommandCost ReplaceChain(Vehicle **chain, DoCommandFlag flags, bool wagon_removal, bool *nothing_to_do)
{
  Vehicle *old_head = *chain;
  assert(old_head->IsPrimaryVehicle());
 
  CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);
 
  if (old_head->type == VEH_TRAIN) {
    /* Store the length of the old vehicle chain, rounded up to whole tiles */
    uint16_t old_total_length = CeilDiv(Train::From(old_head)->gcache.cached_total_length, TILE_SIZE) * TILE_SIZE;
 
    std::vector<ReplaceChainItem> replacements;
 
    /* Collect vehicles and build replacements
     * Note: The replacement vehicles can only successfully build as long as the old vehicles are still in their chain */
    for (Train *w = Train::From(old_head); w != nullptr; w = w->GetNextUnit()) {
      ReplaceChainItem &replacement = replacements.emplace_back(w, nullptr, 0);
 
      CommandCost ret = BuildReplacementVehicle(replacement.old_veh, &replacement.new_veh, true, flags);
      cost.AddCost(ret);
      if (cost.Failed()) break;
 
      replacement.cost = ret.GetCost();
      if (replacement.new_veh != nullptr) *nothing_to_do = false;
    }
    Vehicle *new_head = replacements.front().GetVehicle();
 
    /* Note: When autoreplace has already failed here, old_vehs[] is not completely initialized. But it is also not needed. */
    if (cost.Succeeded()) {
      /* Separate the head, so we can start constructing the new chain */
      Train *second = Train::From(old_head)->GetNextUnit();
      if (second != nullptr) cost.AddCost(CmdMoveVehicle(second, nullptr, DC_EXEC | DC_AUTOREPLACE, true));
 
      assert(Train::From(new_head)->GetNextUnit() == nullptr);
 
      /* Append engines to the new chain
       * We do this from back to front, so that the head of the temporary vehicle chain does not change all the time.
       * That way we also have less trouble when exceeding the unitnumber limit.
       * OTOH the vehicle attach callback is more expensive this way :s */
      Vehicle *last_engine = nullptr; 
      if (cost.Succeeded()) {
        for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
          Vehicle *append = it->GetVehicle();
 
          if (RailVehInfo(append->engine_type)->railveh_type == RAILVEH_WAGON) continue;
 
          if (it->new_veh != nullptr) {
            /* Move the old engine to a separate row with DC_AUTOREPLACE. Else
             * moving the wagon in front may fail later due to unitnumber limit.
             * (We have to attach wagons without DC_AUTOREPLACE.) */
            CmdMoveVehicle(it->old_veh, nullptr, DC_EXEC | DC_AUTOREPLACE, false);
          }
 
          if (last_engine == nullptr) last_engine = append;
          cost.AddCost(CmdMoveVehicle(append, new_head, DC_EXEC, false));
          if (cost.Failed()) break;
        }
        if (last_engine == nullptr) last_engine = new_head;
      }
 
      /* When wagon removal is enabled and the new engines without any wagons are already longer than the old, we have to fail */
      if (cost.Succeeded() && wagon_removal && Train::From(new_head)->gcache.cached_total_length > old_total_length) cost = CommandCost(STR_ERROR_TRAIN_TOO_LONG_AFTER_REPLACEMENT);
 
      /* Append/insert wagons into the new vehicle chain
       * We do this from back to front, so we can stop when wagon removal or maximum train length (i.e. from mammoth-train setting) is triggered.
       */
      if (cost.Succeeded()) {
        for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
          assert(last_engine != nullptr);
          Vehicle *append = it->GetVehicle();
 
          if (RailVehInfo(append->engine_type)->railveh_type == RAILVEH_WAGON) {
            /* Insert wagon after 'last_engine' */
            CommandCost res = CmdMoveVehicle(append, last_engine, DC_EXEC, false);
 
            /* When we allow removal of wagons, either the move failing due
             * to the train becoming too long, or the train becoming longer
             * would move the vehicle to the empty vehicle chain. */
            if (wagon_removal && (res.Failed() ? res.GetErrorMessage() == STR_ERROR_TRAIN_TOO_LONG : Train::From(new_head)->gcache.cached_total_length > old_total_length)) {
              CmdMoveVehicle(append, nullptr, DC_EXEC | DC_AUTOREPLACE, false);
              break;
            }
 
            cost.AddCost(res);
            if (cost.Failed()) break;
          } else {
            /* We have reached 'last_engine', continue with the next engine towards the front */
            assert(append == last_engine);
            last_engine = Train::From(last_engine)->GetPrevUnit();
          }
        }
      }
 
      /* Sell superfluous new vehicles that could not be inserted. */
      if (cost.Succeeded() && wagon_removal) {
        assert(Train::From(new_head)->gcache.cached_total_length <= _settings_game.vehicle.max_train_length * TILE_SIZE);
        for (auto it = std::next(std::begin(replacements)); it != std::end(replacements); ++it) {
          Vehicle *wagon = it->new_veh;
          if (wagon == nullptr) continue;
          if (wagon->First() == new_head) break;
 
          assert(RailVehInfo(wagon->engine_type)->railveh_type == RAILVEH_WAGON);
 
          /* Sell wagon */
          [[maybe_unused]] CommandCost ret = Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, wagon->index, false, false, INVALID_CLIENT_ID);
          assert(ret.Succeeded());
          it->new_veh = nullptr;
 
          /* Revert the money subtraction when the vehicle was built.
           * This value is different from the sell value, esp. because of refitting */
          cost.AddCost(-it->cost);
        }
      }
 
      /* The new vehicle chain is constructed, now take over orders and everything... */
      if (cost.Succeeded()) cost.AddCost(CopyHeadSpecificThings(old_head, new_head, flags));
 
      if (cost.Succeeded()) {
        /* Success ! */
        if ((flags & DC_EXEC) != 0 && new_head != old_head) {
          *chain = new_head;
          AI::NewEvent(old_head->owner, new ScriptEventVehicleAutoReplaced(old_head->index, new_head->index));
        }
 
        /* Transfer cargo of old vehicles and sell them */
        for (auto it = std::begin(replacements); it != std::end(replacements); ++it) {
          Vehicle *w = it->old_veh;
          /* Is the vehicle again part of the new chain?
           * Note: We cannot test 'new_vehs[i] != nullptr' as wagon removal might cause to remove both */
          if (w->First() == new_head) continue;
 
          if ((flags & DC_EXEC) != 0) TransferCargo(w, new_head, true);
 
          /* Sell the vehicle.
           * Note: This might temporarily construct new trains, so use DC_AUTOREPLACE to prevent
           *       it from failing due to engine limits. */
          cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags | DC_AUTOREPLACE, w->index, false, false, INVALID_CLIENT_ID));
          if ((flags & DC_EXEC) != 0) {
            it->old_veh = nullptr;
            if (it == std::begin(replacements)) old_head = nullptr;
          }
        }
 
        if ((flags & DC_EXEC) != 0) CheckCargoCapacity(new_head);
      }
 
      /* If we are not in DC_EXEC undo everything, i.e. rearrange old vehicles.
       * We do this from back to front, so that the head of the temporary vehicle chain does not change all the time.
       * Note: The vehicle attach callback is disabled here :) */
      if ((flags & DC_EXEC) == 0) {
        /* Separate the head, so we can reattach the old vehicles */
        Train *second = Train::From(old_head)->GetNextUnit();
        if (second != nullptr) CmdMoveVehicle(second, nullptr, DC_EXEC | DC_AUTOREPLACE, true);
 
        assert(Train::From(old_head)->GetNextUnit() == nullptr);
 
        for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
          [[maybe_unused]] CommandCost ret = CmdMoveVehicle(it->old_veh, old_head, DC_EXEC | DC_AUTOREPLACE, false);
          assert(ret.Succeeded());
        }
      }
    }
 
    /* Finally undo buying of new vehicles */
    if ((flags & DC_EXEC) == 0) {
      for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
        if (it->new_veh != nullptr) {
          Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, it->new_veh->index, false, false, INVALID_CLIENT_ID);
          it->new_veh = nullptr;
        }
      }
    }
  } else {
    /* Build and refit replacement vehicle */
    Vehicle *new_head = nullptr;
    cost.AddCost(BuildReplacementVehicle(old_head, &new_head, true, flags));
 
    /* Was a new vehicle constructed? */
    if (cost.Succeeded() && new_head != nullptr) {
      *nothing_to_do = false;
 
      /* The new vehicle is constructed, now take over orders and everything... */
      cost.AddCost(CopyHeadSpecificThings(old_head, new_head, flags));
 
      if (cost.Succeeded()) {
        /* The new vehicle is constructed, now take over cargo */
        if ((flags & DC_EXEC) != 0) {
          TransferCargo(old_head, new_head, true);
          *chain = new_head;
 
          AI::NewEvent(old_head->owner, new ScriptEventVehicleAutoReplaced(old_head->index, new_head->index));
        }
 
        /* Sell the old vehicle */
        cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags, old_head->index, false, false, INVALID_CLIENT_ID));
      }
 
      /* If we are not in DC_EXEC undo everything */
      if ((flags & DC_EXEC) == 0) {
        Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, new_head->index, false, false, INVALID_CLIENT_ID);
      }
    }
  }
 
  return cost;
}
 
CommandCost CmdAutoreplaceVehicle(DoCommandFlag flags, VehicleID veh_id)
{
  Vehicle *v = Vehicle::GetIfValid(veh_id);
  if (v == nullptr) return CMD_ERROR;
 
  CommandCost ret = CheckOwnership(v->owner);
  if (ret.Failed()) return ret;
 
  if (v->vehstatus & VS_CRASHED) return CMD_ERROR;
 
  bool free_wagon = false;
  if (v->type == VEH_TRAIN) {
    Train *t = Train::From(v);
    if (t->IsArticulatedPart() || t->IsRearDualheaded()) return CMD_ERROR;
    free_wagon = !t->IsFrontEngine();
    if (free_wagon && t->First()->IsFrontEngine()) return CMD_ERROR;
  } else {
    if (!v->IsPrimaryVehicle()) return CMD_ERROR;
  }
  if (!v->IsChainInDepot()) return CMD_ERROR;
 
  const Company *c = Company::Get(_current_company);
  bool wagon_removal = c->settings.renew_keep_length;
 
  const Group *g = Group::GetIfValid(v->group_id);
  if (g != nullptr) wagon_removal = HasBit(g->flags, GroupFlags::GF_REPLACE_WAGON_REMOVAL);
 
  /* Test whether any replacement is set, before issuing a whole lot of commands that would end in nothing changed */
  Vehicle *w = v;
  bool any_replacements = false;
  while (w != nullptr) {
    EngineID e;
    CommandCost cost = GetNewEngineType(w, c, false, e);
    if (cost.Failed()) return cost;
    any_replacements |= (e != INVALID_ENGINE);
    w = (!free_wagon && w->type == VEH_TRAIN ? Train::From(w)->GetNextUnit() : nullptr);
  }
 
  CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);
  bool nothing_to_do = true;
 
  if (any_replacements) {
    bool was_stopped = free_wagon || ((v->vehstatus & VS_STOPPED) != 0);
 
    /* Stop the vehicle */
    if (!was_stopped) cost.AddCost(DoCmdStartStopVehicle(v, true));
    if (cost.Failed()) return cost;
 
    assert(free_wagon || v->IsStoppedInDepot());
 
    /* We have to construct the new vehicle chain to test whether it is valid.
     * Vehicle construction needs random bits, so we have to save the random seeds
     * to prevent desyncs and to replay newgrf callbacks during DC_EXEC */
    SavedRandomSeeds saved_seeds;
    SaveRandomSeeds(&saved_seeds);
    if (free_wagon) {
      cost.AddCost(ReplaceFreeUnit(&v, flags & ~DC_EXEC, &nothing_to_do));
    } else {
      cost.AddCost(ReplaceChain(&v, flags & ~DC_EXEC, wagon_removal, &nothing_to_do));
    }
    RestoreRandomSeeds(saved_seeds);
 
    if (cost.Succeeded() && (flags & DC_EXEC) != 0) {
      if (free_wagon) {
        ret = ReplaceFreeUnit(&v, flags, &nothing_to_do);
      } else {
        ret = ReplaceChain(&v, flags, wagon_removal, &nothing_to_do);
      }
      assert(ret.Succeeded() && ret.GetCost() == cost.GetCost());
    }
 
    /* Restart the vehicle */
    if (!was_stopped) cost.AddCost(DoCmdStartStopVehicle(v, false));
  }
 
  if (cost.Succeeded() && nothing_to_do) cost = CommandCost(STR_ERROR_AUTOREPLACE_NOTHING_TO_DO);
  return cost;
}
 
CommandCost CmdSetAutoReplace(DoCommandFlag flags, GroupID id_g, EngineID old_engine_type, EngineID new_engine_type, bool when_old)
{
  Company *c = Company::GetIfValid(_current_company);
  if (c == nullptr) return CMD_ERROR;
 
  CommandCost cost;
 
  if (Group::IsValidID(id_g) ? Group::Get(id_g)->owner != _current_company : !IsAllGroupID(id_g) && !IsDefaultGroupID(id_g)) return CMD_ERROR;
  if (!Engine::IsValidID(old_engine_type)) return CMD_ERROR;
  if (Group::IsValidID(id_g) && Group::Get(id_g)->vehicle_type != Engine::Get(old_engine_type)->type) return CMD_ERROR;
 
  if (new_engine_type != INVALID_ENGINE) {
    if (!Engine::IsValidID(new_engine_type)) return CMD_ERROR;
    if (!CheckAutoreplaceValidity(old_engine_type, new_engine_type, _current_company)) return CMD_ERROR;
 
    cost = AddEngineReplacementForCompany(c, old_engine_type, new_engine_type, id_g, when_old, flags);
  } else {
    cost = RemoveEngineReplacementForCompany(c, old_engine_type, id_g, flags);
  }
 
  if (flags & DC_EXEC) {
    GroupStatistics::UpdateAutoreplace(_current_company);
    if (IsLocalCompany()) SetWindowDirty(WC_REPLACE_VEHICLE, Engine::Get(old_engine_type)->type);
 
    const VehicleType vt = Engine::Get(old_engine_type)->type;
    SetWindowDirty(GetWindowClassForVehicleType(vt), VehicleListIdentifier(VL_GROUP_LIST, vt, _current_company).Pack());
  }
  if ((flags & DC_EXEC) && IsLocalCompany()) InvalidateAutoreplaceWindow(old_engine_type, id_g);
 
  return cost;
}