npf.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 "../../debug.h"
#include "../../network/network.h"
#include "../../viewport_func.h"
#include "../../ship.h"
#include "../../roadstop_base.h"
#include "../../vehicle_func.h"
#include "../pathfinder_func.h"
#include "../pathfinder_type.h"
#include "../follow_track.hpp"
#include "aystar.h"
 
#include "../../safeguards.h"
 
static const uint NPF_HASH_BITS = 12; 
/* Do no change below values */
static const uint NPF_HASH_SIZE = 1 << NPF_HASH_BITS;
static const uint NPF_HASH_HALFBITS = NPF_HASH_BITS / 2;
static const uint NPF_HASH_HALFMASK = (1 << NPF_HASH_HALFBITS) - 1;
 
struct NPFFindStationOrTileData {
  TileIndex dest_coords;    
  StationID station_index;  
  bool reserve_path;        
  StationType station_type; 
  bool not_articulated;     
  const Vehicle *v;         
};
 
struct AyStarUserData {
  Owner owner;
  TransportType type;
  RailTypes railtypes;
  RoadTypes roadtypes;
  uint subtype;
};
 
enum AyStarNodeUserDataType {
  NPF_TRACKDIR_CHOICE = 0, 
  NPF_NODE_FLAGS,
};
 
enum NPFNodeFlag {
  NPF_FLAG_SEEN_SIGNAL,       
  NPF_FLAG_2ND_SIGNAL,        
  NPF_FLAG_3RD_SIGNAL,        
  NPF_FLAG_REVERSE,           
  NPF_FLAG_LAST_SIGNAL_RED,   
  NPF_FLAG_LAST_SIGNAL_BLOCK, 
  NPF_FLAG_IGNORE_START_TILE, 
  NPF_FLAG_TARGET_RESERVED,   
  NPF_FLAG_IGNORE_RESERVED,   
};
 
struct NPFFoundTargetData {
  uint best_bird_dist;    
  uint best_path_dist;    
  Trackdir best_trackdir; 
  AyStarNode node;        
  bool res_okay;          
};
 
static AyStar _npf_aystar;
 
/* The cost of each trackdir. A diagonal piece is the full NPF_TILE_LENGTH,
 * the shorter piece is sqrt(2)/2*NPF_TILE_LENGTH =~ 0.7071
 */
#define NPF_STRAIGHT_LENGTH (uint)(NPF_TILE_LENGTH * STRAIGHT_TRACK_LENGTH)
static const uint _trackdir_length[TRACKDIR_END] = {
  NPF_TILE_LENGTH, NPF_TILE_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH,
  0, 0,
  NPF_TILE_LENGTH, NPF_TILE_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH, NPF_STRAIGHT_LENGTH
};
 
static inline bool NPFGetFlag(const AyStarNode *node, NPFNodeFlag flag)
{
  return HasBit(node->user_data[NPF_NODE_FLAGS], flag);
}
 
static inline void NPFSetFlag(AyStarNode *node, NPFNodeFlag flag, bool value)
{
  SB(node->user_data[NPF_NODE_FLAGS], flag, 1, value);
}
 
bool CheckIgnoreFirstTile(const PathNode *node)
{
  return (node->parent == nullptr && HasBit(node->node.user_data[NPF_NODE_FLAGS], NPF_FLAG_IGNORE_START_TILE));
}
 
static uint NPFDistanceTrack(TileIndex t0, TileIndex t1)
{
  const uint dx = Delta(TileX(t0), TileX(t1));
  const uint dy = Delta(TileY(t0), TileY(t1));
 
  const uint straightTracks = 2 * std::min(dx, dy); // The number of straight (not full length) tracks
  /* OPTIMISATION:
   * Original: diagTracks = max(dx, dy) - min(dx,dy);
   * Proof:
   * (dx+dy) - straightTracks  == (min + max) - straightTracks = min + max - 2 * min = max - min */
  const uint diagTracks = dx + dy - straightTracks; // The number of diagonal (full tile length) tracks.
 
  /* Don't factor out NPF_TILE_LENGTH below, this will round values and lose
   * precision */
  return diagTracks * NPF_TILE_LENGTH + straightTracks * NPF_TILE_LENGTH * STRAIGHT_TRACK_LENGTH;
}
 
static uint NPFHash(TileIndex tile, Trackdir dir)
{
  /* TODO: think of a better hash? */
  uint part1 = TileX(tile) & NPF_HASH_HALFMASK;
  uint part2 = TileY(tile) & NPF_HASH_HALFMASK;
 
  assert(IsValidTrackdir(dir));
  assert(IsValidTile(tile));
  return ((part1 << NPF_HASH_HALFBITS | part2) + (NPF_HASH_SIZE * dir / TRACKDIR_END)) % NPF_HASH_SIZE;
}
 
static int32_t NPFCalcZero(AyStar *, AyStarNode *, OpenListNode *)
{
  return 0;
}
 
/* Calculates the heuristic to the target station or tile. For train stations, it
 * takes into account the direction of approach.
 */
static int32_t NPFCalcStationOrTileHeuristic(AyStar *as, AyStarNode *current, OpenListNode *)
{
  NPFFindStationOrTileData *fstd = (NPFFindStationOrTileData*)as->user_target;
  NPFFoundTargetData *ftd = (NPFFoundTargetData*)as->user_path;
  TileIndex from = current->tile;
  TileIndex to = fstd->dest_coords;
  uint dist;
  AyStarUserData *user = (AyStarUserData *)as->user_data;
 
  /* aim for the closest station tile */
  if (fstd->station_index != INVALID_STATION) {
    to = CalcClosestStationTile(fstd->station_index, from, fstd->station_type);
  }
 
  if (user->type == TRANSPORT_ROAD) {
    /* Since roads only have diagonal pieces, we use manhattan distance here */
    dist = DistanceManhattan(from, to) * NPF_TILE_LENGTH;
  } else {
    /* Ships and trains can also go diagonal, so the minimum distance is shorter */
    dist = NPFDistanceTrack(from, to);
  }
 
  Debug(npf, 4, "Calculating H for: ({}, {}). Result: {}", TileX(current->tile), TileY(current->tile), dist);
 
  if (dist < ftd->best_bird_dist) {
    ftd->best_bird_dist = dist;
    ftd->best_trackdir = (Trackdir)current->user_data[NPF_TRACKDIR_CHOICE];
  }
  return dist;
}
 
 
/* Fills AyStarNode.user_data[NPF_TRACKDIRCHOICE] with the chosen direction to
 * get here, either getting it from the current choice or from the parent's
 * choice */
static void NPFFillTrackdirChoice(AyStarNode *current, OpenListNode *parent)
{
  if (parent->path.parent == nullptr) {
    Trackdir trackdir = current->direction;
    /* This is a first order decision, so we'd better save the
     * direction we chose */
    current->user_data[NPF_TRACKDIR_CHOICE] = trackdir;
    Debug(npf, 6, "Saving trackdir: 0x{:X}", trackdir);
  } else {
    /* We've already made the decision, so just save our parent's decision */
    current->user_data[NPF_TRACKDIR_CHOICE] = parent->path.node.user_data[NPF_TRACKDIR_CHOICE];
  }
}
 
/* Will return the cost of the tunnel. If it is an entry, it will return the
 * cost of that tile. If the tile is an exit, it will return the tunnel length
 * including the exit tile. Requires that this is a Tunnel tile */
static uint NPFTunnelCost(AyStarNode *current)
{
  DiagDirection exitdir = TrackdirToExitdir(current->direction);
  TileIndex tile = current->tile;
  if (GetTunnelBridgeDirection(tile) == ReverseDiagDir(exitdir)) {
    /* We just popped out if this tunnel, since were
     * facing the tunnel exit */
    return NPF_TILE_LENGTH * (GetTunnelBridgeLength(current->tile, GetOtherTunnelEnd(current->tile)) + 1);
    /* @todo: Penalty for tunnels? */
  } else {
    /* We are entering the tunnel, the enter tile is just a
     * straight track */
    return NPF_TILE_LENGTH;
  }
}
 
static inline uint NPFBridgeCost(AyStarNode *current)
{
  return NPF_TILE_LENGTH * GetTunnelBridgeLength(current->tile, GetOtherBridgeEnd(current->tile));
}
 
static uint NPFSlopeCost(AyStarNode *current)
{
  TileIndex next = current->tile + TileOffsByDiagDir(TrackdirToExitdir(current->direction));
 
  /* Get center of tiles */
  int x1 = TileX(current->tile) * TILE_SIZE + TILE_SIZE / 2;
  int y1 = TileY(current->tile) * TILE_SIZE + TILE_SIZE / 2;
  int x2 = TileX(next) * TILE_SIZE + TILE_SIZE / 2;
  int y2 = TileY(next) * TILE_SIZE + TILE_SIZE / 2;
 
  int dx4 = (x2 - x1) / 4;
  int dy4 = (y2 - y1) / 4;
 
  /* Get the height on both sides of the tile edge.
   * Avoid testing the height on the tile-center. This will fail for halftile-foundations.
   */
  int z1 = GetSlopePixelZ(x1 + dx4, y1 + dy4, true);
  int z2 = GetSlopePixelZ(x2 - dx4, y2 - dy4, true);
 
  if (z2 - z1 > 1) {
    /* Slope up */
    return _settings_game.pf.npf.npf_rail_slope_penalty;
  }
  return 0;
  /* Should we give a bonus for slope down? Probably not, we
   * could just subtract that bonus from the penalty, because
   * there is only one level of steepness... */
}
 
static uint NPFReservedTrackCost(AyStarNode *current)
{
  TileIndex tile = current->tile;
  TrackBits track = TrackToTrackBits(TrackdirToTrack(current->direction));
  TrackBits res = GetReservedTrackbits(tile);
 
  if (NPFGetFlag(current, NPF_FLAG_3RD_SIGNAL) || NPFGetFlag(current, NPF_FLAG_LAST_SIGNAL_BLOCK) || ((res & track) == TRACK_BIT_NONE && !TracksOverlap(res | track))) return 0;
 
  if (IsTileType(tile, MP_TUNNELBRIDGE)) {
    DiagDirection exitdir = TrackdirToExitdir(current->direction);
    if (GetTunnelBridgeDirection(tile) == ReverseDiagDir(exitdir)) {
      return  _settings_game.pf.npf.npf_rail_pbs_cross_penalty * (GetTunnelBridgeLength(tile, GetOtherTunnelBridgeEnd(tile)) + 1);
    }
  }
  return  _settings_game.pf.npf.npf_rail_pbs_cross_penalty;
}
 
static void NPFMarkTile(TileIndex tile)
{
  if (_debug_npf_level < 1 || _networking) return;
  switch (GetTileType(tile)) {
    case MP_RAILWAY:
      /* DEBUG: mark visited tiles by mowing the grass under them ;-) */
      if (!IsRailDepot(tile)) {
        SetRailGroundType(tile, RAIL_GROUND_BARREN);
        MarkTileDirtyByTile(tile);
      }
      break;
 
    case MP_ROAD:
      if (!IsRoadDepot(tile)) {
        SetRoadside(tile, ROADSIDE_BARREN);
        MarkTileDirtyByTile(tile);
      }
      break;
 
    default:
      break;
  }
}
 
static Vehicle *CountShipProc(Vehicle *v, void *data)
{
  uint *count = (uint *)data;
  /* Ignore other vehicles (aircraft) and ships inside depot. */
  if (v->type == VEH_SHIP && (v->vehstatus & VS_HIDDEN) == 0) (*count)++;
 
  return nullptr;
}
 
static int32_t NPFWaterPathCost(AyStar *, AyStarNode *current, OpenListNode *parent)
{
  int32_t cost = 0;
  Trackdir trackdir = current->direction;
 
  cost = _trackdir_length[trackdir]; // Should be different for diagonal tracks
 
  if (IsBuoyTile(current->tile) && IsDiagonalTrackdir(trackdir)) {
    cost += _settings_game.pf.npf.npf_buoy_penalty; // A small penalty for going over buoys
  }
 
  if (current->direction != NextTrackdir((Trackdir)parent->path.node.direction)) {
    cost += _settings_game.pf.npf.npf_water_curve_penalty;
  }
 
  if (IsDockingTile(current->tile)) {
    /* Check docking tile for occupancy */
    uint count = 0;
    HasVehicleOnPos(current->tile, &count, &CountShipProc);
    cost += count * 3 * _trackdir_length[trackdir];
  }
 
  /* @todo More penalties? */
 
  return cost;
}
 
/* Determine the cost of this node, for road tracks */
static int32_t NPFRoadPathCost(AyStar *, AyStarNode *current, OpenListNode *)
{
  TileIndex tile = current->tile;
  int32_t cost = 0;
 
  /* Determine base length */
  switch (GetTileType(tile)) {
    case MP_TUNNELBRIDGE:
      cost = IsTunnel(tile) ? NPFTunnelCost(current) : NPFBridgeCost(current);
      break;
 
    case MP_ROAD:
      cost = NPF_TILE_LENGTH;
      /* Increase the cost for level crossings */
      if (IsLevelCrossing(tile)) cost += _settings_game.pf.npf.npf_crossing_penalty;
      break;
 
    case MP_STATION: {
      cost = NPF_TILE_LENGTH;
      const RoadStop *rs = RoadStop::GetByTile(tile, GetRoadStopType(tile));
      if (IsDriveThroughStopTile(tile)) {
        /* Increase the cost for drive-through road stops */
        cost += _settings_game.pf.npf.npf_road_drive_through_penalty;
        DiagDirection dir = TrackdirToExitdir(current->direction);
        if (!RoadStop::IsDriveThroughRoadStopContinuation(tile, tile - TileOffsByDiagDir(dir))) {
          /* When we're the first road stop in a 'queue' of them we increase
           * cost based on the fill percentage of the whole queue. */
          const RoadStop::Entry *entry = rs->GetEntry(dir);
          cost += entry->GetOccupied() * _settings_game.pf.npf.npf_road_dt_occupied_penalty / entry->GetLength();
        }
      } else {
        /* Increase cost for filled road stops */
        cost += _settings_game.pf.npf.npf_road_bay_occupied_penalty * (!rs->IsFreeBay(0) + !rs->IsFreeBay(1)) / 2;
      }
      break;
    }
 
    default:
      break;
  }
 
  /* Determine extra costs */
 
  /* Check for slope */
  cost += NPFSlopeCost(current);
 
  /* Check for turns. Road vehicles only really drive diagonal, turns are
   * represented by non-diagonal tracks */
  if (!IsDiagonalTrackdir(current->direction)) {
    cost += _settings_game.pf.npf.npf_road_curve_penalty;
  }
 
  NPFMarkTile(tile);
  Debug(npf, 4, "Calculating G for: ({}, {}). Result: {}", TileX(current->tile), TileY(current->tile), cost);
  return cost;
}
 
 
/* Determine the cost of this node, for railway tracks */
static int32_t NPFRailPathCost(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
  TileIndex tile = current->tile;
  Trackdir trackdir = current->direction;
  int32_t cost = 0;
  /* HACK: We create a OpenListNode manually, so we can call EndNodeCheck */
  OpenListNode new_node;
 
  /* Determine base length */
  switch (GetTileType(tile)) {
    case MP_TUNNELBRIDGE:
      cost = IsTunnel(tile) ? NPFTunnelCost(current) : NPFBridgeCost(current);
      break;
 
    case MP_RAILWAY:
      cost = _trackdir_length[trackdir]; // Should be different for diagonal tracks
      break;
 
    case MP_ROAD: // Railway crossing
      cost = NPF_TILE_LENGTH;
      break;
 
    case MP_STATION:
      /* We give a station tile a penalty. Logically we would only want to give
       * station tiles that are not our destination this penalty. This would
       * discourage trains to drive through busy stations. But, we can just
       * give any station tile a penalty, because every possible route will get
       * this penalty exactly once, on its end tile (if it's a station) and it
       * will therefore not make a difference. */
      cost = NPF_TILE_LENGTH + _settings_game.pf.npf.npf_rail_station_penalty;
 
      if (IsRailWaypoint(tile)) {
        NPFFindStationOrTileData *fstd = (NPFFindStationOrTileData*)as->user_target;
        if (fstd->v->current_order.IsType(OT_GOTO_WAYPOINT) && GetStationIndex(tile) == fstd->v->current_order.GetDestination()) {
          /* This waypoint is our destination; maybe this isn't an unreserved
           * one, so check that and if so see that as the last signal being
           * red. This way waypoints near stations should work better. */
          const Train *train = Train::From(fstd->v);
          CFollowTrackRail ft(train);
          TileIndex t = tile;
          Trackdir td = trackdir;
          while (ft.Follow(t, td)) {
            assert(t != ft.m_new_tile);
            t = ft.m_new_tile;
            if (KillFirstBit(ft.m_new_td_bits) != TRACKDIR_BIT_NONE) {
              /* We encountered a junction; it's going to be too complex to
               * handle this perfectly, so just bail out. There is no simple
               * free path, so try the other possibilities. */
              td = INVALID_TRACKDIR;
              break;
            }
            td = RemoveFirstTrackdir(&ft.m_new_td_bits);
            /* If this is a safe waiting position we're done searching for it */
            if (IsSafeWaitingPosition(train, t, td, true, _settings_game.pf.forbid_90_deg)) break;
          }
          if (td == INVALID_TRACKDIR ||
              !IsSafeWaitingPosition(train, t, td, true, _settings_game.pf.forbid_90_deg) ||
              !IsWaitingPositionFree(train, t, td, _settings_game.pf.forbid_90_deg)) {
            cost += _settings_game.pf.npf.npf_rail_lastred_penalty;
          }
        }
      }
      break;
 
    default:
      break;
  }
 
  /* Determine extra costs */
 
  /* Check for signals */
  if (IsTileType(tile, MP_RAILWAY)) {
    if (HasSignalOnTrackdir(tile, trackdir)) {
      SignalType sigtype = GetSignalType(tile, TrackdirToTrack(trackdir));
      /* Ordinary track with signals */
      if (GetSignalStateByTrackdir(tile, trackdir) == SIGNAL_STATE_RED) {
        /* Signal facing us is red */
        if (!NPFGetFlag(current, NPF_FLAG_SEEN_SIGNAL)) {
          /* Penalize the first signal we
           * encounter, if it is red */
 
          /* Is this a presignal exit or combo? */
          if (!IsPbsSignal(sigtype)) {
            if (sigtype == SIGTYPE_EXIT || sigtype == SIGTYPE_COMBO) {
              /* Penalise exit and combo signals differently (heavier) */
              cost += _settings_game.pf.npf.npf_rail_firstred_exit_penalty;
            } else {
              cost += _settings_game.pf.npf.npf_rail_firstred_penalty;
            }
          }
        }
        /* Record the state of this signal. Path signals are assumed to
         * be green as the signal state of them has no meaning for this. */
        NPFSetFlag(current, NPF_FLAG_LAST_SIGNAL_RED, !IsPbsSignal(sigtype));
      } else {
        /* Record the state of this signal */
        NPFSetFlag(current, NPF_FLAG_LAST_SIGNAL_RED, false);
      }
      if (NPFGetFlag(current, NPF_FLAG_SEEN_SIGNAL)) {
        if (NPFGetFlag(current, NPF_FLAG_2ND_SIGNAL)) {
          NPFSetFlag(current, NPF_FLAG_3RD_SIGNAL, true);
        } else {
          NPFSetFlag(current, NPF_FLAG_2ND_SIGNAL, true);
        }
      } else {
        NPFSetFlag(current, NPF_FLAG_SEEN_SIGNAL, true);
      }
      NPFSetFlag(current, NPF_FLAG_LAST_SIGNAL_BLOCK, !IsPbsSignal(sigtype));
    }
 
    if (HasPbsSignalOnTrackdir(tile, ReverseTrackdir(trackdir)) && !NPFGetFlag(current, NPF_FLAG_3RD_SIGNAL)) {
      cost += _settings_game.pf.npf.npf_rail_pbs_signal_back_penalty;
    }
  }
 
  /* Penalise the tile if it is a target tile and the last signal was
   * red */
  /* HACK: We create a new_node here so we can call EndNodeCheck. Ugly as hell
   * of course... */
  new_node.path.node = *current;
  if (as->EndNodeCheck(as, &new_node) == AYSTAR_FOUND_END_NODE && NPFGetFlag(current, NPF_FLAG_LAST_SIGNAL_RED)) {
    cost += _settings_game.pf.npf.npf_rail_lastred_penalty;
  }
 
  /* Check for slope */
  cost += NPFSlopeCost(current);
 
  /* Check for turns */
  if (current->direction != NextTrackdir((Trackdir)parent->path.node.direction)) {
    cost += _settings_game.pf.npf.npf_rail_curve_penalty;
  }
  /* TODO, with realistic acceleration, also the amount of straight track between
   *      curves should be taken into account, as this affects the speed limit. */
 
  /* Check for reverse in depot */
  if (IsRailDepotTile(tile) && as->EndNodeCheck(as, &new_node) != AYSTAR_FOUND_END_NODE) {
    /* Penalise any depot tile that is not the last tile in the path. This
     * _should_ penalise every occurrence of reversing in a depot (and only
     * that) */
    cost += _settings_game.pf.npf.npf_rail_depot_reverse_penalty;
  }
 
  /* Check for occupied track */
  cost += NPFReservedTrackCost(current);
 
  NPFMarkTile(tile);
  Debug(npf, 4, "Calculating G for: ({}, {}). Result: {}", TileX(current->tile), TileY(current->tile), cost);
  return cost;
}
 
/* Will find any depot */
static int32_t NPFFindDepot(const AyStar *as, const OpenListNode *current)
{
  AyStarUserData *user = (AyStarUserData *)as->user_data;
  /* It's not worth caching the result with NPF_FLAG_IS_TARGET here as below,
   * since checking the cache not that much faster than the actual check */
  return IsDepotTypeTile(current->path.node.tile, user->type) ?
    AYSTAR_FOUND_END_NODE : AYSTAR_DONE;
}
 
static int32_t NPFFindSafeTile(const AyStar *as, const OpenListNode *current)
{
  const Train *v = Train::From(((NPFFindStationOrTileData *)as->user_target)->v);
 
  return (IsSafeWaitingPosition(v, current->path.node.tile, current->path.node.direction, true, _settings_game.pf.forbid_90_deg) &&
      IsWaitingPositionFree(v, current->path.node.tile, current->path.node.direction, _settings_game.pf.forbid_90_deg)) ?
        AYSTAR_FOUND_END_NODE : AYSTAR_DONE;
}
 
/* Will find a station identified using the NPFFindStationOrTileData */
static int32_t NPFFindStationOrTile(const AyStar *as, const OpenListNode *current)
{
  NPFFindStationOrTileData *fstd = (NPFFindStationOrTileData*)as->user_target;
  const AyStarNode *node = &current->path.node;
  TileIndex tile = node->tile;
 
  if (fstd->station_index == INVALID_STATION && tile == fstd->dest_coords) return AYSTAR_FOUND_END_NODE;
 
  if (fstd->v->type == VEH_SHIP) {
    /* Ships do not actually reach the destination station, so we check for a docking tile instead. */
    if (IsDockingTile(tile) && IsShipDestinationTile(tile, fstd->station_index)) return AYSTAR_FOUND_END_NODE;
    return AYSTAR_DONE;
  }
 
  if (IsTileType(tile, MP_STATION) && GetStationIndex(tile) == fstd->station_index) {
    if (fstd->v->type == VEH_TRAIN) return AYSTAR_FOUND_END_NODE;
 
    assert(fstd->v->type == VEH_ROAD);
    /* Only if it is a valid station *and* we can stop there */
    if (GetStationType(tile) == fstd->station_type && (fstd->not_articulated || IsDriveThroughStopTile(tile))) return AYSTAR_FOUND_END_NODE;
  }
  return AYSTAR_DONE;
}
 
static const PathNode *FindSafePosition(PathNode *path, const Train *v)
{
  /* If there is no signal, reserve the whole path. */
  PathNode *sig = path;
 
  for (; path->parent != nullptr; path = path->parent) {
    if (IsSafeWaitingPosition(v, path->node.tile, path->node.direction, true, _settings_game.pf.forbid_90_deg)) {
      sig = path;
    }
  }
 
  return sig;
}
 
static void ClearPathReservation(const PathNode *start, const PathNode *end)
{
  bool first_run = true;
  for (; start != end; start = start->parent) {
    if (IsRailStationTile(start->node.tile) && first_run) {
      SetRailStationPlatformReservation(start->node.tile, TrackdirToExitdir(start->node.direction), false);
    } else {
      UnreserveRailTrack(start->node.tile, TrackdirToTrack(start->node.direction));
    }
    first_run = false;
  }
}
 
static void NPFSaveTargetData(AyStar *as, OpenListNode *current)
{
  AyStarUserData *user = (AyStarUserData *)as->user_data;
  NPFFoundTargetData *ftd = (NPFFoundTargetData*)as->user_path;
  ftd->best_trackdir = (Trackdir)current->path.node.user_data[NPF_TRACKDIR_CHOICE];
  ftd->best_path_dist = current->g;
  ftd->best_bird_dist = 0;
  ftd->node = current->path.node;
  ftd->res_okay = false;
 
  if (as->user_target != nullptr && ((NPFFindStationOrTileData*)as->user_target)->reserve_path && user->type == TRANSPORT_RAIL) {
    /* Path reservation is requested. */
    const Train *v = Train::From(((NPFFindStationOrTileData *)as->user_target)->v);
 
    const PathNode *target = FindSafePosition(&current->path, v);
    ftd->node = target->node;
 
    /* If the target is a station skip to platform end. */
    if (IsRailStationTile(target->node.tile)) {
      DiagDirection dir = TrackdirToExitdir(target->node.direction);
      uint len = Station::GetByTile(target->node.tile)->GetPlatformLength(target->node.tile, dir);
      TileIndex end_tile = TILE_ADD(target->node.tile, (len - 1) * TileOffsByDiagDir(dir));
 
      /* Update only end tile, trackdir of a station stays the same. */
      ftd->node.tile = end_tile;
      if (!IsWaitingPositionFree(v, end_tile, target->node.direction, _settings_game.pf.forbid_90_deg)) return;
      SetRailStationPlatformReservation(target->node.tile, dir, true);
      SetRailStationReservation(target->node.tile, false);
    } else {
      if (!IsWaitingPositionFree(v, target->node.tile, target->node.direction, _settings_game.pf.forbid_90_deg)) return;
    }
 
    for (const PathNode *cur = target; cur->parent != nullptr; cur = cur->parent) {
      if (!TryReserveRailTrack(cur->node.tile, TrackdirToTrack(cur->node.direction))) {
        /* Reservation failed, undo. */
        ClearPathReservation(target, cur);
        return;
      }
    }
 
    ftd->res_okay = true;
  }
}
 
static bool CanEnterTileOwnerCheck(Owner owner, TileIndex tile, DiagDirection enterdir)
{
  if (IsTileType(tile, MP_RAILWAY) || // Rail tile (also rail depot)
      HasStationTileRail(tile) ||     // Rail station tile/waypoint
      IsRoadDepotTile(tile) ||        // Road depot tile
      IsBayRoadStopTile(tile)) { // Road station tile (but not drive-through stops)
    return IsTileOwner(tile, owner);  // You need to own these tiles entirely to use them
  }
 
  switch (GetTileType(tile)) {
    case MP_ROAD:
      /* rail-road crossing : are we looking at the railway part? */
      if (IsLevelCrossing(tile) &&
          DiagDirToAxis(enterdir) != GetCrossingRoadAxis(tile)) {
        return IsTileOwner(tile, owner); // Railway needs owner check, while the street is public
      }
      break;
 
    case MP_TUNNELBRIDGE:
      if (GetTunnelBridgeTransportType(tile) == TRANSPORT_RAIL) {
        return IsTileOwner(tile, owner);
      }
      break;
 
    default:
      break;
  }
 
  return true; // no need to check
}
 
 
static DiagDirection GetDepotDirection(TileIndex tile, TransportType type)
{
  assert(IsDepotTypeTile(tile, type));
 
  switch (type) {
    case TRANSPORT_RAIL:  return GetRailDepotDirection(tile);
    case TRANSPORT_ROAD:  return GetRoadDepotDirection(tile);
    case TRANSPORT_WATER: return GetShipDepotDirection(tile);
    default: return INVALID_DIAGDIR; // Not reached
  }
}
 
static DiagDirection GetSingleTramBit(TileIndex tile)
{
  if (IsNormalRoadTile(tile)) {
    RoadBits rb = GetRoadBits(tile, RTT_TRAM);
    switch (rb) {
      case ROAD_NW: return DIAGDIR_NW;
      case ROAD_SW: return DIAGDIR_SW;
      case ROAD_SE: return DIAGDIR_SE;
      case ROAD_NE: return DIAGDIR_NE;
      default: break;
    }
  }
  return INVALID_DIAGDIR;
}
 
static DiagDirection GetTileSingleEntry(TileIndex tile, TransportType type, uint subtype)
{
  if (type != TRANSPORT_WATER && IsDepotTypeTile(tile, type)) return GetDepotDirection(tile, type);
 
  if (type == TRANSPORT_ROAD) {
    if (IsBayRoadStopTile(tile)) return GetRoadStopDir(tile);
    if ((RoadTramType)subtype == RTT_TRAM) return GetSingleTramBit(tile);
  }
 
  return INVALID_DIAGDIR;
}
 
static inline bool ForceReverse(TileIndex tile, DiagDirection dir, TransportType type, uint subtype)
{
  DiagDirection single_entry = GetTileSingleEntry(tile, type, subtype);
  return single_entry != INVALID_DIAGDIR && single_entry != dir;
}
 
static bool CanEnterTile(TileIndex tile, DiagDirection dir, AyStarUserData *user)
{
  /* Check tunnel entries and bridge ramps */
  if (IsTileType(tile, MP_TUNNELBRIDGE) && GetTunnelBridgeDirection(tile) != dir) return false;
 
  /* Test ownership */
  if (!CanEnterTileOwnerCheck(user->owner, tile, dir)) return false;
 
  /* check correct rail type (mono, maglev, etc) */
  switch (user->type) {
    case TRANSPORT_RAIL: {
      RailType rail_type = GetTileRailType(tile);
      if (!HasBit(user->railtypes, rail_type)) return false;
      break;
    }
 
    case TRANSPORT_ROAD: {
      RoadType road_type = GetRoadType(tile, (RoadTramType)user->subtype);
      if (!HasBit(user->roadtypes, road_type)) return false;
      break;
    }
 
    default: break;
  }
 
  /* Depots, standard roadstops and single tram bits can only be entered from one direction */
  DiagDirection single_entry = GetTileSingleEntry(tile, user->type, user->subtype);
  return single_entry == INVALID_DIAGDIR || single_entry == ReverseDiagDir(dir);
}
 
static TrackdirBits GetDriveableTrackdirBits(TileIndex dst_tile, TileIndex src_tile, Trackdir src_trackdir, TransportType type, uint subtype)
{
  TrackdirBits trackdirbits = TrackStatusToTrackdirBits(GetTileTrackStatus(dst_tile, type, subtype));
 
  if (trackdirbits == TRACKDIR_BIT_NONE && type == TRANSPORT_ROAD && (RoadTramType)subtype == RTT_TRAM) {
    /* GetTileTrackStatus() returns 0 for single tram bits.
     * As we cannot change it there (easily) without breaking something, change it here */
    switch (GetSingleTramBit(dst_tile)) {
      case DIAGDIR_NE:
      case DIAGDIR_SW:
        trackdirbits = TRACKDIR_BIT_X_NE | TRACKDIR_BIT_X_SW;
        break;
 
      case DIAGDIR_NW:
      case DIAGDIR_SE:
        trackdirbits = TRACKDIR_BIT_Y_NW | TRACKDIR_BIT_Y_SE;
        break;
 
      default: break;
    }
  }
 
  Debug(npf, 4, "Next node: ({}, {}) [{}], possible trackdirs: 0x{:X}", TileX(dst_tile), TileY(dst_tile), dst_tile, trackdirbits);
 
  /* Select only trackdirs we can reach from our current trackdir */
  trackdirbits &= TrackdirReachesTrackdirs(src_trackdir);
 
  /* Filter out trackdirs that would make 90 deg turns for trains */
  if (type == TRANSPORT_RAIL && Rail90DegTurnDisallowed(GetTileRailType(src_tile), GetTileRailType(dst_tile))) {
    trackdirbits &= ~TrackdirCrossesTrackdirs(src_trackdir);
  }
 
  Debug(npf, 6, "After filtering: ({}, {}), possible trackdirs: 0x{:X}", TileX(dst_tile), TileY(dst_tile), trackdirbits);
 
  return trackdirbits;
}
 
 
/* Will just follow the results of GetTileTrackStatus concerning where we can
 * go and where not. Uses AyStar.user_data[NPF_TYPE] as the transport type and
 * an argument to GetTileTrackStatus. Will skip tunnels, meaning that the
 * entry and exit are neighbours. Will fill
 * AyStarNode.user_data[NPF_TRACKDIR_CHOICE] with an appropriate value, and
 * copy AyStarNode.user_data[NPF_NODE_FLAGS] from the parent */
static void NPFFollowTrack(AyStar *aystar, OpenListNode *current)
{
  AyStarUserData *user = (AyStarUserData *)aystar->user_data;
  /* We leave src_tile on track src_trackdir in direction src_exitdir */
  Trackdir src_trackdir = current->path.node.direction;
  TileIndex src_tile = current->path.node.tile;
  DiagDirection src_exitdir = TrackdirToExitdir(src_trackdir);
 
  /* Information about the vehicle: TransportType (road/rail/water) and SubType (compatible rail/road types) */
  TransportType type = user->type;
  uint subtype = user->subtype;
 
  /* Initialize to 0, so we can jump out (return) somewhere an have no neighbours */
  aystar->num_neighbours = 0;
  Debug(npf, 4, "Expanding: ({}, {}, {}) [{}]", TileX(src_tile), TileY(src_tile), src_trackdir, src_tile);
 
  /* We want to determine the tile we arrive, and which choices we have there */
  TileIndex dst_tile;
  TrackdirBits trackdirbits;
 
  /* Find dest tile */
  /* Is src_tile valid, and can be used?
   * When choosing track on a junction src_tile is the tile neighboured to the junction wrt. exitdir.
   * But we must not check the validity of this move, as src_tile is totally unrelated to the move, if a roadvehicle reversed on a junction. */
  if (CheckIgnoreFirstTile(&current->path)) {
    /* Do not perform any checks that involve src_tile */
    dst_tile = src_tile + TileOffsByDiagDir(src_exitdir);
    trackdirbits = GetDriveableTrackdirBits(dst_tile, src_tile, src_trackdir, type, subtype);
  } else if (IsTileType(src_tile, MP_TUNNELBRIDGE) && GetTunnelBridgeDirection(src_tile) == src_exitdir) {
    /* We drive through the wormhole and arrive on the other side */
    dst_tile = GetOtherTunnelBridgeEnd(src_tile);
    trackdirbits = TrackdirToTrackdirBits(src_trackdir);
  } else if (ForceReverse(src_tile, src_exitdir, type, subtype)) {
    /* We can only reverse on this tile */
    dst_tile = src_tile;
    src_trackdir = ReverseTrackdir(src_trackdir);
    trackdirbits = TrackdirToTrackdirBits(src_trackdir);
  } else {
    /* We leave src_tile in src_exitdir and reach dst_tile */
    dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDiagDir(src_exitdir));
 
    if (dst_tile != INVALID_TILE && IsNormalRoadTile(dst_tile) && !CanEnterTile(dst_tile, src_exitdir, user)) dst_tile = INVALID_TILE;
 
    if (dst_tile == INVALID_TILE) {
      /* We cannot enter the next tile. Road vehicles can reverse, others reach dead end */
      if (type != TRANSPORT_ROAD || (RoadTramType)subtype == RTT_TRAM) return;
 
      dst_tile = src_tile;
      src_trackdir = ReverseTrackdir(src_trackdir);
    }
 
    trackdirbits = GetDriveableTrackdirBits(dst_tile, src_tile, src_trackdir, type, subtype);
 
    if (trackdirbits == TRACKDIR_BIT_NONE) {
      /* We cannot enter the next tile. Road vehicles can reverse, others reach dead end */
      if (type != TRANSPORT_ROAD || (RoadTramType)subtype == RTT_TRAM) return;
 
      dst_tile = src_tile;
      src_trackdir = ReverseTrackdir(src_trackdir);
 
      trackdirbits = GetDriveableTrackdirBits(dst_tile, src_tile, src_trackdir, type, subtype);
    }
  }
 
  if (NPFGetFlag(&current->path.node, NPF_FLAG_IGNORE_RESERVED)) {
    /* Mask out any reserved tracks. */
    TrackBits reserved = GetReservedTrackbits(dst_tile);
    trackdirbits &= ~TrackBitsToTrackdirBits(reserved);
 
    for (Track t : SetTrackBitIterator(TrackdirBitsToTrackBits(trackdirbits))) {
      if (TracksOverlap(reserved | TrackToTrackBits(t))) trackdirbits &= ~TrackToTrackdirBits(t);
    }
  }
 
  /* Enumerate possible track */
  uint i = 0;
  while (trackdirbits != TRACKDIR_BIT_NONE) {
    Trackdir dst_trackdir = RemoveFirstTrackdir(&trackdirbits);
    Debug(npf, 5, "Expanded into trackdir: {}, remaining trackdirs: 0x{:X}", dst_trackdir, trackdirbits);
 
    /* Tile with signals? */
    if (IsTileType(dst_tile, MP_RAILWAY) && GetRailTileType(dst_tile) == RAIL_TILE_SIGNALS) {
      if (HasSignalOnTrackdir(dst_tile, ReverseTrackdir(dst_trackdir)) && !HasSignalOnTrackdir(dst_tile, dst_trackdir) && IsOnewaySignal(dst_tile, TrackdirToTrack(dst_trackdir))) {
        /* If there's a one-way signal not pointing towards us, stop going in this direction. */
        break;
      }
    }
    {
      /* We've found ourselves a neighbour :-) */
      AyStarNode *neighbour = &aystar->neighbours[i];
      neighbour->tile = dst_tile;
      neighbour->direction = dst_trackdir;
      /* Save user data */
      neighbour->user_data[NPF_NODE_FLAGS] = current->path.node.user_data[NPF_NODE_FLAGS];
      NPFFillTrackdirChoice(neighbour, current);
    }
    i++;
  }
  aystar->num_neighbours = i;
}
 
/*
 * Plan a route to the specified target (which is checked by target_proc),
 * from start1 and if not nullptr, from start2 as well. The type of transport we
 * are checking is in type. reverse_penalty is applied to all routes that
 * originate from the second start node.
 * When we are looking for one specific target (optionally multiple tiles), we
 * should use a good heuristic to perform aystar search. When we search for
 * multiple targets that are spread around, we should perform a breadth first
 * search by specifying CalcZero as our heuristic.
 */
static NPFFoundTargetData NPFRouteInternal(AyStarNode *start1, bool ignore_start_tile1, AyStarNode *start2, bool ignore_start_tile2, NPFFindStationOrTileData *target, AyStar_EndNodeCheck target_proc, AyStar_CalculateH heuristic_proc, AyStarUserData *user, uint reverse_penalty, bool ignore_reserved = false, int max_penalty = 0)
{
  /* Initialize procs */
  _npf_aystar.max_path_cost = max_penalty;
  _npf_aystar.CalculateH = heuristic_proc;
  _npf_aystar.EndNodeCheck = target_proc;
  _npf_aystar.FoundEndNode = NPFSaveTargetData;
  _npf_aystar.GetNeighbours = NPFFollowTrack;
  switch (user->type) {
    default: NOT_REACHED();
    case TRANSPORT_RAIL:  _npf_aystar.CalculateG = NPFRailPathCost;  break;
    case TRANSPORT_ROAD:  _npf_aystar.CalculateG = NPFRoadPathCost;  break;
    case TRANSPORT_WATER: _npf_aystar.CalculateG = NPFWaterPathCost; break;
  }
 
  /* Initialize Start Node(s) */
  start1->user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
  start1->user_data[NPF_NODE_FLAGS] = 0;
  NPFSetFlag(start1, NPF_FLAG_IGNORE_START_TILE, ignore_start_tile1);
  NPFSetFlag(start1, NPF_FLAG_IGNORE_RESERVED, ignore_reserved);
  _npf_aystar.AddStartNode(start1, 0);
  if (start2 != nullptr) {
    start2->user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
    start2->user_data[NPF_NODE_FLAGS] = 0;
    NPFSetFlag(start2, NPF_FLAG_IGNORE_START_TILE, ignore_start_tile2);
    NPFSetFlag(start2, NPF_FLAG_REVERSE, true);
    NPFSetFlag(start2, NPF_FLAG_IGNORE_RESERVED, ignore_reserved);
    _npf_aystar.AddStartNode(start2, reverse_penalty);
  }
 
  /* Initialize result */
  NPFFoundTargetData result;
  result.best_bird_dist = UINT_MAX;
  result.best_path_dist = UINT_MAX;
  result.best_trackdir  = INVALID_TRACKDIR;
  result.node.tile      = INVALID_TILE;
  result.res_okay       = false;
  _npf_aystar.user_path = &result;
 
  /* Initialize target */
  _npf_aystar.user_target = target;
 
  /* Initialize user_data */
  _npf_aystar.user_data = user;
 
  /* GO! */
  [[maybe_unused]] int r = _npf_aystar.Main();
  assert(r != AYSTAR_STILL_BUSY);
 
  if (result.best_bird_dist != 0) {
    if (target != nullptr) {
      Debug(npf, 1, "Could not find route to tile 0x{:X} from 0x{:X}.", target->dest_coords, start1->tile);
    } else {
      /* Assumption: target == nullptr, so we are looking for a depot */
      Debug(npf, 1, "Could not find route to a depot from tile 0x{:X}.", start1->tile);
    }
 
  }
  return result;
}
 
/* Will search as below, but with two start nodes, the second being the
 * reverse. Look at the NPF_FLAG_REVERSE flag in the result node to see which
 * direction was taken (NPFGetFlag(result.node, NPF_FLAG_REVERSE)) */
static NPFFoundTargetData NPFRouteToStationOrTileTwoWay(TileIndex tile1, Trackdir trackdir1, bool ignore_start_tile1, TileIndex tile2, Trackdir trackdir2, bool ignore_start_tile2, NPFFindStationOrTileData *target, AyStarUserData *user)
{
  AyStarNode start1;
  AyStarNode start2;
 
  start1.tile = tile1;
  start2.tile = tile2;
  start1.direction = trackdir1;
  start2.direction = trackdir2;
 
  return NPFRouteInternal(&start1, ignore_start_tile1, (IsValidTile(tile2) ? &start2 : nullptr), ignore_start_tile2, target, NPFFindStationOrTile, NPFCalcStationOrTileHeuristic, user, 0);
}
 
/* Will search from the given tile and direction, for a route to the given
 * station for the given transport type. See the declaration of
 * NPFFoundTargetData above for the meaning of the result. */
static NPFFoundTargetData NPFRouteToStationOrTile(TileIndex tile, Trackdir trackdir, bool ignore_start_tile, NPFFindStationOrTileData *target, AyStarUserData *user)
{
  return NPFRouteToStationOrTileTwoWay(tile, trackdir, ignore_start_tile, INVALID_TILE, INVALID_TRACKDIR, false, target, user);
}
 
/* Search using breadth first. Good for little track choice and inaccurate
 * heuristic, such as railway/road with two start nodes, the second being the reverse. Call
 * NPFGetFlag(result.node, NPF_FLAG_REVERSE) to see from which node the path
 * originated. All paths from the second node will have the given
 * reverse_penalty applied (NPF_TILE_LENGTH is the equivalent of one full
 * tile).
 */
static NPFFoundTargetData NPFRouteToDepotBreadthFirstTwoWay(TileIndex tile1, Trackdir trackdir1, bool ignore_start_tile1, TileIndex tile2, Trackdir trackdir2, bool ignore_start_tile2, NPFFindStationOrTileData *target, AyStarUserData *user, uint reverse_penalty, int max_penalty)
{
  AyStarNode start1;
  AyStarNode start2;
 
  start1.tile = tile1;
  start2.tile = tile2;
  start1.direction = trackdir1;
  start2.direction = trackdir2;
 
  /* perform a breadth first search. Target is nullptr,
   * since we are just looking for any depot...*/
  return NPFRouteInternal(&start1, ignore_start_tile1, (IsValidTile(tile2) ? &start2 : nullptr), ignore_start_tile2, target, NPFFindDepot, NPFCalcZero, user, reverse_penalty, false, max_penalty);
}
 
void InitializeNPF()
{
  static bool first_init = true;
  if (first_init) {
    first_init = false;
    _npf_aystar.Init(NPFHash, NPF_HASH_SIZE);
  } else {
    _npf_aystar.Clear();
  }
  _npf_aystar.loops_per_tick = 0;
  _npf_aystar.max_path_cost = 0;
  /* We will limit the number of nodes for now, until we have a better
   * solution to really fix performance */
  _npf_aystar.max_search_nodes = _settings_game.pf.npf.npf_max_search_nodes;
}
 
static void NPFFillWithOrderData(NPFFindStationOrTileData *fstd, const Vehicle *v, bool reserve_path = false)
{
  /* Ships don't really reach their stations, but the tile in front. So don't
   * save the station id for ships. For roadvehs we don't store it either,
   * because multistop depends on vehicles actually reaching the exact
   * dest_tile, not just any stop of that station.
   * So only for train orders to stations we fill fstd->station_index, for all
   * others only dest_coords */
  if (v->current_order.IsType(OT_GOTO_STATION) || v->current_order.IsType(OT_GOTO_WAYPOINT)) {
    fstd->station_index = v->current_order.GetDestination();
    if (v->type == VEH_TRAIN) {
      fstd->station_type = v->current_order.IsType(OT_GOTO_STATION) ? STATION_RAIL : STATION_WAYPOINT;
    } else if (v->type == VEH_ROAD) {
      fstd->station_type = RoadVehicle::From(v)->IsBus() ? STATION_BUS : STATION_TRUCK;
    } else if (v->type == VEH_SHIP) {
      fstd->station_type = v->current_order.IsType(OT_GOTO_STATION) ? STATION_DOCK : STATION_BUOY;
    }
 
    fstd->not_articulated = v->type == VEH_ROAD && !RoadVehicle::From(v)->HasArticulatedPart();
    /* Let's take the closest tile of the station as our target for vehicles */
    fstd->dest_coords = CalcClosestStationTile(fstd->station_index, v->tile, fstd->station_type);
  } else {
    fstd->dest_coords = v->dest_tile;
    fstd->station_index = INVALID_STATION;
  }
  fstd->reserve_path = reserve_path;
  fstd->v = v;
}
 
/*** Road vehicles ***/
 
FindDepotData NPFRoadVehicleFindNearestDepot(const RoadVehicle *v, int max_penalty)
{
  Trackdir trackdir = v->GetVehicleTrackdir();
 
  AyStarUserData user = { v->owner, TRANSPORT_ROAD, RAILTYPES_NONE, v->compatible_roadtypes, GetRoadTramType(v->roadtype) };
  NPFFoundTargetData ftd = NPFRouteToDepotBreadthFirstTwoWay(v->tile, trackdir, false, INVALID_TILE, INVALID_TRACKDIR, false, nullptr, &user, 0, max_penalty);
 
  if (ftd.best_bird_dist != 0) return FindDepotData();
 
  /* Found target */
  /* Our caller expects a number of tiles, so we just approximate that
   * number by this. It might not be completely what we want, but it will
   * work for now :-) We can possibly change this when the old pathfinder
   * is removed. */
  return FindDepotData(ftd.node.tile, ftd.best_path_dist);
}
 
Trackdir NPFRoadVehicleChooseTrack(const RoadVehicle *v, TileIndex tile, DiagDirection enterdir, bool &path_found)
{
  NPFFindStationOrTileData fstd;
 
  NPFFillWithOrderData(&fstd, v);
  Trackdir trackdir = DiagDirToDiagTrackdir(enterdir);
 
  AyStarUserData user = { v->owner, TRANSPORT_ROAD, RAILTYPES_NONE, v->compatible_roadtypes, GetRoadTramType(v->roadtype) };
  NPFFoundTargetData ftd = NPFRouteToStationOrTile(tile - TileOffsByDiagDir(enterdir), trackdir, true, &fstd, &user);
 
  assert(ftd.best_trackdir != INVALID_TRACKDIR);
 
  /* If ftd.best_bird_dist is 0, we found our target and ftd.best_trackdir contains
   * the direction we need to take to get there, if ftd.best_bird_dist is not 0,
   * we did not find our target, but ftd.best_trackdir contains the direction leading
   * to the tile closest to our target. */
  path_found = (ftd.best_bird_dist == 0);
  return ftd.best_trackdir;
}
 
/*** Ships ***/
 
Track NPFShipChooseTrack(const Ship *v, bool &path_found)
{
  NPFFindStationOrTileData fstd;
  Trackdir trackdir = v->GetVehicleTrackdir();
  assert(trackdir != INVALID_TRACKDIR); // Check that we are not in a depot
 
  NPFFillWithOrderData(&fstd, v);
 
  AyStarUserData user = { v->owner, TRANSPORT_WATER, RAILTYPES_NONE, ROADTYPES_NONE, 0 };
  NPFFoundTargetData ftd = NPFRouteToStationOrTile(v->tile, trackdir, true, &fstd, &user);
 
  assert(ftd.best_trackdir != INVALID_TRACKDIR);
 
  /* If ftd.best_bird_dist is 0, we found our target and ftd.best_trackdir contains
   * the direction we need to take to get there, if ftd.best_bird_dist is not 0,
   * we did not find our target, but ftd.best_trackdir contains the direction leading
   * to the tile closest to our target. */
  path_found = (ftd.best_bird_dist == 0);
  return TrackdirToTrack(ftd.best_trackdir);
}
 
bool NPFShipCheckReverse(const Ship *v, Trackdir *best_td)
{
  NPFFindStationOrTileData fstd;
  NPFFoundTargetData ftd;
 
  NPFFillWithOrderData(&fstd, v);
 
  Trackdir trackdir = v->GetVehicleTrackdir();
  Trackdir trackdir_rev = ReverseTrackdir(trackdir);
  assert(trackdir != INVALID_TRACKDIR);
  assert(trackdir_rev != INVALID_TRACKDIR);
 
  AyStarUserData user = { v->owner, TRANSPORT_WATER, RAILTYPES_NONE, ROADTYPES_NONE, 0 };
  if (best_td != nullptr) {
    DiagDirection entry = ReverseDiagDir(VehicleExitDir(v->direction, v->state));
    TrackdirBits rtds = DiagdirReachesTrackdirs(entry) & TrackStatusToTrackdirBits(GetTileTrackStatus(v->tile, TRANSPORT_WATER, 0, entry));
    Trackdir best = (Trackdir)FindFirstBit(rtds);
    rtds = KillFirstBit(rtds);
    if (rtds == TRACKDIR_BIT_NONE) return false; /* At most one choice. */
    for (; rtds != TRACKDIR_BIT_NONE; rtds = KillFirstBit(rtds)) {
      Trackdir td = (Trackdir)FindFirstBit(rtds);
      ftd = NPFRouteToStationOrTileTwoWay(v->tile, best, false, v->tile, td, false, &fstd, &user);
      if (ftd.best_bird_dist == 0 && NPFGetFlag(&ftd.node, NPF_FLAG_REVERSE)) best = td;
    }
    if (ftd.best_bird_dist == 0) {
      *best_td = best;
      return true;
    }
  } else {
    ftd = NPFRouteToStationOrTileTwoWay(v->tile, trackdir, false, v->tile, trackdir_rev, false, &fstd, &user);
  }
  /* If we didn't find anything, just keep on going straight ahead, otherwise take the reverse flag */
  return ftd.best_bird_dist == 0 && NPFGetFlag(&ftd.node, NPF_FLAG_REVERSE);
}
 
/*** Trains ***/
 
FindDepotData NPFTrainFindNearestDepot(const Train *v, int max_penalty)
{
  const Train *last = v->Last();
  Trackdir trackdir = v->GetVehicleTrackdir();
  Trackdir trackdir_rev = ReverseTrackdir(last->GetVehicleTrackdir());
  NPFFindStationOrTileData fstd;
  fstd.v = v;
  fstd.reserve_path = false;
 
  assert(trackdir != INVALID_TRACKDIR);
  AyStarUserData user = { v->owner, TRANSPORT_RAIL, v->compatible_railtypes, ROADTYPES_NONE, 0 };
  NPFFoundTargetData ftd = NPFRouteToDepotBreadthFirstTwoWay(v->tile, trackdir, false, last->tile, trackdir_rev, false, &fstd, &user, NPF_INFINITE_PENALTY, max_penalty);
  if (ftd.best_bird_dist != 0) return FindDepotData();
 
  /* Found target */
  /* Our caller expects a number of tiles, so we just approximate that
   * number by this. It might not be completely what we want, but it will
   * work for now :-) We can possibly change this when the old pathfinder
   * is removed. */
  return FindDepotData(ftd.node.tile, ftd.best_path_dist, NPFGetFlag(&ftd.node, NPF_FLAG_REVERSE));
}
 
bool NPFTrainFindNearestSafeTile(const Train *v, TileIndex tile, Trackdir trackdir, bool override_railtype)
{
  assert(v->type == VEH_TRAIN);
 
  NPFFindStationOrTileData fstd;
  fstd.v = v;
  fstd.reserve_path = true;
 
  AyStarNode start1;
  start1.tile = tile;
  start1.direction = trackdir;
 
  RailTypes railtypes = v->compatible_railtypes;
  if (override_railtype) railtypes |= GetRailTypeInfo(v->railtype)->compatible_railtypes;
 
  /* perform a breadth first search. Target is nullptr,
   * since we are just looking for any safe tile...*/
  AyStarUserData user = { v->owner, TRANSPORT_RAIL, railtypes, ROADTYPES_NONE, 0 };
  return NPFRouteInternal(&start1, true, nullptr, false, &fstd, NPFFindSafeTile, NPFCalcZero, &user, 0, true).res_okay;
}
 
bool NPFTrainCheckReverse(const Train *v)
{
  NPFFindStationOrTileData fstd;
  NPFFoundTargetData ftd;
  const Train *last = v->Last();
 
  NPFFillWithOrderData(&fstd, v);
 
  Trackdir trackdir = v->GetVehicleTrackdir();
  Trackdir trackdir_rev = ReverseTrackdir(last->GetVehicleTrackdir());
  assert(trackdir != INVALID_TRACKDIR);
  assert(trackdir_rev != INVALID_TRACKDIR);
 
  AyStarUserData user = { v->owner, TRANSPORT_RAIL, v->compatible_railtypes, ROADTYPES_NONE, 0 };
  ftd = NPFRouteToStationOrTileTwoWay(v->tile, trackdir, false, last->tile, trackdir_rev, false, &fstd, &user);
  /* If we didn't find anything, just keep on going straight ahead, otherwise take the reverse flag */
  return ftd.best_bird_dist == 0 && NPFGetFlag(&ftd.node, NPF_FLAG_REVERSE);
}
 
Track NPFTrainChooseTrack(const Train *v, bool &path_found, bool reserve_track, struct PBSTileInfo *target)
{
  NPFFindStationOrTileData fstd;
  NPFFillWithOrderData(&fstd, v, reserve_track);
 
  PBSTileInfo origin = FollowTrainReservation(v);
  assert(IsValidTrackdir(origin.trackdir));
 
  AyStarUserData user = { v->owner, TRANSPORT_RAIL, v->compatible_railtypes, ROADTYPES_NONE, 0 };
  NPFFoundTargetData ftd = NPFRouteToStationOrTile(origin.tile, origin.trackdir, true, &fstd, &user);
 
  if (target != nullptr) {
    target->tile = ftd.node.tile;
    target->trackdir = (Trackdir)ftd.node.direction;
    target->okay = ftd.res_okay;
  }
 
  assert(ftd.best_trackdir != INVALID_TRACKDIR);
 
  /* If ftd.best_bird_dist is 0, we found our target and ftd.best_trackdir contains
   * the direction we need to take to get there, if ftd.best_bird_dist is not 0,
   * we did not find our target, but ftd.best_trackdir contains the direction leading
   * to the tile closest to our target. */
  path_found = (ftd.best_bird_dist == 0);
  /* Discard enterdir information, making it a normal track */
  return TrackdirToTrack(ftd.best_trackdir);
}