/* $Id$ */

/** @file npf.cpp Implementation of the NPF pathfinder. */

#include "stdafx.h"
#include "npf.h"
#include "debug.h"
#include "landscape.h"
#include "depot_base.h"
#include "depot_map.h"
#include "network/network.h"
#include "tunnelbridge_map.h"
#include "functions.h"
#include "vehicle_base.h"
#include "tunnelbridge.h"
#include "pbs.h"
#include "settings_type.h"
#include "pathfind.h"

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
};

/**
 * Calculates the minimum distance traveled to get from t0 to t1 when only
 * using tracks (ie, only making 45 degree turns). Returns the distance in the
 * NPF scale, ie the number of full tiles multiplied by NPF_TILE_LENGTH to
 * prevent rounding.
 */
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 * 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;
}


#if 0
static uint NTPHash(uint key1, uint key2)
{
	/* This function uses the old hash, which is fixed on 10 bits (1024 buckets) */
	return PATHFIND_HASH_TILE(key1);
}
#endif

/**
 * Calculates a hash value for use in the NPF.
 * @param key1 The TileIndex of the tile to hash
 * @param key2 The Trackdir of the track on the tile.
 *
 * @todo Think of a better hash.
 */
static uint NPFHash(uint key1, uint key2)
{
	/* TODO: think of a better hash? */
	uint part1 = TileX(key1) & NPF_HASH_HALFMASK;
	uint part2 = TileY(key1) & NPF_HASH_HALFMASK;

	assert(IsValidTrackdir((Trackdir)key2));
	assert(IsValidTile(key1));
	return ((part1 << NPF_HASH_HALFBITS | part2) + (NPF_HASH_SIZE * key2 / TRACKDIR_END)) % NPF_HASH_SIZE;
}

static int32 NPFCalcZero(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
	return 0;
}

/* Calcs the heuristic to the target station or tile. For train stations, it
 * takes into account the direction of approach.
 */
static int32 NPFCalcStationOrTileHeuristic(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
	NPFFindStationOrTileData *fstd = (NPFFindStationOrTileData*)as->user_target;
	NPFFoundTargetData *ftd = (NPFFoundTargetData*)as->user_path;
	TileIndex from = current->tile;
	TileIndex to = fstd->dest_coords;
	uint dist;

	/* for train-stations, we are going to aim for the closest station tile */
	if (as->user_data[NPF_TYPE] == TRANSPORT_RAIL && fstd->station_index != INVALID_STATION)
		to = CalcClosestStationTile(fstd->station_index, from);

	if (as->user_data[NPF_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: (%d, %d). Result: %d", 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 == NULL) {
		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 = GetSlopeZ(x1 + dx4, y1 + dy4);
	int z2 = GetSlopeZ(x2 - dx4, y2 - dy4);

	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 substract 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) || ((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;
}

/**
 * Mark tiles by mowing the grass when npf debug level >= 1.
 * Will not work for multiplayer games, since it can (will) cause desyncs.
 */
static void NPFMarkTile(TileIndex tile)
{
#ifndef NO_DEBUG_MESSAGES
	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;
	}
#endif
}

static int32 NPFWaterPathCost(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
	/* TileIndex tile = current->tile; */
	int32 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;

	/* @todo More penalties? */

	return cost;
}

/* Determine the cost of this node, for road tracks */
static int32 NPFRoadPathCost(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
	TileIndex tile = current->tile;
	int32 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;
			/* Increase the cost for drive-through road stops */
			if (IsDriveThroughStopTile(tile)) cost += _settings_game.pf.npf.npf_road_drive_through_penalty;
			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: (%d, %d). Result: %d", TileX(current->tile), TileY(current->tile), cost);
	return cost;
}


/* Determine the cost of this node, for railway tracks */
static int32 NPFRailPathCost(AyStar *as, AyStarNode *current, OpenListNode *parent)
{
	TileIndex tile = current->tile;
	Trackdir trackdir = current->direction;
	int32 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;
			break;

		default:
			break;
	}

	/* Determine extra costs */

	/* Check for signals */
	if (IsTileType(tile, MP_RAILWAY)) {
		if (HasSignalOnTrackdir(tile, 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? */
					SignalType sigtype = GetSignalType(tile, TrackdirToTrack(trackdir));
					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 */
				NPFSetFlag(current, NPF_FLAG_LAST_SIGNAL_RED, true);
			} 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);
			}
		}

		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 occurence 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: (%d, %d). Result: %d", TileX(current->tile), TileY(current->tile), cost);
	return cost;
}

/* Will find any depot */
static int32 NPFFindDepot(AyStar *as, OpenListNode *current)
{
	/* 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, (TransportType)as->user_data[NPF_TYPE]) ?
		AYSTAR_FOUND_END_NODE : AYSTAR_DONE;
}

/** Find any safe and free tile. */
static int32 NPFFindSafeTile(AyStar *as, OpenListNode *current)
{
	const Vehicle *v = ((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 NPFFindStationOrTile(AyStar *as, OpenListNode *current)
{
	NPFFindStationOrTileData *fstd = (NPFFindStationOrTileData*)as->user_target;
	AyStarNode *node = &current->path.node;
	TileIndex tile = node->tile;

	/* If GetNeighbours said we could get here, we assume the station type
	 * is correct */
	if (
		(fstd->station_index == INVALID_STATION && tile == fstd->dest_coords) || /* We've found the tile, or */
		(IsTileType(tile, MP_STATION) && GetStationIndex(tile) == fstd->station_index) /* the station */
	) {
		return AYSTAR_FOUND_END_NODE;
	} else {
		return AYSTAR_DONE;
	}
}

/**
 * Find the node containing the first signal on the path.
 *
 * If the first signal is on the very first two tiles of the path,
 * the second signal is returnd. If no suitable signal is present, the
 * last node of the path is returned.
 */
static const PathNode *FindSafePosition(PathNode *path, const Vehicle *v)
{
	/* If there is no signal, reserve the whole path. */
	PathNode *sig = path;

	for(; path->parent != NULL; path = path->parent) {
		if (IsSafeWaitingPosition(v, path->node.tile, path->node.direction, true, _settings_game.pf.forbid_90_deg)) {
			sig = path;
		}
	}

	return sig;
}

/**
 * Lift the reservation of the tiles from @p start till @p end, excluding @p end itself.
 */
static void ClearPathReservation(const PathNode *start, const PathNode *end)
{
	bool first_run = true;
	for (; start != end; start = start->parent) {
		if (IsRailwayStationTile(start->node.tile) && first_run) {
			SetRailwayStationPlatformReservation(start->node.tile, TrackdirToExitdir(start->node.direction), false);
		} else {
			UnreserveRailTrack(start->node.tile, TrackdirToTrack(start->node.direction));
		}
		first_run = false;
	}
}

/**
 * To be called when @p current contains the (shortest route to) the target node.
 * Will fill the contents of the NPFFoundTargetData using
 * AyStarNode[NPF_TRACKDIR_CHOICE]. If requested, path reservation
 * is done here.
 */
static void NPFSaveTargetData(AyStar *as, OpenListNode *current)
{
	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 != NULL && ((NPFFindStationOrTileData*)as->user_target)->reserve_path && as->user_data[NPF_TYPE] == TRANSPORT_RAIL) {
		/* Path reservation is requested. */
		const Vehicle  *v = ((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 (IsRailwayStationTile(target->node.tile)) {
			DiagDirection dir = TrackdirToExitdir(target->node.direction);
			uint len = GetStationByTile(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;
			SetRailwayStationPlatformReservation(target->node.tile, dir, true);
			SetRailwayStationReservation(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 != NULL; cur = cur->parent) {
			if (!TryReserveRailTrack(cur->node.tile, TrackdirToTrack(cur->node.direction))) {
				/* Reservation failed, undo. */
				ClearPathReservation(target, cur);
				return;
			}
		}

		ftd->res_okay = true;
	}
}

/**
 * Finds out if a given company's vehicles are allowed to enter a given tile.
 * @param owner    The owner of the vehicle.
 * @param tile     The tile that is about to be entered.
 * @param enterdir The direction in which the vehicle wants to enter the tile.
 * @return         true if the vehicle can enter the tile.
 * @todo           This function should be used in other places than just NPF,
 *                 maybe moved to another file too.
 */
static bool CanEnterTileOwnerCheck(Owner owner, TileIndex tile, DiagDirection enterdir)
{
	if (IsTileType(tile, MP_RAILWAY) ||             /* Rail tile (also rail depot) */
			IsRailwayStationTile(tile) ||   /* Rail station tile */
			IsRoadDepotTile(tile) ||        /* Road depot tile */
			IsStandardRoadStopTile(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
}


/**
 * Returns the direction the exit of the depot on the given tile is facing.
 */
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 */
	}
}

/** Tests if a tile is a road tile with a single tramtrack (tram can reverse) */
static DiagDirection GetSingleTramBit(TileIndex tile)
{
	if (IsNormalRoadTile(tile)) {
		RoadBits rb = GetRoadBits(tile, ROADTYPE_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;
}

/**
 * Tests if a tile can be entered or left only from one side.
 *
 * Depots, non-drive-through roadstops, and tiles with single trambits are tested.
 *
 * @param tile The tile of interest.
 * @param type The transporttype of the vehicle.
 * @param subtype For TRANSPORT_ROAD the compatible RoadTypes of the vehicle.
 * @return The single entry/exit-direction of the tile, or INVALID_DIAGDIR if there are more or less directions
 */
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 (IsStandardRoadStopTile(tile)) return GetRoadStopDir(tile);
		if (HasBit(subtype, ROADTYPE_TRAM)) return GetSingleTramBit(tile);
	}

	return INVALID_DIAGDIR;
}

/**
 * Tests if a vehicle must reverse on a tile.
 *
 * @param tile The tile of interest.
 * @param dir The direction in which the vehicle drives on a tile.
 * @param type The transporttype of the vehicle.
 * @param subtype For TRANSPORT_ROAD the compatible RoadTypes of the vehicle.
 * @return true iff the vehicle must reverse on the tile.
 */
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;
}

/**
 * Tests if a vehicle can enter a tile.
 *
 * @param tile The tile of interest.
 * @param dir The direction in which the vehicle drives onto a tile.
 * @param type The transporttype of the vehicle.
 * @param subtype For TRANSPORT_ROAD the compatible RoadTypes of the vehicle.
 * @param railtypes For TRANSPORT_RAIL the compatible RailTypes of the vehicle.
 * @param owner The owner of the vehicle.
 * @return true iff the vehicle can enter the tile.
 */
static bool CanEnterTile(TileIndex tile, DiagDirection dir, TransportType type, uint subtype, RailTypes railtypes, Owner owner)
{
	/* Check tunnel entries and bridge ramps */
	if (IsTileType(tile, MP_TUNNELBRIDGE) && GetTunnelBridgeDirection(tile) != dir) return false;

	/* Test ownership */
	if (!CanEnterTileOwnerCheck(owner, tile, dir)) return false;

	/* check correct rail type (mono, maglev, etc) */
	if (type == TRANSPORT_RAIL) {
		RailType rail_type = GetTileRailType(tile);
		if (!HasBit(railtypes, rail_type)) return false;
	}

	/* Depots, standard roadstops and single tram bits can only be entered from one direction */
	DiagDirection single_entry = GetTileSingleEntry(tile, type, subtype);
	if (single_entry != INVALID_DIAGDIR && single_entry != ReverseDiagDir(dir)) return false;

	return true;
}

/**
 * Returns the driveable Trackdirs on a tile.
 *
 * One-way-roads are taken into account. Signals are not tested.
 *
 * @param dst_tile The tile of interest.
 * @param src_trackdir The direction the vehicle is currently moving.
 * @param type The transporttype of the vehicle.
 * @param subtype For TRANSPORT_ROAD the compatible RoadTypes of the vehicle.
 * @return The Trackdirs the vehicle can continue moving on.
 */
static TrackdirBits GetDriveableTrackdirBits(TileIndex dst_tile, Trackdir src_trackdir, TransportType type, uint subtype)
{
	TrackdirBits trackdirbits = TrackStatusToTrackdirBits(GetTileTrackStatus(dst_tile, type, subtype));

	if (trackdirbits == 0 && type == TRANSPORT_ROAD && HasBit(subtype, ROADTYPE_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: (%d, %d) [%d], 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 (_settings_game.pf.forbid_90_deg && (type == TRANSPORT_RAIL || type == TRANSPORT_WATER)) trackdirbits &= ~TrackdirCrossesTrackdirs(src_trackdir);

	DEBUG(npf, 6, "After filtering: (%d, %d), 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)
{
	/* 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);

	/* 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. */
	bool ignore_src_tile = (current->path.parent == NULL && NPFGetFlag(&current->path.node, NPF_FLAG_IGNORE_START_TILE));

	/* Information about the vehicle: TransportType (road/rail/water) and SubType (compatible rail/road types) */
	TransportType type = (TransportType)aystar->user_data[NPF_TYPE];
	uint subtype = aystar->user_data[NPF_SUB_TYPE];

	/* Initialize to 0, so we can jump out (return) somewhere an have no neighbours */
	aystar->num_neighbours = 0;
	DEBUG(npf, 4, "Expanding: (%d, %d, %d) [%d]", 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 */
	if (ignore_src_tile) {
		/* Do not perform any checks that involve src_tile */
		dst_tile = src_tile + TileOffsByDiagDir(src_exitdir);
		trackdirbits = GetDriveableTrackdirBits(dst_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 && !CanEnterTile(dst_tile, src_exitdir, type, subtype, (RailTypes)aystar->user_data[NPF_RAILTYPES], (Owner)aystar->user_data[NPF_OWNER])) 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 || HasBit(subtype, ROADTYPE_TRAM)) return;

			dst_tile = src_tile;
			src_trackdir = ReverseTrackdir(src_trackdir);
		}

		trackdirbits = GetDriveableTrackdirBits(dst_tile, src_trackdir, type, subtype);

		if (trackdirbits == 0) {
			/* We cannot enter the next tile. Road vehicles can reverse, others reach dead end */
			if (type != TRANSPORT_ROAD || HasBit(subtype, ROADTYPE_TRAM)) return;

			dst_tile = src_tile;
			src_trackdir = ReverseTrackdir(src_trackdir);

			trackdirbits = GetDriveableTrackdirBits(dst_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);

		uint bits = TrackdirBitsToTrackBits(trackdirbits);
		int i;
		FOR_EACH_SET_BIT(i, bits) {
			if (TracksOverlap(reserved | TrackToTrackBits((Track)i))) trackdirbits &= ~TrackToTrackdirBits((Track)i);
		}
	}

	/* Enumerate possible track */
	uint i = 0;
	while (trackdirbits != 0) {
		Trackdir dst_trackdir = RemoveFirstTrackdir(&trackdirbits);
		DEBUG(npf, 5, "Expanded into trackdir: %d, 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 NULL, 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 specifiying 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, TransportType type, uint sub_type, Owner owner, RailTypes railtypes, uint reverse_penalty)
{
	int r;
	NPFFoundTargetData result;

	/* Initialize procs */
	_npf_aystar.CalculateH = heuristic_proc;
	_npf_aystar.EndNodeCheck = target_proc;
	_npf_aystar.FoundEndNode = NPFSaveTargetData;
	_npf_aystar.GetNeighbours = NPFFollowTrack;
	switch (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);
	_npf_aystar.addstart(&_npf_aystar, start1, 0);
	if (start2) {
		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);
		_npf_aystar.addstart(&_npf_aystar, start2, reverse_penalty);
	}

	/* Initialize 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[NPF_TYPE] = type;
	_npf_aystar.user_data[NPF_SUB_TYPE] = sub_type;
	_npf_aystar.user_data[NPF_OWNER] = owner;
	_npf_aystar.user_data[NPF_RAILTYPES] = railtypes;

	/* GO! */
	r = AyStarMain_Main(&_npf_aystar);
	assert(r != AYSTAR_STILL_BUSY);

	if (result.best_bird_dist != 0) {
		if (target != NULL) {
			DEBUG(npf, 1, "Could not find route to tile 0x%X from 0x%X.", target->dest_coords, start1->tile);
		} else {
			/* Assumption: target == NULL, 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;
}

NPFFoundTargetData NPFRouteToStationOrTileTwoWay(TileIndex tile1, Trackdir trackdir1, bool ignore_start_tile1, TileIndex tile2, Trackdir trackdir2, bool ignore_start_tile2, NPFFindStationOrTileData *target, TransportType type, uint sub_type, Owner owner, RailTypes railtypes)
{
	AyStarNode start1;
	AyStarNode start2;

	start1.tile = tile1;
	start2.tile = tile2;
	/* We set this in case the target is also the start tile, we will just
	 * return a not found then */
	start1.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
	start1.direction = trackdir1;
	start2.direction = trackdir2;
	start2.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;

	return NPFRouteInternal(&start1, ignore_start_tile1, (IsValidTile(tile2) ? &start2 : NULL), ignore_start_tile2, target, NPFFindStationOrTile, NPFCalcStationOrTileHeuristic, type, sub_type, owner, railtypes, 0);
}

NPFFoundTargetData NPFRouteToStationOrTile(TileIndex tile, Trackdir trackdir, bool ignore_start_tile, NPFFindStationOrTileData *target, TransportType type, uint sub_type, Owner owner, RailTypes railtypes)
{
	return NPFRouteToStationOrTileTwoWay(tile, trackdir, ignore_start_tile, INVALID_TILE, INVALID_TRACKDIR, false, target, type, sub_type, owner, railtypes);
}

NPFFoundTargetData NPFRouteToDepotBreadthFirstTwoWay(TileIndex tile1, Trackdir trackdir1, bool ignore_start_tile1, TileIndex tile2, Trackdir trackdir2, bool ignore_start_tile2, TransportType type, uint sub_type, Owner owner, RailTypes railtypes, uint reverse_penalty)
{
	AyStarNode start1;
	AyStarNode start2;

	start1.tile = tile1;
	start2.tile = tile2;
	/* We set this in case the target is also the start tile, we will just
	 * return a not found then */
	start1.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
	start1.direction = trackdir1;
	start2.direction = trackdir2;
	start2.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;

	/* perform a breadth first search. Target is NULL,
	 * since we are just looking for any depot...*/
	return NPFRouteInternal(&start1, ignore_start_tile1, (IsValidTile(tile2) ? &start2 : NULL), ignore_start_tile2, NULL, NPFFindDepot, NPFCalcZero, type, sub_type, owner, railtypes, reverse_penalty);
}

NPFFoundTargetData NPFRouteToDepotBreadthFirst(TileIndex tile, Trackdir trackdir, bool ignore_start_tile, TransportType type, uint sub_type, Owner owner, RailTypes railtypes)
{
	return NPFRouteToDepotBreadthFirstTwoWay(tile, trackdir, ignore_start_tile, INVALID_TILE, INVALID_TRACKDIR, false, type, sub_type, owner, railtypes, 0);
}

NPFFoundTargetData NPFRouteToDepotTrialError(TileIndex tile, Trackdir trackdir, bool ignore_start_tile, TransportType type, uint sub_type, Owner owner, RailTypes railtypes)
{
	/* Okay, what we're gonna do. First, we look at all depots, calculate
	 * the manhatten distance to get to each depot. We then sort them by
	 * distance. We start by trying to plan a route to the closest, then
	 * the next closest, etc. We stop when the best route we have found so
	 * far, is shorter than the manhattan distance. This will obviously
	 * always find the closest depot. It will probably be most efficient
	 * for ships, since the heuristic will not be to far off then. I hope.
	 */
	Queue depots;
	int r;
	NPFFoundTargetData best_result = {UINT_MAX, UINT_MAX, INVALID_TRACKDIR, {INVALID_TILE, INVALID_TRACKDIR, {0, 0}}, false};
	NPFFoundTargetData result;
	NPFFindStationOrTileData target;
	AyStarNode start;
	Depot *current;
	Depot *depot;

	init_InsSort(&depots);
	/* Okay, let's find all depots that we can use first */
	FOR_ALL_DEPOTS(depot) {
		/* Check if this is really a valid depot, it is of the needed type and
		 * owner */
		if (IsDepotTypeTile(depot->xy, type) && IsTileOwner(depot->xy, owner))
			/* If so, let's add it to the queue, sorted by distance */
			depots.push(&depots, depot, DistanceManhattan(tile, depot->xy));
	}

	/* Now, let's initialise the aystar */

	/* Initialize procs */
	_npf_aystar.CalculateH = NPFCalcStationOrTileHeuristic;
	_npf_aystar.EndNodeCheck = NPFFindStationOrTile;
	_npf_aystar.FoundEndNode = NPFSaveTargetData;
	_npf_aystar.GetNeighbours = NPFFollowTrack;
	switch (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 target */
	target.station_index = INVALID_STATION; /* We will initialize dest_coords inside the loop below */
	_npf_aystar.user_target = &target;

	/* Initialize user_data */
	_npf_aystar.user_data[NPF_TYPE] = type;
	_npf_aystar.user_data[NPF_SUB_TYPE] = sub_type;
	_npf_aystar.user_data[NPF_OWNER] = owner;

	/* Initialize Start Node */
	start.tile = tile;
	start.direction = trackdir; /* We will initialize user_data inside the loop below */

	/* Initialize Result */
	_npf_aystar.user_path = &result;
	best_result.best_path_dist = UINT_MAX;
	best_result.best_bird_dist = UINT_MAX;

	/* Just iterate the depots in order of increasing distance */
	while ((current = (Depot*)depots.pop(&depots))) {
		/* Check to see if we already have a path shorter than this
		 * depot's manhattan distance. HACK: We call DistanceManhattan
		 * again, we should probably modify the queue to give us that
		 * value... */
		if ( DistanceManhattan(tile, current->xy * NPF_TILE_LENGTH) > best_result.best_path_dist)
			break;

		/* Initialize Start Node */
		/* We set this in case the target is also the start tile, we will just
		 * return a not found then */
		start.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
		start.user_data[NPF_NODE_FLAGS] = 0;
		NPFSetFlag(&start, NPF_FLAG_IGNORE_START_TILE, ignore_start_tile);
		_npf_aystar.addstart(&_npf_aystar, &start, 0);

		/* Initialize result */
		result.best_bird_dist = UINT_MAX;
		result.best_path_dist = UINT_MAX;
		result.best_trackdir = INVALID_TRACKDIR;

		/* Initialize target */
		target.dest_coords = current->xy;

		/* GO! */
		r = AyStarMain_Main(&_npf_aystar);
		assert(r != AYSTAR_STILL_BUSY);

		/* This depot is closer */
		if (result.best_path_dist < best_result.best_path_dist)
			best_result = result;
	}
	if (result.best_bird_dist != 0) {
		DEBUG(npf, 1, "Could not find route to any depot from tile 0x%X.", tile);
	}
	return best_result;
}

NPFFoundTargetData NPFRouteToSafeTile(const Vehicle *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;
	/* We set this in case the target is also the start tile, we will just
	 * return a not found then */
	start1.user_data[NPF_TRACKDIR_CHOICE] = INVALID_TRACKDIR;
	start1.direction = trackdir;
	NPFSetFlag(&start1, NPF_FLAG_IGNORE_RESERVED, true);

	RailTypes railtypes = v->u.rail.compatible_railtypes;
	if (override_railtype) railtypes |= GetRailTypeInfo(v->u.rail.railtype)->compatible_railtypes;

	/* perform a breadth first search. Target is NULL,
	 * since we are just looking for any safe tile...*/
	return NPFRouteInternal(&start1, true, NULL, false, &fstd, NPFFindSafeTile, NPFCalcZero, TRANSPORT_RAIL, 0, v->owner, railtypes, 0);
}

void InitializeNPF()
{
	static bool first_init = true;
	if (first_init) {
		first_init = false;
		init_AyStar(&_npf_aystar, NPFHash, NPF_HASH_SIZE);
	} else {
		AyStarMain_Clear(&_npf_aystar);
	}
	_npf_aystar.loops_per_tick = 0;
	_npf_aystar.max_path_cost = 0;
	//_npf_aystar.max_search_nodes = 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;
}

void NPFFillWithOrderData(NPFFindStationOrTileData *fstd, Vehicle *v, bool reserve_path)
{
	/* 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->type == VEH_TRAIN) {
		fstd->station_index = v->current_order.GetDestination();
		/* Let's take the closest tile of the station as our target for trains */
		fstd->dest_coords = CalcClosestStationTile(fstd->station_index, v->tile);
	} else {
		fstd->dest_coords = v->dest_tile;
		fstd->station_index = INVALID_STATION;
	}
	fstd->reserve_path = reserve_path;
	fstd->v = v;
}