/* $Id$ */

/*
 * 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/>.
 */

/** @file tunnel_map.cpp Map accessors for tunnels. */

#include "stdafx.h"
#include "tunnelbridge_map.h"

#include "safeguards.h"


/**
 * Gets the other end of the tunnel. Where a vehicle would reappear when it
 * enters at the given tile.
 * @param tile the tile to search from.
 * @return the tile of the other end of the tunnel.
 */
TileIndex GetOtherTunnelEnd(TileIndex tile)
{
	DiagDirection dir = GetTunnelBridgeDirection(tile);
	TileIndexDiff delta = TileOffsByDiagDir(dir);
	int z = GetTileZ(tile);

	dir = ReverseDiagDir(dir);
	do {
		tile += delta;
	} while (
		!IsTunnelTile(tile) ||
		GetTunnelBridgeDirection(tile) != dir ||
		GetTileZ(tile) != z
	);

	return tile;
}


/**
 * Is there a tunnel in the way in the given direction?
 * @param tile the tile to search from.
 * @param z    the 'z' to search on.
 * @param dir  the direction to start searching to.
 * @return true if and only if there is a tunnel.
 */
bool IsTunnelInWayDir(TileIndex tile, int z, DiagDirection dir)
{
	TileIndexDiff delta = TileOffsByDiagDir(dir);
	int height;

	do {
		tile -= delta;
		if (!IsValidTile(tile)) return false;
		height = GetTileZ(tile);
	} while (z < height);

	return z == height && IsTunnelTile(tile) && GetTunnelBridgeDirection(tile) == dir;
}

/**
 * Is there a tunnel in the way in any direction?
 * @param tile the tile to search from.
 * @param z the 'z' to search on.
 * @return true if and only if there is a tunnel.
 */
bool IsTunnelInWay(TileIndex tile, int z)
{
	return IsTunnelInWayDir(tile, z, (TileX(tile) > (MapMaxX() / 2)) ? DIAGDIR_NE : DIAGDIR_SW) ||
			IsTunnelInWayDir(tile, z, (TileY(tile) > (MapMaxY() / 2)) ? DIAGDIR_NW : DIAGDIR_SE);
}