/**
 * Get the aqueduct that can be build from the
 *  current tile. Aqueducts are only build on sloped tiles.
 */
function Canal::_GetAqueduct(last_node, cur_node, aqueduct_dir)
{
	if (!this._IsInclinedTile(cur_node)) return [];

	for (local i = 1; i < this._max_aqueduct_length; i++) {
		local next_tile = cur_node + i * (cur_node - last_node);
		if (!AIMap.IsValidTile(next_tile)) {
			return [];
		}
		if (AIBridge.BuildBridge(AIVehicle.VT_WATER, 0, cur_node, next_tile)) {
			return [next_tile, aqueduct_dir, AITileList()];
		}
	}

	return [];
}

function Canal::_IsInclinedTile(tile)
{
	local slope = AITile.GetSlope(tile);
	return slope == AITile.SLOPE_SW || slope == AITile.SLOPE_NW || slope == AITile.SLOPE_SE || slope == AITile.SLOPE_NE;
}