/** Callback that returns 'real' vehicles lower or at height \c *(byte*)data .

 * @param v Vehicle to examine.

 * @param data Pointer to height data.

 * @return \a v if conditions are met, else \c NULL.

 */

static Vehicle *EnsureNoVehicleProcZ(Vehicle *v, void *data)

{

	byte z = *(byte*)data;

	if (v->type == VEH_DISASTER || (v->type == VEH_AIRCRAFT && v->subtype == AIR_SHADOW)) return NULL;

	if (v->z_pos > z) return NULL;

	_error_message = STR_ERROR_TRAIN_IN_THE_WAY + v->type;

	return v;

}

/* Ensure there is no vehicle at the ground at the given position.

 * @param tile Position to examine.

 * @return A vehicle has been found.

 */

bool EnsureNoVehicleOnGround(TileIndex tile)

{

	byte z = GetTileMaxZ(tile);

	return !HasVehicleOnPos(tile, &z, &EnsureNoVehicleProcZ);

}

/** Procedure called for every vehicle found in tunnel/bridge in the hash map */

static Vehicle *GetVehicleTunnelBridgeProc(Vehicle *v, void *data)

{

	if (v->type != VEH_TRAIN && v->type != VEH_ROAD && v->type != VEH_SHIP) return NULL;

	if (v == (const Vehicle *)data) return NULL;

	_error_message = STR_ERROR_TRAIN_IN_THE_WAY + v->type;

	return v;

}

/**

 * Finds vehicle in tunnel / bridge

 * @param tile first end

 * @param endtile second end

 * @param ignore Ignore this vehicle when searching

 * @return true if the bridge has a vehicle

 */

bool HasVehicleOnTunnelBridge(TileIndex tile, TileIndex endtile, const Vehicle *ignore)

{

	return HasVehicleOnPos(tile, (void *)ignore, &GetVehicleTunnelBridgeProc) ||

			HasVehicleOnPos(endtile, (void *)ignore, &GetVehicleTunnelBridgeProc);

}