/**
 * Build a Bridge
 * @param end_tile end tile
 * @param flags type of operation
 * @param p1 packed start tile coords (~ dx)
 * @param p2 various bitstuffed elements
 * - p2 = (bit  0- 7) - bridge type (hi bh)
 * - p2 = (bit  8-11) - rail type or road types.
 * - p2 = (bit 15-16) - transport type.
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
	CompanyID company = _current_company;

	RailType railtype = INVALID_RAILTYPE;
	RoadTypes roadtypes = ROADTYPES_NONE;

	/* unpack parameters */
	BridgeType bridge_type = GB(p2, 0, 8);

	if (!IsValidTile(p1)) return_cmd_error(STR_ERROR_BRIDGE_THROUGH_MAP_BORDER);

	TransportType transport_type = Extract<TransportType, 15, 2>(p2);

	/* type of bridge */
	switch (transport_type) {
		case TRANSPORT_ROAD:
			roadtypes = Extract<RoadTypes, 8, 2>(p2);
			if (!HasExactlyOneBit(roadtypes) || !HasRoadTypesAvail(company, roadtypes)) return CMD_ERROR;
			break;

		case TRANSPORT_RAIL:
			railtype = Extract<RailType, 8, 4>(p2);
			if (!ValParamRailtype(railtype)) return CMD_ERROR;
			break;

		case TRANSPORT_WATER:
			break;

		default:
			/* Airports don't have bridges. */
			return CMD_ERROR;
	}
	TileIndex tile_start = p1;
	TileIndex tile_end = end_tile;

	if (company == OWNER_DEITY) {
		if (transport_type != TRANSPORT_ROAD) return CMD_ERROR;
		const Town *town = CalcClosestTownFromTile(tile_start);

		company = OWNER_TOWN;

		/* If we are not within a town, we are not owned by the town */
		if (town == NULL || DistanceSquare(tile_start, town->xy) > town->cache.squared_town_zone_radius[HZB_TOWN_EDGE]) {
			company = OWNER_NONE;
		}
	}

	if (tile_start == tile_end) {
		return_cmd_error(STR_ERROR_CAN_T_START_AND_END_ON);
	}

	Axis direction;
	if (TileX(tile_start) == TileX(tile_end)) {
		direction = AXIS_Y;
	} else if (TileY(tile_start) == TileY(tile_end)) {
		direction = AXIS_X;
	} else {
		return_cmd_error(STR_ERROR_START_AND_END_MUST_BE_IN);
	}

	if (tile_end < tile_start) Swap(tile_start, tile_end);

	uint bridge_len = GetTunnelBridgeLength(tile_start, tile_end);
	if (transport_type != TRANSPORT_WATER) {
		/* set and test bridge length, availability */
		CommandCost ret = CheckBridgeAvailability(bridge_type, bridge_len, flags);
		if (ret.Failed()) return ret;
	} else {
		if (bridge_len > _settings_game.construction.max_bridge_length) return_cmd_error(STR_ERROR_BRIDGE_TOO_LONG);
	}

	int z_start;
	int z_end;
	Slope tileh_start = GetTileSlope(tile_start, &z_start);
	Slope tileh_end = GetTileSlope(tile_end, &z_end);
	bool pbs_reservation = false;

	CommandCost terraform_cost_north = CheckBridgeSlopeNorth(direction, &tileh_start, &z_start);
	CommandCost terraform_cost_south = CheckBridgeSlopeSouth(direction, &tileh_end,   &z_end);

	/* Aqueducts can't be built of flat land. */
	if (transport_type == TRANSPORT_WATER && (tileh_start == SLOPE_FLAT || tileh_end == SLOPE_FLAT)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
	if (z_start != z_end) return_cmd_error(STR_ERROR_BRIDGEHEADS_NOT_SAME_HEIGHT);

	CommandCost cost(EXPENSES_CONSTRUCTION);
	Owner owner;
	bool is_new_owner;
	if (IsBridgeTile(tile_start) && IsBridgeTile(tile_end) &&
			GetOtherBridgeEnd(tile_start) == tile_end &&
			GetTunnelBridgeTransportType(tile_start) == transport_type) {
		/* Replace a current bridge. */

		/* If this is a railway bridge, make sure the railtypes match. */
		if (transport_type == TRANSPORT_RAIL && GetRailType(tile_start) != railtype) {
			return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
		}

		/* Do not replace town bridges with lower speed bridges, unless in scenario editor. */
		if (!(flags & DC_QUERY_COST) && IsTileOwner(tile_start, OWNER_TOWN) &&
				GetBridgeSpec(bridge_type)->speed < GetBridgeSpec(GetBridgeType(tile_start))->speed &&
				_game_mode != GM_EDITOR) {
			Town *t = ClosestTownFromTile(tile_start, UINT_MAX);

			if (t == NULL) {
				return CMD_ERROR;
			} else {
				SetDParam(0, t->index);
				return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
			}
		}

		/* Do not replace the bridge with the same bridge type. */
		if (!(flags & DC_QUERY_COST) && (bridge_type == GetBridgeType(tile_start)) && (transport_type != TRANSPORT_ROAD || (roadtypes & ~GetRoadTypes(tile_start)) == 0)) {
			return_cmd_error(STR_ERROR_ALREADY_BUILT);
		}

		/* Do not allow replacing another company's bridges. */
		if (!IsTileOwner(tile_start, company) && !IsTileOwner(tile_start, OWNER_TOWN) && !IsTileOwner(tile_start, OWNER_NONE)) {
			return_cmd_error(STR_ERROR_AREA_IS_OWNED_BY_ANOTHER);
		}

		cost.AddCost((bridge_len + 1) * _price[PR_CLEAR_BRIDGE]); // The cost of clearing the current bridge.
		owner = GetTileOwner(tile_start);

		/* If bridge belonged to bankrupt company, it has a new owner now */
		is_new_owner = (owner == OWNER_NONE);
		if (is_new_owner) owner = company;

		switch (transport_type) {
			case TRANSPORT_RAIL:
				/* Keep the reservation, the path stays valid. */
				pbs_reservation = HasTunnelBridgeReservation(tile_start);
				break;

			case TRANSPORT_ROAD:
				/* Do not remove road types when upgrading a bridge */
				roadtypes |= GetRoadTypes(tile_start);
				break;

			default: break;
		}
	} else {
		/* Build a new bridge. */

		bool allow_on_slopes = (_settings_game.construction.build_on_slopes && transport_type != TRANSPORT_WATER);

		/* Try and clear the start landscape */
		CommandCost ret = DoCommand(tile_start, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		cost = ret;

		if (transport_type != TRANSPORT_WATER) {
			if (terraform_cost_north.Failed() || (terraform_cost_north.GetCost() != 0 && !allow_on_slopes)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
			cost.AddCost(terraform_cost_north);
		} else {
			Slope tileh_north_aqueduct = GetTileSlope(tile_start);
			if (tileh_north_aqueduct != ComplementSlope(tileh_end)) {
				if (!IsInclinedSlope(tileh_north_aqueduct) && !IsInclinedSlope(GetTileSlope(tile_end))) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
				if (IsSteepSlope(tileh_north_aqueduct)) {
					tileh_north_aqueduct = SlopeWithOneCornerRaised(OppositeCorner(GetHighestSlopeCorner((tileh_north_aqueduct ^ (SLOPE_ELEVATED | SLOPE_STEEP)) ^ tileh_end)));
				} else {
					tileh_north_aqueduct = ComplementSlope(tileh_end) ^ tileh_north_aqueduct;
				}

				/* Mark the tile as already cleared for the terraform command.
				* Do this for all tiles (like trees), not only objects. */
				ClearedObjectArea *coa = FindClearedObject(tile_start);
				if (coa == NULL) {
					coa = _cleared_object_areas.Append();
					coa->first_tile = tile_start;
					coa->area = TileArea(tile_start, 1, 1);
				}

				/* Hide the tile from the terraforming command */
				TileIndex old_first_tile = coa->first_tile;
				coa->first_tile = INVALID_TILE;
				ret = DoCommand(tile_start, tileh_north_aqueduct, 1, flags, CMD_TERRAFORM_LAND);
				coa->first_tile = old_first_tile;
				if (ret.Failed()) return_cmd_error(STR_ERROR_UNABLE_TO_SMOOTH_LAND_AQUEDUCT);
				cost.AddCost(ret);
			}
		}

		/* Try and clear the end landscape */
		ret = DoCommand(tile_end, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		cost.AddCost(ret);

		/* false - end tile slope check */
		if (transport_type != TRANSPORT_WATER) {
			if (terraform_cost_south.Failed() || (terraform_cost_south.GetCost() != 0 && !allow_on_slopes)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
			cost.AddCost(terraform_cost_south);
		} else {
			Slope tileh_south_aqueduct = GetTileSlope(tile_end);
			if (tileh_south_aqueduct != ComplementSlope(tileh_start)) {
				if (!IsInclinedSlope(tileh_south_aqueduct) && !IsInclinedSlope(GetTileSlope(tile_start))) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
				if (IsSteepSlope(tileh_south_aqueduct)) {
					tileh_south_aqueduct = SlopeWithOneCornerRaised(OppositeCorner(GetHighestSlopeCorner((tileh_south_aqueduct ^ (SLOPE_ELEVATED | SLOPE_STEEP)) ^ tileh_start)));
				} else {
					tileh_south_aqueduct = ComplementSlope(tileh_start) ^ tileh_south_aqueduct;
				}

				/* Mark the tile as already cleared for the terraform command.
				* Do this for all tiles (like trees), not only objects. */
				ClearedObjectArea *coa = FindClearedObject(tile_end);
				if (coa == NULL) {
					coa = _cleared_object_areas.Append();
					coa->first_tile = tile_end;
					coa->area = TileArea(tile_end, 1, 1);
				}

				/* Hide the tile from the terraforming command */
				TileIndex old_first_tile = coa->first_tile;
				coa->first_tile = INVALID_TILE;
				ret = DoCommand(tile_end, tileh_south_aqueduct, 1, flags, CMD_TERRAFORM_LAND);
				coa->first_tile = old_first_tile;
				if (ret.Failed()) return_cmd_error(STR_ERROR_UNABLE_TO_SMOOTH_LAND_AQUEDUCT);
				cost.AddCost(ret);
			}
		}

		const TileIndex heads[] = {tile_start, tile_end};
		for (int i = 0; i < 2; i++) {
			if (IsBridgeAbove(heads[i])) {
				TileIndex north_head = GetNorthernBridgeEnd(heads[i]);

				if (direction == GetBridgeAxis(heads[i])) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);

				if (z_start + 1 == GetBridgeHeight(north_head)) {
					return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
				}
			}
		}

		TileIndexDiff delta = (direction == AXIS_X ? TileDiffXY(1, 0) : TileDiffXY(0, 1));
		for (TileIndex tile = tile_start + delta; tile != tile_end; tile += delta) {
			if (GetTileMaxZ(tile) > z_start) return_cmd_error(STR_ERROR_BRIDGE_TOO_LOW_FOR_TERRAIN);

			if (z_start >= (GetTileZ(tile) + _settings_game.construction.max_bridge_height)) {
				/*
				 * Disallow too high bridges.
				 * Properly rendering a map where very high bridges (might) exist is expensive.
				 * See http://www.tt-forums.net/viewtopic.php?f=33&t=40844&start=980#p1131762
				 * for a detailed discussion. z_start here is one heightlevel below the bridge level.
				 */
				return_cmd_error(STR_ERROR_BRIDGE_TOO_HIGH_FOR_TERRAIN);
			}

			if (IsBridgeAbove(tile)) {
				/* Disallow crossing bridges for the time being */
				return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
			}

			switch (GetTileType(tile)) {
				case MP_WATER:
					if (!IsWater(tile) && !IsCoast(tile)) goto not_valid_below;
					break;

				case MP_RAILWAY:
					if (!IsPlainRail(tile)) goto not_valid_below;
					break;

				case MP_ROAD:
					if (IsRoadDepot(tile)) goto not_valid_below;
					break;

				case MP_TUNNELBRIDGE:
					if (IsTunnel(tile)) break;
					if (direction == DiagDirToAxis(GetTunnelBridgeDirection(tile))) goto not_valid_below;
					if (z_start < GetBridgeHeight(tile)) goto not_valid_below;
					break;

				case MP_OBJECT: {
					const ObjectSpec *spec = ObjectSpec::GetByTile(tile);
					if ((spec->flags & OBJECT_FLAG_ALLOW_UNDER_BRIDGE) == 0) goto not_valid_below;
					if (GetTileMaxZ(tile) + spec->height > z_start) goto not_valid_below;
					break;
				}

				case MP_CLEAR:
					break;

				default:
	not_valid_below:;
					/* try and clear the middle landscape */
					ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
					if (ret.Failed()) return ret;
					cost.AddCost(ret);
					break;
			}

			if (flags & DC_EXEC) {
				/* We do this here because when replacing a bridge with another
				 * type calling SetBridgeMiddle isn't needed. After all, the
				 * tile already has the has_bridge_above bits set. */
				SetBridgeMiddle(tile, direction);
			}
		}

		owner = company;
		is_new_owner = true;
	}

	/* do the drill? */
	if (flags & DC_EXEC) {
		DiagDirection dir = AxisToDiagDir(direction);

		Company *c = Company::GetIfValid(company);
		switch (transport_type) {
			case TRANSPORT_RAIL:
				/* Add to company infrastructure count if required. */
				if (is_new_owner && c != NULL) c->infrastructure.rail[railtype] += (bridge_len + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR;
				MakeRailBridgeRamp(tile_start, owner, bridge_type, dir,                 railtype);
				MakeRailBridgeRamp(tile_end,   owner, bridge_type, ReverseDiagDir(dir), railtype);
				SetTunnelBridgeReservation(tile_start, pbs_reservation);
				SetTunnelBridgeReservation(tile_end,   pbs_reservation);
				break;

			case TRANSPORT_ROAD: {
				RoadTypes prev_roadtypes = IsBridgeTile(tile_start) ? GetRoadTypes(tile_start) : ROADTYPES_NONE;
				if (is_new_owner) {
					/* Also give unowned present roadtypes to new owner */
					if (HasBit(prev_roadtypes, ROADTYPE_ROAD) && GetRoadOwner(tile_start, ROADTYPE_ROAD) == OWNER_NONE) ClrBit(prev_roadtypes, ROADTYPE_ROAD);
					if (HasBit(prev_roadtypes, ROADTYPE_TRAM) && GetRoadOwner(tile_start, ROADTYPE_TRAM) == OWNER_NONE) ClrBit(prev_roadtypes, ROADTYPE_TRAM);
				}
				if (c != NULL) {
					/* Add all new road types to the company infrastructure counter. */
					RoadType new_rt;
					FOR_EACH_SET_ROADTYPE(new_rt, roadtypes ^ prev_roadtypes) {
						/* A full diagonal road tile has two road bits. */
						c->infrastructure.road[new_rt] += (bridge_len + 2) * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR;
					}
				}
				Owner owner_road = HasBit(prev_roadtypes, ROADTYPE_ROAD) ? GetRoadOwner(tile_start, ROADTYPE_ROAD) : company;
				Owner owner_tram = HasBit(prev_roadtypes, ROADTYPE_TRAM) ? GetRoadOwner(tile_start, ROADTYPE_TRAM) : company;
				MakeRoadBridgeRamp(tile_start, owner, owner_road, owner_tram, bridge_type, dir,                 roadtypes);
				MakeRoadBridgeRamp(tile_end,   owner, owner_road, owner_tram, bridge_type, ReverseDiagDir(dir), roadtypes);
				break;
			}

			case TRANSPORT_WATER:
				if (is_new_owner && c != NULL) c->infrastructure.water += (bridge_len + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR;
				MakeAqueductBridgeRamp(tile_start, owner, dir);
				MakeAqueductBridgeRamp(tile_end,   owner, ReverseDiagDir(dir));
				break;

			default:
				NOT_REACHED();
		}

		/* Mark all tiles dirty */
		MarkBridgeDirty(tile_start, tile_end, AxisToDiagDir(direction), z_start);
		DirtyCompanyInfrastructureWindows(company);
	}

	if ((flags & DC_EXEC) && transport_type == TRANSPORT_RAIL) {
		Track track = AxisToTrack(direction);
		AddSideToSignalBuffer(tile_start, INVALID_DIAGDIR, company);
		YapfNotifyTrackLayoutChange(tile_start, track);
	}

	/* for human player that builds the bridge he gets a selection to choose from bridges (DC_QUERY_COST)
	 * It's unnecessary to execute this command every time for every bridge. So it is done only
	 * and cost is computed in "bridge_gui.c". For AI, Towns this has to be of course calculated
	 */
	Company *c = Company::GetIfValid(company);
	if (!(flags & DC_QUERY_COST) || (c != NULL && c->is_ai)) {
		bridge_len += 2; // begin and end tiles/ramps

		switch (transport_type) {
			case TRANSPORT_ROAD: cost.AddCost(bridge_len * _price[PR_BUILD_ROAD] * 2 * CountBits(roadtypes)); break;
			case TRANSPORT_RAIL: cost.AddCost(bridge_len * RailBuildCost(railtype)); break;
			default: break;
		}

		if (c != NULL) bridge_len = CalcBridgeLenCostFactor(bridge_len);

		if (transport_type != TRANSPORT_WATER) {
			cost.AddCost((int64)bridge_len * _price[PR_BUILD_BRIDGE] * GetBridgeSpec(bridge_type)->price >> 8);
		} else {
			/* Aqueducts use a separate base cost. */
			cost.AddCost((int64)bridge_len * _price[PR_BUILD_AQUEDUCT]);
		}

	}

	return cost;
}