/**
 *  Copyright (C) 2002-2019   The FreeCol Team
 *
 *  This file is part of FreeCol.
 *
 *  FreeCol 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, either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  FreeCol 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 FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.common.model;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map.Entry;
import java.util.Random;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.ToIntFunction;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Colony;
import static net.sf.freecol.common.model.Constants.*;
import net.sf.freecol.common.model.Direction;
import static net.sf.freecol.common.util.CollectionUtils.*;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.common.util.RandomChoice;
import static net.sf.freecol.common.util.RandomUtils.*;


/**
 * Represents a single tile on the {@code Map}.
 *
 * @see Map
 */
public final class Tile extends UnitLocation implements Named, Ownable {

    private static final Logger logger = Logger.getLogger(Tile.class.getName());

    public static final String TAG = "tile";

    /** Comparator to sort tiles by increasing distance from the edge. */
    public static final Comparator<Tile> edgeDistanceComparator
        = Comparator.comparingInt(Tile::getEdgeDistance);

    /** Comparator to find the smallest high seas count. */
    public static final Comparator<Tile> highSeasComparator
        = Comparator.comparingInt(Tile::getHighSeasCount);

    /** Predicate to identify ordinary sea tiles. */
    public static final Predicate<Tile> isSeaTile = t ->
        !t.isLand() && t.getHighSeasCount() >= 0;

    /**
     * Information that is internal to the native settlements, and only
     * updated on close contact.
     */
    private static class IndianSettlementInternals {

        /** The skill taught at the settlement. */
        public UnitType skill = null;

        /** The goods the settlement is interested in. */
        public List<GoodsType> wantedGoods = null;


        /**
         * Update the internal information from a native settlement.
         *
         * @param is The {@code IndianSettlement} to update.
         */
        public void update(IndianSettlement is) {
            setValues(is.getLearnableSkill(), is.getWantedGoods());
        }

        /**
         * Set the internal values.
         *
         * @param skill The skill taught.
         * @param wanted The wanted goods.
         */
        public void setValues(UnitType skill, List<GoodsType> wanted) {
            this.skill = skill;
            if (wanted == null) {
                this.wantedGoods = null;
            } else if (this.wantedGoods == null) {
                this.wantedGoods = new ArrayList<GoodsType>(wanted);
            } else {
                this.wantedGoods.clear();
                this.wantedGoods.addAll(wanted);
            }
        }
    }

    /**
     * This must be distinct from ColonyTile/Building.UNIT_CHANGE or
     * the colony panel can get confused.
     */
    public static final String UNIT_CHANGE = "TILE_UNIT_CHANGE";

    /**
     * Flag to assign to the high seas count to flag that the high seas
     * connectivity needs recalculation after reading in the map.
     */
    public static final int FLAG_RECALCULATE = Integer.MAX_VALUE;

    /**
     * Warn about colonies that can not produce this amount of
     * a building material.
     */
    private static final int LOW_PRODUCTION_WARNING_VALUE = 4;

    /**
     * The maximum distance that will still be considered "near" when
     * determining the location name.
     *
     * @see #getLocationLabel
     */
    public static final int NEAR_RADIUS = 8;

    public static final int OVERLAY_ZINDEX = 100;
    public static final int FOREST_ZINDEX = 200;
    public static final int RESOURCE_ZINDEX = 400;
    public static final int RUMOUR_ZINDEX = 500;

    /**
     * The type of the tile.
     * Beware: this may appear to be null in the client when the tile is
     * unexplored.
     */
    private TileType type;

    /** The tile coordinates in the enclosing map. */
    private int x, y;

    /** The player that consider this tile to be their land. */
    private Player owner;

    /** The settlement located on this tile, if any. */
    private Settlement settlement;

    /**
     * Indicates which settlement owns this tile (null indicates no
     * owner).  A colony owns the tile it is located on, and every
     * tile it has claimed by successfully moving a worker on to it.
     * Native settlements make more extensive and unpredictable claims.
     * Note that while units and settlements are owned by a player, a
     * tile is owned by a settlement.
     */
    private Settlement owningSettlement;

    /** Stores all Improvements and Resources (if any). */
    private TileItemContainer tileItemContainer;

    /** The region this tile is in. */
    private Region region;

    /** The number of tiles to traverse to get to the high seas. */
    private int highSeasCount = -1;

    /**
     * Does this tile have an explicit moveToEurope state.  If null,
     * just use the defaults (usually not, unless water and on map edge),
     * otherwise use the explicit value provided here.
     */
    private Boolean moveToEurope;

    /** The style of this Tile, as determined by adjacent tiles. */
    private int style;

    /**
     * An artificial contiguous-region number to identify connected
     * parts of the map.  That is, all land tiles with the same
     * contiguity number can be reached by a land unit on any of
     * those tiles in the absence of extra-geographic blockages like
     * settlements and other units.  Similarly for water tiles/naval
     * units.
     *
     * This is used to quickly scope out the sort of paths available
     * to a unit attempting to reach some destination.  It only needs
     * serialization from server to client, as it is set by the
     * TerrainGenerator on map import or creation.
     */
    private int contiguity = -1;

    /** A map of cached tiles for each European player, null in clients. */
    private final java.util.Map<Player, Tile> cachedTiles;

    // Do not serialize below

    /**
     * A cache of native settlement internals for each European
     * player, null in clients.
     */
    private final java.util.Map<Player, IndianSettlementInternals> playerIndianSettlements;


    /**
     * The main tile constructor.
     *
     * @param game The enclosing {@code Game}.
     * @param type The {@code TileType}.
     * @param locX The x-position of this tile on the map.
     * @param locY The y-position of this tile on the map.
     */
    public Tile(Game game, TileType type, int locX, int locY) {
        super(game);

        this.type = type;
        this.x = locX;
        this.y = locY;
        this.owningSettlement = null;
        this.settlement = null;

        if (game.isInServer()) {
            this.cachedTiles = new HashMap<>();
            this.playerIndianSettlements = new HashMap<>();
        } else {
            this.cachedTiles = null;
            this.playerIndianSettlements = null;
        }
    }

    /**
     * Create a new {@code Tile} with the given identifier.
     * The object should later be initialized by calling either
     * {@link #readFromXML(FreeColXMLReader)}.
     *
     * @param game The enclosing {@code Game}.
     * @param id The object identifier.
     */
    public Tile(Game game, String id) {
        super(game, id);

        if (game.isInServer()) {
            this.cachedTiles = new HashMap<>();
            this.playerIndianSettlements = new HashMap<>();
        } else {
            this.cachedTiles = null;
            this.playerIndianSettlements = null;
        }
    }


    //
    // Basic accessors and mutators
    //

    /**
     * Gets the type of this Tile.
     *
     * @return The {@code TileType}.
     */
    public TileType getType() {
        return type;
    }

    /**
     * Sets the type for this Tile.
     *
     * -til: Changes appearance.
     *
     * @param t The new {@code TileType} for this {@code Tile}.
     */
    public void setType(TileType t) {
        type = t;
    }

    /**
     * Check if the tile has been explored.
     *
     * @return True if this is an explored {@code Tile}.
     */
    public boolean isExplored() {
        return type != null;
    }

    /**
     * Is this a land tile?
     *
     * @return True if this a land {@code Tile}.
     */
    public boolean isLand() {
        return type != null && !type.isWater();
    }

    /**
     * Is this a forested tile?
     *
     * @return True if this is a forested {@code Tile}.
     */
    public boolean isForested() {
        return type != null && type.isForested();
    }

    /**
     * Gets the x-coordinate of this tile.
     *
     * @return The x-coordinate of this {@code Tile}.
     */
    public int getX() {
        return x;
    }

    /**
     * Gets the y-coordinate of this tile.
     *
     * @return The y-coordinate of this {@code Tile}.
     */
    public int getY() {
        return y;
    }

    /**
     * Get the map in which this tile belongs.
     *
     * @return The enclosing {@code Map}.
     */
    public Map getMap() {
        return getGame().getMap();
    }

    /**
     * Gets the settlement on this tile.
     *
     * @return The {@code Settlement} that is located on this
     *     {@code Tile}, or null if none is present.
     * @see #setSettlement
     */
    @Override
    public Settlement getSettlement() {
        return settlement;
    }

    /**
     * Put a settlement onto this tile.  A tile can only have one
     * settlement located on it.  The settlement will also become the
     * owner of this tile.
     *
     * -til: Changes appearance.
     *
     * @param settlement A {@code Settlement} to put on this
     *     {@code Tile}.
     * @see #getSettlement
     */
    public void setSettlement(Settlement settlement) {
        this.settlement = settlement;
    }

    /**
     * Does this tile have a settlement.
     *
     * @return True if there is a settlement present.
     */
    public boolean hasSettlement() {
        return settlement != null;
    }

    /**
     * Gets the owning settlement for this tile.
     *
     * @return The {@code Settlement} that owns this {@code Tile}.
     * @see #setOwner
     */
    public Settlement getOwningSettlement() {
        return owningSettlement;
    }

    /**
     * Sets the settlement that owns this tile.
     *
     * -til: Changes appearance.
     *
     * @param owner The {@code Settlement} to own this {@code Tile}.
     * @see #getOwner
     */
    public void setOwningSettlement(Settlement owner) {
        this.owningSettlement = owner;
    }

    /**
     * Gets this tiles {@code TileItemContainer}.
     *
     * @return The {@code TileItemContainer}.
     */
    public TileItemContainer getTileItemContainer() {
        return tileItemContainer;
    }

    /**
     * Sets the {@code TileItemContainer}.
     *
     * @param newTileItemContainer The new {@code TileItemContainer} value.
     */
    public void setTileItemContainer(TileItemContainer newTileItemContainer) {
        tileItemContainer = newTileItemContainer;
    }

    /**
     * Get the completed tile items for this tile.
     *
     * @return A list of completed {@code TileItem}s.
     */
    public List<TileItem> getCompleteItems() {
        return (tileItemContainer == null) ? Collections.<TileItem>emptyList()
            : tileItemContainer.getCompleteItems();
    }

    /**
     * Get the tile region.
     *
     * @return The tile {@code Region}.
     */
    public Region getRegion() {
        return region;
    }

    /**
     * Set the tile region.
     *
     * -til: Changes appearance.
     *
     * @param newRegion The new {@code Region} value.
     */
    public void setRegion(final Region newRegion) {
        this.region = newRegion;
    }

    /**
     * Get the discoverable region of this tile.
     *
     * @return Any discoverable {@code Region}.
     */
    public Region getDiscoverableRegion() {
        return (region == null) ? null : region.getDiscoverableRegion();
    }

    /**
     * Gets whether this tile is connected to the high seas.
     *
     * @return True if this {@code Tile} is connected to the high seas.
     */
    public boolean isHighSeasConnected() {
        return highSeasCount >= 0;
    }

    /**
     * Gets the high seas count.
     *
     * @return The high seas count value.
     */
    public int getHighSeasCount() {
        return this.highSeasCount;
    }

    /**
     * Set the high seas count.
     *
     * @param count The new high seas count value.
     */
    public void setHighSeasCount(final int count) {
        this.highSeasCount = count;
    }

    /**
     * Is this a land tile on the sea coast (lakes do not count).
     *
     * @return True if this is a coastland tile.
     */
    public boolean isCoastland() {
        return isLand() && getHighSeasCount() > 0;
    }

    /**
     * Get the move-to-Europe state of the tile.
     *
     * @return The move-to-Europe state of the {@code Tile}.
     */
    public Boolean getMoveToEurope() {
        return moveToEurope;
    }

    /**
     * Set the move-to-Europe state of the tile.
     *
     * @param moveToEurope The new move-to-Europe state for the
     *     {@code Tile}.
     */
    public void setMoveToEurope(Boolean moveToEurope) {
        this.moveToEurope = moveToEurope;
    }

    /**
     * Can a unit move to the high seas from this tile?
     *
     * @return True if a unit can move to high seas from this tile.
     */
    public boolean isDirectlyHighSeasConnected() {
        return (moveToEurope != null) ? moveToEurope
            : (type == null) ? false
            : type.isDirectlyHighSeasConnected();
    }

    /**
     * Is this tile on a river corner?
     *
     * @return True if this is a river corner.
     */
    public boolean isRiverCorner() {
        List<Tile> tiles = transform(getSurroundingTiles(0, 1),
                                     Tile::isOnRiver);
        switch (tiles.size()) {
        case 0: case 1:
            return false;
        case 2:
            return tiles.get(0).isAdjacent(tiles.get(1));
        case 3:
            return tiles.get(0).isAdjacent(tiles.get(1))
                || tiles.get(1).isAdjacent(tiles.get(2))
                || tiles.get(2).isAdjacent(tiles.get(0));
        default:
            break;
        }
        return true;
    }

    /**
     * Get the minimum distance in tiles from this tile to the map edge.
     *
     * @return The distance to the edge.
     */
    private int getEdgeDistance() {
        final Map map = getMap();
        final int x = getX(), y = getY();
        return Math.min(Math.min(x, map.getWidth() - x),
                        Math.min(y, map.getHeight() - y));
    }

    /**
     * Get the style value.
     *
     * @return The {@code Tile} style.
     */
    public int getStyle() {
        return style;
    }

    /**
     * Set the tile style.
     *
     * -til: Changes appearance.
     *
     * @param newStyle The new style value.
     */
    public void setStyle(final int newStyle) {
        this.style = newStyle;
    }

    /**
     * Get the contiguity identifier for this tile.
     *
     * @return A contiguity number.
     */
    public int getContiguity() {
        return contiguity;
    }

    /**
     * Sets the contiguity identifier for this tile.
     *
     * @param contiguity A contiguity number.
     */
    public void setContiguity(int contiguity) {
        this.contiguity = contiguity;
    }

    /**
     * Is this tile connected to another across the same contiguous piece
     * of land or water?
     *
     * @param other The other {@code Tile} to check.
     * @return True if the {@code Tile}s are connected.
     */
    public boolean isConnectedTo(Tile other) {
        return getContiguity() == other.getContiguity();
    }

    /**
     * Get the adjacent tiles that have a given contiguity.
     *
     * @param contiguity The contiguity to search for.
     * @return A set of {@code Tile}s with the required contiguity.
     */
    public Set<Tile> getContiguityAdjacent(final int contiguity) {
        return transform(getSurroundingTiles(1, 1),
                         matchKey(contiguity, Tile::getContiguity),
                         Function.<Tile>identity(), Collectors.toSet());
    }

    /**
     * Is this tile on or adjacent to a navigable river but not the ocean.
     *
     * @return True if on a navigable river.
     */
    public boolean isOnRiver() {
        final TileType greatRiver
            = getSpecification().getTileType("model.tile.greatRiver");
        final TileType ocean
            = getSpecification().getTileType("model.tile.ocean");
        boolean ret = getType() == greatRiver;
        for (Tile t : getSurroundingTiles(1)) {
            if (t.getType() == ocean) return false;
            ret |= t.getType() == greatRiver;
        }
        return ret;
    }

    /**
     * Quick test whether this tile is trivially blocked to moves from
     * a unit.  This is a simplification, use getMoveType().isProgress()
     * for the full details.
     *
     * @param unit The {@code Unit} to test.
     * @return True if the unit can not move to this tile.
     */
    public boolean isBlocked(Unit unit) {
        Player owner = unit.getOwner();

        Unit u = getFirstUnit();
        if (u != null && !owner.owns(u)) return true; // Blocked by unit

        if (isLand()) {
            Settlement s = getSettlement();
            if (unit.isNaval()) {
                return s == null || !owner.owns(s); // Land, not our settlement
            } else {
                return s != null && !owner.owns(s); // Not our settlement
            }
        } else {
            return !unit.isNaval(); // Can not swim
        }
    }
       
    /**
     * Gets the {@code IndianSettlementInternals} for the given player.
     *
     * @param player The {@code Player} to query.
     * @return The {@code IndianSettlementInternals} for the given player,
     *     or null if none present.
     */
    private IndianSettlementInternals getPlayerIndianSettlement(Player player) {
        return (playerIndianSettlements == null) ? null
            : playerIndianSettlements.get(player);
    }


    //
    // Tile Item (LCR, Resource, TileImprovement) handling
    //

    /**
     * Gets a list of {@code TileImprovements}.
     *
     * @return A list of all the {@code TileImprovements}.
     */
    public List<TileImprovement> getTileImprovements() {
        return (tileItemContainer == null)
            ? Collections.<TileImprovement>emptyList()
            : tileItemContainer.getImprovements();
    }

    /**
     * Gets a list of completed {@code TileImprovements}.
     *
     * @return A list of all completed {@code TileImprovements}.
     */
    public List<TileImprovement> getCompleteTileImprovements() {
        return (tileItemContainer == null)
            ? Collections.<TileImprovement>emptyList()
            : tileItemContainer.getCompleteImprovements();
    }

    /**
     * Does this tile contain a completed improvement of the given type?
     *
     * @param type The {@code TileImprovementType} to look for.
     * @return True if there is a completed improvement present.
     */
    public boolean hasTileImprovement(TileImprovementType type) {
        return (type.isChangeType()) ? type.changeContainsTarget(getType())
            : (tileItemContainer == null) ? false
            : tileItemContainer.hasImprovement(type);
    }

    /**
     * Gets the TileImprovement of a given type, or null if there is no match.
     *
     * @param type The {@code TileImprovementType} to look for.
     * @return The {@code TileImprovement} of the requested type found,
     *     or null if none.
     */
    public TileImprovement getTileImprovement(TileImprovementType type) {
        return (tileItemContainer == null) ? null
            : tileItemContainer.getImprovement(type);
    }

    /**
     * Does this tile have a LCR?
     *
     * @return True if this {@code Tile} has a
     *     {@code LostCityRumour} on it.
     */
    public boolean hasLostCityRumour() {
        return tileItemContainer != null
            && tileItemContainer.getLostCityRumour() != null;
    }

    /**
     * Gets a lost city rumour on this tile.
     *
     * @return The {@code LostCityRumour} on this
     *     {@code Tile}, or null if none found.
     */
    public LostCityRumour getLostCityRumour() {
        return (tileItemContainer == null) ? null
            : tileItemContainer.getLostCityRumour();
    }

    /**
     * Does this tile have a resource?
     *
     * @return True if this is a resource {@code Tile}.
     */
    public boolean hasResource() {
        return tileItemContainer != null
            && tileItemContainer.getResource() != null;
    }

    /**
     * Does this tile have a river?
     *
     * @return True if this is a river {@code Tile}.
     */
    public boolean hasRiver() {
        return getRiver() != null;
    }

    /**
     * Gets the river on this tile.
     *
     * @return A river {@code TileImprovement}, or null if none present.
     */
    public TileImprovement getRiver() {
        return (tileItemContainer == null) ? null
            : tileItemContainer.getRiver();
    }

    /**
     * Gets the style of a river improvement on this tile.
     *
     * @return The river {@code TileImprovementStyle}.
     */
    public TileImprovementStyle getRiverStyle() {
        TileImprovement river;
        return (tileItemContainer == null) ? null
            : ((river = tileItemContainer.getRiver()) == null) ? null
            : river.getStyle();
    }

    /**
     * Does this tile have a road?
     *
     * @return True if this {@code Tile} has a road.
     */
    public boolean hasRoad() {
        return getRoad() != null;
    }

    /**
     * Gets the road on this tile.
     *
     * @return A road {@code TileImprovement}, or null if none present.
     */
    public TileImprovement getRoad() {
        return (tileItemContainer == null) ? null : tileItemContainer.getRoad();
    }

    /**
     * Adds a tile item to this tile.
     *
     * -til: Changes appearance.
     *
     * @param item The {@code TileItem} to add.
     * @return True if the item was added.
     */
    private boolean addTileItem(TileItem item) {
        if (item == null) return false;
        if (tileItemContainer == null) {
            tileItemContainer = new TileItemContainer(getGame(), this);
        }
        TileItem added = tileItemContainer.tryAddTileItem(item);
        return added != null;
    }

    /**
     * Removes a tile item from this tile.
     *
     * -til: Changes appearance.
     *
     * @param <T> The actual {@code TileItem} type.
     * @param item The {@code TileItem} to remove.
     * @return The item removed, or null on failure.
     */
    private <T extends TileItem> T removeTileItem(T item) {
        if (item == null || tileItemContainer == null) return null;
        return tileItemContainer.removeTileItem(item);
    }

    /**
     * Adds a lost city rumour to this tile.
     *
     * -til: Changes appearance.
     *
     * @param rumour The {@code LostCityRumour} to add.
     */
    public void addLostCityRumour(LostCityRumour rumour) {
        addTileItem(rumour);
    }

    /**
     * Removes the lost city rumour from this {@code Tile} if there
     * is one.
     *
     * -til: Changes appearance.
     *
     * @return The removed {@code LostCityRumour}.
     */
    public LostCityRumour removeLostCityRumour() {
        return removeTileItem(getLostCityRumour());
    }

    /**
     * Adds a new river to this tile.
     *
     * -til: Changes appearance.
     *
     * @param magnitude The magnitude of the river to be created
     * @param conns The encoded river size/connections.
     * @return The new river added, or null on failure.
     */
    public TileImprovement addRiver(int magnitude, String conns) {
        if (magnitude == TileImprovement.NO_RIVER) return null;
        TileImprovementType riverType = getSpecification()
            .getTileImprovementType("model.improvement.river");
        TileImprovement river = new TileImprovement(getGame(), this, riverType,
            TileImprovementStyle.getInstance(TileImprovement.EMPTY_RIVER_STYLE));
        river.setTurnsToComplete(0);
        river.setMagnitude(magnitude);
        river.updateRiverConnections(conns);
        // Have to return getRiver() because "river" might be merged into an
        // existing one.
        return (addTileItem(river)) ? getRiver() : null;
    }

    /**
     * Removes a river from this tile.
     *
     * -til: Changes appearance.
     */
    public void removeRiver() {
        TileImprovement river = getRiver();
        if (river == null) return;
        river.updateRiverConnections(null);
        removeTileItem(river);
    }

    /**
     * Adds a road to this tile.  It is not complete.
     *
     * -til: Changes appearance.
     *
     * @return The new road added, or the existing one.
     */
    public TileImprovement addRoad() {
        TileImprovementType roadType = getSpecification()
            .getTileImprovementType("model.improvement.road");
        TileImprovement road = new TileImprovement(getGame(), this, roadType,
            TileImprovementStyle.getInstance(TileImprovement.EMPTY_ROAD_STYLE));
        road.setMagnitude(1);
        return (addTileItem(road)) ? road : null;
    }

    /**
     * Removes a road from this tile.
     *
     * -til: Changes appearance.
     *
     * @return The removed road.
     */
    public TileImprovement removeRoad() {
        TileImprovement road = getRoad();
        if (road == null) return null;
        road.updateRoadConnections(false);
        return removeTileItem(road);
    }

    /**
     * Gets the resource on this tile.
     *
     * @return A {@code Resource}, or null if none present.
     */
    public Resource getResource() {
        return (tileItemContainer == null) ? null
            : tileItemContainer.getResource();
    }

    /**
     * Adds a resource to this tile.
     *
     * -til: Changes appearance.
     *
     * @param resource The {@code Resource} to add.
     */
    public void addResource(Resource resource) {
        addTileItem(resource);
    }

    /**
     * Removes a resource from this tile.
     *
     * -til: Changes appearance.
     *
     * @return The removed {@code Resource}.
     */
    public Resource removeResource() {
        Resource resource = getResource();
        if (resource == null) return null;
        return removeTileItem(resource);
    }

    /**
     * Get the number of turns it takes for a non-expert pioneer to build
     * the given {@code TileImprovementType}.
     * It will check if it is valid for this {@code TileType}.
     *
     * @param workType The {@code TileImprovementType} to check.
     * @return The number of turns it should take a non-expert pioneer
     *     to finish the work.
     */
    public int getWorkAmount(TileImprovementType workType) {
        return (workType == null) ? -1
            : (getTileImprovement(workType) != null) ? -1
            // Return the basic work turns + additional work turns
            : getType().getBasicWorkTurns() + workType.getAddWorkTurns();
    }

    /**
     * Check if a given improvement type is valid for this tile.
     *
     * @param type The {@code TileImprovementType} to check.
     * @return True if this tile can be improved with the improvement type.
     */
    public boolean isImprovementTypeAllowed(TileImprovementType type) {
        TileImprovement ti;
        return type != null
            && type.isTileTypeAllowed(getType())
            && ((ti = getTileImprovement(type)) == null || !ti.isComplete());
    }
        
    /**
     * Check if a given improvement is valid for this tile.
     *
     * @param tip The {@code TileImprovement} to check.
     * @return True if this tile can be improved with the improvement.
     */
    public boolean isImprovementAllowed(TileImprovement tip) {
        final TileImprovementType type = tip.getType();
        if (!isImprovementTypeAllowed(type)) return false;
        TileImprovementType req = type.getRequiredImprovementType();
        if (req != null && getTileImprovement(req) == null) return false;
        TileImprovement ti = getTileImprovement(type);
        return ti == null || !ti.isComplete();
    }

    /**
     * Gets a weighted list of natural disasters than can strike
     * this tile.  This list comprises all natural disasters that can
     * strike a tile of this type or a completed tile improvement
     * present.
     *
     * @return A stream of {@code Disaster} choices.
     */
    public Stream<RandomChoice<Disaster>> getDisasterChoices() {
        return concat(type.getDisasterChoices(),
                      flatten(getCompleteTileImprovements(),
                              TileImprovement::getDisasterChoices));
    }


    //
    // Naming
    //

    /**
     * Gets a description of the {@code Tile}, with the name of
     * the tile and any improvements on it (road/plow/etc) from
     * {@code TileItemContainer}.
     *
     * @return The description label for this {@code Tile}.
     */
    public StringTemplate getLabel() {
        StringTemplate label = (type != null) ? StringTemplate.key(type)
            : StringTemplate.key("unexplored");
        if (tileItemContainer != null) {
            List<TileItem> keys = tileItemContainer.getCompleteItems();
            if (!keys.isEmpty()) {
                label = StringTemplate.label("/").addNamed(type);
                for (Named key : keys) label.addNamed(key);
            }
        }
        return label;
    }
    /**
     * Get a simple label for this tile, with just its coordinates.
     *
     * @return A simple {@code StringTemplate} label.
     */
    public StringTemplate getSimpleLabel() {
        return StringTemplate.template("model.tile.simpleLabel")
            .addAmount("%x%", getX())
            .addAmount("%y%", getY());
    }

    /**
     * Get a label for a nearby location.
     *
     * @param direction The {@code Direction} from this tile to the
     *     nearby location.
     * @param location A {@code StringTemplate} describing the location.
     * @return A {@code StringTemplate} stating that the location
     *     is nearby.
     */
    private StringTemplate getNearLocationLabel(Direction direction,
                                               StringTemplate location) {
        return StringTemplate.template("model.tile.nearLocation")
            .addNamed("%direction%", direction)
            .addStringTemplate("%location%", location);
    }
    
    /**
     * Get a detailed label for this tile.
     *
     * @return A suitable {@code StringTemplate}.
     */
    private StringTemplate getDetailedLocationLabel() {
        Settlement nearSettlement = null;
        for (Tile tile : getSurroundingTiles(NEAR_RADIUS)) {
            nearSettlement = tile.getSettlement();
            if (nearSettlement != null && nearSettlement.getName() != null) {
                Direction d = Map.getRoughDirection(tile, this);
                StringTemplate t = StringTemplate
                    .template("model.tile.nameLocation");
                if (d == null) {
                    t.addName("%location%", nearSettlement.getName());
                } else {
                    t.addStringTemplate("%location%",
                        getNearLocationLabel(d, nearSettlement.getLocationLabel()));
                }
                if (type == null) {
                    t.add("%name%", "unexplored");
                } else {
                    t.addNamed("%name%", type);
                }
                return t;
            }
        }
        return (region != null && region.getName() != null)
            ? StringTemplate.template("model.tile.nameLocation")
                .addNamed("%name%", type)
                .addStringTemplate("%location%", region.getLabel())
            : getSimpleLabel();
    }

    /**
     * Get a detailed label for this tile for a given player.
     *
     * @param player The {@code Player} to produce a label for.
     * @return A suitable {@code StringTemplate}.
     */
    private StringTemplate getDetailedLocationLabelFor(Player player) {
        Settlement nearSettlement = null;
        for (Tile tile : getSurroundingTiles(NEAR_RADIUS)) {
            nearSettlement = tile.getSettlement();
            if (nearSettlement != null
                && nearSettlement.hasContacted(player)) {
                Direction d = Map.getRoughDirection(tile, this);
                StringTemplate t = StringTemplate
                    .template("model.tile.nameLocation")
                        .addStringTemplate("%location%", (d == null)
                            ? nearSettlement.getLocationLabelFor(player)
                            : getNearLocationLabel(d,
                                nearSettlement.getLocationLabelFor(player)));
                if (type == null) {
                    t.add("%name%", "unexplored");
                } else {
                    t.addNamed("%name%", type);
                }
                return t;
            }
        }
        return (region != null && region.getName() != null)
            ? StringTemplate.template("model.tile.nameLocation")
                .addNamed("%name%", type)
                .addStringTemplate("%location%", region.getLabel())
            : getSimpleLabel();
    }

    /**
     * Get a label for this tile assuming it is a colony tile of
     * a given colony.
     *
     * @param colony The {@code Colony} assumed to own this tile.
     * @return A suitable {@code StringTemplate}, or null if this
     *     tile is not close enough to the colony to be a colony tile.
     */
    public StringTemplate getColonyTileLocationLabel(Colony colony) {
        Tile ct = colony.getTile();
        StringTemplate t = StringTemplate.template("model.tile.nameLocation");
        if (ct == this) {
            t.addStringTemplate("%location%",
                StringTemplate.key("colonyCenter"));
        } else {
            Direction d = getMap().getDirection(ct, this);
            if (d == null) return null;
            t.addNamed("%location%", d);
        }
        if (type == null) {
            t.add("%name%", "unexplored");
        } else {
            t.addNamed("%name%", type);
        }
        return t;
    }


    //
    // Map / geographic routines
    //

    /**
     * Gets the distance in tiles between this tile and the specified
     * one.
     *
     * @param tile The {@code Tile} to check the distance to.
     * @return The distance.
     */
    public int getDistanceTo(Tile tile) {
        return getMap().getDistance(this, tile);
    }

    /**
     * Gets the direction to a neighbouring tile from this one.
     *
     * @param tile The other {@code Tile}.
     * @return The direction to the other {@code Tile}, or null
     *     if the other tile is not a neighbour.
     */
    public Direction getDirection(Tile tile) {
        return getMap().getDirection(this, tile);
    }

    /**
     * Get the neighbouring tile in the given direction.
     *
     * @param direction The {@code Direction} to check in.
     * @return The neighbouring {@code Tile} in the given
     *     {@code Direction}, or null if none present.
     */
    public Tile getNeighbourOrNull(Direction direction) {
        return getMap().getAdjacentTile(x, y, direction);
    }

    /**
     * Determines whether this tile is adjacent to the specified tile.
     *
     * @param tile A potentially adjacent {@code Tile}.
     * @return True if the {@code Tile} is adjacent to this
     *     {@code Tile}.
     */
    public boolean isAdjacent(Tile tile) {
        return (tile == null) ? false
            : any(getSurroundingTiles(1, 1), matchKey(tile));
    }

    /**
     * Is this tile in the polar regions?
     *
     * @return True if the {@code Tile} is polar.
     */
    public boolean isPolar() {
        return getMap().isPolar(this);
    }

    /**
     * Is this tile land locked?
     *
     * @return True if land locked.
     */
    public boolean isLandLocked() {
        return (!isLand()) ? false
            : all(getSurroundingTiles(1, 1), Tile::isLand);
    }

    /**
     * Is this a shoreline tile?
     *
     * The tile can be water or land, and the water can be ocean,
     * river or an inland lake.  If this is true for a land tile with
     * a colony, the colony can build docks.
     *
     * @return True if this {@code Tile} is on the shore.
     */
    public boolean isShore() {
        return any(getSurroundingTiles(1, 1), t -> t.isLand() != this.isLand());
    }

    /**
     * Is this a good tile to put hills on?
     *
     * Used by the terrain generator.
     *
     * @return True if this is a good potential hill tile.
     */
    public boolean isGoodHillTile() {
        return isLand() && !getType().isElevation()
            // Not too close to the ocean/lake, as this helps with
            // good locations for building colonies on shore.
            && all(getSurroundingTiles(1, 1), Tile::isLand);
    }

    /**
     * Is this a good tile to put mountains on?
     *
     * Used by the terrain generator.
     *
     * @param mountains The mountain tile type.
     * @return True if this is a good potential elevated tile.
     */
    public boolean isGoodMountainTile(TileType mountains) {
        return isGoodHillTile()
            // Not too close to an existing mountain range
            && none(getSurroundingTiles(1, 3), t -> t.getType() == mountains);
    }

    /**
     * Is this a good tile to start a river on?
     *
     * Used by the terrain generator.
     *
     * @param riverType The river <code>TileImprovementType</code>.
     * @return True if this is a good place to start a river.
     */
    public boolean isGoodRiverTile(TileImprovementType riverType) {
        return riverType.isTileTypeAllowed(getType())
            // check the river source/spring is not too close to the ocean
            && all(getSurroundingTiles(1, 2), Tile::isLand);
    }

    /**
     * Gets all the tiles surrounding a tile within the given range.
     * The center tile is not included.
     *
     * @param range How far away do we need to go starting from this.
     * @return The tiles surrounding this {@code Tile}.
     */
    public Iterable<Tile> getSurroundingTiles(int range) {
        return getMap().getCircleTiles(this, true, range);
    }

    /**
     * Gets all the tiles surrounding this tile within the given
     * inclusive upper and lower bounds.
     *
     * getSurroundingTiles(r) is equivalent to getSurroundingTiles(1, r),
     * thus this tile is included if rangeMin is zero.
     *
     * @param rangeMin The inclusive minimum distance from this
     *     {@code Tile}.
     * @param rangeMax The inclusive maximum distance from this
     *     {@code Tile}.
     * @return A list of the tiles surrounding this {@code Tile}.
     */
    public List<Tile> getSurroundingTiles(int rangeMin, int rangeMax) {
        List<Tile> result = new ArrayList<>();
        if (rangeMin > rangeMax || rangeMin < 0) return result;

        if (rangeMin == 0) result.add(this);

        if (rangeMax > 0) {
            for (Tile t : getSurroundingTiles(rangeMax)) {
                // add all tiles up to rangeMax
                result.add(t);
            }
        }
        if (rangeMin > 1) {
            for (Tile t : getSurroundingTiles(rangeMin - 1)) {
                // remove the tiles closer than rangeMin
                result.remove(t);
            }
        }
        return result;
    }

    /**
     * Determine whether this tile has adjacent tiles that are unexplored.
     *
     * @return True if at least one neighbouring {@code Tile}s is
     *     unexplored.
     */
    public boolean hasUnexploredAdjacent() {
        return !all(getSurroundingTiles(1, 1), Tile::isExplored);
    }

    /**
     * Get the number of tiles adjacent to this one that are of the same
     * land/water type such as to be nominally accessible to a unit.
     *
     * @return The number of adjacent available tiles.
     */
    public int getAvailableAdjacentCount() {
        return count(getSurroundingTiles(1, 1),
                     matchKey(isLand(), Tile::isLand));
    }

    /**
     * Get the adjacent colonies.
     *
     * @return A list of adjacent {@code Colony}s.
     */
    public List<Colony> getAdjacentColonies() {
        return transform(getSurroundingTiles(0,1), isNotNull(Tile::getColony),
                         Tile::getColony);
    }

    /**
     * Finds the nearest settlement to this tile.
     *
     * @param owner If non-null, the settlement should be owned by this player.
     * @param radius The maximum radius of the search.
     * @param same If true, require the settlement to be on the same land mass.
     * @return The nearest settlement, or null if none.
     */
    public Settlement getNearestSettlement(Player owner, int radius,
                                           boolean same) {
        if (radius <= 0) radius = INFINITY;
        Map map = getGame().getMap();
        for (Tile t : map.getCircleTiles(this, true, radius)) {
            if (t == this
                || (same && !isConnectedTo(t))) continue;
            Settlement settlement = t.getSettlement();
            if (settlement != null
                && (owner == null || owner.owns(settlement))) {
                return settlement;
            }
        }
        return null;
    }

    /**
     * Finds a safe tile to put a unit on, near to this one.
     * Useful on return from Europe.
     *
     * @param player The owner of the unit to place (may be null).
     * @param random An optional pseudo-random number source.
     * @return A vacant {@code Tile} near this one.
     */
    public Tile getSafeTile(Player player, Random random) {
        if ((getFirstUnit() == null || getFirstUnit().getOwner() == player)
            && (!hasSettlement() || getSettlement().getOwner() == player)) {
            return this;
        }

        for (int r = 1; true; r++) {
            List<Tile> tiles = getSurroundingTiles(r, r);
            if (tiles.isEmpty()) return null;
            if (random != null) {
                randomShuffle(logger, "Safe tile", tiles, random);
            }
            for (Tile t : tiles) {
                if ((t.getFirstUnit() == null
                        || t.getFirstUnit().getOwner() == player)
                    && (t.getSettlement() == null
                        || t.getSettlement().getOwner() == player)) {
                    return t;
                }
            }
        }
    }

    /**
     * Get the defence value for this tile type.
     *
     * @return The defence value.
     */
    public double getDefenceValue() {
        final TileType type = getType();
        return (type == null) ? 0.0
            : applyModifiers(1.0f, null, type.getDefenceModifiers());
    }

    /**
     * Get the defence bonus as a percent.
     *
     * @return The percentage defence bonus.
     */
    public int getDefenceBonusPercentage() {
        return (int)getType().apply(100f, getGame().getTurn(), Modifier.DEFENCE)
            - 100;
    }

    /**
     * Get a list of surrounding land tiles, sorted with the most
     * defensible first.  Useful when planning an attack.
     *
     * @param player A {@code Player} to use to check for
     *     tile access.
     * @return A list of land {@code Tile}s.
     */
    public List<Tile> getSafestSurroundingLandTiles(Player player) {
        final Predicate<Tile> safeTilePred = t ->
            (t.isLand()
                && (!t.hasSettlement() || player.owns(t.getSettlement())));
        final Comparator<Tile> defenceComp
            = cachingDoubleComparator(Tile::getDefenceValue).reversed();
        return transform(getSurroundingTiles(0, 1), safeTilePred,
                         Function.<Tile>identity(), defenceComp);
    }
                    
    /**
     * Get the adjacent land tile with the best defence bonus.
     * Useful for incoming attackers as a disembark site.
     *
     * @param player A {@code Player} to use to check for
     *     tile access.
     * @return The most defensible adjacent land {@code Tile}.
     */
    public Tile getBestDisembarkTile(Player player) {
        return find(getSafestSurroundingLandTiles(player),
            Tile::isHighSeasConnected);
    }

    /**
     * Is this tile dangerous for a naval unit to enter?
     * That is, is there an adjacent settlement that is likely to bombard it.
     *
     * @param ship The naval {@code Unit} to check.
     * @return True if moving the ship to this tile exposes it to attack.
     */
    public boolean isDangerousToShip(Unit ship) {
        final Player player = ship.getOwner();
        final Predicate<Tile> dangerPred = t -> {
            Settlement settlement = t.getSettlement();
            return (settlement == null) ? false
                : !player.owns(settlement)
                    && settlement.canBombardEnemyShip()
                    && (player.atWarWith(settlement.getOwner())
                        || ship.hasAbility(Ability.PIRACY));
        };
        return any(getSurroundingTiles(0, 1), dangerPred);
    }

    /**
     * Get any safe sites for a naval transport unit to stop at to disembark
     * a unit to this tile.  To be safe, the tile must be adjacent to this
     * one but not adjacent to a dangerous settlement.
     *
     * @param unit The transport {@code Unit} that needs a anchoring site.
     * @return A list of suitable {@code Tile}s.
     */
    public List<Tile> getSafeAnchoringTiles(Unit unit) {
        return transform(getSurroundingTiles(0, 1),
                         t -> (!t.isLand() && t.isHighSeasConnected()
                             && !t.isDangerousToShip(unit)));
    }


    //
    // Type and Ownership
    //

    /**
     * Changes the type of this tile.
     * The map generator et al should just use setType(), whereas this
     * routine should be called for the special case of a change of an
     * existing tile type (e.g. pioneer clearing forest).
     *
     * -til: Changes appearance.
     *
     * @param type The new {@code TileType}.
     */
    public void changeType(TileType type) {
        setType(type);

        if (tileItemContainer != null) {
            tileItemContainer.removeIncompatibleImprovements();
        }
        if (!isLand()) settlement = null;

        updateColonyTiles();
    }

    /**
     * Is this tile under active use?
     *
     * @return True if a {@code Colony} is using this {@code Tile}.
     */
    public boolean isInUse() {
        return getOwningSettlement() instanceof Colony
            && ((Colony)getOwningSettlement()).isTileInUse(this);
    }

    /**
     * Changes the owning settlement for this tile.
     *
     * -til: Changes appearance.
     *
     * @param settlement The new owning {@code Settlement} for
     *     this {@code Tile}.
     */
    public void changeOwningSettlement(Settlement settlement) {
        if (owningSettlement != null) {
            owningSettlement.removeTile(this);
        }
        setOwningSettlement(settlement);//-til
        if (settlement != null) {
            settlement.addTile(this);
        }
    }

    /**
     * Change the tile ownership.  Also change the owning settlement
     * as the two are commonly related.
     *
     * -til: Changes appearance.
     *
     * @param player The {@code Player} to own the tile.
     * @param settlement The {@code Settlement} to own the
     *     {@code Tile}.
     */
    public void changeOwnership(Player player, Settlement settlement) {
        setOwner(player);//-til
        changeOwningSettlement(settlement);//-til
    }

    /**
     * A colony is proposed to be built on this tile.  Collect
     * warnings if this has disadvantages.
     *
     * @param unit The {@code Unit} which is to build the colony.
     * @return A {@code StringTemplate} containing the warnings,
     *      or null if none.
     */
    public StringTemplate getBuildColonyWarnings(Unit unit) {
        final Specification spec = getSpecification();
        final Player owner = unit.getOwner();
        boolean landLocked = true;
        boolean ownedByEuropeans = false;
        boolean ownedBySelf = false;
        boolean ownedByIndians = false;

        // Collect the building and food goods types
        List<GoodsType> typeList = spec.getGoodsTypeList();
        java.util.Map<GoodsType, Integer> goodsMap
            = new HashMap<>(typeList.size());
        for (GoodsType goodsType : typeList) {
            if (goodsType.isBuildingMaterial()) {
                while (goodsType.isRefined()) {
                    goodsType = goodsType.getInputType();
                }
            } else if (!goodsType.isFoodType()) {
                continue;
            }
            goodsMap.put(goodsType, 0);
        }
        // Supercede with positive unattended production from this tile
        for (ProductionType productionType : getType()
                 .getAvailableProductionTypes(true)) {
            for (AbstractGoods ag : productionType.getOutputList()) {
                GoodsType goodsType = ag.getType();
                if (!goodsMap.containsKey(goodsType)) continue;
                // Use full production with the tile bonuses
                int potential = getPotentialProduction(goodsType, null);
                Integer oldPotential = goodsMap.get(goodsType);
                if (oldPotential == null || potential > oldPotential) {
                    goodsMap.put(goodsType, potential);
                }
            }
        }
        // Add in potential attended production from other tiles
        for (Tile t : getSurroundingTiles(1)) {
            if (!t.isLand()) landLocked = false;
            forEachMapEntry(goodsMap, e -> e.setValue(e.getValue()
                    + t.getPotentialProduction(e.getKey(),
                        spec.getDefaultUnitType(owner))));
            Player tileOwner = t.getOwner();
            if (owner == tileOwner) {
                if (t.getOwningSettlement() != null) {
                    // we are using newTile
                    ownedBySelf = true;
                } else {
                    for (Tile ownTile : t.getSurroundingTiles(1)) {
                        Colony colony = ownTile.getColony();
                        if (colony != null && colony.getOwner() == owner) {
                            // newTile can be used from an own colony
                            ownedBySelf = true;
                            break;
                        }
                    }
                }
            } else if (tileOwner != null && tileOwner.isEuropean()) {
                ownedByEuropeans = true;
            } else if (tileOwner != null) {
                ownedByIndians = true;
            }
        }

        StringTemplate ret = StringTemplate.label("\n");
        if (landLocked) {
            ret.add("warning.landLocked");
        }
        int food = sum(goodsMap.entrySet(), e -> e.getKey().isFoodType(),
                       Entry::getValue);
        if (food < 8) {
            ret.add("warning.noFood");
        }
        final Predicate<Entry<GoodsType, Integer>> loPred = e ->
            !e.getKey().isFoodType() && e.getValue() < LOW_PRODUCTION_WARNING_VALUE;
        forEachMapEntry(goodsMap, loPred, e ->
            ret.addStringTemplate(StringTemplate
                .template("warning.noBuildingMaterials")
                .addNamed("%goods%", e.getKey())));
        if (ownedBySelf) ret.add("warning.ownLand");
        if (ownedByEuropeans) ret.add("warning.europeanLand");
        if (ownedByIndians) ret.add("warning.nativeLand");
        return ret;
    }

    //
    // Production
    //

    /**
     * Can this tile produce a given goods type?  To produce goods
     * either the tile type must have a suitable production type, or
     * the tile item container contains suitable resource.
     *
     * @param goodsType The {@code GoodsType} to produce.
     * @param unitType An optional {@code UnitType} to use.
     * @return True if the tile can produce the goods.
     */
    public boolean canProduce(GoodsType goodsType, UnitType unitType) {
        return (type != null && type.canProduce(goodsType, unitType))
            || (tileItemContainer != null
                && tileItemContainer.canProduce(goodsType, unitType));
    }

    /**
     * Get the base production exclusive of any bonuses.
     *
     * @param productionType An optional {@code ProductionType} to use,
     *     if null the best available one is used.
     * @param goodsType The {@code GoodsType} to produce.
     * @param unitType An optional {@code UnitType} to use.
     * @return The base production due to tile type and resources.
     */
    public int getBaseProduction(ProductionType productionType,
                                 GoodsType goodsType, UnitType unitType) {
        if (type == null || goodsType == null
            || !goodsType.isFarmed()) return 0;
        int amount = type.getBaseProduction(productionType, goodsType,
                                            unitType);
        return (amount < 0) ? 0 : amount;
    }

    /**
     * Get the potential production of this tile for a given goods type
     * and optional worker type.
     *
     * @param goodsType The {@code GoodsType} to check the
     *     potential for.
     * @param unitType An optional {@code UnitType} to do the work.
     * @return The potential production of this {@code Tile} to
     *     produce the given {@code GoodsType}.
     */
    public int getPotentialProduction(GoodsType goodsType,
                                      UnitType unitType) {
        if (!canProduce(goodsType, unitType)) return 0;

        int amount = getBaseProduction(null, goodsType, unitType);
        amount = (int)applyModifiers(amount, getGame().getTurn(),
                                     getProductionModifiers(goodsType, unitType));
        return (amount < 0) ? 0 : amount;
    }

    /**
     * Get the production modifiers for this tile.
     *
     * @param goodsType The {@code GoodsType} to produce.
     * @param unitType An optional {@code UnitType} to do the work.
     * @return A stream of production {@code Modifier}s.
     */
    public Stream<Modifier> getProductionModifiers(GoodsType goodsType,
                                                   UnitType unitType) {
        return (tileItemContainer != null && canProduce(goodsType, unitType))
            ? tileItemContainer.getProductionModifiers(goodsType, unitType)
            : Stream.<Modifier>empty();
    }

    /**
     * Gets the maximum potential for producing the given type of
     * goods with a given unit if this tile is (perhaps changed to)
     * a given tile type.
     *
     * @param goodsType The {@code GoodsType} to check.
     * @param unitType A {@code UnitType} to do the work.
     * @param tileType A {@code TileType} to change to.
     * @return The maximum potential.
     */
    private int getMaximumPotential(GoodsType goodsType, UnitType unitType,
                                    TileType tileType) {
        float potential = tileType.getPotentialProduction(goodsType, unitType);
        if (tileType == getType()) { // Handle the resource in the noop case
            Resource resource = (tileItemContainer == null) ? null
                : tileItemContainer.getResource();
            if (resource != null) {
                potential = resource.applyBonus(goodsType, unitType,
                                                (int)potential);
            }
        }
        // Try applying all possible non-natural improvements.
        final List<TileImprovementType> improvements
            = getSpecification().getTileImprovementTypeList();
        for (TileImprovementType ti : transform(improvements, ti ->
                (!ti.isNatural() && ti.isTileTypeAllowed(tileType)
                    && ti.getBonus(goodsType) > 0))) {
            potential = ti.getProductionModifier(goodsType).applyTo(potential);
        }
        return (int)potential;
    }

    /**
     * Gets the maximum potential for producing the given type of
     * goods.  The maximum potential is the potential of a tile after
     * the tile has been plowed/built road on.
     *
     * @param goodsType The {@code GoodsType} to check.
     * @param unitType A {@code UnitType} to do the work.
     * @return The maximum potential.
     */
    public int getMaximumPotential(GoodsType goodsType, UnitType unitType) {
        // If we consider maximum potential to the effect of having
        // all possible improvements done, iterate through the
        // improvements and get the bonuses of all related ones.  If
        // there are options to change TileType using an improvement,
        // consider that too.
        final List<TileImprovementType> improvements
            = getSpecification().getTileImprovementTypeList();

        // Collect all the possible tile type changes.
        List<TileType> tileTypes = transform(improvements,
            ti -> !ti.isNatural() && ti.getChange(getType()) != null,
            ti -> ti.getChange(getType()));
        tileTypes.add(0, getType()); //...including the noop case.

        // Find the maximum production under each tile type change.
        return max(tileTypes, tt ->
                   getMaximumPotential(goodsType, unitType, tt));
    }

    /**
     * Sort possible goods types according to potential.
     *
     * @return A list of goods, highest potential production first.
     */
    public List<AbstractGoods> getSortedPotential() {
        return getSortedPotential(null, null);
    }

    /**
     * Sort possible goods types according to potential.
     *
     * @param unit the {@code Unit} to work on this {@code Tile}
     * @return A list of goods, highest potential production first.
     */
    public List<AbstractGoods> getSortedPotential(Unit unit) {
        return getSortedPotential(unit.getType(), unit.getOwner());
    }

    /**
     * Sort possible goods types according to potential.
     *
     * @param unitType The {@code UnitType} to do the work.
     * @param owner the {@code Player} owning the unit.
     * @return A list of goods, highest potential production first.
     */
    public List<AbstractGoods> getSortedPotential(UnitType unitType,
                                                  Player owner) {
        // Defend against calls while partially read.
        if (getType() == null) return Collections.<AbstractGoods>emptyList();
        
        final ToIntFunction<GoodsType> productionMapper = cacheInt(gt ->
            getPotentialProduction(gt, unitType));
        final Predicate<GoodsType> productionPred = gt ->
            productionMapper.applyAsInt(gt) > 0;
        final Function<GoodsType, AbstractGoods> goodsMapper = gt ->
            new AbstractGoods(gt, productionMapper.applyAsInt(gt));
        final Comparator<AbstractGoods> goodsComp
            = ((owner == null || owner.getMarket() == null)
                ? AbstractGoods.descendingAmountComparator
                : owner.getMarket().getSalePriceComparator());
        // It is necessary to consider all farmed goods, since the
        // tile might have a resource that produces goods not produced
        // by the tile type.
        return transform(getSpecification().getFarmedGoodsTypeList(),
                         productionPred, goodsMapper, goodsComp);
    }

    /**
     * Get the best food type to produce here.
     *
     * @return The {@code AbstractGoods} to produce.
     */
    public AbstractGoods getBestFoodProduction() {
        final Comparator<AbstractGoods> goodsComp
            = Comparator.comparingInt(ag ->
                getPotentialProduction(ag.getType(), null));
        return maximize(flatten(getType().getAvailableProductionTypes(true),
                                ProductionType::getOutputs),
                        AbstractGoods::isFoodType, goodsComp);
    }


    //
    // Colony and cached Tile maintenance
    //

    /**
     * Update production after a change to this tile.
     */
    private void updateColonyTiles() {
        WorkLocation wl = find(flatten(getGame().getAllColonies(null),
                                       Colony::getAvailableWorkLocations),
                               matchKey(this, WorkLocation::getWorkTile));
        if (wl != null) wl.updateProductionType();
    }

    /**
     * Get the cached tile map.
     *
     * @return The map of cached tiles.
     */
    private java.util.Map<Player, Tile> getCachedTiles() {
        return this.cachedTiles;
    }

    /**
     * Get the cached tile map.
     *
     * @param cachedTiles The new map of cached {@code Tile}s.
     */
    private void setCachedTiles(java.util.Map<Player, Tile> cachedTiles) {
        if (this.cachedTiles != null) {
            this.cachedTiles.clear();
            if (cachedTiles != null) this.cachedTiles.putAll(cachedTiles);
        }
    }

    /**
     * Get a players view of this tile.
     *
     * @param player The {@code Player} who owns the view.
     * @return The view of this {@code Tile}.
     */
    private Tile getCachedTile(Player player) {
        return (cachedTiles == null) ? null
            : (player.isEuropean()) ? cachedTiles.get(player)
            : this;
    }

    /**
     * Set a players view of this tile.
     *
     * @param player The {@code Player} who owns the view.
     * @param tile The view of the {@code Tile} (either this
     *     tile, or an uninterned copy of it).
     */
    public void setCachedTile(Player player, Tile tile) {
        if (cachedTiles == null || !player.isEuropean()) return;
        cachedTiles.put(player, tile);
    }

    /**
     * Set the players view of this tile to the tile itself if
     * the player can see it.  Useful when the cache needs to be cleared
     * forcibly such as when a native settlement is removed.
     */
    public void seeTile() {
        for (Player p : transform(getGame().getLiveEuropeanPlayers(),
                                  p -> p.canSee(this))) {
            seeTile(p);
        }
    }

    /**
     * Set a players view of this tile to the tile itself.
     *
     * @param player The {@code Player} who owns the view.
     */
    public void seeTile(Player player) {
        setCachedTile(player, this);
    }

    /**
     * Get a copy of this tile suitable for caching (lacking units).
     *
     * @return An uninterned copy of this {@code Tile}.
     */
    public Tile getTileToCache() {
        Tile tile = this.copy(getGame());
        tile.clearUnitList();
        // Set the unit count for a copied colony.
        // Beware though, we may be caching a tile with a colony that is
        // being destroyed, where the unit count has already gone to zero.
        Colony colony = getColony();
        if (colony != null) {
            tile.getColony()
                .setDisplayUnitCount(Math.min(1, colony.getUnitCount()));
        }
        return tile;
    }

    /**
     * A change is about to occur on this tile.  Cache it if unseen.
     */
    public void cacheUnseen() {
        cacheUnseen(null, null);
    }

    /**
     * A change is about to occur on this tile.  Cache it if unseen.
     *
     * @param player A {@code Player} that currently may not be able
     *     to see the tile, but will as a result of the change, and so
     *     should not cache it.
     */
    public void cacheUnseen(Player player) {
        cacheUnseen(player, null);
    }

    /**
     * A change may have occured on this tile.  Establish caches where
     * needed.  Use the copied tile if supplied (which should have
     * been created previously with {@link #getTileToCache},
     *
     * @param copied An optional {@code Tile} to cache.
     */
    public void cacheUnseen(Tile copied) {
        cacheUnseen(null, copied);
    }

    /**
     * A change may have occured on this tile.  Establish caches where
     * needed.  Use the copied tile if supplied (which should have
     * been created previously with {@link #getTileToCache}.
     *
     * @param player A {@code Player} that currently may not be able
     *     to see the tile, but will as a result of the change, and so
     *     should not cache it.
     * @param copied An optional {@code Tile} to cache.
     */
    private void cacheUnseen(Player player, Tile copied) {
        if (cachedTiles == null) return;
        for (Player p : transform(getGame().getLiveEuropeanPlayers(player),
                p -> !p.canSee(this) && getCachedTile(p) == this)) {
            if (copied == null) copied = getTileToCache();
            setCachedTile(p, copied);
        }
    }

    /**
     * Updates the information about the native settlement on this
     * {@code Tile} for the given {@code Player}.
     *
     * @param player The {@code Player}.
     */
    public void updateIndianSettlement(Player player) {
        if (playerIndianSettlements == null || !player.isEuropean()) return;
        IndianSettlementInternals isi = getPlayerIndianSettlement(player);
        IndianSettlement is = getIndianSettlement();
        if (is == null) {
            if (isi != null) removeIndianSettlementInternals(player);
        } else {
            if (isi == null) {
                isi = new IndianSettlementInternals();
                playerIndianSettlements.put(player, isi);
            }
            isi.update(is);
        }
    }

    public void removeIndianSettlementInternals(Player player) {
        if (playerIndianSettlements == null) return;
        playerIndianSettlements.remove(player);
    }

    public UnitType getLearnableSkill(Player player) {
        IndianSettlementInternals isi = getPlayerIndianSettlement(player);
        return (isi == null) ? null : isi.skill;
    }

    public List<GoodsType> getWantedGoods(Player player) {
        IndianSettlementInternals isi = getPlayerIndianSettlement(player);
        return (isi == null) ? null : isi.wantedGoods;
    }

    /**
     * Set native settlement information.  Do not check the current
     * map state as we might leak destruction information.
     *
     * @param player The {@code Player} to pet belonged to.
     * @param skill The skill taught by the settlement.
     * @param wanted The goods wanted by the settlement.
     */
    private void setIndianSettlementInternals(Player player, UnitType skill,
                                              List<GoodsType> wanted) {
        IndianSettlementInternals isi = getPlayerIndianSettlement(player);
        if (isi == null) {
            isi = new IndianSettlementInternals();
            playerIndianSettlements.put(player, isi);
        }
        isi.setValues(skill, wanted);
    }

    /**
     * Checks if this {@code Tile} has been explored by the given
     * {@code Player}.
     *
     * If we are in the server, then the presence of a cached tile
     * determines whether exploration has happened.  In the client
     * there are no cached tiles, but if the tile is explored the
     * server will have updated the client with the tile type (checked
     * by isExplored()).
     *
     * @param player The {@code Player}.
     * @return True if this {@code Tile} has been explored
     *     by the given {@code Player}.
     */
    public boolean isExploredBy(Player player) {
        return (!player.isEuropean()) ? true
            : (!isExplored()) ? false
            : (cachedTiles == null) ? true
            : getCachedTile(player) != null;
    }

    /**
     * Explore/unexplore a tile for a player.
     *
     * @param player The {@code Player} that is exploring.
     * @param reveal The exploration state.
     */
    public void setExplored(Player player, boolean reveal) {
        if (cachedTiles == null || !player.isEuropean()) return;
        if (reveal) {
            seeTile(player);
        } else {
            cachedTiles.remove(player);
        }
    }


    //
    // Unit manipulation
    //

    /**
     * Gets the unit that is currently defending this tile.
     * <p>If this tile has a settlement, the units inside the
     * settlement are also considered as potential defenders.
     * <p>As this method is quite expensive, it should not be used to
     * test for the presence of enemy units.
     *
     * @param attacker The {@code Unit} that would be attacking
     *     this {@code Tile}.
     * @return The {@code Unit} that has been chosen to defend this
     *     {@code Tile}.
     */
    public Unit getDefendingUnit(Unit attacker) {
        CombatModel cm = getGame().getCombatModel();
        Unit defender = null;
        double defenderPower = -1.0, power;

        // Check the units on the tile...
        for (Unit u : transform(getUnits(), u -> isLand() != u.isNaval())) {
            // On land, ships are normally docked in port and
            // cannot defend.  Except if beached (see below).
            // On ocean tiles, land units behave as ship cargo and
            // can not defend.
            power = cm.getDefencePower(attacker, u);
            if (Unit.betterDefender(defender, defenderPower, u, power)) {
                defender = u;
                defenderPower = power;
            }
        }

        // ...then a settlement defender if any...
        if ((defender == null || !defender.isDefensiveUnit())
            && hasSettlement()) {
            Unit u = null;
            try {
                // HACK: The AI is prone to removing all units in a
                // settlement which causes Colony.getDefendingUnit()
                // to throw.
                u = settlement.getDefendingUnit(attacker);
            } catch (IllegalStateException e) {
                logger.log(Level.WARNING, "Empty settlement: "
                    + settlement.getName(), e);
            }
            // This routine can be called on the client for the pre-combat
            // popup where enemy settlement defenders are not visible,
            // thus u == null is valid.
            if (u != null) {
                power = cm.getDefencePower(attacker, u);
                if (Unit.betterDefender(defender, defenderPower, u, power)) {
                    defender = u;
                    //defenderPower = power;
                }
            }
        }

        // ...finally, if we have failed to find a valid defender
        // for a land tile, allow a beached naval unit to defend (and
        // lose) as a last resort.
        if (defender == null && isLand()) defender = getFirstUnit();

        return defender;
    }

    /**
     * Gets the unit that is occupying the tile.
     *
     * @return The {@code Unit} that is occupying this {@code Tile}.
     * @see #isOccupied()
     */
    public Unit getOccupyingUnit() {
        Unit unit = getFirstUnit();
        Player owner = null;
        if (getOwningSettlement() != null) {
            owner = getOwningSettlement().getOwner();
        }
        return (owner != null && unit != null && unit.getOwner() != owner
            && unit.getOwner().atWarWith(owner))
            ? find(getUnits(), Unit::isOffensiveUnit)
            : null;
    }

    /**
     * Checks whether there is an enemy unit occupying this tile.
     * Units can not produce in occupied tiles.
     *
     * @return True if an enemy unit is occupying this {@code Tile}.
     */
    public boolean isOccupied() {
        return getOccupyingUnit() != null;
    }


    // Interface Location
    //   getSettlement and getColony are simple accessors of Tile
    // Inherits
    //   FreeColObject.getId
    //   UnitLocation.getUnitCount
    //   UnitLocation.getUnitList
    //   UnitLocation.getGoodsContainer

    /**
     * {@inheritDoc}
     */
    @Override
    public Tile getTile() {
        return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public StringTemplate getLocationLabel() {
        return (settlement != null) ? settlement.getLocationLabel()
            : getDetailedLocationLabel();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public StringTemplate getLocationLabelFor(Player player) {
        return (settlement != null) ? settlement.getLocationLabelFor(player)
            : getDetailedLocationLabelFor(player);
    }

    /**
     * {@inheritDoc}
     *
     * -til: Changes appearance with TileItems.
     */
    @Override
    public boolean add(Locatable locatable) {
        if (locatable instanceof TileItem) {
            return addTileItem((TileItem) locatable);//-til

        } else if (locatable instanceof Unit) {
            if (super.add(locatable)) {
                ((Unit)locatable).setState(Unit.UnitState.ACTIVE);
                return true;
            }
            return false;

        } else {
            return super.add(locatable);
        }
    }

    /**
     * {@inheritDoc}
     *
     * -til: Changes appearance with TileItems.
     */
    @Override
    public boolean remove(Locatable locatable) {
        if (locatable instanceof TileItem) {
            return removeTileItem((TileItem)locatable)
                == locatable;//-til

        } else {
            return super.remove(locatable);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean contains(Locatable locatable) {
        if (locatable instanceof TileItem) {
            return tileItemContainer != null
                && tileItemContainer.contains((TileItem) locatable);
        } else {
            return super.contains(locatable);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean canAdd(Locatable locatable) {
        if (locatable instanceof Unit) {
            return ((Unit)locatable).isTileAccessible(this);
        } else if (locatable instanceof TileImprovement) {
            return ((TileImprovement)locatable).getType()
                .isTileTypeAllowed(getType());
        } else {
            return false;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location up() {
        return (hasSettlement()) ? getSettlement()
            : this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public int getRank() {
        return getX() + getY() * getMap().getWidth();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String toShortString() {
        StringBuilder sb = new StringBuilder(16);
        TileType type = getType();
        sb.append(getX()).append(',').append(getY())
            .append('-').append((type == null) ? "?" : type.getSuffix());
        return sb.toString();
    }


    // Interface Named

    /**
     * {@inheritDoc}
     */
    @Override
    public String getNameKey() {
        if (getGame().isInClient()) {
            return (isExplored()) ? getType().getNameKey() : "unexplored";
        } else {
            Player player = getGame().getCurrentPlayer();
            if (player != null) {
                return (getCachedTile(player) == null) ? "unexplored"
                    : getType().getNameKey();
            } else {
                logger.warning("player == null");
                return "";
            }
        }
    }


    // Interface Ownable

    /**
     * {@inheritDoc}
     */
    @Override
    public Player getOwner() {
        return owner;
    }

    /**
     * {@inheritDoc}
     *
     * -til: Changes appearance.
     */
    @Override
    public void setOwner(Player owner) {
        this.owner = owner;
    }


    // Override FreeColGameObject

    /**
     * {@inheritDoc}
     */
    @Override
    public void disposeResources() {
        if (settlement != null) {
            settlement.disposeResources();
            settlement = null;
        }
        if (tileItemContainer != null) {
            tileItemContainer.disposeResources();
            tileItemContainer = null;
        }
        super.disposeResources();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public FreeColGameObject getLinkTarget(Player player) {
        return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public IntegrityType checkIntegrity(boolean fix, LogBuilder lb) {
        IntegrityType result = super.checkIntegrity(fix, lb);
        Settlement settlement = getSettlement();
        if (settlement != null) {
            result = result.combine(settlement.checkIntegrity(fix, lb));
        }
        if (tileItemContainer != null) {
            result = result.combine(tileItemContainer.checkIntegrity(fix, lb));
        }
        if (type == null) {
            lb.add("\n  Tile has no type: ", getId());
            result = result.fail(); // Fundamentally unfixable
        } else if (isLand() && Boolean.TRUE.equals(moveToEurope)) {
            lb.add("\n  Tile is land but has move-to-Europe: ", getId());
            if (fix) {
                moveToEurope = Boolean.FALSE;
                result = result.fix();
            } else {
                result = result.fail();
            }
        }
        return result;
    }


    // Override FreeColObject

    /**
     * {@inheritDoc}
     */
    @Override
    public Stream<Ability> getAbilities(String id,
                                        FreeColSpecObjectType fcgot,
                                        Turn turn) {
        // Delegate to type
        return getType().getAbilities(id, fcgot, turn);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public <T extends FreeColObject> boolean copyIn(T other) {
        Tile o = copyInCast(other, Tile.class);
        if (o == null || !super.copyIn(o)) return false;
        final Game game = getGame();
        this.type = o.getType();
        this.x = o.getX();
        this.y = o.getY();
        this.owner = game.updateRef(o.getOwner());
        // Allow settlement creation, might be first sight
        this.settlement = game.update(o.getSettlement(), true);
        this.owningSettlement = game.updateRef(o.getOwningSettlement());
        // Allow TIC creation, might be the first time we see the tile
        this.tileItemContainer = game.update(o.getTileItemContainer(), true);
        this.region = game.updateRef(o.getRegion());
        this.highSeasCount = o.getHighSeasCount();
        this.moveToEurope = o.getMoveToEurope();
        this.style = o.getStyle();
        this.contiguity = o.getContiguity();
        // Do not need to update the cached tiles, they live server-side
        this.setCachedTiles(o.getCachedTiles());
        return true;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public FreeColObject getDisplayObject() {
        return getType();
    }


    // Serialization

    private static final String CACHED_TILE_TAG = "cachedTile";
    private static final String CONNECTED_TAG = "connected";
    private static final String CONTIGUITY_TAG = "contiguity";
    private static final String COPIED_TAG = "copied";
    private static final String MOVE_TO_EUROPE_TAG = "moveToEurope";
    private static final String OWNER_TAG = "owner";
    private static final String OWNING_SETTLEMENT_TAG = "owningSettlement";
    private static final String PLAYER_TAG = "player";
    private static final String REGION_TAG = "region";
    private static final String STYLE_TAG = "style";
    private static final String TYPE_TAG = "type";
    private static final String X_TAG = "x";
    private static final String Y_TAG = "y";
    // @compat 0.11.0
    public static final String OLD_PLAYER_EXPLORED_TILE_TAG = "playerExploredTile";
    // end @compat 0.11.0
    // @compat 0.11.3
    public static final String OLD_TILE_ITEM_CONTAINER_TAG = "tileitemcontainer";
    // end @compat 0.11.3
    

    /**
     * {@inheritDoc}
     */
    @Override
    public void toXML(FreeColXMLWriter xw, String tag) throws XMLStreamException {
        // Special override of tile output serialization that handles
        // the tile caching.
        final Player player = xw.getClientPlayer();
        Tile tile;

        if (player == null) { // 1. Not writing to a player, just write tile.
            this.internalToXML(xw, tag);

        } else if ((tile = getCachedTile(player)) != null) { // 2. Cached tile.
            tile.internalToXML(xw, tag);

        } else if (isExploredBy(player)) { // 3. Tile is explored, write it
            this.internalToXML(xw, tag);

        } else { // 4. Tile is not explored.
            xw.writeStartElement(tag);

            xw.writeAttribute(ID_ATTRIBUTE_TAG, getId());

            xw.writeAttribute(X_TAG, this.x);

            xw.writeAttribute(Y_TAG, this.y);

            xw.writeEndElement();
        }
    }

    /**
     * Fundamental (post-cache) version of toXML.
     *
     * @param xw The {@code FreeColXMLWriter} to write to.
     * @param tag The tag to use.
     * @exception XMLStreamException if there are any problems writing
     *     to the stream.
     */
    private void internalToXML(FreeColXMLWriter xw, String tag)
        throws XMLStreamException {
        xw.writeStartElement(tag);

        writeAttributes(xw);

        writeChildren(xw);

        xw.writeEndElement();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes(FreeColXMLWriter xw) throws XMLStreamException {
        super.writeAttributes(xw);

        xw.writeAttribute(X_TAG, this.x);

        xw.writeAttribute(Y_TAG, this.y);

        xw.writeAttribute(TYPE_TAG, type);

        if (owner != null) {
            xw.writeAttribute(OWNER_TAG, owner);
        }

        if (owningSettlement != null) {
            if (owningSettlement.isDisposed()
                || owningSettlement.getId() == null) {
                // Owning settlement is a special case because it is a
                // reference to something outside this tile.  If the
                // tile being written here is a cached copy, and the
                // owning settlement referred to therein has really
                // been destroyed, then we risk corrupting or at least
                // confusing the client by referring to the disposed
                // settlement.  So clear out such cases.  This is an
                // information leak, but a better option than the
                // crashes caused by the alternative.
                this.owningSettlement = null;
            } else {
                xw.writeAttribute(OWNING_SETTLEMENT_TAG, owningSettlement);
            }
        }

        xw.writeAttribute(STYLE_TAG, style);

        if (region != null) {
            xw.writeAttribute(REGION_TAG, region);
        }

        if (moveToEurope != null) {
            xw.writeAttribute(MOVE_TO_EUROPE_TAG,
                              moveToEurope.booleanValue());
        }

        if (highSeasCount >= 0) {
            xw.writeAttribute(CONNECTED_TAG, highSeasCount);
        }

        if (contiguity >= 0) {
            xw.writeAttribute(CONTIGUITY_TAG, contiguity);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeChildren(FreeColXMLWriter xw) throws XMLStreamException {
        // Show tile contents (e.g. enemy units) if not scoped to a
        // player that can not see the tile, and there is no blocking
        // enemy settlement.
        final Player player = xw.getClientPlayer();
        if ((player == null || player.canSee(this)) 
            && (settlement == null
                || xw.validFor(settlement.getOwner()))) {
            super.writeChildren(xw);
        }

        if (settlement != null) settlement.toXML(xw);

        if (tileItemContainer != null) tileItemContainer.toXML(xw);

        // Save the cached tiles to saved games.
        if (cachedTiles != null && xw.validForSave()) {
            for (Player p : getGame().getLiveEuropeanPlayerList()) {
                Tile t = getCachedTile(p);
                if (t == null) continue;

                if (t == this && getIndianSettlement() != null) {
                    // Always save client view of native settlements
                    // because of the hidden information.
                    t = getTileToCache();
                    t.setIndianSettlementInternals(p, getLearnableSkill(p),
                                                   getWantedGoods(p));
                }

                xw.writeStartElement(CACHED_TILE_TAG);

                xw.writeAttribute(PLAYER_TAG, p);

                xw.writeAttribute(COPIED_TAG, t != this);
                if (t != this) {
                    // Only write copied tiles, with limited scope.
                    FreeColXMLWriter.WriteScope ws
                        = xw.replaceScope(FreeColXMLWriter.WriteScope.toClient(p));
                    try {
                        // Do not call toXML!  It will look for a cached tile
                        // inside t which is already a cached copy!
                        t.internalToXML(xw, TAG);
                    } finally {
                        xw.replaceScope(ws);
                    }
                }

                xw.writeEndElement();
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes(FreeColXMLReader xr) throws XMLStreamException {
        super.readAttributes(xr);

        final Specification spec = getSpecification();
        final Game game = getGame();

        x = xr.getAttribute(X_TAG, 0);

        y = xr.getAttribute(Y_TAG, 0);

        type = xr.getType(spec, TYPE_TAG, TileType.class, (TileType)null);
        if (type == null) { // Unexplored tile.
            style = 0;
            highSeasCount = -1;
            owner = null;
            region = null;
            moveToEurope = null;
            contiguity = -1;
            owningSettlement = null;
            return;
        }

        style = xr.getAttribute(STYLE_TAG, 0);

        String str = xr.getAttribute(CONNECTED_TAG, (String)null);
        if (str == null || str.isEmpty()) {
            highSeasCount = -1;
        } else {
            try {
                highSeasCount = Integer.parseInt(str);
            } catch (NumberFormatException nfe) {
                highSeasCount = -1;
            }
        }

        owner = xr.findFreeColGameObject(game, OWNER_TAG,
                                         Player.class, (Player)null, false);

        region = xr.findFreeColGameObject(game, REGION_TAG,
                                          Region.class, (Region)null, false);
        
        moveToEurope = (xr.hasAttribute(MOVE_TO_EUROPE_TAG))
            ? xr.getAttribute(MOVE_TO_EUROPE_TAG, false)
            : null;

        contiguity = xr.getAttribute(CONTIGUITY_TAG, -1);

        // Tiles are added to the settlement owned tiles list in Map.
        // Doing it here can cause cache weirdness.
        Location loc = xr.getLocationAttribute(game, OWNING_SETTLEMENT_TAG,
                                               true);
        owningSettlement = (loc instanceof Settlement) ? (Settlement)loc
            : null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readChildren(FreeColXMLReader xr) throws XMLStreamException {
        // Clear containers.
        settlement = null;

        super.readChildren(xr);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readChild(FreeColXMLReader xr) throws XMLStreamException {
        final Game game = getGame();
        final String tag = xr.getLocalName();

        if (CACHED_TILE_TAG.equals(tag)) {
            Player player = xr.findFreeColGameObject(game, PLAYER_TAG, 
                Player.class, (Player)null, true);
            boolean copied = xr.getAttribute(COPIED_TAG, false);

            if (copied) { // Tile needs to be read
                FreeColXMLReader.ReadScope rs
                    = xr.replaceScope(FreeColXMLReader.ReadScope.NOINTERN);
                try {
                    xr.nextTag();
                    xr.expectTag(Tile.TAG);
                    Tile tile = xr.readFreeColObject(game, Tile.class);

                    // Temporary workaround for BR#2618 on input
                    Colony colony = tile.getColony();
                    int apparent;
                    if (colony != null
                        && (apparent = colony.getApparentUnitCount()) <= 0) {
                        logger.warning("Copied colony " + colony.getId()
                            + " display unit count set to 1 from corrupt: "
                            + apparent);
                        colony.setDisplayUnitCount(1);
                    }
                    // end workaround

                    IndianSettlement is = tile.getIndianSettlement();
                    if (is == null) {
                        removeIndianSettlementInternals(player);
                    } else {
                        setIndianSettlementInternals(player,
                            is.getLearnableSkill(), is.getWantedGoods());
                    }
                    setCachedTile(player, tile);
                } finally {
                    xr.replaceScope(rs);
                }
            } else {
                setCachedTile(player, this);
            }

            xr.closeTag(CACHED_TILE_TAG);

        } else if (Colony.TAG.equals(tag)) {
            settlement = xr.readFreeColObject(game, Colony.class);

        } else if (IndianSettlement.TAG.equals(tag)) {
            settlement = xr.readFreeColObject(game, IndianSettlement.class);

        // @compat 0.11.0
        } else if (OLD_PLAYER_EXPLORED_TILE_TAG.equals(tag)) {
            // Do not process this any more, but at least set a cached tile.
            Player player = xr.findFreeColGameObject(game, PLAYER_TAG, 
                Player.class, (Player)null, true);
            xr.swallowTag(OLD_PLAYER_EXPLORED_TILE_TAG);
            if (player != null) setCachedTile(player, this);
        // end @compat 0.11.0

        } else if (TileItemContainer.TAG.equals(tag)
                   // @compat 0.11.3
                   || OLD_TILE_ITEM_CONTAINER_TAG.equals(tag)
                   // end @compat 0.11.3
                   ) {
            tileItemContainer = xr.readFreeColObject(game,
                TileItemContainer.class);

        } else {
            super.readChild(xr);
        }
    }

    /**
     * {@inheritDoc}
     */
    public String getXMLTagName() { return TAG; }


    // Override

    /**
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(64);
        sb.append('[').append(getId())
            .append(' ').append((type == null) ? "unknown" : type.getSuffix())
            .append(' ').append(x).append(',').append(y)
            .append((!hasSettlement()) ? "" : " " + getSettlement().getName())
            .append(']');
        return sb.toString();
    }
}