/// <summary>
        /// Find the best move for a unit.
        /// </summary>
        /// <param name="u">The unit to move</param>
        /// <param name="board">The board to find units on</param>
        /// <param name="task">The task the unit should do</param>
        /// <returns>A move that is decided as the best move for this unit this turn.</returns>
        public static Move BestMove(Unit u, Tile[,] board, Task task)
        {
            if (task == Task.improve)
            {
                //Get dictionary of amount of friendly units of type.
                Dictionary <UnitType, int> friendlies = AIUtil.Count(board, new LookupConstraint(new PlayerConstraint(false)));

                UnitType build       = UnitType.builder; //The unit that needs to be built
                bool     needToBuild = false;            //Whether there is a unit to build

                //Find the first type in the build order that is not built yet.
                foreach (UnitType test in BUILD_ORDER)
                {
                    if (!friendlies.ContainsKey(test))
                    {
                        build       = test;
                        needToBuild = true;
                        break;
                    }
                    if (friendlies[test] == 0)
                    {
                        build       = test;
                        needToBuild = true;
                        break;
                    }
                    friendlies[test]--;
                }
                if (!needToBuild)
                {
                    return(null);
                }

                //Check if the build target can be built (resources wise)
                if (!(build.Cost() <= Game.instance.computer.resources || COMPUTER_INFINATE_RESOURCES))
                {
                    return(null);
                }

                //Checks if the current unit is able to build the type
                if (u.GetBuildable().Contains(build))
                {
                    //Find all possibilites of building
                    List <Move> options = u.BuildAroundMove(board, build, 1);

                    //Make sure there is enough moves left for the unit to build
                    options.RemoveAll((o) => { return(o.cost > u.movesLeft); });

                    //If there is an option to build the target, do it.
                    if (options.Count > 0)
                    {
                        Move res = options[0];
                        return(res);
                    }
                    //Otherwise, if the unit is a builder, move to the nearest tile where building will be possible.
                    else
                    {
                        if (u.type == UnitType.builder)
                        {
                            //Find path to the nearest tile where the build target can be built
                            List <ALocation> path = PathFinder.PathToNearestTile(u.type, board, u.TileX, u.TileY, build.BuildableTiles()[0]);
                            //If a non empty path is found, walk it
                            if (path != null && path.Count != 0)
                            {
                                return(new MovementMove(u, path[0].x, path[0].y));
                            }
                        }
                    }
                }
            }

            if (task == Task.forward)
            {
                //Find the resource tile that is open
                Tile target = null;
                if (board[3, 2].buildingOn == null)
                {
                    target = board[3, 2];
                }
                if (board[4, 2].buildingOn == null)
                {
                    target = board[4, 2];
                }
                if (board[2, 3].buildingOn == null)
                {
                    target = board[2, 3];
                }
                if (board[2, 4].buildingOn == null)
                {
                    target = board[2, 4];
                }

                if (target != null)
                {
                    //Find all build options of the harvester of the open tile.
                    List <Move> options = u.BuildAroundMove(board, target.type.GetHarvesterType(), 1);

                    //If a good build option is found, return it.
                    options.RemoveAll((o) => { return(o.cost > u.movesLeft); });
                    if (options.Count > 0)
                    {
                        Move res = options[0];
                        return(res);
                    }
                    //Otherwise, find a path to that tile.
                    else
                    {
                        List <ALocation> path = PathFinder.PathToNearestTile(u.type, board, u.px / Tile.TILE_WIDTH, u.py / Tile.TILE_HEIGHT, target.type);
                        if (path != null && path.Count != 0)
                        {
                            return(new MovementMove(u, path[0].x, path[0].y));
                        }
                    }
                }
            }

            if (task == Task.defend)
            {
                //First see if the unit can attack. If so, attack.
                List <Move> attacks = u.DefaultAttackAroundMove(board);
                if (attacks.Count > 0)
                {
                    return(attacks[0]);
                }

                //If the unit can't attack, find a path to the nearest enemy unit in the friendly base.
                List <ALocation> path = PathFinder.PathToNearestUnit(u.type, board, u.TileX, u.TileY, new LookupConstraint(new PlayerConstraint(true), new DistanceConstraint(10, 10, 4)));
                if (path != null && path.Count > 0)
                {
                    //If a path is found, move along it.
                    int i = Math.Min(Math.Max(0, path.Count - 2), u.movesLeft - 1);
                    return(new MovementMove(u, path[i].x, path[i].y));
                }

                //If no path is found, push instead of defending.
                return(BestMove(u, board, Task.push));
            }

            if (task == Task.push)
            {
                if (u.type.GetDamage() > 0)
                {
                    //Find the move that maximizes map control, calculating 3 moves ahead.
                    return(DepthSearch.GetBestMoveMin(u, board));
                }
                if (u.type.IsTraining())
                {
                    //Build a unit.
                    List <Move> options = u.BuildAroundMove(board, u.GetBuildable()[0], 1).Where(m => m.cost <= u.movesLeft).ToList();
                    if (options.Count == 0)
                    {
                        return(null);
                    }
                    Move build = options[0];
                    return(build);
                }
            }

            if (task == Task.destroy)
            {
                //Try to attack a nearby unit.
                List <Move> attacks = u.DefaultAttackAroundMove(board);
                if (attacks.Count > 0)
                {
                    return(attacks[0]);
                }

                //If no nearby units, find the nearest unit and go towards it.
                List <ALocation> path = PathFinder.PathToNearestUnit(u.type, board, u.TileX, u.TileY, true);
                if (path == null || path.Count == 0)
                {
                    return(null);
                }
                int i = Math.Min(Math.Max(0, path.Count - 2), u.movesLeft - 1);
                return(new MovementMove(u, path[i].x, path[i].y));
            }

            if (task == Task.retreat)
            {
                //Find a path to the friendly base.
                List <ALocation> path = PathFinder.PathToCoordinates(u.type, board, u.TileX, u.TileY, 10, 10);
                if (path == null || path.Count == 0)
                {
                    //If no path is found, find a path to a tile that is close to the friendly base.
                    List <ALocation> path2 = PathFinder.PathToNearestTile(u.type, board, u.TileX, u.TileY, new TileLookupConstraint(new DistanceTileConstraint(10, 10, 3)));
                    if (path2 == null || path2.Count == 0)
                    {
                        return(null);
                    }
                    int i2 = Math.Min(Math.Max(0, path2.Count - 2), u.movesLeft - 1);
                    return(new MovementMove(u, path2[i2].x, path2[i2].y));
                }
                int i = Math.Min(Math.Max(0, path.Count - 2), u.movesLeft - 1);
                return(new MovementMove(u, path[i].x, path[i].y));
            }

            return(null);
        }