/// <summary>
/// Find out whether there is a ship on a given location and return its boundaries
/// </summary>
/// <param name="board">Board on which to find the ship</param>
/// <param name="ix">Location to check</param>
/// <param name="shipRange">Boundaries of the found ship</param>
/// <returns>
/// The method returns <see cref="ShipFindingResult.NoShip"/> if there is no ship on the specified cell.
/// It returns <see cref="ShipFindingResult.PartialShip"/> if there is a ship on the specified cell, but it
/// cannot be said for sure how long it is (because of <see cref="SquareContent.Unknown"/> cells in front or
/// behind the ship). If a ship was found and the size of the ship could be determined, the function returns
/// <see cref="ShipFindingResult.CompleteShip"/>.
/// </returns>
public static ShipFindingResult TryFindShip(this IReadOnlyBoard board, BoardIndex ix, out BoardIndexRange shipRange)
{
// Note pattern matching
if (board[ix] is not SquareContent.HitShip and not SquareContent.Ship)
{
// No ship at specified index
shipRange = new BoardIndexRange();
return(ShipFindingResult.NoShip);
}
// Note local method returning tuple
(BoardIndex ix, bool complete) FindShipEdge(BoardIndex current, Direction direction, bool prev)
{
bool canMoveFurther;
do
{
BoardIndex next;
if (prev)
{
canMoveFurther = current.TryPrevious(direction, out next);
}
else
{
canMoveFurther = current.TryNext(direction, out next);
}
if (canMoveFurther)
{
current = next;
}
}while (canMoveFurther && board[current] is not SquareContent.Water and not SquareContent.Unknown);
var complete = board[current] is not SquareContent.Unknown;
if (board[current] is not SquareContent.Water and not SquareContent.Unknown)
{
return(current, complete);
}
if (!prev)
{
return(direction == Direction.Horizontal ? current.PreviousColumn() : current.PreviousRow(), complete);
}
return(direction == Direction.Horizontal ? current.NextColumn() : current.NextRow(), complete);
}
// Note local method receiving tuple
bool TryDirection(Direction direction, out (BoardIndexRange range, ShipFindingResult complete) result)
{
var(beginningIx, beginningComplete) = FindShipEdge(ix, direction, true);
var(endIx, endComplete) = FindShipEdge(ix, direction, false);
result = (new BoardIndexRange(beginningIx, endIx),
beginningComplete&& endComplete ? ShipFindingResult.CompleteShip : ShipFindingResult.PartialShip);
return(result.range.Length > 1);
}
// Go left and find first water
if (TryDirection(Direction.Horizontal, out var resultHorizontal))
{
shipRange = resultHorizontal.range;
return(resultHorizontal.complete);
}
// Note discard operator to indicate that result is not relevant
_ = TryDirection(Direction.Vertical, out var resultVertical);
shipRange = resultVertical.range;
return(resultVertical.complete);
}
/// <summary>
/// Find out whether there is a ship on a given location and return its boundaries
/// </summary>
/// <param name="board">Board on which to find the ship</param>
/// <param name="ix">Location to check</param>
/// <param name="shipRange">Boundaries of the found ship</param>
/// <returns>
/// The method returns <see cref="ShipFindingResult.NoShip"/> if there is no ship on the specified cell.
/// It returns <see cref="ShipFindingResult.PartialShip"/> if there is a ship on the specified cell, but it
/// cannot be said for sure how long it is (because of <see cref="SquareContent.Unknown"/> cells in front or
/// behind the ship). If a ship was found and the size of the ship could be determined, the function returns
/// <see cref="ShipFindingResult.CompleteShip"/>.
/// </returns>
public static ShipFindingResult TryFindShip(this IReadOnlyBoard board, BoardIndex ix, out BoardIndexRange shipRange)
{
// Note pattern matching
if (board[ix] is not SquareContent.HitShip and not SquareContent.Ship and not SquareContent.SunkenShip)
{
// No ship at specified index
shipRange = new BoardIndexRange();
return(ShipFindingResult.NoShip);
}
// Note local method returning tuple
(BoardIndex ix, bool complete) FindShipEdge(BoardIndex current, Direction direction, bool prev)
{
bool canMoveFurther;
do
{
BoardIndex next;
if (prev)
{
canMoveFurther = current.TryPrevious(direction, out next);
}
else
{
canMoveFurther = current.TryNext(direction, out next);
}
if (canMoveFurther)
{
current = next;
}
}while (canMoveFurther && board[current] is not SquareContent.Water and not SquareContent.Unknown);
var complete = board[current] is not SquareContent.Unknown;
if (board[current] is not SquareContent.Water and not SquareContent.Unknown)
{
return(current, complete);
}
if (!prev)
{
return(direction == Direction.Horizontal ? current.PreviousColumn() : current.PreviousRow(), complete);
}
return(direction == Direction.Horizontal ? current.NextColumn() : current.NextRow(), complete);
}
// Note local method receiving tuple
bool TryDirection(Direction direction, out (BoardIndexRange range, ShipFindingResult complete) result)
{
var(beginningIx, beginningComplete) = FindShipEdge(ix, direction, true);
var(endIx, endComplete) = FindShipEdge(ix, direction, false);
result = (new BoardIndexRange(beginningIx, endIx),
beginningComplete&& endComplete ? ShipFindingResult.CompleteShip : ShipFindingResult.PartialShip);
return(result.range.Length > 1);
}
// Check if the ship is placed horizontally
var isHorizontal = TryDirection(Direction.Horizontal, out var resultHorizontal);
if (isHorizontal)
{
shipRange = resultHorizontal.range;
return(resultHorizontal.complete);
}
// Check if the ship is placed vertically
var isVertical = TryDirection(Direction.Vertical, out var resultVertical);
shipRange = resultVertical.range;
// When only a single square of a ship is known, no orientation can be determined and therefore the ship is only partial.
if (!isHorizontal && !isVertical)
{
return(ShipFindingResult.PartialShip);
}
return(resultVertical.complete);
}