260 lines
9.0 KiB
C#
260 lines
9.0 KiB
C#
using Shogi.Domain.Pathing;
|
|
using Shogi.Domain.Pieces;
|
|
using BoardTile = System.Collections.Generic.KeyValuePair<System.Numerics.Vector2, Shogi.Domain.Pieces.Piece>;
|
|
|
|
namespace Shogi.Domain
|
|
{
|
|
internal class StandardRules
|
|
{
|
|
private readonly ShogiBoardState boardState;
|
|
|
|
internal StandardRules(ShogiBoardState board)
|
|
{
|
|
boardState = board;
|
|
}
|
|
|
|
/// <summary>
|
|
/// Move a piece from a board tile to another board tile ignorant of check or check-mate.
|
|
/// </summary>
|
|
/// <param name="fromNotation">The position of the piece being moved expressed in board notation.</param>
|
|
/// <param name="toNotation">The target position expressed in board notation.</param>
|
|
/// <param name="isPromotionRequested">True if a promotion is expected as a result of this move.</param>
|
|
/// <returns>A <see cref="MoveResult" /> describing the success or failure of the move.</returns>
|
|
internal MoveResult Move(string fromNotation, string toNotation, bool isPromotionRequested = false)
|
|
{
|
|
var from = ShogiBoardState.FromBoardNotation(fromNotation);
|
|
var to = ShogiBoardState.FromBoardNotation(toNotation);
|
|
var fromPiece = boardState[from];
|
|
if (fromPiece == null)
|
|
{
|
|
return new MoveResult(false, $"Tile [{fromNotation}] is empty. There is no piece to move.");
|
|
}
|
|
|
|
if (fromPiece.Owner != boardState.WhoseTurn)
|
|
{
|
|
return new MoveResult(false, "Not allowed to move the opponents piece");
|
|
}
|
|
|
|
var path = fromPiece.GetPathFromStartToEnd(from, to);
|
|
|
|
if (boardState.IsPathBlocked(path))
|
|
{
|
|
return new MoveResult(false, "Another piece obstructs the desired move.");
|
|
}
|
|
|
|
if (boardState[to] != null)
|
|
{
|
|
boardState.Capture(to);
|
|
}
|
|
|
|
if (isPromotionRequested && (boardState.IsWithinPromotionZone(to) || boardState.IsWithinPromotionZone(from)))
|
|
{
|
|
fromPiece.Promote();
|
|
}
|
|
|
|
boardState[to] = fromPiece;
|
|
boardState[from] = null;
|
|
|
|
boardState.RememberAsMostRecentMove(from, to);
|
|
var otherPlayer = boardState.WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
|
|
boardState.WhoseTurn = otherPlayer;
|
|
|
|
return new MoveResult(true);
|
|
}
|
|
|
|
/// Move a piece from the hand to the board ignorant if check or check-mate.
|
|
/// </summary>
|
|
/// <param name="pieceInHand"></param>
|
|
/// <param name="to">The target position expressed in board notation.</param>
|
|
/// <returns>A <see cref="MoveResult" /> describing the success or failure of the simulation.</returns>
|
|
internal MoveResult Move(WhichPiece pieceInHand, string toNotation)
|
|
{
|
|
var to = ShogiBoardState.FromBoardNotation(toNotation);
|
|
var index = boardState.ActivePlayerHand.FindIndex(p => p.WhichPiece == pieceInHand);
|
|
if (index == -1)
|
|
{
|
|
return new MoveResult(false, $"{pieceInHand} does not exist in the hand.");
|
|
}
|
|
if (boardState[to] != null)
|
|
{
|
|
return new MoveResult(false, $"Illegal move - attempting to capture while playing a piece from the hand.");
|
|
}
|
|
|
|
switch (pieceInHand)
|
|
{
|
|
case WhichPiece.Knight:
|
|
{
|
|
// Knight cannot be placed onto the farthest two ranks from the hand.
|
|
if ((boardState.WhoseTurn == WhichPlayer.Player1 && to.Y > 6)
|
|
|| (boardState.WhoseTurn == WhichPlayer.Player2 && to.Y < 2))
|
|
{
|
|
return new MoveResult(false, "Knight has no valid moves after placed.");
|
|
}
|
|
break;
|
|
}
|
|
case WhichPiece.Lance:
|
|
case WhichPiece.Pawn:
|
|
{
|
|
// Lance and Pawn cannot be placed onto the farthest rank from the hand.
|
|
if ((boardState.WhoseTurn == WhichPlayer.Player1 && to.Y == 8)
|
|
|| (boardState.WhoseTurn == WhichPlayer.Player2 && to.Y == 0))
|
|
{
|
|
return new MoveResult(false, $"{pieceInHand} has no valid moves after placed.");
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Mutate the board.
|
|
boardState[to] = boardState.ActivePlayerHand[index];
|
|
boardState.ActivePlayerHand.RemoveAt(index);
|
|
//MoveHistory.Add(move);
|
|
return new MoveResult(true);
|
|
}
|
|
|
|
/// <summary>
|
|
/// Determines if the last move put the player who moved in check.
|
|
/// </summary>
|
|
/// <remarks>
|
|
/// This strategy recognizes that a "discover check" could only occur from a subset of pieces: Rook, Bishop, Lance.
|
|
/// In this way, only those pieces need to be considered when evaluating if a move placed the moving player in check.
|
|
/// </remarks>
|
|
internal bool IsPlayerInCheckAfterMove()
|
|
{
|
|
var previousMovedPiece = boardState[boardState.PreviousMoveTo];
|
|
if (previousMovedPiece == null) throw new ArgumentNullException(nameof(previousMovedPiece), $"No piece exists at position {boardState.PreviousMoveTo}.");
|
|
var kingPosition = previousMovedPiece.Owner == WhichPlayer.Player1 ? boardState.Player1KingPosition : boardState.Player2KingPosition;
|
|
|
|
var isCheck = false;
|
|
|
|
// Get line equation from king through the now-unoccupied location.
|
|
var direction = Vector2.Subtract(kingPosition, boardState.PreviousMoveFrom);
|
|
var slope = Math.Abs(direction.Y / direction.X);
|
|
var path = ShogiBoardState.GetPathAlongDirectionFromStartToEdgeOfBoard(boardState.PreviousMoveFrom, Vector2.Normalize(direction));
|
|
var threat = boardState.QueryFirstPieceInPath(path);
|
|
if (threat == null || threat.Owner == previousMovedPiece.Owner) return false;
|
|
// If absolute slope is 45°, look for a bishop along the line.
|
|
// If absolute slope is 0° or 90°, look for a rook along the line.
|
|
// if absolute slope is 0°, look for lance along the line.
|
|
if (float.IsInfinity(slope))
|
|
{
|
|
isCheck = threat.WhichPiece switch
|
|
{
|
|
WhichPiece.Lance => !threat.IsPromoted,
|
|
WhichPiece.Rook => true,
|
|
_ => false
|
|
};
|
|
}
|
|
else if (slope == 1)
|
|
{
|
|
isCheck = threat.WhichPiece switch
|
|
{
|
|
WhichPiece.Bishop => true,
|
|
_ => false
|
|
};
|
|
}
|
|
else if (slope == 0)
|
|
{
|
|
isCheck = threat.WhichPiece switch
|
|
{
|
|
WhichPiece.Rook => true,
|
|
_ => false
|
|
};
|
|
}
|
|
|
|
return isCheck;
|
|
}
|
|
|
|
internal bool IsOpponentInCheckAfterMove() => IsOpposingKingThreatenedByPosition(boardState.PreviousMoveTo);
|
|
|
|
internal bool IsOpposingKingThreatenedByPosition(Vector2 position)
|
|
{
|
|
var previousMovedPiece = boardState[position];
|
|
if (previousMovedPiece == null) return false;
|
|
|
|
var kingPosition = previousMovedPiece.Owner == WhichPlayer.Player1 ? boardState.Player2KingPosition : boardState.Player1KingPosition;
|
|
var path = previousMovedPiece.GetPathFromStartToEnd(position, kingPosition);
|
|
var threatenedPiece = boardState.QueryFirstPieceInPath(path);
|
|
if (!path.Any() || threatenedPiece == null) return false;
|
|
|
|
return threatenedPiece.WhichPiece == WhichPiece.King;
|
|
}
|
|
|
|
internal bool IsOpponentInCheckMate()
|
|
{
|
|
// Assume checkmate, then try to disprove.
|
|
if (!boardState.InCheck.HasValue) return false;
|
|
// Get all pieces from opponent who threaten the king in question.
|
|
var opponent = boardState.WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
|
|
var tilesOccupiedByOpponent = boardState.GetTilesOccupiedBy(opponent);
|
|
var kingPosition = boardState.WhoseTurn == WhichPlayer.Player1
|
|
? boardState.Player1KingPosition
|
|
: boardState.Player2KingPosition;
|
|
var threats = tilesOccupiedByOpponent.Where(tile => PieceHasLineOfSight(tile, kingPosition)).ToList();
|
|
if (threats.Count == 1)
|
|
{
|
|
/* If there is exactly one threat it is possible to block the check.
|
|
* Foreach piece owned by whichPlayer
|
|
* if piece can intercept check, return false;
|
|
*/
|
|
var threat = threats.Single();
|
|
var pathFromThreatToKing = threat.Value.GetPathFromStartToEnd(threat.Key, kingPosition);
|
|
var tilesThatCouldBlockTheThreat = boardState.GetTilesOccupiedBy(boardState.WhoseTurn);
|
|
foreach (var threatBlockingPosition in pathFromThreatToKing)
|
|
{
|
|
var tilesThatDoBlockThreat = tilesThatCouldBlockTheThreat
|
|
.Where(tile => PieceHasLineOfSight(tile, threatBlockingPosition))
|
|
.ToList();
|
|
|
|
if (tilesThatDoBlockThreat.Any())
|
|
{
|
|
return false; // Cannot be check-mate if a piece can intercept the threat.
|
|
}
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* If no ability to block the check, maybe the king can evade check by moving.
|
|
*/
|
|
|
|
foreach (var maybeSafePosition in GetPossiblePositionsForKing(this.boardState.WhoseTurn))
|
|
{
|
|
threats = tilesOccupiedByOpponent
|
|
.Where(tile => PieceHasLineOfSight(tile, maybeSafePosition))
|
|
.ToList();
|
|
if (!threats.Any())
|
|
{
|
|
return false;
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
private IList<Vector2> GetPossiblePositionsForKing(WhichPlayer whichPlayer)
|
|
{
|
|
var kingPosition = whichPlayer == WhichPlayer.Player1
|
|
? boardState.Player1KingPosition
|
|
: boardState.Player2KingPosition;
|
|
|
|
return King.KingPaths
|
|
.Select(path => path.Direction + kingPosition)
|
|
.Where(newPosition => newPosition.IsInsideBoardBoundary())
|
|
// Where tile at position is empty, meaning the king could move there.
|
|
.Where(newPosition => boardState[newPosition] == null)
|
|
.ToList();
|
|
}
|
|
|
|
private bool PieceHasLineOfSight(BoardTile tile, Vector2 lineOfSightTarget)
|
|
{
|
|
var path = tile.Value.GetPathFromStartToEnd(tile.Key, lineOfSightTarget);
|
|
return path
|
|
.SkipLast(1)
|
|
.All(position => boardState[ShogiBoardState.ToBoardNotation(position)] == null);
|
|
}
|
|
}
|
|
}
|