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235
Shogi.Domain/ValueObjects/ShogiBoard.cs
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235
Shogi.Domain/ValueObjects/ShogiBoard.cs
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using System.Text;
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namespace Shogi.Domain.ValueObjects;
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/// <summary>
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/// Facilitates Shogi board state transitions, cognisant of Shogi rules.
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/// The board is always from Player1's perspective.
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/// [0,0] is the lower-left position, [8,8] is the higher-right position
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/// </summary>
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public sealed class ShogiBoard
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{
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private readonly StandardRules rules;
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public ShogiBoard(BoardState initialState)
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{
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BoardState = initialState;
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rules = new StandardRules(BoardState);
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}
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public BoardState BoardState { get; }
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/// <summary>
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/// Move a piece from a board position to another board position, potentially capturing an opponents piece. Respects all rules of the game.
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/// </summary>
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/// <remarks>
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/// The strategy involves simulating a move on a throw-away board state that can be used to
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/// validate legal vs illegal moves without having to worry about reverting board state.
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/// </remarks>
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/// <exception cref="InvalidOperationException"></exception>
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public void Move(string from, string to, bool isPromotion)
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{
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var simulationState = new BoardState(BoardState);
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var simulation = new StandardRules(simulationState);
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var moveResult = simulation.Move(from, to, isPromotion);
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if (!moveResult.Success)
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{
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throw new InvalidOperationException(moveResult.Reason);
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}
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// If already in check, assert the move that resulted in check no longer results in check.
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if (BoardState.InCheck == BoardState.WhoseTurn
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&& simulation.IsOpposingKingThreatenedByPosition(BoardState.PreviousMove.To))
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{
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throw new InvalidOperationException("Unable to move because you are still in check.");
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}
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var otherPlayer = BoardState.WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
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if (simulation.IsPlayerInCheckAfterMove())
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{
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throw new InvalidOperationException("Illegal move. This move places you in check.");
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}
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_ = rules.Move(from, to, isPromotion);
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if (rules.IsOpponentInCheckAfterMove())
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{
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BoardState.InCheck = otherPlayer;
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if (rules.IsOpponentInCheckMate())
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{
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BoardState.IsCheckmate = true;
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}
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}
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else
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{
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BoardState.InCheck = null;
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}
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BoardState.WhoseTurn = otherPlayer;
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}
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public void Move(WhichPiece pieceInHand, string to)
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{
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var index = BoardState.ActivePlayerHand.FindIndex(p => p.WhichPiece == pieceInHand);
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if (index == -1)
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{
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throw new InvalidOperationException($"{pieceInHand} does not exist in the hand.");
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}
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if (BoardState[to] != null)
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{
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throw new InvalidOperationException("Illegal placement of piece from the hand. Destination is not empty.");
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}
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var toVector = Notation.FromBoardNotation(to);
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switch (pieceInHand)
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{
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case WhichPiece.Knight:
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{
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// Knight cannot be placed onto the farthest two ranks from the hand.
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if (BoardState.WhoseTurn == WhichPlayer.Player1 && toVector.Y > 6
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|| BoardState.WhoseTurn == WhichPlayer.Player2 && toVector.Y < 2)
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{
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throw new InvalidOperationException("Illegal move. Knight has no valid moves after placement.");
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}
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break;
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}
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case WhichPiece.Lance:
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case WhichPiece.Pawn:
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{
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// Lance and Pawn cannot be placed onto the farthest rank from the hand.
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if (BoardState.WhoseTurn == WhichPlayer.Player1 && toVector.Y == 8
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|| BoardState.WhoseTurn == WhichPlayer.Player2 && toVector.Y == 0)
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{
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throw new InvalidOperationException($"Illegal move. {pieceInHand} has no valid moves after placement.");
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}
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break;
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}
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}
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var tempBoard = new BoardState(BoardState);
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var simulation = new StandardRules(tempBoard);
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var moveResult = simulation.Move(pieceInHand, to);
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if (!moveResult.Success)
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{
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throw new InvalidOperationException(moveResult.Reason);
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}
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var otherPlayer = tempBoard.WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
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if (BoardState.InCheck == BoardState.WhoseTurn)
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{
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//if (simulation.IsPlayerInCheckAfterMove(boardState.PreviousMoveTo, toVector, boardState.WhoseTurn))
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//{
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// throw new InvalidOperationException("Illegal move. You're still in check!");
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//}
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}
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var kingPosition = otherPlayer == WhichPlayer.Player1 ? tempBoard.Player1KingPosition : tempBoard.Player2KingPosition;
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//if (simulation.IsPlayerInCheckAfterMove(toVector, kingPosition, otherPlayer))
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//{
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//}
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//rules.Move(from, to, isPromotion);
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//if (rules.IsPlayerInCheckAfterMove(fromVector, toVector, otherPlayer))
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//{
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// board.InCheck = otherPlayer;
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// board.IsCheckmate = rules.EvaluateCheckmate();
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//}
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//else
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//{
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// board.InCheck = null;
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//}
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BoardState.WhoseTurn = otherPlayer;
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}
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/// <summary>
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/// Prints a ASCII representation of the board for debugging board state.
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/// </summary>
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/// <returns></returns>
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public string ToStringStateAsAscii()
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{
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var builder = new StringBuilder();
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builder.Append(" ");
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builder.Append("Player 2(.)");
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builder.AppendLine();
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for (var rank = 8; rank >= 0; rank--)
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{
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// Horizontal line
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builder.Append(" - ");
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for (var file = 0; file < 8; file++) builder.Append("- - ");
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builder.Append("- -");
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// Print Rank ruler.
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builder.AppendLine();
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builder.Append($"{rank + 1} ");
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// Print pieces.
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builder.Append(" |");
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for (var x = 0; x < 9; x++)
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{
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var piece = BoardState[x, rank];
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if (piece == null)
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{
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builder.Append(" ");
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}
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else
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{
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builder.AppendFormat("{0}", ToAscii(piece));
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}
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builder.Append('|');
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}
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builder.AppendLine();
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}
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// Horizontal line
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builder.Append(" - ");
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for (var x = 0; x < 8; x++) builder.Append("- - ");
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builder.Append("- -");
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builder.AppendLine();
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builder.Append(" ");
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builder.Append("Player 1");
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builder.AppendLine();
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builder.AppendLine();
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// Print File ruler.
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builder.Append(" ");
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builder.Append(" A B C D E F G H I ");
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return builder.ToString();
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}
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/// <summary>
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///
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/// </summary>
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/// <param name="piece"></param>
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/// <returns>
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/// A string with three characters.
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/// The first character indicates promotion status.
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/// The second character indicates piece.
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/// The third character indicates ownership.
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/// </returns>
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private static string ToAscii(Piece piece)
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{
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var builder = new StringBuilder();
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if (piece.IsPromoted) builder.Append('^');
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else builder.Append(' ');
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var name = piece.WhichPiece switch
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{
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WhichPiece.King => "K",
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WhichPiece.GoldGeneral => "G",
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WhichPiece.SilverGeneral => "S",
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WhichPiece.Bishop => "B",
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WhichPiece.Rook => "R",
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WhichPiece.Knight => "k",
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WhichPiece.Lance => "L",
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WhichPiece.Pawn => "P",
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_ => throw new ArgumentException($"Unknown value for {nameof(WhichPiece)}."),
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};
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builder.Append(name);
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if (piece.Owner == WhichPlayer.Player2) builder.Append('.');
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else builder.Append(' ');
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return builder.ToString();
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}
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}
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