/// <summary>
/// Checks if a <paramref name="move"/> is legal (does not place own king under check).
/// </summary>
/// <typeparam name="TChess">Derived type. <paramref name="chess"/>
/// must be <typeparamref name="TChess"/>.</typeparam>
/// <param name="chess">A given set of <see cref="Chess"/> rules.</param>
/// <param name="move">A given <see cref="Move"/>.</param>
/// <returns><see langword="true"/> if the move is legal.
/// Otherwise, <see langword="false"/>.</returns>
/// <exception cref="ArgumentException"><paramref name="chess"/> must
/// be a <typeparamref name="TChess"/> instance.</exception>
public static bool IsLegal <TChess>(this IChess chess, Move move) where TChess : Chess
{
// Legal restraints
if (!(chess is TChess))
{
throw new ArgumentException(
message: "Chess must be a TChess instance",
paramName: nameof(chess));
}
// Create a new chess state instance...
IChess chessInstance = (TChess)Activator.CreateInstance(
typeof(TChess),
new object[] { (TChess)chess });
// Legal logic for castle
if (move.Type == MoveType.Castle)
{
return(chessInstance.IsCastlingLegal <TChess>(move));
}
// ... use it to get moved IPiece color
var color = chessInstance.Position[move.FromSquare].Color;
// Execute given move on instance...
chessInstance.Process(move, out IPiece piece);
// ... and returns wether own king is not checked
return(!chessInstance.IsChecked <TChess>(color));
}
/// <summary>
/// Checks if castling is legal or not, for a given castles <paramref name="move"/>.
/// </summary>
/// <typeparam name="TChess">Derived type. <paramref name="chess"/>
/// must be <typeparamref name="TChess"/>.</typeparam>
/// <param name="chess">A given set of <see cref="Chess"/> rules.</param>
/// <param name="move">A given <see cref="Move"/>.</param>
/// <returns><see langword="true"/> if the move is legal.
/// Otherwise, <see langword="false"/>.</returns>
private static bool IsCastlingLegal <TChess>(this IChess chess, Move move) where TChess : Chess
{
// Get the castling king
var king = chess.Position[move.FromSquare];
// Castle can't occur when king is checked
if (chess.IsChecked <TChess>(king.Color))
{
return(false);
}
// Define the type of castle
var kingSideCastle = move.ToSquare.File == Files.g;
// Determines the rook squares
var rookFromSquare = new Square(
kingSideCastle ? Files.h : Files.a,
move.FromSquare.Rank
);
var rookToSquare = new Square(
kingSideCastle ? Files.f : Files.d,
move.ToSquare.Rank
);
// Remove rook
((Chess)chess).RemovePiece(rookFromSquare, out IPiece rook);
// Get all squares between fromSquare and toSquare
var currentSquare = new Square(move.FromSquare);
var kingSquares = Helper
.InBetweenSquares(move.FromSquare, move.ToSquare)
.ToList()
.Append(move.ToSquare)
.ToList();
// Loop and test for checks
foreach (var square in kingSquares)
{
// Move king along the castling path...
if (!chess.Process(
new Move(
currentSquare,
square,
MoveType.Normal),
out IPiece p))
{
return(false);
}
// ... and check for checks.
if (chess.IsChecked <TChess>(king.Color))
{
return(false);
}
currentSquare = new Square(square);
}
// Put rook at his destination square
((Chess)chess).PlaceAt(rookToSquare, rook);
return(true);
}
