/// <summary>
/// Sets up the board using the given FEN string. It's possible not all
/// pieces are present.
/// </summary>
/// <param name="fen">FEN string that describes the position
/// (https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation)</param>
private void CreateAndPlacePieces(string fen)
{
Reset();
// String starts on the back rank on the A file then moves Left->Right
// Top->Bottom
string fenString = fen.Trim();
activePlayer = FenParser.ExtractActivePlayer(fenString);
FenParser.ExtractCastlingRights(fenString, ref whiteCastlingRights, ref blackCastlingRights);
enPassantValid = FenParser.ExtractEnPassantTarget(fenString, out enPassantTarget);
FenParser.ExtractMoveCounts(fenString, ref halfMoveCount, ref fullMoveCount);
List <ChessPiece> pieces = FenParser.ExtractPieces(fenString);
foreach (ChessPiece fenPiece in pieces)
{
// For pawns and rooks and kings, deployment matters, check if they're on their home
// rank/square and if not, set it to true
if (fenPiece.Job == PieceClass.Pawn)
{
if (PawnHomeRank(fenPiece.Color) != fenPiece.Rank)
{
fenPiece.Deployed = true;
}
}
else if (fenPiece.Job == PieceClass.Rook)
{
if (((fenPiece.File.ToInt() != 1) && (fenPiece.File.ToInt() != 8)) ||
(fenPiece.Rank != RookHomeRank(fenPiece.Color)))
{
fenPiece.Deployed = true;
}
}
else if (fenPiece.Job == PieceClass.King)
{
// Both colors should be on the E file and their home rank
int homeRank = (fenPiece.Color == PieceColor.White) ? 1 : 8;
if ((fenPiece.Rank != homeRank) || (fenPiece.File != new PieceFile('e')))
{
fenPiece.Deployed = true;
}
}
if (fenPiece.Color == PieceColor.White)
{
whitePieces.Add(fenPiece);
}
else
{
blackPieces.Add(fenPiece);
}
}
}
/// <summary>
/// Move a piece from startFile:startRank -> targetFile:targetRank. Because
/// self-play is the only mode enabled right now, these moves are always
/// going to be considered valid, since they came from the chess engine
/// (and we will assume it is correct). In the future, this will likely
/// remain, and validation of the legallity for the player can be handled
/// above this call
/// </summary>
/// <param name="moveInfo">detailed move information struct</param>
public void MovePiece(ref MoveInformation moveInfo)
{
// Get the player piece at the starting location
// Piece should never be null if chess logic is sound
PieceFile startFile = moveInfo.Start.File;
int startRank = moveInfo.Start.Rank;
PieceFile targetFile = moveInfo.End.File;
int targetRank = moveInfo.End.Rank;
ChessPiece playerPiece = FindPieceAt(startFile, startRank);
if (playerPiece.Color != activePlayer)
{
// This also should not be able to happen with correct game logic
throw new InvalidOperationException();
}
// Get each side's pieces
List <ChessPiece> playerPieces = ActivePlayerPieces;
List <ChessPiece> opponentPieces = OpponentPlayerPieces;
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// PRE-MOVE CHECKS
// We have to detect castling. It does not come across the wire as O-O or O-O-O
// but rather as a regular move like e1g1. Separate the detection from the move
// of the rook
bool isCastling = IsCastling(playerPiece, targetFile);
// We also need to check for an en-passant capture if the pieces is a pawn
if (playerPiece.Job == PieceClass.Pawn)
{
moveInfo.CapturedPiece = HandleEnPassant(startFile, startRank, targetFile, targetRank);
}
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// RAW MOVE(S)
playerPiece.Move(targetFile, targetRank);
if (isCastling)
{
PerformCastle(targetFile, ref moveInfo); // Also move the rook if needed
}
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// POST-MOVE CHECKS/UPDATES
// For normal captures, just do a quick iteration of the opponent pieces
// there are only 16 of these total in normal chess
foreach (ChessPiece enemyPiece in opponentPieces)
{
if ((enemyPiece.Rank == targetRank) && // Enemy piece is located in
(enemyPiece.File == targetFile) && // the square we just moved to
!enemyPiece.Captured) // and it's not already captured
{
enemyPiece.Captured = true; // Stop drawing it (capture)
moveInfo.CapturedPiece = enemyPiece; // Record the capture
break; // exit the search loop
}
}
// save the last capture state for external callers
lastMoveWasCapture = moveInfo.IsCapture;
Moves.Add(moveInfo);
// Update our FEN
currentFEN = FenParser.ApplyMoveToFEN(currentFEN, moveInfo.ToString());
enPassantValid = FenParser.ExtractEnPassantTarget(currentFEN, out enPassantTarget);
FenParser.ExtractCastlingRights(CurrentFEN, ref whiteCastlingRights, ref blackCastlingRights);
FenParser.ExtractMoveCounts(CurrentFEN, ref halfMoveCount, ref fullMoveCount);
// Flip players - easy to just do here rather than parse the FEN again
activePlayer = OppositeColor(activePlayer);
}