static IEnumerable <Move> GetCastlingMoves(Checkerboard checkerboard, Pawn king)
{
if (checkerboard.AllMoves.Any(move => move.Pawn == king) || checkerboard.CheckIfCheck(checkerboard.CurrentColorToMove))
{
yield break;
}
var rookH = checkerboard.GetPawns(king.PawnColor).FirstOrDefault(p => p.PawnType == PawnType.Rook && p.Position.Letter == 7);
if (rookH != null &&
!checkerboard.AllMoves.Any(m => m.Pawn == rookH) &&
GetPositionsInBetween(king.PawnColor, false).Any(pos => checkerboard.GetPawn(pos.Letter, pos.Digit) == null) &&
!checkerboard.GetPawns(king.PawnColor.Opposite())
.Any(p => p.GetAvailableMoves(checkerboard)
.Any(m => (m.NewPawnPos.Digit == rookH.Position.Digit - 1 && m.NewPawnPos.Letter == rookH.Position.Letter) ||
(m.NewPawnPos.Digit == rookH.Position.Digit - 2 && m.NewPawnPos.Letter == rookH.Position.Letter))))
{
yield return(checkerboard.GetCastlingMove(king, new Position(6, king.PawnColor == PawnColor.White ? 1 : 8), rookH, new Position(5, king.PawnColor == PawnColor.White ? 1 : 8)));
}
var rookA = checkerboard.GetPawns(king.PawnColor).FirstOrDefault(p => p.PawnType == PawnType.Rook && p.Position.Letter == 0);
if (rookA != null &&
!checkerboard.AllMoves.Any(m => m.Pawn == rookA) &&
GetPositionsInBetween(king.PawnColor, true).Any(pos => checkerboard.GetPawn(pos.Letter, pos.Digit) == null) &&
!checkerboard.GetPawns(king.PawnColor.Opposite())
.Any(p => p.GetAvailableMoves(checkerboard)
.Any(m => m.NewPawnPos.Digit == rookH.Position.Digit + 1 && m.NewPawnPos.Letter == rookH.Position.Letter ||
(m.NewPawnPos.Digit == rookH.Position.Digit + 2 && m.NewPawnPos.Letter == rookH.Position.Letter) ||
(m.NewPawnPos.Digit == rookH.Position.Digit + 3 && m.NewPawnPos.Letter == rookH.Position.Letter))))
{
yield return(checkerboard.GetCastlingMove(king, new Position(2, king.PawnColor == PawnColor.White ? 1 : 8), rookH, new Position(4, king.PawnColor == PawnColor.White ? 1 : 8)));
}
IEnumerable <Position> GetPositionsInBetween(PawnColor pawnColor, bool smallCastle)
{
if (pawnColor == PawnColor.White && smallCastle)
{
yield return(new Position(5, 1));
yield return(new Position(6, 1));
}
else if (pawnColor == PawnColor.White)
{
yield return(new Position(1, 1));
yield return(new Position(2, 1));
yield return(new Position(3, 1));
}
else if (smallCastle)
{
yield return(new Position(5, 8));
yield return(new Position(6, 8));
}
else
{
yield return(new Position(1, 8));
yield return(new Position(2, 8));
yield return(new Position(3, 8));
}
}
}