ChessDotNet.Pieces.Pawn.IsValidMove C# (CSharp) Method

        public override bool IsValidMove(Move move, ChessGame game)
        {
            ChessUtilities.ThrowIfNull(move, "move");
            ChessUtilities.ThrowIfNull(game, "game");
            Position origin = move.OriginalPosition;
            Position destination = move.NewPosition;

            Piece promotion = null;
            if (move.Promotion.HasValue && ValidPromotionPieces.Contains(move.Promotion.Value))
            {
                promotion = game.MapPgnCharToPiece(char.ToUpper(move.Promotion.Value), move.Player);
            }
            PositionDistance posDelta = new PositionDistance(origin, destination);
            if ((posDelta.DistanceX != 0 || posDelta.DistanceY != 1) && (posDelta.DistanceX != 1 || posDelta.DistanceY != 1)
                        && (posDelta.DistanceX != 0 || posDelta.DistanceY != 2))
                return false;
            if (Owner == Player.White)
            {
                if (origin.Rank > destination.Rank)
                    return false;
                if (destination.Rank == 8)
                {
                    if (promotion == null)
                        return false;
                    if (promotion.Owner != Player.White)
                        return false;
                    if (!ValidPromotionPieces.Contains(promotion.GetFenCharacter()))
                        return false;
                }
            }
            if (Owner == Player.Black)
            {
                if (origin.Rank < destination.Rank)
                    return false;
                if (destination.Rank == 1)
                {
                    if (promotion == null)
                        return false;
                    if (promotion.Owner != Player.Black)
                        return false;
                    if (!ValidPromotionPieces.Contains(promotion.GetFenCharacter()))
                        return false;
                }
            }
            bool checkEnPassant = false;
            if (posDelta.DistanceY == 2)
            {
                if ((origin.Rank != 2 && Owner == Player.White)
                    || (origin.Rank != 7 && Owner == Player.Black))
                    return false;
                if (origin.Rank == 2 && game.GetPieceAt(origin.File, 3) != null)
                    return false;
                if (origin.Rank == 7 && game.GetPieceAt(origin.File, 6) != null)
                    return false;
            }
            Piece pieceAtDestination = game.GetPieceAt(destination);
            if (posDelta.DistanceX == 0 && (posDelta.DistanceY == 1 || posDelta.DistanceY == 2))
            {
                if (pieceAtDestination != null)
                    return false;
            }
            else
            {
                if (pieceAtDestination == null)
                    checkEnPassant = true;
                else if (pieceAtDestination.Owner == Owner)
                    return false;
            }
            if (checkEnPassant)
            {
                ReadOnlyCollection<DetailedMove> _moves = game.Moves;
                if (_moves.Count == 0)
                {
                    return false;
                }
                if ((origin.Rank != 5 && Owner == Player.White)
                    || (origin.Rank != 4 && Owner == Player.Black))
                    return false;
                Move latestMove = _moves[_moves.Count - 1];
                if (latestMove.Player != ChessUtilities.GetOpponentOf(Owner))
                    return false;
                if (!(game.GetPieceAt(latestMove.NewPosition) is Pawn))
                    return false;
                if (game.GetPieceAt(latestMove.NewPosition).Owner == Owner)
                    return false;
                if (Owner == Player.White)
                {
                    if (latestMove.OriginalPosition.Rank != 7 || latestMove.NewPosition.Rank != 5)
                        return false;
                }
                else // (m.Player == Players.Black)
                {
                    if (latestMove.OriginalPosition.Rank != 2 || latestMove.NewPosition.Rank != 4)
                        return false;
                }
                if (destination.File != latestMove.NewPosition.File)
                    return false;
            }
            return true;
        }