yep

Shogi.Domain/ValueObjects/BoardState.cs

@@ -95,6 +95,92 @@ public class BoardState
 		set => this[Notation.ToBoardNotation(x, y)] = value;
 	}
 
+	/// <summary>
+	/// Move a piece from a board tile to another board tile ignorant of check or check-mate.
+	/// If a piece is captured during the move, state will change to reflect that.
+	/// If a piece should promote during the move, state will change to reflect that.
+	/// </summary>
+	/// <param name="fromNotation">The position of the piece being moved expressed in board notation.</param>
+	/// <param name="toNotation">The target position expressed in board notation.</param>
+	/// <param name="isPromotionRequested">True if a promotion is expected as a result of this move.</param>
+	/// <returns>A <see cref="MoveResult" /> describing the success or failure of the move.</returns>
+	internal MoveResult Move(string fromNotation, string toNotation, bool isPromotionRequested = false)
+	{
+		var from = Notation.FromBoardNotation(fromNotation);
+		var to = Notation.FromBoardNotation(toNotation);
+		if (this[toNotation] != null)
+		{
+			Capture(to);
+		}
+
+		var fromPiece = this[fromNotation]
+			?? throw new InvalidOperationException($"No piece exists at position {fromNotation}.");
+		if (isPromotionRequested && 
+			(IsWithinPromotionZone(to) || IsWithinPromotionZone(from)))
+		{
+			fromPiece.Promote();
+		}
+
+		this[toNotation] = fromPiece;
+		this[fromNotation] = null;
+
+		PreviousMove = new Move(from, to);
+		var otherPlayer = WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
+		WhoseTurn = otherPlayer;
+
+		return new MoveResult(true);
+	}
+
+	/// Move a piece from the hand to the board ignorant of check or check-mate.
+	/// </summary>
+	/// <param name="pieceInHand"></param>
+	/// <param name="to">The target position expressed in board notation.</param>
+	/// <returns>A <see cref="MoveResult" /> describing the success or failure of the simulation.</returns>
+	internal MoveResult Move(WhichPiece pieceInHand, string toNotation)
+	{
+		var index = ActivePlayerHand.FindIndex(p => p.WhichPiece == pieceInHand);
+		if (index == -1)
+		{
+			return new MoveResult(false, $"{pieceInHand} does not exist in the hand.");
+		}
+		if (this[toNotation] != null)
+		{
+			return new MoveResult(false, "Illegal move - attempting to capture while playing a piece from the hand.");
+		}
+
+		var to = Notation.FromBoardNotation(toNotation);
+		switch (pieceInHand)
+		{
+			case WhichPiece.Knight:
+				{
+					// Knight cannot be placed onto the farthest two ranks from the hand.
+					if (WhoseTurn == WhichPlayer.Player1 && to.Y > 6
+							|| WhoseTurn == WhichPlayer.Player2 && to.Y < 2)
+					{
+						return new MoveResult(false, "Knight has no valid moves after placed.");
+					}
+					break;
+				}
+			case WhichPiece.Lance:
+			case WhichPiece.Pawn:
+				{
+					// Lance and Pawn cannot be placed onto the farthest rank from the hand.
+					if (WhoseTurn == WhichPlayer.Player1 && to.Y == 8
+							|| WhoseTurn == WhichPlayer.Player2 && to.Y == 0)
+					{
+						return new MoveResult(false, $"{pieceInHand} has no valid moves after placed.");
+					}
+					break;
+				}
+		}
+
+		// Mutate the board.
+		this[toNotation] = ActivePlayerHand[index];
+		ActivePlayerHand.RemoveAt(index);
+		PreviousMove = new Move(pieceInHand, to);
+		return new MoveResult(true);
+	}
+
 	/// <summary>
 	/// Returns true if the given path can be traversed without colliding into a piece.
 	/// </summary>
@@ -107,8 +193,6 @@ public class BoardState
 
 	internal bool IsWithinPromotionZone(Vector2 position)
 	{
-
-
 		// TODO: Move this promotion zone logic into the StandardRules class.
 		return WhoseTurn == WhichPlayer.Player1 && position.Y > 5
 		|| WhoseTurn == WhichPlayer.Player2 && position.Y < 3;
@@ -127,9 +211,8 @@ public class BoardState
 
 	internal void Capture(Vector2 to)
 	{
-		var piece = this[to];
-		if (piece == null) throw new InvalidOperationException("Cannot capture. Piece at position does not exist.");
-
+		var piece = this[to] 
+			?? throw new InvalidOperationException("Cannot capture. Piece at position does not exist.");
 		piece.Capture(WhoseTurn);
 		ActivePlayerHand.Add(piece);
 	}