add move preconditions

app/src/main/java/chess/io/Command.java

@@ -3,5 +3,17 @@ package chess.io;
 import chess.model.Game;
 
 public abstract class Command {
+
+	public enum CommandResult {
+		/** The command was successfull. Should update display and switch player turn. */
+		Moved,
+		/** The command was successfull. Should not update anything */
+		NotMoved,
+		/** The command was successfull. Should only update display */
+		ActionNeeded,
+		/** The command was not successfull */
+		NotAllowed;
+	}
+
 	public abstract CommandResult execute(Game game, OutputSystem outputSystem);
 }

app/src/main/java/chess/io/CommandExecutor.java

@@ -1,6 +1,6 @@
 package chess.io;
 
-import chess.io.commands.MoveCommand;
+import chess.io.Command.CommandResult;
 import chess.model.Game;
 import chess.model.Game.GameStatus;
 
@@ -28,21 +28,21 @@ public class CommandExecutor {
 	}
 
 	private void processResult(Command command, CommandResult result) {
-		if (result != CommandResult.Moved)
-			return;
-
-		if (command instanceof MoveCommand move) {
-			boolean needsPromote = this.game.pawnShouldBePromoted();
-			if (needsPromote)
-				this.outputSystem.promotePawn(move.getMove().getFinish());
-			
-			if (checkGameStatus())
+		switch (result) {
+			case NotAllowed:
+			case NotMoved:
 				return;
 
-			if(!needsPromote)
+			case ActionNeeded:
+				this.outputSystem.updateDisplay();
+				return;
+
+			case Moved:
+				if (checkGameStatus())
+					return;
 				switchPlayerTurn();
-		} else if (command instanceof PlayerCommand) {
-			switchPlayerTurn();
+				this.outputSystem.updateDisplay();
+				return;
 		}
 	}
 

app/src/main/java/chess/io/CommandResult.java

@@ -1,5 +0,0 @@
-package chess.io;
-
-public enum CommandResult {
-	Moved, NotMoved, NotAllowed;
-}

app/src/main/java/chess/io/OutputSystem.java

@@ -20,4 +20,6 @@ public interface OutputSystem {
 	void gameStarted();
 
 	void promotePawn(Coordinate pieceCoords);
+
+	void updateDisplay();
 }

app/src/main/java/chess/io/commands/CastlingCommand.java

@@ -1,14 +1,17 @@
 package chess.io.commands;
 
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.io.PlayerCommand;
 import chess.model.Game;
 
-public class CastlingCommand extends PlayerCommand{
+public class CastlingCommand extends PlayerCommand {
 
 	@Override
 	public CommandResult execute(Game game, OutputSystem outputSystem) {
+		// we must promote the pending pawn before
+		if (game.pawnShouldBePromoted())
+			return CommandResult.NotAllowed;
+
 		return CommandResult.NotAllowed;
 	}
 

app/src/main/java/chess/io/commands/GetAllowedMovesCommand.java

@@ -4,7 +4,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 import chess.io.Command;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.model.ChessBoard;
 import chess.model.Coordinate;

app/src/main/java/chess/io/commands/GetPieceAtCommand.java

@@ -1,7 +1,6 @@
 package chess.io.commands;
 
 import chess.io.Command;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.model.Coordinate;
 import chess.model.Game;

app/src/main/java/chess/io/commands/GrandCastlingCommand.java

@@ -1,6 +1,5 @@
 package chess.io.commands;
 
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.io.PlayerCommand;
 import chess.model.Game;
@@ -9,6 +8,10 @@ public class GrandCastlingCommand extends PlayerCommand {
 
 	@Override
 	public CommandResult execute(Game game, OutputSystem outputSystem) {
+		// we must promote the pending pawn before
+		if (game.pawnShouldBePromoted())
+			return CommandResult.NotAllowed;
+
 		return CommandResult.NotAllowed;
 	}
 

app/src/main/java/chess/io/commands/MoveCommand.java

@@ -1,9 +1,9 @@
 package chess.io.commands;
 
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.io.PlayerCommand;
 import chess.model.ChessBoard;
+import chess.model.Coordinate;
 import chess.model.Game;
 import chess.model.Move;
 import chess.model.Piece;
@@ -50,6 +50,9 @@ public class MoveCommand extends PlayerCommand {
 			return CommandResult.NotAllowed;
 		}
 
+		if (shouldPromote(game, outputSystem)) 
+			return CommandResult.ActionNeeded;
+
 		return CommandResult.Moved;
 	}
 
@@ -60,4 +63,14 @@ public class MoveCommand extends PlayerCommand {
 		board.undoMove(move, deadPiece);
 	}
 
+	private boolean shouldPromote(Game game, OutputSystem outputSystem) {
+		Coordinate pawnPos = game.pawnPromotePosition();
+
+		if (pawnPos == null)
+			return false;
+
+		outputSystem.promotePawn(pawnPos);
+		return true;
+	}
+
 }

app/src/main/java/chess/io/commands/NewGameCommand.java

@@ -1,7 +1,6 @@
 package chess.io.commands;
 
 import chess.io.Command;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.model.ChessBoard;
 import chess.model.Color;

app/src/main/java/chess/io/commands/PromoteCommand.java

@@ -1,6 +1,5 @@
 package chess.io.commands;
 
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.io.PlayerCommand;
 import chess.model.ChessBoard;

app/src/main/java/chess/io/commands/SurrenderCommand.java

@@ -1,7 +1,6 @@
 package chess.io.commands;
 
 import chess.io.Command;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.model.Color;
 import chess.model.Game;

app/src/main/java/chess/io/commands/UndoCommand.java

@@ -1,7 +1,6 @@
 package chess.io.commands;
 
 import chess.io.Command;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.model.Game;
 

app/src/main/java/chess/simplerender/Window.java

@@ -13,8 +13,8 @@ import javax.swing.JPanel;
 import javax.swing.SwingUtilities;
 
 import chess.io.Command;
+import chess.io.Command.CommandResult;
 import chess.io.CommandExecutor;
-import chess.io.CommandResult;
 import chess.io.OutputSystem;
 import chess.io.commands.GetAllowedMovesCommand;
 import chess.io.commands.GetPieceAtCommand;
@@ -44,11 +44,7 @@ public class Window extends JFrame implements OutputSystem {
 	}
 
 	private CommandResult sendCommand(Command command) {
-		CommandResult result = this.commandExecutor.executeCommand(command);
-		if (result == CommandResult.Moved) {
-			updateBoard();
-		}
-		return result;
+		return this.commandExecutor.executeCommand(command);
 	}
 
 	private Color getCellColor(int x, int y) {
@@ -241,4 +237,9 @@ public class Window extends JFrame implements OutputSystem {
 		});
 	}
 
+	@Override
+	public void updateDisplay() {
+		updateBoard();
+	}
+
 }