Working on move history navigation

* Enabled "next" and "previous" buttons
* Added corresponding methods to Board
* Added Move#invert()
* Rendering variation count in MoveNodeRenderer

The added functionality does not work correctly at the moment. This is
probably caused due to missing synchronization between the state of the
board, the game and the user interface.

src/dev/kske/chess/board/Board.java

@@ -8,6 +8,8 @@ import java.util.Map;
 import java.util.Objects;
 
 import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.event.EventBus;
+import dev.kske.chess.event.MoveEvent;
 
 /**
  * Project: <strong>Chess</strong><br>
@@ -120,6 +122,32 @@ public class Board {
 		log.removeLast();
 	}
 
+	public void selectPreviousNode() {
+		MoveNode	moveNode	= log.getLast();
+		Move		move		= moveNode.move;
+
+		// Revert the move
+		move.revert(this, moveNode.capturedPiece);
+
+		// Select previous move node
+		log.selectPreviousNode();
+
+		// Dispatch move event
+		EventBus.getInstance().dispatch(new MoveEvent(move.invert(), getGameEventType(log.getActiveColor().opposite())));
+	}
+
+	public void selectNextNode(int index) {
+		log.selectNextNode(index);
+		MoveNode	moveNode	= log.getLast();
+		Move		move		= moveNode.move;
+
+		// Execute the next move
+		move.execute(this);
+
+		// Dispatch move event
+		EventBus.getInstance().dispatch(new MoveEvent(move, getGameEventType(log.getActiveColor().opposite())));
+	}
+
 	/**
 	 * Generated every legal move for one color
 	 *

src/dev/kske/chess/board/Move.java

@@ -43,6 +43,10 @@ public class Move {
 		board.set(pos, board.get(dest));
 		board.set(dest, capturedPiece);
 	}
+	
+	public Move invert() {
+		return new Move(dest, pos);
+	}
 
 	public static Move fromLAN(String move) {
 		Position	pos		= Position.fromLAN(move.substring(0, 2));

src/dev/kske/chess/game/Game.java

@@ -29,7 +29,7 @@ import dev.kske.chess.ui.OverlayComponent;
  */
 public class Game {
 
-	private Map<Color, Player>	players	= new HashMap<>();
+	private Map<Color, Player>	players	= new HashMap<>(2);
 	private Board				board;
 	private OverlayComponent	overlayComponent;
 	private BoardComponent		boardComponent;

src/dev/kske/chess/ui/GamePane.java

@@ -12,6 +12,7 @@ import javax.swing.JButton;
 import javax.swing.JComponent;
 import javax.swing.JLabel;
 import javax.swing.JList;
+import javax.swing.JOptionPane;
 import javax.swing.JPanel;
 import javax.swing.JScrollPane;
 import javax.swing.ListSelectionModel;
@@ -95,11 +96,29 @@ public class GamePane extends JComponent {
 		moveSelectionPanel.add(btnFirst);
 
 		btnPrevious = new JButton("Previous");
-		btnPrevious.setEnabled(false);
+		btnPrevious.addActionListener((evt) -> {
+			if (game != null) {
+				game.getBoard().selectPreviousNode();
+				getBoardPane().getOverlayComponent().clearArrow();
+				repaint();
+			}
+		});
 		moveSelectionPanel.add(btnPrevious);
 
 		btnNext = new JButton("Next");
-		btnNext.setEnabled(false);
+		btnNext.addActionListener((evt) -> {
+			if(game != null) {
+				int numVariations = game.getBoard().getLog().getLast().getVariations().size();
+				int index;
+				if(numVariations == 1)
+					index = 1;
+				else
+					index = Integer.parseInt(JOptionPane.showInputDialog("Enter the variation index."));
+				game.getBoard().selectNextNode(index);
+				getBoardPane().getOverlayComponent().clearArrow();
+				repaint();
+			}
+		});
 		moveSelectionPanel.add(btnNext);
 
 		btnLast = new JButton("Last");

src/dev/kske/chess/ui/MoveNodeRenderer.java

@@ -26,7 +26,10 @@ public class MoveNodeRenderer extends JLabel implements ListCellRenderer<MoveNod
 	public Component getListCellRendererComponent(JList<? extends MoveNode> list, MoveNode node, int index,
 			boolean isSelected, boolean cellHasFocus) {
 		setBorder(new EmptyBorder(5, 5, 5, 5));
-		setText(node.move.toLAN());
+		
+		int numVariations = node.hasVariations() ? node.getVariations().size() : 0; 
+		setText(String.format("%s (%d)", node.move.toLAN(), numVariations));
+		
 		setBackground(isSelected ? Color.red : Color.white);
 		setOpaque(true);
 		return this;