Allow moves to be undone

src/js/Components.js

@@ -4,6 +4,7 @@ const saveGameKey = "connect-force-save";
 const newGameClass = "new-game";
 const saveGameClass = "save-game";
 const loadGameClass = "load-game";
+const undoClass = "undo-game";
 
 /**
  * Gets a component which represents the specified {@link game `game`}.
@@ -35,6 +36,10 @@ export function App(game)
                 {
                     game.load(JSON.parse(localStorage.getItem(saveGameKey)));
                 }
+                else if (target.classList.contains(undoClass))
+                {
+                    game.undo();
+                }
                 else
                 {
                     for (let y = 0; y < game.board.length; y++)
@@ -49,7 +54,6 @@ export function App(game)
                             {
                                 if (game.addChip(x, y))
                                 {
-                                    game.state.turnCount++;
                                     game.draw();
                                 }
                             }
@@ -141,7 +145,8 @@ export function MenuBar()
         { className: "menu-bar" },
         [Button, ["New Game", { className: newGameClass }]],
         [Button, ["Save Game", { className: saveGameClass }]],
-        [Button, ["Load Game", { className: loadGameClass }]]
+        [Button, ["Load Game", { className: loadGameClass }]],
+        [Button, ["Undo Last Move", { className: undoClass }]]
     ];
 }
 

src/js/Game.js

@@ -22,6 +22,13 @@ export class Game
      */
     static #height = 6;
 
+    /**
+     * The previous states of the game.
+     *
+     * @type {IState[]}
+     */
+    #previousStates = [];
+
     /**
      * The state of the game.
      *
@@ -140,7 +147,7 @@ export class Game
      */
     load(data)
     {
-        this.#state = data;
+        this.setState([], data);
         this.draw();
     }
 
@@ -157,10 +164,27 @@ export class Game
      */
     reset()
     {
-        this.#state = State.create(Game.#width, Game.#height);
+        this.setState([], State.create(Game.#width, Game.#height));
         this.draw();
     }
 
+    /**
+     * Reverts the last move.
+     */
+    undo()
+    {
+        this.#state = this.#previousStates.pop();
+
+        if (!this.#state)
+        {
+            this.reset();
+        }
+        else
+        {
+            this.draw();
+        }
+    }
+
     /**
      * Replaces the content of the board with the current state.
      */
@@ -171,6 +195,55 @@ export class Game
         SuiWeb.render([App, this], container);
     }
 
+    /**
+     * Sets the value located at the specified {@link path `path`} to the specified {@link value `value`}.
+     *
+     * @param  {(keyof any)[]} path
+     * The path of the value to set.
+     *
+     * @param {any} value
+     * The value to set.
+     */
+    setState(path, value)
+    {
+        this.#previousStates.push(this.#state);
+        this.#state = { ...this.#state };
+        this.#state.turnCount++;
+
+        if (path.length === 0)
+        {
+            this.#state = value;
+        }
+        else if (path.length === 1)
+        {
+            this.#state = {
+                ...this.#state,
+                [path[0]]: value
+            };
+        }
+        else
+        {
+            let target = /** @type {any} */ (this.#state);
+
+            while (path.length > 1)
+            {
+                if (Array.isArray(target[path[0]]))
+                {
+                    target[path[0]] = [...target[path[0]]];
+                }
+                else
+                {
+                    target[path[0]] = { ...target[path[0]] };
+                }
+
+                target = target[path[0]];
+                path = path.slice(1);
+            }
+
+            target[path[0]] = value;
+        }
+    }
+
     /**
      * Adds a chip to the board indicated by the {@link x `x`} and the {@link y `y`} coordinate.
      *
@@ -191,7 +264,7 @@ export class Game
             {
                 if (this.board[i][x] === "")
                 {
-                    this.board[i][x] = this.currentPlayer;
+                    this.setState(["board", i, x], this.currentPlayer);
                     return true;
                 }
             }