text: function GameManager(size, InputManager, Actuator, ScoreManager) {
    this.size         = size; // Size of the grid
    this.inputManager = new InputManager;
    this.scoreManager = new ScoreManager;
    this.actuator     = new Actuator;
  
    this.startTiles   = 2;
  
    this.inputManager.on("move", this.move.bind(this));
    this.inputManager.on("restart", this.restart.bind(this));
    this.inputManager.on("keepPlaying", this.keepPlaying.bind(this));
  
    this.setup();
  }
  
  // Restart the game
  GameManager.prototype.restart = function () {
    this.actuator.continue();
    this.setup();
  };
  
  // Keep playing after winning
  GameManager.prototype.keepPlaying = function () {
    this.keepPlaying = true;
    this.actuator.continue();
  };
  
  GameManager.prototype.isGameTerminated = function () {
    if (this.over || (this.won && !this.keepPlaying)) {
      return true;
    } else {
      return false;
    }
  };
  
  // Set up the game
  GameManager.prototype.setup = function () {
    this.grid        = new Grid(this.size);
  
    this.score       = 0;
    this.over        = false;
    this.won         = false;
    this.keepPlaying = false;
  
    // Add the initial tiles
    this.addStartTiles();
  
    // Update the actuator
    this.actuate();
  };
  
  // Set up the initial tiles to start the game with
  GameManager.prototype.addStartTiles = function () {
    for (var i = 0; i < this.startTiles; i++) {
      this.addRandomTile();
    }
  };
  
  // Adds a tile in a random position
  GameManager.prototype.addRandomTile = function () {
    if (this.grid.cellsAvailable()) {
      var value = (Math.random() < 0.5 ? 2 : (Math.random() < 0.75 ? 4 : 64) );
      var tile = new Tile(this.grid.randomAvailableCell(), value);
  
      this.grid.insertTile(tile);
    }
  };
  
  // Sends the updated grid to the actuator
  GameManager.prototype.actuate = function () {
    if (this.scoreManager.get() < this.score) {
      this.scoreManager.set(this.score);
    }
  
    this.actuator.actuate(this.grid, {
      score:      this.score,
      over:       this.over,
      won:        this.won,
      bestScore:  this.scoreManager.get(),
      terminated: this.isGameTerminated()
    });
  
  };
  
  // Save all tile positions and remove merger info
  GameManager.prototype.prepareTiles = function () {
    this.grid.eachCell(function (x, y, tile) {
      if (tile) {
        tile.mergedFrom = null;
        tile.savePosition();
      }
    });
  };
  
  // Move a tile and its representation
  GameManager.prototype.moveTile = function (tile, cell) {
    this.grid.cells[tile.x][tile.y] = null;
    this.grid.cells[cell.x][cell.y] = tile;
    tile.updatePosition(cell);
  };
  
  // Move tiles on the grid in the specified direction
  GameManager.prototype.move = function (direction) {
    // 0: up, 1: right, 2:down, 3: left
    var self = this;
  
    if (this.isGameTerminated()) return; // Don't do anything if the game's over
  
    var cell, tile;
  
    var vector     = this.getVector(direction);
    var traversals = this.buildTraversals(vector);
    var moved      = false;
  
    // Save the current tile positions and remove merger information
    this.prepareTiles();
  
    // Traverse the grid in the right direction and move tiles
    traversals.x.forEach(function (x) {
      traversals.y.forEach(function (y) {
        cell = { x: x, y: y };
        tile = self.grid.cellContent(cell);
  
        if (tile) {
          var positions = self.findFarthestPosition(cell, vector);
          var next      = self.grid.cellContent(positions.next);
  
          // Only one merger per row traversal?
          if (next && next.value === tile.value && !next.mergedFrom) {
            var merged = new Tile(positions.next, tile.value * 2);
            merged.mergedFrom = [tile, next];
  
            self.grid.insertTile(merged);
            self.grid.removeTile(tile);
  
            // Converge the two tiles' positions
            tile.updatePosition(positions.next);
  
            // Update the score
            self.score += merged.value;
  
            // The mighty 1048576 tile
            if (merged.value === 1048576) self.won = true;
          } else {
            self.moveTile(tile, positions.farthest);
          }
  
          if (!self.positionsEqual(cell, tile)) {
            moved = true; // The tile moved from its original cell!
          }
        }
      });
    });
  
    if (moved) {
      this.addRandomTile();
  
      if (!this.movesAvailable()) {
        this.over = true; // Game over!
      }
  
      this.actuate();
    }
  };
  
  // Get the vector representing the chosen direction
  GameManager.prototype.getVector = function (direction) {
    // Vectors representing tile movement
    var map = {
      0: { x: -1, y: -1 }, // up left
      1: { x: 0,  y: -1 }, // up right
      2: { x: -1, y: 0 },  // left
      3: { x: 1,  y: 0 },  // right
      4: { x: 0,  y: 1 },  // down left
      5: { x: 1,  y: 1 }   // down right
    };
  
    return map[direction];
  };
  
  // Build a list of positions to traverse in the right order
  GameManager.prototype.buildTraversals = function (vector) {
    var traversals = { x: [], y: [] };
  
    for (var pos = 0; pos < 2 * this.size - 1; pos++) {
      traversals.x.push(pos);
      traversals.y.push(pos);
    }
  
    // Always traverse from the farthest cell in the chosen direction
    if (vector.x === 1) traversals.x = traversals.x.reverse();
    if (vector.y === 1) traversals.y = traversals.y.reverse();
  
    return traversals;
  };
  
  GameManager.prototype.findFarthestPosition = function (cell, vector) {
    var previous;
  
    // Progress towards the vector direction until an obstacle is found
    do {
      previous = cell;
      cell     = { x: previous.x + vector.x, y: previous.y + vector.y };
    } while (this.grid.withinBounds(cell) &&
             this.grid.cellAvailable(cell));
  
    return {
      farthest: previous,
      next: cell // Used to check if a merge is required
    };
  };
  
  GameManager.prototype.movesAvailable = function () {
    return this.grid.cellsAvailable() || this.tileMatchesAvailable();
  };
  
  // Check for available matches between tiles (more expensive check)
  GameManager.prototype.tileMatchesAvailable = function () {
    var self = this;
  
    var tile;
  
    for (var x = 0; x < 2 * this.size - 1; x++) {
      for (var y = 0; y < 2 * this.size - 1; y++) {
        tile = this.grid.cellContent({ x: x, y: y });
  
        if (tile) {
          for (var direction = 0; direction < 4; direction++) {
            var vector = self.getVector(direction);
            var cell   = { x: x + vector.x, y: y + vector.y };
  
            var other  = self.grid.cellContent(cell);
  
            if (other && other.value === tile.value) {
              return true; // These two tiles can be merged
            }
          }
        }
      }
    }
  
    return false;
  };
  
  GameManager.prototype.positionsEqual = function (first, second) {
    return first.x === second.x && first.y === second.y;
  };
  