document.addEventListener("DOMContentLoaded", function () {
  window.requestAnimationFrame(function () {
    var manager = new GameManager(4, KeyboardInputManager, HTMLActuator);
  });
});


function GameManager(size, InputManager, Actuator) {
  this.size         = size; 
  this.inputManager = new InputManager;
  this.actuator     = new Actuator;

  this.startTiles   = 2;

  this.inputManager.on("move", this.move.bind(this));
  this.inputManager.on("restart", this.restart.bind(this));

  this.setup();
}

GameManager.prototype.restart = function () {
  this.actuator.restart();
  this.setup();
};

GameManager.prototype.setup = function () {
  this.grid         = new Grid(this.size);

  this.score        = 0;
  this.over         = false;
  this.won          = false;

  this.addStartTiles();

  this.actuate();
};

GameManager.prototype.addStartTiles = function () {
  for (var i = 0; i < this.startTiles; i++) {
    this.addRandomTile();
  }
};

GameManager.prototype.addRandomTile = function () {
  if (this.grid.cellsAvailable()) {
    var value = Math.random() < 0.9 ? 2 : 4;
    var tile = new Tile(this.grid.randomAvailableCell(), value);

    this.grid.insertTile(tile);
  }
};

GameManager.prototype.actuate = function () {
  this.actuator.actuate(this.grid, {
    score: this.score,
    over:  this.over,
    won:   this.won
  });
};

GameManager.prototype.prepareTiles = function () {
  this.grid.eachCell(function (x, y, tile) {
    if (tile) {
      tile.mergedFrom = null;
      tile.savePosition();
    }
  });
};

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);
};

GameManager.prototype.move = function (direction) {

  var self = this;

  if (this.over || this.won) return; 

  var cell, tile;

  var vector     = this.getVector(direction);
  var traversals = this.buildTraversals(vector);
  var moved      = false;

  this.prepareTiles();

  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);

        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);

          tile.updatePosition(positions.next);

          self.score += merged.value;

          if (merged.value === 2048) self.won = true;
        } else {
          self.moveTile(tile, positions.farthest);
        }

        if (!self.positionsEqual(cell, tile)) {
          moved = true; 
        }
      }
    });
  });

  if (moved) {
    this.addRandomTile();

    if (!this.movesAvailable()) {
      this.over = true; 
    }

    this.actuate();
  }
};

GameManager.prototype.getVector = function (direction) {

  var map = {
    0: { x: 0,  y: -1 }, 
    1: { x: 1,  y: 0 },  
    2: { x: 0,  y: 1 },  
    3: { x: -1, y: 0 }   
  };

  return map[direction];
};

GameManager.prototype.buildTraversals = function (vector) {
  var traversals = { x: [], y: [] };

  for (var pos = 0; pos < this.size; pos++) {
    traversals.x.push(pos);
    traversals.y.push(pos);
  }

  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;

  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 
  };
};

GameManager.prototype.movesAvailable = function () {
  return this.grid.cellsAvailable() || this.tileMatchesAvailable();
};

GameManager.prototype.tileMatchesAvailable = function () {
  var self = this;

  var tile;

  for (var x = 0; x < this.size; x++) {
    for (var y = 0; y < this.size; 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) {
          }

          if (other && other.value === tile.value) {
            return true; 
          }
        }
      }
    }
  }

  return false;
};

GameManager.prototype.positionsEqual = function (first, second) {
  return first.x === second.x && first.y === second.y;
};



function Grid(size) {
  this.size = size;

  this.cells = [];

  this.build();
}

Grid.prototype.build = function () {
  for (var x = 0; x < this.size; x++) {
    var row = this.cells[x] = [];

    for (var y = 0; y < this.size; y++) {
      row.push(null);
    }
  }
};

Grid.prototype.randomAvailableCell = function () {
  var cells = this.availableCells();

  if (cells.length) {
    return cells[Math.floor(Math.random() * cells.length)];
  }
};

Grid.prototype.availableCells = function () {
  var cells = [];

  this.eachCell(function (x, y, tile) {
    if (!tile) {
      cells.push({ x: x, y: y });
    }
  });

  return cells;
};

Grid.prototype.eachCell = function (callback) {
  for (var x = 0; x < this.size; x++) {
    for (var y = 0; y < this.size; y++) {
      callback(x, y, this.cells[x][y]);
    }
  }
};

Grid.prototype.cellsAvailable = function () {
  return !!this.availableCells().length;
};

Grid.prototype.cellAvailable = function (cell) {
  return !this.cellOccupied(cell);
};

Grid.prototype.cellOccupied = function (cell) {
  return !!this.cellContent(cell);
};

Grid.prototype.cellContent = function (cell) {
  if (this.withinBounds(cell)) {
    return this.cells[cell.x][cell.y];
  } else {
    return null;
  }
};

Grid.prototype.insertTile = function (tile) {
  this.cells[tile.x][tile.y] = tile;
};

Grid.prototype.removeTile = function (tile) {
  this.cells[tile.x][tile.y] = null;
};

Grid.prototype.withinBounds = function (position) {
  return position.x >= 0 && position.x < this.size &&
         position.y >= 0 && position.y < this.size;
};


function HTMLActuator() {
  this.tileContainer    = document.getElementsByClassName("tile-container")[0];
  this.scoreContainer   = document.getElementsByClassName("score-container")[0];
  this.messageContainer = document.getElementsByClassName("game-message")[0];

  this.score = 0;
}

HTMLActuator.prototype.actuate = function (grid, metadata) {
  var self = this;

  window.requestAnimationFrame(function () {
    self.clearContainer(self.tileContainer);

    grid.cells.forEach(function (column) {
      column.forEach(function (cell) {
        if (cell) {
          self.addTile(cell);
        }
      });
    });

    self.updateScore(metadata.score);

    if (metadata.over) self.message(false); 
    if (metadata.won) self.message(true); 
  });
};

HTMLActuator.prototype.restart = function () {
  this.clearMessage();
};

HTMLActuator.prototype.clearContainer = function (container) {
  while (container.firstChild) {
    container.removeChild(container.firstChild);
  }
};

HTMLActuator.prototype.addTile = function (tile) {
  var self = this;

  var element   = document.createElement("div");
  var position  = tile.previousPosition || { x: tile.x, y: tile.y };
  positionClass = this.positionClass(position);

  var classes = ["tile", "tile-" + tile.value, positionClass];
  this.applyClasses(element, classes);

  element.textContent = tile.value;

  if (tile.previousPosition) {
    window.requestAnimationFrame(function () {
      classes[2] = self.positionClass({ x: tile.x, y: tile.y });
      self.applyClasses(element, classes); 
    });
  } else if (tile.mergedFrom) {
    classes.push("tile-merged");
    this.applyClasses(element, classes);

    tile.mergedFrom.forEach(function (merged) {
      self.addTile(merged);
    });
  } else {
    classes.push("tile-new");
    this.applyClasses(element, classes);
  }

  this.tileContainer.appendChild(element);
};

HTMLActuator.prototype.applyClasses = function (element, classes) {
  element.setAttribute("class", classes.join(" "));
};

HTMLActuator.prototype.normalizePosition = function (position) {
  return { x: position.x + 1, y: position.y + 1 };
};

HTMLActuator.prototype.positionClass = function (position) {
  position = this.normalizePosition(position);
  return "tile-position-" + position.x + "-" + position.y;
};

HTMLActuator.prototype.updateScore = function (score) {
  this.clearContainer(this.scoreContainer);

  var difference = score - this.score;
  this.score = score;

  this.scoreContainer.textContent = this.score;

  if (difference > 0) {
    var addition = document.createElement("div");
    addition.classList.add("score-addition");
    addition.textContent = "+" + difference;

    this.scoreContainer.appendChild(addition);
  }
};

HTMLActuator.prototype.message = function (won) {
  var type    = won ? "game-won" : "game-over";
  var message = won ? "You win!" : "Game over!"

  this.messageContainer.classList.add(type);
  this.messageContainer.getElementsByTagName("p")[0].textContent = message;
};

HTMLActuator.prototype.clearMessage = function () {
  this.messageContainer.classList.remove("game-won", "game-over");
};

function KeyboardInputManager() {
  this.events = {};

  this.listen();
}

KeyboardInputManager.prototype.on = function (event, callback) {
  if (!this.events[event]) {
    this.events[event] = [];
  }
  this.events[event].push(callback);
};

KeyboardInputManager.prototype.emit = function (event, data) {
  var callbacks = this.events[event];
  if (callbacks) {
    callbacks.forEach(function (callback) {
      callback(data);
    });
  }
};

KeyboardInputManager.prototype.listen = function () {
  var self = this;

  var map = {
    38: 0, 
    39: 1, 
    40: 2, 
    37: 3, 
    75: 0,
    76: 1,
    74: 2,
    72: 3
  };

  document.addEventListener("keydown", function (event) {
    var modifiers = event.altKey || event.ctrlKey || event.metaKey ||
                    event.shiftKey;
    var mapped    = map[event.which];

    if (!modifiers) {
      if (mapped !== undefined) {
        event.preventDefault();
        self.emit("move", mapped);
      }

      if (event.which === 32) self.restart.bind(self)(event);
    }
  });

  var retry = document.getElementsByClassName("retry-button")[0];
  retry.addEventListener("click", this.restart.bind(this));

  var gestures = [Hammer.DIRECTION_UP, Hammer.DIRECTION_RIGHT,
                  Hammer.DIRECTION_DOWN, Hammer.DIRECTION_LEFT];

  var gameContainer = document.getElementsByClassName("game-container")[0];
  var handler       = Hammer(gameContainer, {
    drag_block_horizontal: true,
    drag_block_vertical: true
  });
  
  handler.on("swipe", function (event) {
    event.gesture.preventDefault();
    mapped = gestures.indexOf(event.gesture.direction);

    if (mapped !== -1) self.emit("move", mapped);
  });
};

KeyboardInputManager.prototype.restart = function (event) {
  event.preventDefault();
  this.emit("restart");
};





function Tile(position, value) {
  this.x                = position.x;
  this.y                = position.y;
  this.value            = value || 2;

  this.previousPosition = null;
  this.mergedFrom       = null;
}

Tile.prototype.savePosition = function () {
  this.previousPosition = { x: this.x, y: this.y };
};

Tile.prototype.updatePosition = function (position) {
  this.x = position.x;
  this.y = position.y;
};