add twitter sharing to game over screen

js/html_actuator.js

@@ -2,6 +2,7 @@ function HTMLActuator() {
   this.tileContainer    = document.getElementsByClassName("tile-container")[0];
   this.scoreContainer   = document.getElementsByClassName("score-container")[0];
   this.messageContainer = document.getElementsByClassName("game-message")[0];
+  this.sharingContainer = document.getElementsByClassName("score-sharing")[0];
 
   this.score = 0;
 }
@@ -28,6 +29,7 @@ HTMLActuator.prototype.actuate = function (grid, metadata) {
 };
 
 HTMLActuator.prototype.restart = function () {
+  if (ga) ga("send", "event", "game", "restart");
   this.clearMessage();
 };
 
@@ -98,8 +100,26 @@ HTMLActuator.prototype.message = function (won) {
 
   this.messageContainer.classList.add(type);
   this.messageContainer.getElementsByTagName("p")[0].textContent = message;
+
+  this.clearContainer(this.sharingContainer);
+  this.sharingContainer.appendChild(this.scoreTweetButton());
+  twttr.widgets.load();
 };
 
 HTMLActuator.prototype.clearMessage = function () {
   this.messageContainer.classList.remove("game-won", "game-over");
 };
+
+HTMLActuator.prototype.scoreTweetButton = function () {
+  var tweet = document.createElement("a");
+  tweet.classList.add("twitter-share-button");
+  tweet.setAttribute("href", "https://twitter.com/share");
+  tweet.setAttribute("data-via", "gabrielecirulli");
+  tweet.textContent = "Tweet";
+
+  var text = "I scored " + this.score + " points at 2048, a game where you " +
+             "join numbers to score high!";
+  tweet.setAttribute("data-text", text);
+
+  return tweet;
+};