implement tile movement

js/keyboard_input_manager.js

@@ -0,0 +1,43 @@
+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, // Up
+    39: 1, // Right
+    40: 2, // Down
+    37: 3  // Left
+  };
+
+  document.addEventListener("keydown", function (event) {
+    var modifiers = event.altKey && event.ctrlKey && event.metaKey &&
+                    event.shiftKey;
+    var mapped    = map[event.which];
+
+    if (!modifiers && mapped !== undefined) {
+      event.preventDefault();
+      self.emit("move", mapped);
+    }
+  });
+};