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function KeyboardInputManager() {
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  this.events = {};
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  this.listen();
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}
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KeyboardInputManager.prototype.on = function (event, callback) {
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  if (!this.events[event]) {
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    this.events[event] = [];
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  }
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  this.events[event].push(callback);
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};
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KeyboardInputManager.prototype.emit = function (event, data) {
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  var callbacks = this.events[event];
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  if (callbacks) {
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    callbacks.forEach(function (callback) {
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      callback(data);
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    });
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  }
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};
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KeyboardInputManager.prototype.listen = function () {
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  var self = this;
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  var map = {
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    38: 0, // Up
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    39: 1, // Right
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    40: 2, // Down
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    37: 3, // Left
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    75: 0, // vim keybindings
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    76: 1,
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    74: 2,
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    72: 3,
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    87: 0, // W
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    68: 1, // D
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    83: 2, // S
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    65: 3  // A
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  };
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  document.addEventListener("keydown", function (event) {
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    var modifiers = event.altKey || event.ctrlKey || event.metaKey ||
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                    event.shiftKey;
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    var mapped    = map[event.which];
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    if (!modifiers) {
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      if (mapped !== undefined) {
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        event.preventDefault();
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        self.emit("move", mapped);
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      }
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      if (event.which === 32) self.restart.bind(self)(event);
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    }
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  });
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  var retry = document.getElementsByClassName("retry-button")[0];
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  retry.addEventListener("click", this.restart.bind(this));
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  retry.addEventListener("touchend", this.restart.bind(this));
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  // Listen to swipe events
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  var touchStartClientX, touchStartClientY;
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  var gameContainer = document.getElementsByClassName("game-container")[0];
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  gameContainer.addEventListener("touchstart", function (event) {
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    if (event.touches.length > 1) return;
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    touchStartClientX = event.touches[0].clientX;
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    touchStartClientY = event.touches[0].clientY;
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    event.preventDefault();
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  });
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  gameContainer.addEventListener("touchmove", function (event) {
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    event.preventDefault();
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  });
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  gameContainer.addEventListener("touchend", function (event) {
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    if (event.touches.length > 0) return;
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    var dx = event.changedTouches[0].clientX - touchStartClientX;
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    var absDx = Math.abs(dx);
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    var dy = event.changedTouches[0].clientY - touchStartClientY;
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    var absDy = Math.abs(dy);
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    if (Math.max(absDx, absDy) > 10) {
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      // (right : left) : (down : up)
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      self.emit("move", absDx > absDy ? (dx > 0 ? 1 : 3) : (dy > 0 ? 2 : 0));
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    }
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  });
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};
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KeyboardInputManager.prototype.restart = function (event) {
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  event.preventDefault();
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  this.emit("restart");
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};
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