HORIZON PROJECT

/**

 * Expose `Emitter`.

 */

if (typeof module !== 'undefined') {

  module.exports = Emitter;

}

/**

 * Initialize a new `Emitter`.

 *

 * @api public

 */

function Emitter(obj) {

  if (obj) return mixin(obj);

};

/**

 * Mixin the emitter properties.

 *

 * @param {Object} obj

 * @return {Object}

 * @api private

 */

function mixin(obj) {

  for (var key in Emitter.prototype) {

    obj[key] = Emitter.prototype[key];

  }

  return obj;

}

/**

 * Listen on the given `event` with `fn`.

 *

 * @param {String} event

 * @param {Function} fn

 * @return {Emitter}

 * @api public

 */

Emitter.prototype.on =

Emitter.prototype.addEventListener = function(event, fn){

  this._callbacks = this._callbacks || {};

  (this._callbacks['$' + event] = this._callbacks['$' + event] || [])

    .push(fn);

  return this;

};

/**

 * Adds an `event` listener that will be invoked a single

 * time then automatically removed.

 *

 * @param {String} event

 * @param {Function} fn

 * @return {Emitter}

 * @api public

 */

Emitter.prototype.once = function(event, fn){

  function on() {

    this.off(event, on);

    fn.apply(this, arguments);

  }

  on.fn = fn;

  this.on(event, on);

  return this;

};

/**

 * Remove the given callback for `event` or all

 * registered callbacks.

 *

 * @param {String} event

 * @param {Function} fn

 * @return {Emitter}

 * @api public

 */

Emitter.prototype.off =

Emitter.prototype.removeListener =

Emitter.prototype.removeAllListeners =

Emitter.prototype.removeEventListener = function(event, fn){

  this._callbacks = this._callbacks || {};

  // all

  if (0 == arguments.length) {

    this._callbacks = {};

    return this;

  }

  // specific event

  var callbacks = this._callbacks['$' + event];

  if (!callbacks) return this;

  // remove all handlers

  if (1 == arguments.length) {

    delete this._callbacks['$' + event];

    return this;

  }

  // remove specific handler

  var cb;

  for (var i = 0; i < callbacks.length; i++) {

    cb = callbacks[i];

    if (cb === fn || cb.fn === fn) {

      callbacks.splice(i, 1);

      break;

    }

  }

  return this;

};

/**

 * Emit `event` with the given args.

 *

 * @param {String} event

 * @param {Mixed} ...

 * @return {Emitter}

 */

Emitter.prototype.emit = function(event){

  this._callbacks = this._callbacks || {};

  var args = [].slice.call(arguments, 1)

    , callbacks = this._callbacks['$' + event];

  if (callbacks) {

    callbacks = callbacks.slice(0);

    for (var i = 0, len = callbacks.length; i < len; ++i) {

      callbacks[i].apply(this, args);

    }

  }

  return this;

};

/**

 * Return array of callbacks for `event`.

 *

 * @param {String} event

 * @return {Array}

 * @api public

 */

Emitter.prototype.listeners = function(event){

  this._callbacks = this._callbacks || {};

  return this._callbacks['$' + event] || [];

};

/**

 * Check if this emitter has `event` handlers.

 *

 * @param {String} event

 * @return {Boolean}

 * @api public

 */

Emitter.prototype.hasListeners = function(event){

  return !! this.listeners(event).length;

};