class EventEmitter {
  constructor() {
    this.__z_e_listeners = {}
  }
  on (evt, handler, context) {
    var handlers = this.__z_e_listeners[evt]
    if (handlers === undefined) {
      handlers = []
      this.__z_e_listeners[evt] = handlers
    }
    var item = {
      handler: handler,
      context: context,
    }
    handlers.push(item)
    return item
  }

  off (evt, handler, context) {
    var handlers = this.__z_e_listeners[evt]
    if (handlers !== undefined) {
      var size = handlers.length
      for (var i = 0; i < size; i++) {
        var item = handlers[i]
        if (item.handler === handler && item.context === context) {
          handlers.splice(i, 1)
          return
        }
      }
    }
  }

  emit (type, event) {
    var hanlders = this.__z_e_listeners[type]
    if (hanlders !== undefined) {
      var size = hanlders.length
      for (var i = 0; i < size; i++) {
        var ef = hanlders[i]
        var handler = ef.handler
        var context = ef.context
        handler.apply(context, [event])
      }
    }
  }
}

module.exports = new EventEmitter()