'use strict'
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const EventEmitter = require('events').EventEmitter
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/**
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* A CorkedEmitter is a variant of an EventEmitter where events emitted
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* wait for the appearance of the first listener of any kind. That is,
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* a CorkedEmitter will store all .emit()s it receives, to be replayed
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* later when an .on() is applied.
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* It is meant for situations where the consumers of the emitter are
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* unable to register listeners right away, and cannot afford to miss
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* any events emitted from the start.
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* Note that, whenever the first emitter (for any event) appears,
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* the emitter becomes uncorked and works as usual for ALL events, and
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* will not cache anything anymore. This is necessary to avoid
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* re-ordering emits - either everything is being buffered, or nothing.
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*/
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function CorkedEmitter () {
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const self = this
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EventEmitter.call(self)
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/**
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* An array of arguments objects (array-likes) to emit on open.
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*/
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self._outstandingEmits = []
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/**
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* Whether the normal flow of emits is restored yet.
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*/
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self._opened = false
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// When the first listener appears, we enqueue an opening.
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// It is not done immediately, so that other listeners can be
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// registered in the same critical section.
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self.once('newListener', function () {
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setImmediate(function releaseStoredEvents () {
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self._opened = true
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self._outstandingEmits.forEach(function (args) {
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self.emit.apply(self, args)
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})
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})
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})
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}
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CorkedEmitter.prototype = Object.create(EventEmitter.prototype)
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CorkedEmitter.prototype.emit = function emit (eventName) {
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if (this._opened || eventName === 'newListener') {
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EventEmitter.prototype.emit.apply(this, arguments)
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} else {
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this._outstandingEmits.push(arguments)
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}
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}
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module.exports = CorkedEmitter
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