inflight.js

var wrappy = require('wrappy')
var reqs = Object.create(null)
var once = require('once')

module.exports = wrappy(inflight)

function inflight (key, cb) {
  if (reqs[key]) {
    reqs[key].push(cb)
    return null
  } else {
    reqs[key] = [cb]
    return makeres(key)
  }
}

function makeres (key) {
  return once(function RES () {
    var cbs = reqs[key]
    var len = cbs.length
    var args = slice(arguments)
    for (var i = 0; i < len; i++) {
      cbs[i].apply(null, args)
    }
    if (cbs.length > len) {
      // added more in the interim.
      // de-zalgo, just in case, but don't call again.
      cbs.splice(0, len)
      process.nextTick(function () {
        RES.apply(null, args)
      })
    } else {
      delete reqs[key]
    }
  })
}

function slice (args) {
  var length = args.length
  var array = []

  for (var i = 0; i < length; i++) array[i] = args[i]
  return array
}