var keys = exports.keys =
function (object) {
  return values(Object.keys(object))
}

function abortCb(cb, abort, onAbort) {
  cb(abort)
  onAbort && onAbort(abort === true ? null: abort)
  return
}

var once = exports.once =
function (value, onAbort) {
  return function (abort, cb) {
    if(abort)
      return abortCb(cb, abort, onAbort)
    if(value != null) {
      var _value = value; value = null
      cb(null, _value)
    } else
      cb(true)
  }
}

var values = exports.values = exports.readArray =
function (array, onAbort) {
  if(!array)
    return function (abort, cb) {
      if(abort) return abortCb(cb, abort, onAbort)
      return cb(true)
    }
  if(!Array.isArray(array))
    array = Object.keys(array).map(function (k) {
      return array[k]
    })
  var i = 0
  return function (abort, cb) {
    if(abort)
      return abortCb(cb, abort, onAbort)
    cb(i >= array.length || null, array[i++])
  }
}


var count = exports.count =
function (max) {
  var i = 0; max = max || Infinity
  return function (end, cb) {
    if(end) return cb && cb(end)
    if(i > max)
      return cb(true)
    cb(null, i++)
  }
}

var infinite = exports.infinite =
function (generate) {
  generate = generate || Math.random
  return function (end, cb) {
    if(end) return cb && cb(end)
    return cb(null, generate())
  }
}

//a stream that ends immediately.
var empty = exports.empty = function () {
  return function (abort, cb) {
    cb(true)
  }
}

//a stream that errors immediately.
var error = exports.error = function (err) {
  return function (abort, cb) {
    cb(err)
  }
}