'use strict'

function id (e) { return e }
var prop = require('../util/prop')

module.exports = function asyncMap (map) {
  if(!map) return id
  map = prop(map)
  var busy = false, abortCb, aborted
  return function (read) {
    return function next (abort, cb) {
      if(aborted) return cb(aborted)
      if(abort) {
        aborted = abort
        if(!busy) read(abort, function (err) {
          //incase the source has already ended normally,
          //we should pass our own error.
          cb(abort)
        })
        else read(abort, function (err) {
          //if we are still busy, wait for the mapper to complete.
          if(busy) abortCb = cb
          else cb(abort)
        })
      }
      else
        read(null, function (end, data) {
          if(end) cb(end)
          else if(aborted) cb(aborted)
          else {
            busy = true
            map(data, function (err, data) {
              busy = false
              if(aborted) {
                cb(aborted)
                abortCb && abortCb(aborted)
              }
              else if(err) next (err, cb)
              else cb(null, data)
            })
          }
        })
    }
  }
}