{flatten, isArray} = require "../helpers"

_concurrent = (funcs) ->
  if funcs.length is 0
    return (cb) ->
      cb "EMPTY-UNION", null
  (args, cb = ->) ->
    args = (args for i in [1..funcs.length]) unless isArray args
    if args.length isnt funcs.length
      throw new Error("Number of actual parameters doesn't match!!!")
    counter = funcs.length
    result  = null
    errors  = []
    for i in [0..counter-1]
      do (i = i) ->
        if not result?
          funcs[i] args[i], (err, data) ->
            return if result?
            counter--
            if err
              errors[i] = err
              if counter is 0
                cb errors, null
            else
              result = data
              cb null, data
    return


concurrent = (funcs...) ->
  _concurrent flatten funcs
concurrent.doc = '''
# `concurrent(aFn1, aFn2, ..., aFnk)` generates a new async function
# which takes an array of k elements and a callback `cb` as arguments,
# runs the functions cuncurrently with the elements of the array,
# respectively.
# The first function which succeeds, (err = null), calls `cb`
# with its results.
'''

module.exports = concurrent