'use strict';

var atoa = require('atoa');
var a = require('./a');
var once = require('./once');
var queue = require('./queue');
var errored = require('./errored');
var debounce = require('./debounce');
var CONCURRENTLY = require('./CONCURRENTLY');

module.exports = function concurrent (tasks, concurrency, done) {
  if (typeof concurrency === 'function') { done = concurrency; concurrency = CONCURRENTLY; }
  var d = once(done);
  var q = queue(worker, concurrency);
  var keys = Object.keys(tasks);
  var results = a(tasks) ? [] : {};
  q.unshift(keys);
  q.on('drain', function completed () { d(null, results); });
  function worker (key, next) {
    debounce(tasks[key], [proceed]);
    function proceed () {
      var args = atoa(arguments);
      if (errored(args, d)) { return; }
      results[key] = args.shift();
      next();
    }
  }
};