var async = require('./async.js')
    , abort = require('./abort.js')
    ;
  
  // API
  module.exports = iterate;
  
  /**
   * Iterates over each job object
   *
   * @param {array|object} list - array or object (named list) to iterate over
   * @param {function} iterator - iterator to run
   * @param {object} state - current job status
   * @param {function} callback - invoked when all elements processed
   */
  function iterate(list, iterator, state, callback)
  {
    // store current index
    var key = state['keyedList'] ? state['keyedList'][state.index] : state.index;
  
    state.jobs[key] = runJob(iterator, key, list[key], function(error, output)
    {
      // don't repeat yourself
      // skip secondary callbacks
      if (!(key in state.jobs))
      {
        return;
      }
  
      // clean up jobs
      delete state.jobs[key];
  
      if (error)
      {
        // don't process rest of the results
        // stop still active jobs
        // and reset the list
        abort(state);
      }
      else
      {
        state.results[key] = output;
      }
  
      // return salvaged results
      callback(error, state.results);
    });
  }
  
  /**
   * Runs iterator over provided job element
   *
   * @param   {function} iterator - iterator to invoke
   * @param   {string|number} key - key/index of the element in the list of jobs
   * @param   {mixed} item - job description
   * @param   {function} callback - invoked after iterator is done with the job
   * @returns {function|mixed} - job abort function or something else
   */
  function runJob(iterator, key, item, callback)
  {
    var aborter;
  
    // allow shortcut if iterator expects only two arguments
    if (iterator.length == 2)
    {
      aborter = iterator(item, async(callback));
    }
    // otherwise go with full three arguments
    else
    {
      aborter = iterator(item, key, async(callback));
    }
  
    return aborter;
  }