'use strict';

let debug = require('debug');

module.exports = {
  promisedNaturalAdd: promisedNaturalAdd,
  cbToPromise: cbToPromise
};

// NOTE: functions passed to `then` are named with the aim to make it
// clearer for some part audience
// Remember what a promise is, returning one from a custom function
function promisedNaturalAdd(num1, num2) {
  let d = debug('helpers:promisedNaturalAdd');
  d('Delayed Natural Add: START');
  let p = new Promise(function (resolve, reject) {
    // This executes synchronous
    d('Executing promise callback');
    if ((num1 < 0) || (num2 < 0)) {
      reject(new Error('arguments must be natural numbers'));
      return;
    }

    resolve(num1 + num2);
  }).then(
    // This two functions are called asynchronous.
    // It does NOT matter if the functions passed to
    // the Promise constructor are called synchronously or asynchronously
    function resolve(res) {
      d('This only forward the result');
      return res;
    },
    function reject(err) {
      d('This only forward the error');
      throw err;
    }
  );

  d('Delayed Natural Add: END');
  return p;
}


function cbToPromise(fn) {
  let params = Array.prototype.slice.call(arguments, 1);

  return new Promise((resolve, reject) => {
    params.push(function (err) {
      if (err) {
        reject(err);
        return;
      }

      switch (arguments.length) {
        case 1:
          resolve();
          break;
        case 2:
          resolve(arguments[1]);
          break;
        default:
          resolve(Array.prototype.slice.call(arguments, 1));
      }
    });

    fn.apply(null, params);
  });
}