promisify geddy models

promisify_models.js

"use strict";

/*
Usage:

require('./promisify_models')(geddy.model);

geddy.model.allPromise()
  .then(function(result) { ... })
  .catch(function(err) { throw err; });

var user = geddy.model.User.create({});

geddy.model.User.savePromise(user)
  .then(function(result) { ... })
  .catch(function(err) { throw err; });
*/

function promisify(self, fn, instance)
{
  return function() {
    var args = Array.prototype.slice.call(arguments);
    var origCallback = null;

    if (instance) {
      self = args.shift();
    }

    if (typeof args[args.length - 1] === 'function') {
      origCallback = args.pop();
    }

    return new Promise(function(resolve, reject) {
      function callback(err, result) {
        var args = Array.prototype.slice.call(arguments);
        var err = args.shift();

        if (origCallback) origCallback.apply(null, arguments);
        if (err) {
          reject(err);
          return;
        }

        resolve.apply(null, args);
      }

      args.push(callback);
      self[fn].apply(self, args);
    });
  }
}

module.exports = function(model) {
  Object.keys(model.descriptionRegistry).forEach(function(name) {
    model[name].allPromise = promisify(model[name], 'all');
    model[name].firstPromise = promisify(model[name], 'first');
    model[name].countPromise = promisify(model[name], 'count');
    model[name].removePromise = promisify(model[name], 'remove');
    model[name].savePromise = promisify(model[name], 'save', true);
  });
};

module.exports.promisify = promisify;