'use strict';

/* global Promise */

(function(exports) {

  var datastore;

  var storeName = 'homescreen_settings';

  // Indicates the initialization state
  var readyState;

  // Event listeners
  var listeners = Object.create(null);

  function init() {
    return new Promise(function doInit(resolve, reject) {
      if (readyState === 'initialized') {
        resolve();
        return;
      }

      if (readyState === 'initializing') {
        document.addEventListener('vps-initialized', function oninitalized() {
          document.removeEventListener('vps-initialized', oninitalized);
          resolve();
        });
        return;
      }

      readyState = 'initializing';

      if (!navigator.getDataStores) {
        console.error('Home screen settings store: ' +
                      'DataStore API is not working');
        reject({ name: 'NO_DATASTORE' });
        readyState = 'failed';
        return;
      }

      navigator.getDataStores(storeName).then(function(ds) {
        if (ds.length < 1) {
          console.error('Home screen settings store: ' +
                        'Cannot get access to the Store');
          reject({ name: 'NO_ACCESS_TO_DATASTORE' });
          readyState = 'failed';
          return;
        }

        datastore = ds[0];
        datastore.addEventListener('change', onchangeHandler);
        readyState = 'initialized';
        document.dispatchEvent(new CustomEvent('vps-initialized'));
        resolve();
      }, reject);
    });
  }

  function onchangeHandler(event) {
    var operation = event.operation;
    var callbacks = listeners[operation];
    callbacks && callbacks.forEach(function iterCallback(callback) {
      datastore.get(event.id).then(function got(result) {
        callback.method.call(callback.context || this, {
          type: operation,
          target: {
            name: event.id,
            value: result
          }
        });
      });
    });
  }

  function addEventListener(type, callback) {
    var context;
    if (!(type in listeners)) {
      listeners[type] = [];
    }

    var cb = callback;
    if (typeof cb === 'object') {
      context = cb;
      cb = cb.handleEvent;
    }

    if (cb) {
      listeners[type].push({
        method: cb,
        context: context
      });
      init();
    }
  }

  function removeEventListener(type, callback) {
    if (!(type in listeners)) {
      return false;
    }

    var callbacks = listeners[type];
    var length = callbacks.length;
    for (var i = 0; i < length; i++) {

      var thisCallback = callback;
      if (typeof thisCallback === 'object') {
        thisCallback = callback.handleEvent;
      }

      if (callbacks[i] && callbacks[i].method === thisCallback) {
        callbacks.splice(i, 1);
        return true;
      }
    }

    return false;
  }

  function get(id) {
    return new Promise(function doGet(resolve, reject) {
      init().then(function onInitialized() {
        datastore.get(id).then(resolve, reject);
      }, reject);
    });
  }

  function put(id, value) {
    return new Promise(function doAdd(resolve, reject) {
      init().then(function onInitialized() {
        datastore.put(value, id).then(function success() {
          resolve(); // Setting was updated
        }, reject);
      }, reject);
    });
  }

  function setStoreName(name) {
    if (readyState === 'initializing') {
      document.addEventListener('vps-initialized',
        function deferSetStoreName() {
          document.removeEventListener('vps-initialized', deferSetStoreName);
          setStoreName(name);
        });
      return;
    }

    readyState = 'uninitialized';
    storeName = name;
  }

  exports.homescreenSettings = {
   /*
    * This method returns a setting value
    *
    * @param{String} String param that represents an identifier
    */
    get: get,

    /*
     * This method updates a setting in the datastore
     *
     * @param{String} The setting identifier
     *
     * @param{Object} The setting value
     */
     put: put,

    /*
     * Method registers the specified listener on the API
     *
     * @param{String} A string representing the event type to listen for
     *
     * @param{Function} The method that receives a notification when an event of
     *                  the specified type occurs
     *
     */
    addEventListener: addEventListener,

    /*
     * Method removes the specified listener on the API
     *
     * @param{String} A string representing the event type to listen for
     *
     * @param{Function} The method that received a notification when an event of
     *                  the specified type occurs
     *
     */
    removeEventListener: removeEventListener,

    /*
     * Method allows setting an alternative datastore. Must be called before
     * use of any other methods.
     *
     * @param{String} The name of the alternative datastore to use
     */
    setStoreName: setStoreName
  };

}(window));