/*
 * A simple module to replace Backbone.sync with localStorage-based persistence.
 * Models are given GUIDS, and saved into a JSON object. Simple as that.
 */

function S4() {
   return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
};

// Generate a pseudo-GUID by concatenating random hexadecimal.
function guid() {
   return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
};

// Our Store is represented by a single JS object in localStorage. Create it with a meaningful name, like the name you'd give a table.
var Store = function(name) {
  this.name = name;
  var store = localStorage.getItem(this.name);
  this.data = (store && JSON.parse(store)) || {};
};

_.extend(Store.prototype, {
  // Save the current state of the Store to localStorage.
  save: function() {
    localStorage.setItem(this.name, JSON.stringify(this.data));
  },
  // Add a model, giving it a (hopefully)-unique GUID, if it doesn't already have an id of it's own.
  create: function(model) {
    if (!model.id) model.id = model.attributes.id = guid();
    this.data[model.id] = model;
    this.save();
    return model;
  },
  // Update a model by replacing its copy in this.data.
  update: function(model) {
    this.data[model.id] = model;
    this.save();
    return model;
  },
  // Retrieve a model from this.data by id.
  find: function(model) {
    return this.data[model.id];
  },
  // Return the array of all models currently in storage.
  findAll: function() {
    return _.values(this.data);
  },
  // Delete a model from this.data, returning it.
  destroy: function(model) {
    delete this.data[model.id];
    this.save();
    return model;
  }
});

// Override Backbone.sync to use delegate to the model or collection's localStorage property, which should be an instance of Store.
Backbone.sync = function(method, model, success, error) {
  var resp;
  // var store = model.localStorage || model.collection.localStorage;
  // prioritize the collection over the model
  var store = model.localStorage || model.collection.localStorage;
  switch (method) {
    case "read":    resp = model.id ? store.find(model) : store.findAll(); break;
    case "create":  resp = store.create(model);                            break;
    case "update":  resp = store.update(model);                            break;
    case "delete":  resp = store.destroy(model);                           break;
  }
  if (resp) {
    success(resp);
  } else {
    error("Record not found");
  }
};