backbone.sessionStorage.coffee

###*
Backbone sessionStorage Adapter
Based on https://github.com/jeromegn/Backbone.localStorage
###
(->
  
  # A simple module to replace `Backbone.sync` with *sessionStorage*-based
  # persistence. Models are given GUIDS, and saved into a JSON object. Simple
  # as that.
  
  # Hold reference to Underscore.js and Backbone.js in the closure in order
  # to make things work even if they are removed from the global namespace
  
  # Generate four random hex digits.
  S4 = ->
    (((1 + Math.random()) * 0x10000) | 0).toString(16).substring 1
  
  # Generate a pseudo-GUID by concatenating random hexadecimal.
  guid = ->
    S4() + S4() + "-" + S4() + "-" + S4() + "-" + S4() + "-" + S4() + S4() + S4()
  _ = @_
  Backbone = @Backbone
  
  # Our Store is represented by a single JS object in *sessionStorage*. Create it
  # with a meaningful name, like the name you'd give a table.
  # window.Store is deprectated, use Backbone.SessionStorage instead
  Backbone.SessionStorage = window.Store = (name) ->
    @name = name
    store = @sessionStorage().getItem(@name)
    @records = (store and store.split(",")) or []
    return

  _.extend Backbone.SessionStorage::,
    
    # Save the current state of the **Store** to *sessionStorage*.
    save: ->
      @sessionStorage().setItem @name, @records.join(",")
      return

    
    # Add a model, giving it a (hopefully)-unique GUID, if it doesn't already
    # have an id of it's own.
    create: (model) ->
      unless model.id
        model.id = guid()
        model.set model.idAttribute, model.id
      @sessionStorage().setItem @name + "-" + model.id, JSON.stringify(model)
      @records.push model.id.toString()
      @save()
      model.toJSON()

    
    # Update a model by replacing its copy in `this.data`.
    update: (model) ->
      @sessionStorage().setItem @name + "-" + model.id, JSON.stringify(model)
      @records.push model.id.toString()  unless _.include(@records, model.id.toString())
      @save()
      model.toJSON()

    
    # Retrieve a model from `this.data` by id.
    find: (model) ->
      stored = @sessionStorage().getItem(@name + "-" + model.id)
      if stored
        JSON.parse stored
      else
        null

    
    # Return the array of all models currently in storage.
    findAll: ->
      _(@records).chain().map((id) ->
        JSON.parse @sessionStorage().getItem(@name + "-" + id)
      , this).compact().value()

    
    # Delete a model from `this.data`, returning it.
    destroy: (model) ->
      @sessionStorage().removeItem @name + "-" + model.id
      @records = _.reject(@records, (record_id) ->
        record_id is model.id.toString()
      )
      @save()
      model

    sessionStorage: ->
      sessionStorage

  
  # sessionSync delegate to the model or collection's
  # *sessionStorage* property, which should be an instance of `Store`.
  # window.Store.sync and Backbone.sessionSync is deprectated, use Backbone.SessionStorage.sync instead
  Backbone.SessionStorage.sync = (method, model, options, error) ->
    store = model.sessionStorage or model.collection.sessionStorage
    
    # Backwards compatibility with Backbone <= 0.3.3
    if typeof options is "function"
      options =
        success: options
        error: error
    resp = undefined
    syncDfd = $.Deferred()
    switch method
      when "read"
        resp = (if model.id? then store.find(model) else store.findAll())
      when "create"
        resp = store.create(model)
      when "update"
        resp = store.update(model)
      when "delete"
        resp = store.destroy(model)
    if resp
      options.success resp
      syncDfd.resolve()
    else
      options.error "Record not found"  if options.error
      syncDfd.reject()
    syncDfd.promise()

  Backbone.SessionStorage.ajaxSync = Backbone.sync
  Backbone.sessionStorageEnabled = true
  Backbone.bypassSessionStorage = (obj, func, options) ->
    Backbone.sessionStorageEnabled = false
    result = func.call(obj, options or {})
    Backbone.sessionStorageEnabled = true
    result

  Backbone.getSyncMethod = (model) ->
    return Backbone.SessionStorage.sync  if (model.sessionStorage or (model.collection and model.collection.sessionStorage)) and Backbone.sessionStorageEnabled
    Backbone.SessionStorage.ajaxSync

  
  # Override 'Backbone.sync' to default to localSync,
  # the original 'Backbone.sync' is still available in 'Backbone.ajaxSync'
  Backbone.sync = (method, model, options, error) ->
    Backbone.getSyncMethod(model).apply this, [
      method
      model
      options
      error
    ]

  return
)()