Make editing work, building towards drag/drop saving

common/static/coffee/src/xmodule.coffee

@@ -10,8 +10,13 @@
       return
 
     try
-      $(element).data('module', new window[moduleType](element))
-      $(document).trigger('XModule.loaded', [element])
+      module = new window[moduleType](element)
+      if $(element).hasClass('xmodule_edit')
+        $(document).trigger('XModule.loaded.edit', [element, module])
+
+      if $(element).hasClass('xmodule_display')
+        $(document).trigger('XModule.loaded.display', [element, module])
+
     catch error
       console.error "Unable to load #{moduleType}: #{error.message}" if console
 
@@ -29,3 +34,40 @@
       modules = $(selector)
 
     modules.each (idx, element) -> XModule.loadModule element
+
+class @XModule.Descriptor
+
+  callbacks: []
+
+  ###
+  Register a callback method to be called when the state of this
+  descriptor is updated. The callback will be passed the results
+  of calling the save method on this descriptor.
+  ###
+  onUpdate: (callback) ->
+    @callbacks.push(callback)
+
+  ###
+  Notify registered callbacks that the state of this descriptor has changed
+  ###
+  update: =>
+    data = @save()
+    callback(data) for callback in @callbacks
+
+  ###
+  Bind the module to an element. This may be called multiple times,
+  if the element content has changed and so the module needs to be rebound
+
+  @method: constructor
+  @param {html element} the .xmodule_edit section containing all of the descriptor content
+  ###
+  constructor: (@element) -> return
+
+  ###
+  Return the current state of the descriptor (to be written to the module store)
+
+  @method: save
+  @returns {object} An object containing children and data attributes (both optional).
+                    The contents of the attributes will be saved to the server
+  ###
+  save: -> return {}