Ember js Mixin Not Compiling Grouping Result

I am using Ember App Kit not ember -cli

I am getting some response from the server like [{date: '2014-01-15T16:22:16-08:00', message: 'Tidal wave occurred'}, {date: '2014-01-15T05:00:16-08:00', message: 'Tornado destroyed town'}, {date: '2014-01-13T14:22:16-08:00', message: 'Volcanic eruption, likely'}, {date: '2014-01-13T16:24:16-08:00', message: 'Ice shelf calving off completely'}, {date: '2014-01-11T11:27:26-08:00', message: 'Mother-in-law visiting'}]

And I am trying to group it by date so that the output looks like

`Today
----------
4:22 pm - Tidal wave occurred
5:00 am - Tornado destroyed town

Monday
----------
2:22 pm - Volcanic eruption, likely

This is my model app/model

`Model = DS.Model.extend

  date: DS.attr "string"
  message: DS.attr "string"


`export default Model`

This is my route --app/routes/test

Route = Ember.Route.extend 

  model: () ->
    return @store.find "my-model"

`export default Route`

This is my mixin to group by date --app/mixin/groupable-mixin.coffee

  Mixin = Ember.Mixin.create
  group: null
  ungroupedContent: null

  groupedContent: (->
    model = @
    groupedContent = Ember.A([])

    groupCallback = @get('group')
    ungroupedContent = @get('ungroupedContent')

    return groupedContent unless groupCallback
    return groupedContent unless ungroupedContent

    ungroupedContent.forEach (item) ->
      group = groupCallback.call(model, item)
      return unless groupKey = group.get('key')

      foundGroup = groupedContent.findProperty('group.key', groupKey)

      unless foundGroup
        foundGroup = groupedContent.pushObject Ember.ArrayProxy.create
          group: group,
          content: Ember.A([])

      foundGroup.get('content').pushObject(item)

    groupedContent
  ).property('group', 'ungroupedContent.@each')

  `export default Mixin`

This is my controller app/controller/test.coffee

    'import GroupMixin from "app/mixins/groupable-mixin" '

Controller = Ember.ArrayController.extend GroupMixin,
  ungroupedContentBinding: 'content' # tell Groupable where your default content is

  # the callback that will be called for every
  # item in your content array -
  # just return the same 'key' to put it in the same group
  group: (activity) ->
    Ember.Object.create
      key: moment.utc(activity.get('date')).format('YYYY-MM-DD') # using momentjs to pluck the day from the date
      description: 'some string describing this group (if you want)'
# Controller = Em.ArrayController.extend()


`export default Controller`

And this is my template-app/templates/test.hbs

{{#each groupedContent}}
  {{group.key}} - {{group.description}}

  {{#each content}}
   {{message}}
  {{/each}}
{{/each}}

However when i do grunt server I get the following response

Warning: Error compiling tmp/javascript/app/mixins/groupable-mixin.js Used --force, continuing.

And when I do grunt server --force I see the following

Ho wo resolve this .Am i using mixin correctly.Am i importing the mixin correctly in controller?