Set up the versions modal to display changes between versions when you select two of them.

app/locale/en.coffee

@@ -712,3 +712,14 @@
     files: "Files"
     top_simulators: "Top Simulators"
     source_document: "Source Document"
+    document: "Document" # note to diplomats: not a physical document, a document in MongoDB, ie a record in a database
+
+  delta:
+    added: "Added"
+    modified: "Modified"
+    deleted: "Deleted"
+    moved_index: "Moved Index"
+    text_diff: "Text Diff"
+    merge_conflict_with: "MERGE CONFLICT WITH"
+    no_changes: "No Changes"
+    

app/models/CocoModel.coffee

@@ -162,6 +162,10 @@ class CocoModel extends Backbone.Model
   getDelta: ->
     differ = deltasLib.makeJSONDiffer()
     differ.diff @_revertAttributes, @attributes
+    
+  getDeltaWith: (otherModel) ->
+    differ = deltasLib.makeJSONDiffer()
+    differ.diff @attributes, otherModel.attributes
 
   applyDelta: (delta) ->
     newAttributes = $.extend(true, {}, @attributes)
@@ -172,6 +176,10 @@ class CocoModel extends Backbone.Model
     delta = @getDelta()
     deltasLib.expandDelta(delta, @_revertAttributes, @schema())
 
+  getExpandedDeltaWith: (otherModel) ->
+    delta = @getDeltaWith(otherModel)
+    deltasLib.expandDelta(delta, @attributes, @schema())
+
   watch: (doWatch=true) ->
     $.ajax("#{@urlRoot}/#{@id}/watch", {type:'PUT', data:{on:doWatch}})
     @watching = -> doWatch

app/models/SuperModel.coffee

@@ -31,8 +31,9 @@ module.exports = class SuperModel extends Backbone.Model
 
     else
       @registerModel(model)
-      console.debug 'Registering model', model.getURL()
-      return @addModelResource(model, name, fetchOptions, value).load()
+      res = @addModelResource(model, name, fetchOptions, value)
+      if not res.isLoaded then res.load()
+      return res
 
   loadCollection: (collection, name, fetchOptions, value=1) ->
     url = collection.getURL()
@@ -52,7 +53,9 @@ module.exports = class SuperModel extends Backbone.Model
       @listenToOnce collection, 'sync', (c) ->
         console.debug 'Registering collection', url
         @registerCollection c
-      return @addModelResource(collection, name, fetchOptions, value).load()
+      res = @addModelResource(collection, name, fetchOptions, value)
+      res.load() if not (res.isLoading or res.isLoaded)
+      return res
 
   # replace or overwrite
   shouldSaveBackups: (model) -> false

app/templates/editor/delta.jade

@@ -37,10 +37,12 @@ mixin deltaPanel(delta, conflict)
   
     if delta.conflict && !conflict
       .panel-body
-        strong MERGE CONFLICT WITH
+        strong(data-i18n="delta.merge_conflict_with") MERGE CONFLICT WITH
         +deltaPanel(delta.conflict, true)
 
 .panel-group(id='delta-accordion-'+(counter))
   for delta in deltas
     +deltaPanel(delta)
+  if !deltas.length
+    alert.alert-warning(data-i18n="delta.no_changes") No changes
     

app/templates/modal/versions.jade

@@ -10,15 +10,21 @@ block modal-body-content
   if dataList
     table.table.table-condensed
       tr
+        th
         th(data-i18n="general.name") Name
         th(data-i18n="general.version") Version
         th(data-i18n="general.commit_msg") Commit Message
       for data in dataList
         tr
+          td
+            input(type="checkbox", value=data._id).select
           td
             a(href="/editor/#{page}/#{data.slug || data._id}")
               | #{data.name}
           td #{data.version.major}.#{data.version.minor}
           td #{data.commitMessage}
 
+  div.delta-container
+    div.delta-view
+
 block modal-footer-content

app/views/editor/delta.coffee

@@ -9,19 +9,63 @@ TEXTDIFF_OPTIONS =
   viewType: 1
   
 module.exports = class DeltaView extends CocoView
+  
+  ###
+  Takes a CocoModel instance (model) and displays changes since the 
+  last save (attributes vs _revertAttributes).
+  
+  * If headModel is included, will look for and display conflicts with the changes in model.
+  * If comparisonModel is included, will show deltas between model and comparisonModel instead
+    of changes within model itself.
+    
+  ###
+  
   @deltaCounter: 0
   className: "delta-view"
   template: template
 
   constructor: (options) ->
     super(options)
-    @model = options.model
-    @headModel = options.headModel
-    @expandedDeltas = @model.getExpandedDelta()
+    @expandedDeltas = []
+    @skipPaths = options.skipPaths
+    
+    for modelName in ['model', 'headModel', 'comparisonModel']
+      continue unless m = options[modelName]
+      @[modelName] = @supermodel.loadModel(m, 'document').model
+    
+    @buildDeltas() if @supermodel.finished()
+    console.log 'done constructing'
+    
+  onLoaded: ->
+    @buildDeltas()
+    super()
+    
+  buildDeltas: ->
+    if @comparisonModel
+      @expandedDeltas = @model.getExpandedDeltaWith(@comparisonModel)
+    else
+      @expandedDeltas = @model.getExpandedDelta()
+      
+    @filterExpandedDeltas()
+      
     if @headModel
       @headDeltas = @headModel.getExpandedDelta()
       @conflicts = deltasLib.getConflicts(@headDeltas, @expandedDeltas)
 
+  filterExpandedDeltas: ->
+    return unless @skipPaths
+    for path, i in @skipPaths
+      @skipPaths[i] = [path] if _.isString(path)
+    newDeltas = []
+    for delta in @expandedDeltas
+      skip = false
+      for skipPath in @skipPaths
+        if _.isEqual _.first(delta.dataPath, skipPath.length), skipPath
+          skip = true
+          break
+      newDeltas.push delta unless skip
+    @expandedDeltas = newDeltas
+
   getRenderData: ->
     c = super()
     c.deltas = @expandedDeltas

app/views/modal/versions_modal.coffee

@@ -1,6 +1,7 @@
 ModalView = require 'views/kinds/ModalView'
 template = require 'templates/modal/versions'
 tableTemplate = require 'templates/kinds/table'
+DeltaView = require 'views/editor/delta'
 
 class VersionsViewCollection extends Backbone.Collection
   url: ""
@@ -20,6 +21,9 @@ module.exports = class VersionsModalView extends ModalView
   id: ""
   url: ""
   page: ""
+  
+  events:
+    'change input.select': 'onSelectionChanged'
 
   constructor: (options, @ID, @model) ->
     super options
@@ -36,6 +40,18 @@ module.exports = class VersionsModalView extends ModalView
     @startsLoading = false
     @render()
 
+  onSelectionChanged: ->
+    rows = @$el.find 'input.select:checked'
+    deltaEl = @$el.find '.delta-view'
+    @deltaView?.destroy()
+    deltaEl.empty()
+    if rows.length isnt 2 then return 
+    
+    laterVersion = new @model(_id:$(rows[0]).val())
+    earlierVersion = new @model(_id:$(rows[1]).val())
+    @deltaView = new DeltaView({model:earlierVersion, comparisonModel:laterVersion, skipPaths:['_id','version', 'commitMessage', 'parent', 'created', 'slug', 'index']})
+    @insertSubView(@deltaView, deltaEl)
+
   getRenderData: (context={}) ->
     context = super(context)
     context.page = @page