Version at

README.md

@@ -140,6 +140,9 @@ post.destroy
 # undelete post
 post.undo! user
 
+# post version at
+post.version_at(yyyy, mm, dd, hh, min, sec)
+
 # disable tracking for comments within a block
 Comment.disable_tracking do
   comment.update_attributes(:title => "Test 3")

lib/mongoid/history/trackable.rb

@@ -84,6 +84,16 @@ def undo!(modifier = nil, options_or_version = nil)
         save!
       end
 
+      def version_at(year, month = nil, day = nil, hour = nil, minute = nil, second = nil)
+        at = Time.new(year, month, day, hour, minute, second)
+        duplicate = self.dup
+        history_tracks.where(:created_at.gt => at, action: "update").desc(:version).map do |h|
+          undo_attr = h.undo_attr(modifier)
+          duplicate.attributes.merge!(undo_attr)
+        end
+        duplicate
+      end
+
       def redo!(modifier = nil, options_or_version = nil)
         versions = get_versions_criteria(options_or_version).to_a
         versions.sort! { |v1, v2| v1.version <=> v2.version }

spec/integration/integration_spec.rb

@@ -619,6 +619,29 @@ class Foo < Comment
       end
     end
 
+    describe "version_at" do
+      before :each do
+        [Time.new(2014,01,01), Time.new(2014,01,02), Time.new(2014,01,03), Time.new(2014,01,04) ].each_with_index do |time, index|
+          post.history_tracks.create(created_at: time,
+                                     association_chain: [{"name"=>"Post", "id"=> post.id}],
+                                     modified: {"title"=>"Test #{index + 1}"},
+                                     original: {"title"=>"Test #{index}"},
+                                     version: index+1,
+                                     action: "update",
+                                     scope: "post",
+                                     modifier_id: user.id)
+        end
+      end
+
+      it "should get version_at" do
+        post.version_at(2013,12,31).title.should == "Test 0"
+        post.version_at(2014,01,01,12).title.should == "Test 1"
+        post.version_at(2014,01,02).title.should == "Test 2"
+        post.version_at(2014,01,03,23,59,59).title.should == "Test 3"
+      end
+
+    end
+
     describe "trackables" do
       before :each do
         comment.update_attributes(title: "Test2") # version == 2