added revert methods for post

app/models/post.rb

@@ -788,6 +788,33 @@ class Post < ActiveRecord::Base
         )
       end
     end
+    
+    def revert_to(target)
+      base_tags = []
+      base_rating = "q"
+      base_source = nil
+      base_parent_id = nil
+      
+      versions.each do |version|
+        if version.id <= target.id
+          base_tags += version.add_tag_array
+          base_tags -= version.del_tag_array
+          base_rating = version.rating if version.rating
+          base_source = version.source if version.source
+          base_parent_id = version.parent_id if version.parent_id
+        end
+      end
+      
+      self.tag_string = base_tags.sort.join(" ")
+      self.rating = base_rating
+      self.source = base_source
+      self.parent_id = base_parent_id
+    end
+    
+    def revert_to!(target)
+      revert_to(target)
+      save!
+    end
   end
   
   include FileMethods

test/unit/post_test.rb

@@ -596,4 +596,39 @@ class PostTest < ActiveSupport::TestCase
       end
     end
   end
+
+  context "Reverting: " do
+    context "a post that has been updated" do
+      setup do
+        @post = Factory.create(:post, :rating => "q", :tag_string => "aaa")
+        @post.update_attributes(:tag_string => "aaa bbb ccc ddd")
+        @post.update_attributes(:tag_string => "bbb xxx yyy", :source => "xyz")
+        @post.update_attributes(:tag_string => "bbb mmm yyy", :source => "abc")
+      end
+    
+      context "and then reverted to an early version" do
+        setup do
+          @post.revert_to(@post.versions[1])
+        end
+        
+        should "correctly revert all fields" do
+          assert_equal("aaa bbb ccc ddd", @post.tag_string)
+          assert_equal(nil, @post.source)
+          assert_equal("q", @post.rating)
+        end
+      end
+      
+      context "and then reverted to a later version" do
+        setup do
+          @post.revert_to(@post.versions[-2])
+        end
+        
+        should "correctly revert all fields" do
+          assert_equal("bbb xxx yyy", @post.tag_string)
+          assert_equal("xyz", @post.source)
+          assert_equal("q", @post.rating)
+        end
+      end
+    end
+  end
 end