fix #1724 for posts

app/controllers/post_versions_controller.rb

@@ -13,4 +13,12 @@ class PostVersionsController < ApplicationController
 
   def search
   end
+
+  def undo
+    @post_version = PostVersion.find(params[:id])
+    @post_version.undo!
+    respond_with(@post_version) do |format|
+      format.js
+    end
+  end
 end

app/models/post_version.rb

@@ -112,4 +112,31 @@ class PostVersion < ActiveRecord::Base
   def truncated_source
     source.gsub(/^http:\/\//, "").sub(/\/.+/, "")
   end
+
+  def undo
+    changes = diff(previous)
+    added = changes[:added_tags] - changes[:obsolete_added_tags]
+    removed = changes[:removed_tags] - changes[:obsolete_removed_tags]
+
+    added.each do |tag|
+      if tag =~ /^source:/
+        post.source = ""
+      else
+        escaped_tag = Regexp.escape(tag)
+        post.tag_string = post.tag_string.sub(/(?:\A| )#{escaped_tag}(?:\Z| )/, " ").strip
+      end
+    end
+    removed.each do |tag|
+      if tag =~ /^source:(.+)$/
+        post.source = $1
+      else
+        post.tag_string = "#{post.tag_string} #{tag}".strip
+      end
+    end
+  end
+
+  def undo!
+    undo
+    post.save!
+  end
 end

app/views/post_versions/_listing.html.erb

@@ -36,6 +36,9 @@
           <td><%= post_version_diff(post_version) %></td>
           <% if CurrentUser.is_member? %>
             <td>
+              <% if post_version.id != post_version.post.versions.first.id %>
+                <%= link_to "Undo", undo_post_version_path(post_version), :method => :put, :remote => true %> |
+              <% end %>
               <%= link_to "Revert to", revert_post_path(post_version.post_id, :version_id => post_version.id), :method => :put, :remote => true %>
             </td>
           <% end %>

app/views/post_versions/undo.js.erb

@@ -0,0 +1 @@
+location.reload();

config/routes.rb

@@ -159,6 +159,9 @@ Danbooru::Application.routes.draw do
   resources :post_appeals
   resources :post_flags
   resources :post_versions, :only => [:index, :search] do
+    member do
+      put :undo
+    end
     collection do
       get :search
     end