add new model for post replacements, add undo functionality

app/models/post.rb

@@ -7,8 +7,6 @@ class Post < ActiveRecord::Base
   class RevertError < Exception ; end
   class SearchError < Exception ; end
 
-  DELETION_GRACE_PERIOD = 30.days
-
   before_validation :initialize_uploader, :on => :create
   before_validation :merge_old_changes
   before_validation :normalize_tags
@@ -51,6 +49,7 @@ class Post < ActiveRecord::Base
   has_many :approvals, :class_name => "PostApproval", :dependent => :destroy
   has_many :disapprovals, :class_name => "PostDisapproval", :dependent => :destroy
   has_many :favorites, :dependent => :destroy
+  has_many :replacements, class_name: "PostReplacement"
 
   if PostArchive.enabled?
     has_many :versions, lambda {order("post_versions.updated_at ASC")}, :class_name => "PostArchive", :dependent => :destroy
@@ -1430,50 +1429,9 @@ class Post < ActiveRecord::Base
       ModAction.log("undeleted post ##{id}")
     end
 
-    def replace!(url, replacer = CurrentUser.user)
-      # TODO for posts with notes we need to rescale the notes if the dimensions change.
-      if notes.size > 0
-        raise NotImplementedError.new("Replacing images with notes not yet supported.")
-      end
-
-      # TODO for ugoiras we need to replace the frame data.
-      if is_ugoira?
-        raise NotImplementedError.new("Replacing ugoira images not yet supported.")
-      end
-
-      # TODO images hosted on s3 need to be deleted from s3 instead of the local filesystem.
-      if Danbooru.config.use_s3_proxy?(self)
-        raise NotImplementedError.new("Replacing S3 hosted images not yet supported.")
-      end
-
-      transaction do
-        upload = Upload.create!(source: url, rating: self.rating, tag_string: self.tag_string)
-        upload.process_upload
-        upload.update(status: "completed", post_id: id)
-
-        # queue the deletion *before* updating the post so that we use the old
-        # md5/file_ext to delete the old files. if saving the post fails,
-        # this is rolled back so the job won't run.
-        Post.delay(queue: "default", run_at: Time.now + DELETION_GRACE_PERIOD).delete_files(id, file_path, large_file_path, preview_file_path)
-
-        self.md5 = upload.md5
-        self.file_ext = upload.file_ext
-        self.image_width = upload.image_width
-        self.image_height = upload.image_height
-        self.file_size = upload.file_size
-        self.source = upload.source
-        self.tag_string = upload.tag_string
-
-        comments.create!({creator: User.system, body: presenter.comment_replacement_message(replacer), do_not_bump_post: true}, without_protection: true)
-        ModAction.log(presenter.modaction_replacement_message)
-
-        save!
-      end
-
-      # point of no return: these things can't be rolled back, so we do them
-      # only after the transaction successfully commits.
-      distribute_files
-      update_iqdb_async
+    def replace!(url)
+      replacement = replacements.create(replacement_url: url)
+      replacement.process!
     end
   end
 

app/models/post_replacement.rb

@@ -0,0 +1,64 @@
+class PostReplacement < ActiveRecord::Base
+  DELETION_GRACE_PERIOD = 30.days
+
+  belongs_to :post
+  belongs_to :creator, class_name: "User"
+  before_validation :initialize_fields
+  attr_accessible :replacement_url
+
+  def initialize_fields
+    self.creator = CurrentUser.user
+    self.original_url = post.source
+  end
+
+  def undo!
+    undo_replacement = post.replacements.create(replacement_url: original_url)
+    undo_replacement.process!
+  end
+
+  def process!
+    # TODO for posts with notes we need to rescale the notes if the dimensions change.
+    if post.notes.any?
+      raise NotImplementedError.new("Replacing images with notes not yet supported.")
+    end
+
+    # TODO for ugoiras we need to replace the frame data.
+    if post.is_ugoira?
+      raise NotImplementedError.new("Replacing ugoira images not yet supported.")
+    end
+
+    # TODO images hosted on s3 need to be deleted from s3 instead of the local filesystem.
+    if Danbooru.config.use_s3_proxy?(post)
+      raise NotImplementedError.new("Replacing S3 hosted images not yet supported.")
+    end
+
+    transaction do
+      upload = Upload.create!(source: replacement_url, rating: post.rating, tag_string: post.tag_string)
+      upload.process_upload
+      upload.update(status: "completed", post_id: post.id)
+
+      # queue the deletion *before* updating the post so that we use the old
+      # md5/file_ext to delete the old files. if saving the post fails,
+      # this is rolled back so the job won't run.
+      Post.delay(queue: "default", run_at: Time.now + DELETION_GRACE_PERIOD).delete_files(post.id, post.file_path, post.large_file_path, post.preview_file_path)
+
+      post.md5 = upload.md5
+      post.file_ext = upload.file_ext
+      post.image_width = upload.image_width
+      post.image_height = upload.image_height
+      post.file_size = upload.file_size
+      post.source = upload.source
+      post.tag_string = upload.tag_string
+
+      post.comments.create!({creator: User.system, body: post.presenter.comment_replacement_message(creator), do_not_bump_post: true}, without_protection: true)
+      ModAction.log(post.presenter.modaction_replacement_message)
+
+      post.save!
+    end
+
+    # point of no return: these things can't be rolled back, so we do them
+    # only after the transaction successfully commits.
+    post.distribute_files
+    post.update_iqdb_async
+  end
+end