FEATURE: Add `freeze_original` option to `PostMover` (#29880)

* FEATURE: Add `freeze_original` option to `PostMover`

This option will allow the api user to specify if the original topic should be `frozen`(locked and posts not deleted neither moved)

With this option when moving topic posts your posts will be `copied` to the new topic and the original topic will be kept there.

* DEV: update tests to check raw instead of ids

* DEV: Implement `freeze_original` option for `PostMover`

update specs to use `*array` matcher

* DEV: add tests to `MovedPost` model in post mover

* DEV: Update `MovedPost` model rspec

* DEV: add back empty line to `post_mover.rb`

app/models/post_mover.rb

@@ -7,11 +7,14 @@ class PostMover
     @move_types ||= Enum.new(:new_topic, :existing_topic)
   end
 
-  def initialize(original_topic, user, post_ids, move_to_pm: false)
+  # options:
+  # freeze_original: :boolean  - if true, the original topic will be frozen but not deleted and posts will be "copied" to topic
+  def initialize(original_topic, user, post_ids, move_to_pm: false, options: {})
     @original_topic = original_topic
     @user = user
     @post_ids = post_ids
     @move_to_pm = move_to_pm
+    @options = options
   end
 
   def to_topic(id, participants: nil, chronological_order: false)
@@ -90,6 +93,14 @@ class PostMover
     @first_post_number_moved =
       posts.first.is_first_post? ? posts[1]&.post_number : posts.first.post_number
 
+    if @options[:freeze_original] # in this case we need to add the moderator post after the last copied post
+      from_posts = @original_topic.posts.where("post_number > ?", posts.last.post_number)
+
+      shift_post_numbers(from_posts) if !moving_all_posts
+
+      @first_post_number_moved = posts.last.post_number + 1
+    end
+
     move_each_post
     handle_moved_references
 
@@ -281,15 +292,22 @@ class PostMover
 
     update[:reply_to_user_id] = nil unless @move_map[post.reply_to_post_number]
 
-    post.attributes = update
+    moved_post =
-    post.save(validate: false)
+      if @options[:freeze_original]
+        post.dup
+      else
+        post
+      end
 
-    DiscourseEvent.trigger(:post_moved, post, original_topic.id)
+    moved_post.attributes = update
+    moved_post.save(validate: false)
+
+    DiscourseEvent.trigger(:post_moved, moved_post, original_topic.id)
 
     # Move any links from the post to the new topic
-    post.topic_links.update_all(topic_id: destination_topic.id)
+    moved_post.topic_links.update_all(topic_id: destination_topic.id)
 
-    post
+    moved_post
   end
 
   def move_same_topic(post)
@@ -331,6 +349,10 @@ class PostMover
     SQL
   end
 
+  def shift_post_numbers(from_posts)
+    from_posts.each { |post| post.update_columns(post_number: post.post_number + 1) }
+  end
+
   def move_incoming_emails
     DB.exec <<~SQL
       UPDATE incoming_emails ie
@@ -683,6 +705,7 @@ class PostMover
 
   def close_topic_and_schedule_deletion
     @original_topic.update_status("closed", true, @user)
+    return if @options[:freeze_original] # we only close the topic when freezing it
 
     days_to_deleting = SiteSetting.delete_merged_stub_topics_after_days
     if days_to_deleting == 0

spec/models/post_mover_spec.rb

@@ -2637,5 +2637,158 @@ RSpec.describe PostMover do
         expect(topic_1.deleted_at).not_to be_nil
       end
     end
+
+    context "with freeze_original option" do
+      fab!(:original_topic) { Fabricate(:topic) }
+      fab!(:destination_topic) { Fabricate(:topic) }
+      fab!(:op) { Fabricate(:post, topic: original_topic, raw: "op of this topic") }
+      fab!(:op_of_destination) do
+        Fabricate(:post, topic: destination_topic, raw: "op of this topic")
+      end
+      fab!(:first_post) { Fabricate(:post, topic: original_topic, raw: "first_post") }
+      fab!(:second_post) { Fabricate(:post, topic: original_topic, raw: "second_post") }
+      fab!(:third_post) { Fabricate(:post, topic: original_topic, raw: "third_post") }
+
+      it "keeps a post when moving it to a new topic" do
+        new_topic =
+          PostMover.new(
+            original_topic,
+            Discourse.system_user,
+            [first_post.id],
+            options: {
+              freeze_original: true,
+            },
+          ).to_new_topic("Hi I'm a new topic, with a copy of the old posts")
+        expect(new_topic.posts.map(&:raw)).to include(first_post.raw)
+        expect(original_topic.posts.map(&:raw)).to include(first_post.raw)
+      end
+
+      it "keeps a post when moving to an existing topic" do
+        PostMover.new(
+          original_topic,
+          Discourse.system_user,
+          [first_post.id],
+          options: {
+            freeze_original: true,
+          },
+        ).to_topic(destination_topic.id)
+        expect(destination_topic.posts.map(&:raw)).to include(first_post.raw)
+        expect(original_topic.posts.map(&:raw)).to include(first_post.raw)
+      end
+
+      it "creates a MovedPost record when moving to an existing topic" do
+        PostMover.new(
+          original_topic,
+          Discourse.system_user,
+          [first_post.id],
+          options: {
+            freeze_original: true,
+          },
+        ).to_topic(destination_topic.id)
+        expect(
+          MovedPost.exists?(
+            old_topic_id: original_topic.id,
+            new_topic_id: destination_topic.id,
+            old_post_id: first_post.id,
+          ),
+        ).to eq(true)
+      end
+
+      it "creates the moderator message in the correct position" do
+        PostMover.new(
+          original_topic,
+          Discourse.system_user,
+          [first_post.id, second_post.id],
+          options: {
+            freeze_original: true,
+          },
+        ).to_topic(destination_topic.id)
+
+        moderator_post =
+          original_topic.reload.ordered_posts.find_by(post_number: second_post.post_number + 1) # the next post
+        expect(moderator_post).to be_present
+        expect(moderator_post.post_type).to eq(Post.types[:small_action])
+        expect(moderator_post.action_code).to eq("split_topic")
+      end
+
+      it "keeps posts when moving all posts to a new topic" do
+        all_posts_from_original_topic = original_topic.ordered_posts.map(&:raw)
+
+        new_topic =
+          PostMover.new(
+            original_topic,
+            Discourse.system_user,
+            original_topic.posts.map(&:id),
+            options: {
+              freeze_original: true,
+            },
+          ).to_new_topic("Hi I'm a new topic, with a copy of the old posts")
+
+        expect(original_topic.deleted_at).to be_nil
+        expect(original_topic.closed?).to eq(true)
+
+        expect(original_topic.posts.map(&:raw)).to include(*all_posts_from_original_topic)
+        expect(new_topic.posts.map(&:raw)).to include(*all_posts_from_original_topic)
+      end
+
+      it "does not get deleted when moved all posts to topic" do
+        SiteSetting.delete_merged_stub_topics_after_days = 0
+        all_posts_from_original_topic = original_topic.posts.map(&:raw)
+
+        PostMover.new(
+          original_topic,
+          Discourse.system_user,
+          original_topic.posts.map(&:id),
+          options: {
+            freeze_original: true,
+          },
+        ).to_topic(destination_topic.id)
+
+        expect(original_topic.deleted_at).to be_nil
+        expect(original_topic.closed?).to eq(true)
+
+        expect(original_topic.posts.map(&:raw)).to include(*all_posts_from_original_topic)
+        expect(destination_topic.posts.map(&:raw)).to include(*all_posts_from_original_topic)
+      end
+
+      it "keeps all posts when moving to a new PM" do
+        moving_posts = [first_post, second_post]
+        pm =
+          PostMover.new(
+            original_topic,
+            Discourse.system_user,
+            moving_posts.map(&:id),
+            move_to_pm: true,
+            options: {
+              freeze_original: true,
+            },
+          ).to_new_topic("Hi I'm a new PM, with a copy of the old posts")
+
+        expect(original_topic.posts.map(&:raw)).to include(*moving_posts.map(&:raw))
+        expect(pm.posts.map(&:raw)).to include(*moving_posts.map(&:raw))
+      end
+
+      it "keep all posts when moving to an existing PM" do
+        pm = Fabricate(:private_message_topic)
+        pm_with_posts = Fabricate(:private_message_topic)
+        moving_posts = [
+          Fabricate(:post, topic: pm_with_posts),
+          Fabricate(:post, topic: pm_with_posts),
+        ]
+
+        PostMover.new(
+          pm_with_posts,
+          Discourse.system_user,
+          moving_posts.map(&:id),
+          move_to_pm: true,
+          options: {
+            freeze_original: true,
+          },
+        ).to_topic(pm.id)
+
+        expect(pm_with_posts.posts.map(&:raw)).to include(*moving_posts.map(&:raw))
+        expect(pm.posts.map(&:raw)).to include(*moving_posts.map(&:raw))
+      end
+    end
   end
 end