FEATURE: add first post likes data serializer (#31216)

This PR adds two attributes (`op_can_like` & `op_liked`) to
`TopicListItemSerializer`.

We've also added `serialize_topic_op_likes_data` theme modifier so that
these two attributes are only added when a theme or component needs this
data.

app/models/theme_modifier_set.rb

@@ -149,6 +149,7 @@ end
 #  custom_homepage               :boolean
 #  serialize_post_user_badges    :string           is an Array
 #  theme_setting_modifiers       :jsonb
+#  serialize_topic_op_likes_data :boolean
 #
 # Indexes
 #

app/serializers/topic_list_item_serializer.rb

@@ -10,6 +10,8 @@ class TopicListItemSerializer < ListableTopicSerializer
              :last_poster_username,
              :category_id,
              :op_like_count,
+             :op_can_like,
+             :op_liked,
              :pinned_globally,
              :liked_post_numbers,
              :featured_link,
@@ -32,6 +34,42 @@ class TopicListItemSerializer < ListableTopicSerializer
     object.first_post && object.first_post.like_count
   end
 
+  def include_op_can_like?
+    theme_modifier_helper.serialize_topic_op_likes_data
+  end
+
+  def op_can_like
+    return false if !scope.user || !object.first_post
+
+    first_post = object.first_post
+    return false if first_post.user_id == scope.user.id
+    return false unless scope.post_can_act?(first_post, :like)
+
+    first_post_liked =
+      PostAction.where(
+        user_id: scope.user.id,
+        post_id: first_post.id,
+        post_action_type_id: PostActionType.types[:like],
+      ).first
+    return scope.can_delete?(first_post_liked) if first_post_liked
+
+    true
+  end
+
+  def include_op_liked?
+    theme_modifier_helper.serialize_topic_op_likes_data
+  end
+
+  def op_liked
+    return false if !scope.user || !object.first_post
+
+    PostAction.where(
+      user_id: scope.user.id,
+      post_id: object.first_post.id,
+      post_action_type_id: PostActionType.types[:like],
+    ).exists?
+  end
+
   def last_poster_username
     posters.find { |poster| poster.user.id == object.last_post_user_id }.try(:user).try(:username)
   end
@@ -93,4 +131,10 @@ class TopicListItemSerializer < ListableTopicSerializer
   def include_allowed_user_count?
     object.private_message?
   end
+
+  private
+
+  def theme_modifier_helper
+    @theme_modifier_helper ||= ThemeModifierHelper.new(request: scope.request)
+  end
 end

db/migrate/20250205174221_add_serialize_topic_op_likes_data_theme_modifier.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+class AddSerializeTopicOpLikesDataThemeModifier < ActiveRecord::Migration[7.2]
+  def change
+    add_column :theme_modifier_sets, :serialize_topic_op_likes_data, :boolean, null: true
+  end
+end

spec/serializers/topic_list_item_serializer_spec.rb

@@ -96,4 +96,58 @@ RSpec.describe TopicListItemSerializer do
       expect(json[:posters].length).to eq(1)
     end
   end
+
+  describe "correctly serializes op_likes data" do
+    let(:user) { Fabricate(:user) }
+    let(:moderator) { Fabricate(:moderator) }
+    let(:first_post) { Fabricate(:post, topic: topic, user: user) }
+
+    before { topic.update!(first_post: first_post) }
+
+    it "serializes op_can_like" do
+      allow_any_instance_of(ThemeModifierHelper).to receive(
+        :serialize_topic_op_likes_data,
+      ).and_return(true)
+      json = TopicListItemSerializer.new(topic, scope: Guardian.new(moderator), root: false).as_json
+
+      expect(json[:op_can_like]).to eq(true)
+    end
+
+    it "does not include op_can_like when theme modifier disallows" do
+      allow_any_instance_of(ThemeModifierHelper).to receive(
+        :serialize_topic_op_likes_data,
+      ).and_return(false)
+      json = TopicListItemSerializer.new(topic, scope: Guardian.new(moderator), root: false).as_json
+
+      expect(json.key?(:op_can_like)).to eq(false)
+    end
+
+    it "serializes op_liked" do
+      allow_any_instance_of(ThemeModifierHelper).to receive(
+        :serialize_topic_op_likes_data,
+      ).and_return(true)
+      PostAction.create!(
+        user: user,
+        post: first_post,
+        post_action_type_id: PostActionType.types[:like],
+      )
+      json = TopicListItemSerializer.new(topic, scope: Guardian.new(user), root: false).as_json
+
+      expect(json[:op_liked]).to eq(true)
+    end
+
+    it "does not include op_liked when theme modifier disallows" do
+      allow_any_instance_of(ThemeModifierHelper).to receive(
+        :serialize_topic_op_likes_data,
+      ).and_return(false)
+      PostAction.create!(
+        user: user,
+        post: first_post,
+        post_action_type_id: PostActionType.types[:like],
+      )
+      json = TopicListItemSerializer.new(topic, scope: Guardian.new(user), root: false).as_json
+
+      expect(json.key?(:op_liked)).to eq(false)
+    end
+  end
 end