Add timeline of public posts about a trending link to REST API

app/controllers/api/v1/timelines/link_controller.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+class Api::V1::Timelines::LinkController < Api::BaseController
+  before_action :set_preview_card
+  before_action :set_statuses
+
+  after_action :insert_pagination_headers, unless: -> { @statuses.empty? }
+
+  def show
+    cache_if_unauthenticated!
+    render json: @statuses, each_serializer: REST::StatusSerializer, relationships: StatusRelationshipsPresenter.new(@statuses, current_user&.account_id)
+  end
+
+  private
+
+  def set_preview_card
+    @preview_card = PreviewCard.joins(:trend).merge(PreviewCardTrend.allowed).find_by!(url: params[:url])
+  end
+
+  def set_statuses
+    @statuses = @preview_card.nil? ? [] : cache_collection(link_timeline_statuses, Status)
+  end
+
+  def link_timeline_statuses
+    link_feed.get(
+      limit_param(DEFAULT_STATUSES_LIMIT),
+      params[:max_id],
+      params[:since_id],
+      params[:min_id]
+    )
+  end
+
+  def link_feed
+    LinkFeed.new(@preview_card, current_account)
+  end
+
+  def insert_pagination_headers
+    set_pagination_headers(next_path, prev_path)
+  end
+
+  def pagination_params(core_params)
+    params.slice(:local, :limit, :only_media).permit(:local, :limit, :only_media).merge(core_params)
+  end
+
+  def next_path
+    api_v1_timelines_link_url params[:id], pagination_params(max_id: pagination_max_id)
+  end
+
+  def prev_path
+    api_v1_timelines_link_url params[:id], pagination_params(min_id: pagination_since_id)
+  end
+
+  def pagination_max_id
+    @statuses.last.id
+  end
+
+  def pagination_since_id
+    @statuses.first.id
+  end
+end

app/models/link_feed.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class LinkFeed < PublicFeed
+  # @param [PreviewCard] preview_card
+  # @param [Account] account
+  def initialize(preview_card, account)
+    @preview_card = preview_card
+    super(account)
+  end
+
+  # @param [Integer] limit
+  # @param [Integer] max_id
+  # @param [Integer] since_id
+  # @param [Integer] min_id
+  # @return [Array<Status>]
+  def get(limit, max_id = nil, since_id = nil, min_id = nil)
+    scope = public_scope
+
+    scope.merge!(discoverable)
+    scope.merge!(attached_to_preview_card)
+
+    scope.cache_ids.to_a_paginated_by_id(limit, max_id: max_id, since_id: since_id, min_id: min_id)
+  end
+
+  private
+
+  def attached_to_preview_card
+    Status.joins(:preview_cards_statuses).where(preview_cards_statuses: { preview_card_id: @preview_card.id })
+  end
+
+  def discoverable
+    Account.discoverable
+  end
+end

config/routes/api.rb

@@ -39,6 +39,7 @@ namespace :api, format: false do
     namespace :timelines do
       resource :home, only: :show, controller: :home
       resource :public, only: :show, controller: :public
+      resource :link, only: :show, controller: :link
       resources :tag, only: :show
       resources :list, only: :show
     end