Specs for precompute feed service (#3142)

* Add spec for precompute feed service

* Refactor PrecomputeFeedService

* spec wip

app/services/precompute_feed_service.rb

@@ -1,20 +1,48 @@
 # frozen_string_literal: true
 
 class PrecomputeFeedService < BaseService
-  # Fill up a user's home/mentions feed from DB and return a subset
-  # @param [Symbol] type :home or :mentions
-  # @param [Account] account
-  def call(_, account)
+  LIMIT = FeedManager::MAX_ITEMS / 4
+
+  def call(account)
+    @account = account
+    populate_feed
+  end
+
+  private
+
+  attr_reader :account
+
+  def populate_feed
     redis.pipelined do
-      # NOTE: Added `id desc, account_id desc` to `ORDER BY` section to optimize query.
-      Status.as_home_timeline(account).order(account_id: :desc).limit(FeedManager::MAX_ITEMS / 4).each do |status|
-        next if status.direct_visibility? || FeedManager.instance.filter?(:home, status, account.id)
-        redis.zadd(FeedManager.instance.key(:home, account.id), status.id, status.reblog? ? status.reblog_of_id : status.id)
+      statuses.each do |status|
+        process_status(status)
       end
     end
   end
 
-  private
+  def process_status(status)
+    add_status_to_feed(status) unless skip_status?(status)
+  end
+
+  def skip_status?(status)
+    status.direct_visibility? || status_filtered?(status)
+  end
+
+  def add_status_to_feed(status)
+    redis.zadd(account_home_key, status.id, status.reblog? ? status.reblog_of_id : status.id)
+  end
+
+  def status_filtered?(status)
+    FeedManager.instance.filter?(:home, status, account.id)
+  end
+
+  def account_home_key
+    FeedManager.instance.key(:home, account.id)
+  end
+
+  def statuses
+    Status.as_home_timeline(account).order(account_id: :desc).limit(LIMIT)
+  end
 
   def redis
     Redis.current