Change lists to reflect added and removed users retroactively (#32930)

app/services/add_accounts_to_list_service.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class AddAccountsToListService < BaseService
+  def call(list, accounts)
+    @list = list
+    @accounts = accounts
+
+    return if @accounts.empty?
+
+    update_list!
+    merge_into_list!
+  end
+
+  private
+
+  def update_list!
+    ApplicationRecord.transaction do
+      @accounts.each do |account|
+        @list.accounts << account
+      end
+    end
+  end
+
+  def merge_into_list!
+    MergeWorker.push_bulk(merge_account_ids) do |account_id|
+      [account_id, @list.id, 'list']
+    end
+  end
+
+  def merge_account_ids
+    ListAccount.where(list: @list, account: @accounts).where.not(follow_id: nil).pluck(:account_id)
+  end
+end