Change auto-following admin-selected accounts, show in recommendations (#16078)

app/models/account_suggestions/setting_source.rb

@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+class AccountSuggestions::SettingSource < AccountSuggestions::Source
+  def key
+    :staff
+  end
+
+  def get(account, skip_account_ids: [], limit: 40)
+    return [] unless setting_enabled?
+
+    as_ordered_suggestions(
+      scope(account).where(setting_to_where_condition).where.not(id: skip_account_ids),
+      usernames_and_domains
+    ).take(limit)
+  end
+
+  def remove(_account, _target_account_id)
+    nil
+  end
+
+  private
+
+  def scope(account)
+    Account.searchable
+           .followable_by(account)
+           .not_excluded_by_account(account)
+           .not_domain_blocked_by_account(account)
+           .where(locked: false)
+           .where.not(id: account.id)
+  end
+
+  def usernames_and_domains
+    @usernames_and_domains ||= setting_to_usernames_and_domains
+  end
+
+  def setting_enabled?
+    setting.present?
+  end
+
+  def setting_to_where_condition
+    usernames_and_domains.map do |(username, domain)|
+      Arel::Nodes::Grouping.new(
+        Account.arel_table[:username].lower.eq(username.downcase).and(
+          Account.arel_table[:domain].lower.eq(domain&.downcase)
+        )
+      )
+    end.reduce(:or)
+  end
+
+  def setting_to_usernames_and_domains
+    setting.split(',').map do |str|
+      username, domain = str.strip.gsub(/\A@/, '').split('@', 2)
+      domain           = nil if TagManager.instance.local_domain?(domain)
+
+      next if username.blank?
+
+      [username, domain]
+    end.compact
+  end
+
+  def setting
+    Setting.bootstrap_timeline_accounts
+  end
+
+  def to_ordered_list_key(account)
+    [account.username, account.domain]
+  end
+end