Change followers page to relationships page in admin UI (#12927)

Allow browsing and filtering all relationships instead of just
followers, unify the codebase with the user-facing relationship
manager, add ability to see who the user invited

app/controllers/relationships_controller.rb

@@ -19,53 +19,13 @@ class RelationshipsController < ApplicationController
   rescue ActionController::ParameterMissing
     # Do nothing
   ensure
-    redirect_to relationships_path(current_params)
+    redirect_to relationships_path(filter_params)
   end
 
   private
 
   def set_accounts
-    @accounts = relationships_scope.page(params[:page]).per(40)
-  end
-
-  def relationships_scope
-    scope = begin
-      if following_relationship?
-        current_account.following.eager_load(:account_stat).reorder(nil)
-      else
-        current_account.followers.eager_load(:account_stat).reorder(nil)
-      end
-    end
-
-    scope.merge!(Follow.recent)             if params[:order].blank? || params[:order] == 'recent'
-    scope.merge!(Account.by_recent_status)  if params[:order] == 'active'
-    scope.merge!(mutual_relationship_scope) if mutual_relationship?
-    scope.merge!(moved_account_scope)       if params[:status] == 'moved'
-    scope.merge!(primary_account_scope)     if params[:status] == 'primary'
-    scope.merge!(by_domain_scope)           if params[:by_domain].present?
-    scope.merge!(dormant_account_scope)     if params[:activity] == 'dormant'
-
-    scope
-  end
-
-  def mutual_relationship_scope
-    Account.where(id: current_account.following)
-  end
-
-  def moved_account_scope
-    Account.where.not(moved_to_account_id: nil)
-  end
-
-  def primary_account_scope
-    Account.where(moved_to_account_id: nil)
-  end
-
-  def dormant_account_scope
-    AccountStat.where(last_status_at: nil).or(AccountStat.where(AccountStat.arel_table[:last_status_at].lt(1.month.ago)))
-  end
-
-  def by_domain_scope
-    Account.where(domain: params[:by_domain])
+    @accounts = RelationshipFilter.new(current_account, filter_params).results.page(params[:page]).per(40)
   end
 
   def form_account_batch_params
@@ -84,7 +44,7 @@ class RelationshipsController < ApplicationController
     params[:relationship] == 'followed_by'
   end
 
-  def current_params
+  def filter_params
     params.slice(:page, *RelationshipFilter::KEYS).permit(:page, *RelationshipFilter::KEYS)
   end