extract filter/sort/paging logic to finder class

app/controllers/admin/runners_controller.rb

@@ -2,11 +2,7 @@ class Admin::RunnersController < Admin::ApplicationController
   before_action :runner, except: :index
 
   def index
-    sort = params[:sort] == 'contacted_asc' ? { contacted_at: :asc } : { id: :desc }
-    @runners = Ci::Runner.order(sort)
-    @runners = @runners.search(params[:search]) if params[:search].present?
-    @runners = @runners.public_send(params[:status]) if params[:status].present? && Ci::Runner::AVAILABLE_STATUSES.include?(params[:status])
-    @runners = @runners.page(params[:page]).per(30)
+    @runners = Admin::RunnersFinder.new(params: params).execute
     @active_runners_cnt = Ci::Runner.online.count
   end
 

app/finders/admin/runners_finder.rb

+class Admin::RunnersFinder < UnionFinder
+  NUMBER_OF_RUNNERS_PER_PAGE = 30
+
+  def initialize(params:)
+    @params = params
+  end
+
+  def execute
+    search!
+    filter_by_status!
+    sort!
+    paginate!
+
+    @runners
+  end
+
+  private
+
+  def search!
+    @runners =
+      if @params[:search].present?
+        Ci::Runner.search(@params[:search])
+      else
+        Ci::Runner.all
+      end
+  end
+
+  def filter_by_status!
+    if @params[:status].present? && Ci::Runner::AVAILABLE_STATUSES.include?(@params[:status])
+      @runners = @runners.public_send(@params[:status]) # rubocop:disable GitlabSecurity/PublicSend
+    end
+  end
+
+  def sort!
+    sort = @params[:sort] == 'contacted_asc' ? { contacted_at: :asc } : { id: :desc }
+    @runners = @runners.order(sort)
+  end
+
+  def paginate!
+    @runners = @runners.page(@params[:page]).per(NUMBER_OF_RUNNERS_PER_PAGE)
+  end
+end

spec/finders/admin/runners_finder_spec.rb

+require 'spec_helper'
+
+describe Admin::RunnersFinder do
+  describe '#execute' do
+    context 'with empty params' do
+      it 'returns all runners' do
+        runner1 = create :ci_runner, active: true
+        runner2 = create :ci_runner, active: false
+
+        expect(described_class.new(params: {}).execute).to match_array [runner1, runner2]
+      end
+    end
+
+    context 'filter by search term' do
+      it 'calls Ci::Runner.search' do
+        expect(Ci::Runner).to receive(:search).with('term').and_call_original
+
+        described_class.new(params: { search: 'term' }).execute
+      end
+    end
+
+    context 'filter by status' do
+      it 'calls the corresponding scope on Ci::Runner' do
+        expect(Ci::Runner).to receive(:paused).and_call_original
+
+        described_class.new(params: { status: 'paused' }).execute
+      end
+    end
+
+    context 'sort' do
+      context 'without sort param' do
+        it 'sorts by id' do
+          runner1 = create :ci_runner
+          runner2 = create :ci_runner
+          runner3 = create :ci_runner
+
+          expect(described_class.new(params: {}).execute).to eq [runner3, runner2, runner1]
+        end
+      end
+
+      context 'with sort param' do
+        it 'sorts by specified attribute' do
+          runner1 = create :ci_runner, contacted_at: 1.minute.ago
+          runner2 = create :ci_runner, contacted_at: 3.minutes.ago
+          runner3 = create :ci_runner, contacted_at: 2.minutes.ago
+
+          expect(described_class.new(params: { sort: 'contacted_asc' }).execute).to eq [runner2, runner3, runner1]
+        end
+      end
+    end
+
+    context 'paginate' do
+      it 'returns the runners for the specified page' do
+        stub_const('Admin::RunnersFinder::NUMBER_OF_RUNNERS_PER_PAGE', 1)
+        runner1 = create :ci_runner
+        runner2 = create :ci_runner
+
+        expect(described_class.new(params: { page: 1 }).execute).to eq [runner2]
+        expect(described_class.new(params: { page: 2 }).execute).to eq [runner1]
+      end
+    end
+  end
+end