feature: paginating params preprocessing

lib/apress/api/api_controller/pagination.rb

@@ -2,6 +2,45 @@ module Apress
   module Api
     module ApiController
       module Pagination
+        class InvalidPaginationError < StandardError; end
+
+        extend ActiveSupport::Concern
+
+        included do
+          attr_reader :per_page, :page
+          alias_method :current_page, :page
+          rescue_from InvalidPaginationError, with: :bad_request
+        end
+
+        DEFAULT_PER_PAGE = 30
+        MAX_PER_PAGE = 100
+
+        # Public: sets page and per_page variables
+        #
+        # options - Hash, configuration
+        #           :per_page - Hash, per_page value configuration
+        #                       :max - Integer, max per_page value
+        #                       :defuault - Integer, default value for per_page
+        # Examples
+        #   prepare_pagination(per_page: {max: 110, default: 40})
+        #
+        #   or with defaults max - 100 and default - 30
+        #
+        #   prepare_pagination
+        #
+        # Returns nothing
+        def prepare_pagination(options = {})
+          per_page = options.fetch(:per_page, {})
+          max_per_page = per_page.fetch(:max, MAX_PER_PAGE)
+          default_per_page = per_page.fetch(:default, DEFAULT_PER_PAGE)
+
+          @page = params.fetch(:page, 1).to_i
+          raise InvalidPaginationError if @page <= 0
+
+          @per_page = params.fetch(:per_page, default_per_page).to_i
+          raise InvalidPaginationError unless (1..max_per_page).include?(@per_page)
+        end
+
         def pagination_headers(collection)
           headers["X-Total-Count"] = collection.total_entries.to_s
           headers["X-Total-Pages"] = collection.total_pages.to_s

spec/controllers/api_controller/pagination_spec.rb

@@ -1,15 +1,60 @@
 require "spec_helper"
 
 describe Apress::Api::ApiController::Base, type: :controller do
-  controller do
-    def index
-      render json: {status: "ok"}
+  describe '#prepare_pagination' do
+    controller do
+      skip_before_filter :authenticate
+
+      def index
+        prepare_pagination(per_page: {max: 100, default: 40})
+        head 204
+      end
+    end
+
+    context 'when params present' do
+      context 'when params are valid' do
+        it 'sets variables' do
+          get :index, page: 2, per_page: 5
+
+          expect(assigns(:page)).to eq 2
+          expect(assigns(:per_page)).to eq 5
+        end
+      end
+
+      context 'when params are invalid' do
+        it 'returns 400 for negative page' do
+          get :index, page: -1
+
+          expect(response.status).to eq 400
+        end
+
+        it 'returns 400 for > max per_page value' do
+          get :index, per_page: 101
+
+          expect(response.status).to eq 400
+        end
+      end
+    end
+
+    context 'when no params are set' do
+      it 'sets defaults' do
+        get :index
+
+        expect(assigns(:page)).to eq 1
+        expect(assigns(:per_page)).to eq 40
+      end
     end
   end
 
   describe "#pagination_headers" do
     let(:collection) { double(total_entries: 30, total_pages: 10) }
 
+    controller do
+      def index
+        render json: {status: "ok"}
+      end
+    end
+
     context "when auth successfull" do
       before do
         get :index