Add pagination functionality to the projects

Gemfile

@@ -11,6 +11,7 @@ gem 'cancancan', '~> 3.3'
 gem 'faraday'
 gem 'importmap-rails'
 gem 'jbuilder'
+gem 'kaminari'
 gem 'pg', '~> 1.1'
 gem 'puma', '~> 5.6'
 gem 'rack-cors'

Gemfile.lock

@@ -126,6 +126,18 @@ GEM
       activesupport (>= 5.0.0)
     jmespath (1.6.2)
     json (2.6.2)
+    kaminari (1.2.2)
+      activesupport (>= 4.1.0)
+      kaminari-actionview (= 1.2.2)
+      kaminari-activerecord (= 1.2.2)
+      kaminari-core (= 1.2.2)
+    kaminari-actionview (1.2.2)
+      actionview
+      kaminari-core (= 1.2.2)
+    kaminari-activerecord (1.2.2)
+      activerecord
+      kaminari-core (= 1.2.2)
+    kaminari-core (1.2.2)
     loofah (2.19.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -282,6 +294,7 @@ DEPENDENCIES
   faraday
   importmap-rails
   jbuilder
+  kaminari
   pg (~> 1.1)
   pry-byebug
   puma (~> 5.6)

app/controllers/api/projects_controller.rb

@@ -5,11 +5,13 @@ class ProjectsController < ApiController
     before_action :require_oauth_user, only: %i[create update index destroy]
     before_action :load_project, only: %i[show update destroy]
     before_action :load_projects, only: %i[index]
+    after_action :pagination_link_header, only: [:index]
     load_and_authorize_resource
     skip_load_resource only: :create
 
     def index
-      render :index, formats: [:json]
+      @paginated_projects = @projects.page(params[:page])
+      render index: @paginated_projects, formats: [:json]
     end
 
     def show
@@ -51,7 +53,7 @@ def load_project
     end
 
     def load_projects
-      @projects = Project.where(user_id: current_user)
+      @projects = Project.where(user_id: current_user).order(updated_at: :desc)
     end
 
     def project_params
@@ -65,5 +67,47 @@ def project_params
         }
       )
     end
+
+    def pagination_link_header
+      pagination_links = []
+      pagination_links << page_links(first_page, 'first')
+      pagination_links << page_links(last_page, 'last')
+      pagination_links << page_links(next_page, 'next')
+      pagination_links << page_links(prev_page, 'prev')
+
+      pagination_links.compact_blank!
+      headers['Link'] = pagination_links.join(', ')
+    end
+
+    def page_links(to_page, rel_type)
+      return if to_page.nil?
+
+      page_info = "page=#{to_page}"
+      "<#{request.base_url}/api/projects?#{page_info}>; rel=\"#{rel_type}\""
+    end
+
+    def page
+      params.key?(:page) ? params[:page].to_i : 1
+    end
+
+    def total_pages
+      @projects.page(1).total_pages
+    end
+
+    def first_page
+      @projects.page(page).first_page? ? nil : 1
+    end
+
+    def last_page
+      @projects.page(page).last_page? ? nil : total_pages
+    end
+
+    def next_page
+      @projects.page(page).next_page
+    end
+
+    def prev_page
+      @projects.page(page).prev_page
+    end
   end
 end

app/views/api/projects/index.json.jbuilder

@@ -1,3 +1,3 @@
 # frozen_string_literal: true
 
-json.array! @projects, :identifier, :project_type, :name, :user_id, :updated_at
+json.array! @paginated_projects, :identifier, :project_type, :name, :user_id, :updated_at

config/initializers/cors.rb

@@ -5,6 +5,6 @@
 Rails.application.config.middleware.insert_before 0, Rack::Cors do
   allow do
     origins origins_array
-    resource '*', headers: :any, methods: %i[get post patch put delete]
+    resource '*', headers: :any, methods: %i[get post patch put delete], expose: ['Link']
   end
 end

config/initializers/kaminari_config.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+Kaminari.configure do |config|
+  config.default_per_page = 8
+end

spec/request/projects/index_spec.rb

@@ -3,6 +3,8 @@
 require 'rails_helper'
 
 RSpec.describe 'Project index requests', type: :request do
+  include PaginationLinksMock
+
   let(:user_id) { 'e0675b6c-dc48-4cd6-8c04-0f7ac05af51a' }
   let(:project_keys) { %w[identifier project_type name user_id updated_at] }
 
@@ -41,6 +43,43 @@
     end
   end
 
+  context 'when the projects index has pagination' do
+    before do
+      create_list(:project, 10, user_id:)
+      mock_oauth_user(user_id)
+    end
+
+    it 'returns the default number of projects on the first page' do
+      get '/api/projects'
+      returned = JSON.parse(response.body)
+      expect(returned.length).to eq(8)
+    end
+
+    it 'returns the next set of projects on the next page' do
+      get '/api/projects?page=2'
+      returned = JSON.parse(response.body)
+      expect(returned.length).to eq(4)
+    end
+
+    it 'has the correct response headers for the first page' do
+      last_link = page_links(2, 'last')
+      next_link = page_links(2, 'next')
+      expected_link_header = [last_link, next_link].join(', ')
+
+      get '/api/projects'
+      expect(response.headers['Link']).to eq expected_link_header
+    end
+
+    it 'has the correct response headers for the next page' do
+      first_link = page_links(1, 'first')
+      prev_link = page_links(1, 'prev')
+      expected_link_header = [first_link, prev_link].join(', ')
+
+      get '/api/projects?page=2'
+      expect(response.headers['Link']).to eq expected_link_header
+    end
+  end
+
   context 'when no user' do
     it 'returns unauthorized' do
       get '/api/projects'

spec/support/pagination_links_mock.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module PaginationLinksMock
+  def page_links(to_page, rel_type)
+    page_info = "page=#{to_page}"
+    "<http://www.example.com/api/projects?#{page_info}>; rel=\"#{rel_type}\""
+  end
+end