Use ProjectLoader in Api::PublicProjectsController

This is closely based on how `Api::ProjectsController` works although
it's not obvious that its behaviour is tested. However, there is a spec
for `ProjectLoader` itself, so I've just added examples to make sure
it's wired up to the controller correctly.

One thing I've added is to raise `ActiveRecord::RecordNotFound` if
`ProjectLoader#load` returns `nil` which seems possible. This will
result in a 404 Not Found response which is what I was already asserting
in `spec/features/public_project/updating_a_public_project_spec.rb`. As
far as I can tell, `Api::ProjectsController` actions which make use of
`ProjectLoader#load` (e.g. the `update` action) do not check for the
project being `nil` and so will probably respond with a 500 Internal
Server Error when the code (e.g. in `Project::Update`) calls a method on
the `nil` project. This doesn't seem great!

Author: floehopper

app/controllers/api/public_projects_controller.rb

@@ -32,7 +32,9 @@ def update
     private
 
     def load_project
-      @project = Project.find_by!(identifier: params[:id])
+      loader = ProjectLoader.new(params[:id], [params[:locale]])
+      @project = loader.load
+      raise ActiveRecord::RecordNotFound if @project.blank?
     end
 
     def create_params

spec/features/public_project/updating_a_public_project_spec.rb

@@ -4,7 +4,7 @@
 
 RSpec.describe 'Updating a public project', type: :request do
   let(:creator) { build(:user) }
-  let(:project) { create(:project) }
+  let(:project) { create(:project, locale: 'en') }
   let(:headers) { { Authorization: UserProfileMock::TOKEN } }
   let(:params) { { project: { name: 'New name' } } }
 

spec/requests/public_projects/update_spec.rb

@@ -3,7 +3,9 @@
 require 'rails_helper'
 
 RSpec.describe 'Update public project requests' do
-  let(:project) { create(:project) }
+  let(:locale) { 'fr' }
+  let(:project_loader) { instance_double(ProjectLoader) }
+  let(:project) { create(:project, locale: 'en') }
   let(:creator) { build(:user) }
   let(:params) { { project: { name: 'New name' } } }
 
@@ -14,11 +16,26 @@
       before do
         authenticated_in_hydra_as(creator)
 
+        allow(ProjectLoader).to receive(:new).and_return(project_loader)
+        allow(project_loader).to receive(:load).and_return(project)
+
         response = OperationResponse.new
         response[:project] = project
         allow(PublicProject::Update).to receive(:call).and_return(response)
       end
 
+      it 'builds ProjectLoader with identifier & locale' do
+        put("/api/public_projects/#{project.identifier}?locale=#{locale}", headers:, params:)
+
+        expect(ProjectLoader).to have_received(:new).with(project.identifier, [locale])
+      end
+
+      it 'uses ProjectLoader#load to find the project based on identifier & locale' do
+        put("/api/public_projects/#{project.identifier}?locale=#{locale}", headers:, params:)
+
+        expect(project_loader).to have_received(:load)
+      end
+
       it 'returns success' do
         put("/api/public_projects/#{project.identifier}", headers:, params:)