Extract ProjectScoping concern & Current.project_scope

To remove duplication and simplify the code. This means there is now
only one place where we use the `project_type` param to override the
default scope on Project to give access to scratch projects. What's
more, it should be easier to add this to other controller actions in the
future.

Note that the underlying value of `Current.project_scope` will get reset
to `nil` after every request [1]. Also note that the default value
functionality for these attributes wasn't added until Rails v7.2 [2], so
we have to override the reader method to provide the default value if
the underlying value is `nil`.

[1]: https://api.rubyonrails.org/v7.1.3.4/classes/ActiveSupport/CurrentAttributes.html
[2]: https://github.com/rails/rails/blob/v7.2.0/activesupport/CHANGELOG.md

Author: floehopper

app/controllers/api/projects/remixes_controller.rb

@@ -36,18 +36,14 @@ def create
       private
 
       def project
-        @project ||= project_scope.find_by!(identifier: params[:project_id])
+        @project ||= Current.project_scope.find_by!(identifier: params[:project_id])
       end
 
       def load_and_authorize_remix
-        @project = project_scope.find_by!(remixed_from_id: project.id, user_id: current_user&.id)
+        @project = Current.project_scope.find_by!(remixed_from_id: project.id, user_id: current_user&.id)
         authorize! :show, @project
       end
 
-      def project_scope
-        Project.only_scratch(params[:project_type] == Project::Types::SCRATCH)
-      end
-
       def remix_params
         params.require(:project)
               .permit(:name,

app/controllers/api/projects_controller.rb

@@ -69,7 +69,7 @@ def verify_lesson_belongs_to_school
     def load_project
       project_loader = ProjectLoader.new(params[:id], [params[:locale]])
       @project = if action_name == 'show'
-                   project_loader.load(include_images: true, only_scratch: params[:project_type] == Project::Types::SCRATCH)
+                   project_loader.load(include_images: true)
                  else
                    project_loader.load
                  end

app/controllers/api_controller.rb

@@ -4,6 +4,7 @@ class ApiController < ActionController::API
   class ::ParameterError < StandardError; end
 
   include Identifiable
+  include ProjectScoping
 
   rescue_from ActionController::ParameterMissing, with: -> { bad_request }
   rescue_from ActiveRecord::RecordNotFound, with: -> { not_found }

app/controllers/concerns/project_scoping.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module ProjectScoping
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :set_project_scope
+  end
+
+  private
+
+  def set_project_scope
+    only_scratch = params[:project_type] == Project::Types::SCRATCH
+    Current.project_scope = Project.only_scratch(only_scratch)
+  end
+end

app/models/current.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class Current < ActiveSupport::CurrentAttributes
+  attribute :project_scope
+
+  def project_scope
+    super || Project
+  end
+end

lib/project_loader.rb

@@ -8,8 +8,8 @@ def initialize(identifier, locales)
     @locales = [*locales, 'en', nil]
   end
 
-  def load(include_images: false, only_scratch: false)
-    query = Project.only_scratch(only_scratch)
+  def load(include_images: false)
+    query = Current.project_scope
     query = query.where(identifier:, locale: @locales)
     query = query.includes(images_attachments: :blob) if include_images
     query.min_by { |project| @locales.find_index(project.locale) }