Extract Project.only_scratch scope

I want to do something similar in the
`Api::Projects::RemixesController`. By making this scope available, I'll
be able to reduce the amount of duplication.

Author: floehopper

app/models/project.rb

@@ -35,6 +35,9 @@ module Types
   default_scope -> { where.not(project_type: Types::SCRATCH) }
 
   scope :internal_projects, -> { where(user_id: nil) }
+  scope :only_scratch, lambda { |only_scratch|
+    only_scratch ? unscoped.where(project_type: Project::Types::SCRATCH) : self
+  }
 
   has_paper_trail(
     if: ->(p) { p&.school_id },

lib/project_loader.rb

@@ -9,7 +9,7 @@ def initialize(identifier, locales)
   end
 
   def load(include_images: false, only_scratch: false)
-    query = only_scratch ? Project.unscoped.where(project_type: Project::Types::SCRATCH) : Project
+    query = Project.only_scratch(only_scratch)
     query = query.where(identifier:, locale: @locales)
     query = query.includes(images_attachments: :blob) if include_images
     query.min_by { |project| @locales.find_index(project.locale) }

spec/models/project_spec.rb

@@ -342,4 +342,53 @@
       expect(described_class.all).not_to include(scratch_project)
     end
   end
+
+  describe 'only_scratch scope' do
+    let!(:python_project) { create(:project, project_type: Project::Types::PYTHON) }
+    let!(:html_project) { create(:project, project_type: Project::Types::HTML) }
+    let!(:project_with_unknown_type) { create(:project, project_type: 'unknown') }
+    let!(:scratch_project) { create(:project, project_type: Project::Types::SCRATCH) }
+
+    let(:projects_in_scope) { described_class.only_scratch(only_scratch) }
+
+    context 'when only_scratch is false' do
+      let(:only_scratch) { false }
+
+      it 'includes python projects' do
+        expect(projects_in_scope).to include(python_project)
+      end
+
+      it 'includes html projects' do
+        expect(projects_in_scope).to include(html_project)
+      end
+
+      it 'includes projects with unknown type' do
+        expect(projects_in_scope).to include(project_with_unknown_type)
+      end
+
+      it 'does not include scratch projects' do
+        expect(projects_in_scope).not_to include(scratch_project)
+      end
+    end
+
+    context 'when only_scratch is true' do
+      let(:only_scratch) { true }
+
+      it 'does not include python projects' do
+        expect(projects_in_scope).not_to include(python_project)
+      end
+
+      it 'does not include html projects' do
+        expect(projects_in_scope).not_to include(html_project)
+      end
+
+      it 'does not include projects with unknown type' do
+        expect(projects_in_scope).not_to include(project_with_unknown_type)
+      end
+
+      it 'includes scratch projects' do
+        expect(projects_in_scope).to include(scratch_project)
+      end
+    end
+  end
 end