Move npm packages lookup into own finder

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

ee/app/finders/packages/npm_packages_finder.rb

+# frozen_string_literal: true
+class Packages::NpmPackagesFinder
+  attr_reader :project, :package_name
+
+  def initialize(project, package_name)
+    @project = project
+    @package_name = package_name
+  end
+
+  def execute
+    packages
+  end
+
+  private
+
+  def packages
+    project.packages
+      .only_npm
+      .with_name(package_name)
+      .last_of_each_version
+      .preload_files
+  end
+end

ee/app/models/packages/package.rb

@@ -15,6 +15,7 @@ class Packages::Package < ActiveRecord::Base
   enum package_type: { maven: 1, npm: 2 }
 
   scope :with_name, ->(name) { where(name: name) }
+  scope :only_npm, -> { where(package_type: 'npm') }
   scope :preload_files, -> { preload(:package_files) }
 
   def self.for_projects(projects)

ee/lib/api/npm_packages.rb

@@ -41,10 +41,8 @@ module API
       authorize!(:read_package, project)
       forbidden! unless project.feature_available?(:packages)
 
-      packages = project.packages
-        .with_name(package_name)
-        .last_of_each_version
-        .preload_files
+      packages = ::Packages::NpmPackagesFinder
+        .new(project, package_name).execute
 
       present NpmPackagePresenter.new(project, package_name, packages),
         with: EE::API::Entities::NpmPackage
@@ -69,7 +67,7 @@ module API
       get ':id/packages/npm/*package_name/-/*file_name', format: false do
         authorize_download_package!
 
-        package = user_project.packages
+        package = user_project.packages.only_npm
           .by_name_and_file_name(params[:package_name], params[:file_name])
 
         package_file = ::Packages::PackageFileFinder

ee/spec/finders/packages/npm_packages_finder_spec.rb

+# frozen_string_literal: true
+require 'spec_helper'
+
+describe Packages::NpmPackagesFinder do
+  let(:package) { create(:npm_package) }
+  let(:project) { package.project }
+
+  describe '#execute!' do
+    it 'returns project packages' do
+      finder = described_class.new(project, package.name)
+
+      expect(finder.execute).to eq([package])
+    end
+
+    it 'returns an empty collection' do
+      finder = described_class.new(project, 'baz')
+
+      expect(finder.execute).to be_empty
+    end
+  end
+end