Add: #406 ユーザーのカスタムCSS (#825)

* Add: #406 ユーザーのカスタムCSS

* Fix lint

* Fix lint

* カスタムCSSの保存先を変更

* キャッシュを考慮して別URLに変更

spec/requests/user_custom_css_spec.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'User custom CSS' do
+  let(:user)       { Fabricate(:user) }
+  let(:custom_css) { '* { display: none !important; }' }
+
+  describe 'GET /user_custom.css' do
+    context 'without sign in' do
+      it 'returns 422' do
+        get '/user_custom.css'
+
+        expect(response).to have_http_status(401)
+      end
+    end
+
+    context 'with sign in but custom css is not enabled' do
+      before do
+        user.update!(custom_css_text: custom_css)
+        sign_in user
+      end
+
+      it 'returns custom css' do
+        get '/user_custom.css'
+
+        expect(response).to have_http_status(200)
+        expect(response.content_type).to include 'text/css'
+        expect(response.body.strip).to eq custom_css
+      end
+    end
+
+    context 'with sign in and custom css is enabled' do
+      before do
+        user.update!(custom_css_text: custom_css, settings: { 'web.use_custom_css': true })
+        sign_in user
+      end
+
+      it 'returns custom css' do
+        get '/user_custom.css'
+
+        expect(response).to have_http_status(200)
+        expect(response.content_type).to include 'text/css'
+        expect(response.body.strip).to eq custom_css
+      end
+    end
+  end
+end