FEATURE: Native theme support

This feature introduces the concept of themes. Themes are an evolution
of site customizations.

Themes introduce two very big conceptual changes:

- A theme may include other "child themes", children can include grand
children and so on.

- A theme may specify a color scheme

The change does away with the idea of "enabled" color schemes.

It also adds a bunch of big niceties like

- You can source a theme from a git repo

- History for themes is much improved

- You can only have a single enabled theme. Themes can be selected by
    users, if you opt for it.

On a technical level this change comes with a whole bunch of goodies

- All CSS is now compiled using a custom pipeline that uses libsass
    see /lib/stylesheet

- There is a single pipeline for css compilation (in the past we used
    one for customizations and another one for the rest of the app

- The stylesheet pipeline is now divorced of sprockets, there is no
   reliance on sprockets for CSS bundling

- CSS is generated with source maps everywhere (including themes) this
    makes debugging much easier

- Our "live reloader" is smarter and avoid a flash of unstyled content
   we run a file watcher in "puma" in dev so you no longer need to run
   rake autospec to watch for CSS changes

spec/controllers/admin/themes_controller_spec.rb

@@ -0,0 +1,101 @@
+require 'rails_helper'
+
+describe Admin::ThemesController do
+
+  it "is a subclass of AdminController" do
+    expect(Admin::UsersController < Admin::AdminController).to eq(true)
+  end
+
+  context 'while logged in as an admin' do
+    before do
+      @user = log_in(:admin)
+    end
+
+    context ' .index' do
+      it 'returns success' do
+        theme = Theme.new(name: 'my name', user_id: -1)
+        theme.set_field(:common, :scss, '.body{color: black;}')
+        theme.set_field(:desktop, :after_header, '<b>test</b>')
+
+        theme.remote_theme = RemoteTheme.new(
+          remote_url: 'awesome.git',
+          remote_version: '7',
+          local_version: '8',
+          remote_updated_at: Time.zone.now
+        )
+
+        theme.save!
+
+        # this will get serialized as well
+        ColorScheme.create_from_base(name: "test", colors: [])
+
+        xhr :get, :index
+
+        expect(response).to be_success
+
+        json = ::JSON.parse(response.body)
+
+        expect(json["extras"]["color_schemes"].length).to eq(2)
+        theme_json = json["themes"].find{|t| t["id"] == theme.id}
+        expect(theme_json["theme_fields"].length).to eq(2)
+        expect(theme_json["remote_theme"]["remote_version"]).to eq("7")
+      end
+    end
+
+    context ' .create' do
+      it 'creates a theme' do
+        xhr :post, :create, theme: {name: 'my test name', theme_fields: [name: 'scss', target: 'common', value: 'body{color: red;}']}
+        expect(response).to be_success
+
+        json = ::JSON.parse(response.body)
+
+        expect(json["theme"]["theme_fields"].length).to eq(1)
+        expect(UserHistory.where(action: UserHistory.actions[:change_theme]).count).to eq(1)
+      end
+    end
+
+    context ' .update' do
+      it 'can change default theme' do
+        theme = Theme.create(name: 'my name', user_id: -1)
+        xhr :put, :update, id: theme.id, theme: { default: true }
+        expect(SiteSetting.default_theme_key).to eq(theme.key)
+      end
+
+      it 'can unset default theme' do
+        theme = Theme.create(name: 'my name', user_id: -1)
+        SiteSetting.default_theme_key = theme.key
+        xhr :put, :update, id: theme.id, theme: { default: false}
+        expect(SiteSetting.default_theme_key).to be_blank
+      end
+
+      it 'updates a theme' do
+
+        theme = Theme.new(name: 'my name', user_id: -1)
+        theme.set_field(:common, :scss, '.body{color: black;}')
+        theme.save
+
+        child_theme = Theme.create(name: 'my name', user_id: -1)
+
+        xhr :put, :update, id: theme.id,
+            theme: {
+          child_theme_ids: [child_theme.id],
+          name: 'my test name',
+          theme_fields: [name: 'scss', target: 'common', value: 'body{color: red;}']
+        }
+        expect(response).to be_success
+
+        json = ::JSON.parse(response.body)
+
+        fields = json["theme"]["theme_fields"]
+
+        expect(fields.length).to eq(1)
+        expect(fields.first["value"]).to eq('body{color: red;}')
+
+        expect(json["theme"]["child_themes"].length).to eq(1)
+
+        expect(UserHistory.where(action: UserHistory.actions[:change_theme]).count).to eq(1)
+      end
+    end
+  end
+
+end