Add support for multiple themes (#4959)

* Add support for selecting a theme

* Fix codeclimate issues

* Look up site default style if current user is not available due to e.g. not being logged in

* Remove outdated comment in common.js

* Address requested changes in themes PR

* Fix codeclimate issues

* Explicitly check current_account in application controller and only check theme availability if non-nil

* codeclimate

* explicit precedence with &&

* Fix code style in application_controller according to @nightpool's suggestion, use default style in embedded.html.haml

* codeclimate: indentation + return

6 files changed, 28 insertions, 18 deletions

diff --git a/config/locales/en.yml b/config/locales/en.yml
index 9013f0ac9..0f3812aff 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -461,6 +461,8 @@ en:
     settings: Settings
     two_factor_authentication: Two-factor Authentication
     your_apps: Your applications
+  themes:
+    default: Mastodon
   statuses:
     open_in_web: Open in web
     over_character_limit: character limit of %{max} exceeded
diff --git a/config/locales/simple_form.en.yml b/config/locales/simple_form.en.yml
index fb8524a24..c535a22fe 100644
--- a/config/locales/simple_form.en.yml
+++ b/config/locales/simple_form.en.yml
@@ -13,6 +13,7 @@ en:
           one: <span class="note-counter">1</span> character left
           other: <span class="note-counter">%{count}</span> characters left
         setting_noindex: Affects your public profile and status pages
+        setting_theme: Affects how Mastodon looks when you're logged in from any device.
       imports:
         data: CSV file exported from another Mastodon instance
       sessions:
@@ -44,6 +45,7 @@ en:
         setting_noindex: Opt-out of search engine indexing
         setting_system_font_ui: Use system's default font
         setting_unfollow_modal: Show confirmation dialog before unfollowing someone
+        setting_theme: Site theme 
         severity: Severity
         type: Import type
         username: Username
diff --git a/config/settings.yml b/config/settings.yml
index ba63afa92..c437b4ccb 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -24,6 +24,7 @@ defaults: &defaults
   auto_play_gif: false
   system_font_ui: false
   noindex: false
+  theme: 'default'
   notification_emails:
     follow: false
     reblog: false
diff --git a/config/themes.yml b/config/themes.yml
new file mode 100644
index 000000000..a1049fae7
--- /dev/null
+++ b/config/themes.yml
@@ -0,0 +1 @@
+default: styles/application.scss
diff --git a/config/webpack/configuration.js b/config/webpack/configuration.js
index 6ef484c3a..822329490 100644
--- a/config/webpack/configuration.js
+++ b/config/webpack/configuration.js
@@ -9,6 +9,9 @@ const configPath = resolve('config', 'webpacker.yml');
 const loadersDir = join(__dirname, 'loaders');
 const settings = safeLoad(readFileSync(configPath), 'utf8')[env.NODE_ENV];
 
+const themePath = resolve('config', 'themes.yml');
+const themes = safeLoad(readFileSync(themePath), 'utf8');
+
 function removeOuterSlashes(string) {
   return string.replace(/^\/*/, '').replace(/\/*$/, '');
 }
@@ -29,6 +32,7 @@ const output = {
 
 module.exports = {
   settings,
+  themes,
   env,
   loadersDir,
   output,
diff --git a/config/webpack/shared.js b/config/webpack/shared.js
index b097a5fe4..ea2da6aa7 100644
--- a/config/webpack/shared.js
+++ b/config/webpack/shared.js
@@ -1,13 +1,12 @@
 // Note: You must restart bin/webpack-dev-server for changes to take effect
 
-const { existsSync } = require('fs');
 const webpack = require('webpack');
 const { basename, dirname, join, relative, resolve, sep } = require('path');
 const { sync } = require('glob');
 const ExtractTextPlugin = require('extract-text-webpack-plugin');
 const ManifestPlugin = require('webpack-manifest-plugin');
 const extname = require('path-complete-extname');
-const { env, settings, output, loadersDir } = require('./configuration.js');
+const { env, settings, themes, output, loadersDir } = require('./configuration.js');
 const localePackPaths = require('./generateLocalePacks');
 
 const extensionGlob = `**/*{${settings.extensions.join(',')}}*`;
@@ -15,20 +14,25 @@ const entryPath = join(settings.source_path, settings.source_entry_path);
 const packPaths = sync(join(entryPath, extensionGlob));
 const entryPacks = [...packPaths, ...localePackPaths].filter(path => path !== join(entryPath, 'custom.js'));
 
-const customApplicationStyle = resolve(join(settings.source_path, 'styles/custom.scss'));
-const originalApplicationStyle = resolve(join(settings.source_path, 'styles/application.scss'));
+const themePaths = Object.keys(themes).reduce(
+  (themePaths, name) => {
+    themePaths[name] = resolve(join(settings.source_path, themes[name]));
+    return themePaths;
+  }, {});
 
 module.exports = {
-  entry: entryPacks.reduce(
-    (map, entry) => {
-      const localMap = map;
-      let namespace = relative(join(entryPath), dirname(entry));
-      if (namespace === join('..', '..', '..', 'tmp', 'packs')) {
-        namespace = ''; // generated by generateLocalePacks.js
-      }
-      localMap[join(namespace, basename(entry, extname(entry)))] = resolve(entry);
-      return localMap;
-    }, {}
+  entry: Object.assign(
+    entryPacks.reduce(
+      (map, entry) => {
+        const localMap = map;
+        let namespace = relative(join(entryPath), dirname(entry));
+        if (namespace === join('..', '..', '..', 'tmp', 'packs')) {
+          namespace = ''; // generated by generateLocalePacks.js
+        }
+        localMap[join(namespace, basename(entry, extname(entry)))] = resolve(entry);
+        return localMap;
+      }, {}
+    ), themePaths
   ),
 
   output: {
@@ -67,10 +71,6 @@ module.exports = {
   ],
 
   resolve: {
-    alias: {
-      'mastodon-application-style': existsSync(customApplicationStyle) ?
-                                    customApplicationStyle : originalApplicationStyle,
-    },
     extensions: settings.extensions,
     modules: [
       resolve(settings.source_path),