Add workaround to avoid duplicating theme css

In order to support both a theme toggle and to automatically use the
user's selected theme based on browser/system defaults the stylesheets
has to be duplicated twice since the latter requires the css to be
wrapped around a media query.

This duplication is a painful experience to deal with when adding or
changing existing styles. Even more so when it involves jumping around
the behemoth default.css from and back to whatever sections you were
just working on.

I don't believe the we the Invidious team will be able to agree to a
proper solution anytime soon (eg css post-processor, modern css
light-dark feature, etc) so this commit is here as a stopgap measure.

The workaround is to move the theming styles to two separate files
which are read at runtime and used to generate a combined stylesheet
with the necessary duplication for the media query. This combined
stylesheet is then delivered on a new route added to Invidious,
bypassing the static file handler.

assets/css/carousel.css

@@ -97,23 +97,3 @@ DEALINGS IN THE SOFTWARE.
     width: 50%;
     z-index: 1;
 }
-
-.light-theme .slider-nav {
-    background-color: #ddd;
-}
-
-.dark-theme .slider-nav  {
-    background-color: #0005;
-}
-
-@media (prefers-color-scheme: light) {
-    .no-theme .slider-nav {
-        background-color: #ddd;
-    }
-}
-
-@media (prefers-color-scheme: dark) {
-    .no-theme .slider-nav {
-        background-color: #0005;
-    }
-}

assets/css/dark.css

@@ -0,0 +1,81 @@
+/* Contains the CSS for the Invidious dark theme
+
+--------
+This file should not get loaded by the user as the css here will be used
+to generate theme.css as to support user-agent dark/light theme
+in addition to the class-based swap method without duplicating any styles.
+------
+
+*/
+
+.dark-theme a:hover,
+.dark-theme a:active,
+.dark-theme summary:hover,
+.dark-theme a:focus,
+.dark-theme summary:focus {
+  color: rgb(0, 182, 240);
+}
+
+.dark-theme .pure-button-primary:hover,
+.dark-theme .pure-button-primary:focus,
+.dark-theme .pure-button-secondary:hover,
+.dark-theme .pure-button-secondary:focus {
+  color: #fff !important;
+  border-color: rgb(0, 182, 240) !important;
+  background-color: rgba(0, 182, 240, 1) !important;
+}
+
+.dark-theme .pure-button-secondary {
+  background-color: #0002;
+  color: #ddd;
+}
+
+.dark-theme a {
+  color: #adadad;
+  text-decoration: none;
+}
+
+body.dark-theme {
+  background-color: rgba(35, 35, 35, 1);
+  color: #f0f0f0;
+}
+
+.dark-theme .pure-form legend,
+.dark-theme .pure-menu-heading  {
+  color: #f0f0f0;
+}
+
+.dark-theme input,
+.dark-theme select,
+.dark-theme textarea {
+  color: rgba(35, 35, 35, 1);
+}
+
+.dark-theme .pure-form input[type="file"] {
+  color: #f0f0f0;
+}
+
+.dark-theme .searchbar input {
+  background-color: inherit;
+  color: inherit;
+}
+
+.dark-theme .error-card {
+  border: 1px solid #5e5e5e;
+}
+
+.dark-theme footer {
+  color: #adadad;
+}
+
+.dark-theme footer a {
+  color: #adadad !important;
+}
+
+.dark-theme #filters-box {
+	background: #373737;
+}
+
+.dark-theme .slider-nav  {
+  background-color: #0005;
+}

assets/css/default.css

@@ -466,22 +466,6 @@ footer {
   max-height: 30vh;
 }
 
-.light-theme footer {
-  color: #7c7c7c;
-}
-
-.dark-theme footer {
-  color: #adadad;
-}
-
-.light-theme footer a {
-  color: #7c7c7c !important;
-}
-
-.dark-theme footer a {
-  color: #adadad !important;
-}
-
 footer span {
   margin: 4px 0;
   display: block;
@@ -508,236 +492,6 @@ span > select {
 }
 
 
-/*
- * Light theme
- */
-
-.light-theme a:hover,
-.light-theme a:active,
-.light-theme summary:hover,
-.light-theme a:focus,
-.light-theme summary:focus {
-  color: #075A9E !important;
-}
-
-.light-theme .pure-button-primary:hover,
-.light-theme .pure-button-primary:focus,
-.light-theme .pure-button-secondary:hover,
-.light-theme .pure-button-secondary:focus {
-  color: #fff !important;
-  border-color: rgba(0, 182, 240, 0.75) !important;
-  background-color: rgba(0, 182, 240, 0.75) !important;
-}
-
-.light-theme .pure-button-secondary:not(.low-profile) {
-  color: #335d7a;
-  background-color: #fff2;
-}
-
-.light-theme a {
-  color: #335d7a;
-  text-decoration: none;
-}
-
-/* All links that do not fit with the default color goes here */
-.light-theme a:not([data-id]) > .icon,
-.light-theme .pure-u-lg-1-5 > .h-box > a[href^="/watch?"],
-.light-theme .playlist-restricted > ol > li > a {
-  color: #303030;
-}
-
-.light-theme .pure-menu-heading {
-  color: #565d64;
-}
-
-.light-theme .error-card {
-  border: 1px solid black;
-}
-
-@media (prefers-color-scheme: light) {
-  .no-theme a:hover,
-  .no-theme a:active,
-  .no-theme summary:hover,
-  .no-theme a:focus,
-  .no-theme summary:focus {
-    color: #075A9E !important;
-  }
-
-  .no-theme .pure-button-primary:hover,
-  .no-theme .pure-button-primary:focus,
-  .no-theme .pure-button-secondary:hover,
-  .no-theme .pure-button-secondary:focus {
-    color: #fff !important;
-    border-color: rgba(0, 182, 240, 0.75) !important;
-    background-color: rgba(0, 182, 240, 0.75) !important;
-  }
-
-  .no-theme .pure-button-secondary:not(.low-profile) {
-    color: #335d7a;
-    background-color: #fff2;
-  }
-
-  .no-theme a {
-    color: #335d7a;
-    text-decoration: none;
-  }
-
-  /* All links that do not fit with the default color goes here */
-  .no-theme a:not([data-id]) > .icon,
-  .no-theme .pure-u-lg-1-5 > .h-box > a[href^="/watch?"],
-  .no-theme .playlist-restricted > ol > li > a {
-    color: #303030;
-  }
-
-  .no-theme footer {
-    color: #7c7c7c;
-  }
-
-  .no-theme footer a {
-    color: #7c7c7c !important;
-  }
-
-  .light-theme .pure-menu-heading {
-    color: #565d64;
-  }
-
-  .no-theme .error-card {
-    border: 1px solid black;
-  }
-}
-
-
-/*
- * Dark theme
- */
-
-.dark-theme a:hover,
-.dark-theme a:active,
-.dark-theme summary:hover,
-.dark-theme a:focus,
-.dark-theme summary:focus {
-  color: rgb(0, 182, 240);
-}
-
-.dark-theme .pure-button-primary:hover,
-.dark-theme .pure-button-primary:focus,
-.dark-theme .pure-button-secondary:hover,
-.dark-theme .pure-button-secondary:focus {
-  color: #fff !important;
-  border-color: rgb(0, 182, 240) !important;
-  background-color: rgba(0, 182, 240, 1) !important;
-}
-
-.dark-theme .pure-button-secondary {
-  background-color: #0002;
-  color: #ddd;
-}
-
-.dark-theme a {
-  color: #adadad;
-  text-decoration: none;
-}
-
-body.dark-theme {
-  background-color: rgba(35, 35, 35, 1);
-  color: #f0f0f0;
-}
-
-.dark-theme .pure-form legend {
-  color: #f0f0f0;
-}
-
-.dark-theme .pure-menu-heading {
-  color: #f0f0f0;
-}
-
-.dark-theme input,
-.dark-theme select,
-.dark-theme textarea {
-  color: rgba(35, 35, 35, 1);
-}
-
-.dark-theme .pure-form input[type="file"] {
-  color: #f0f0f0;
-}
-
-.dark-theme .searchbar input {
-  background-color: inherit;
-  color: inherit;
-}
-
-.dark-theme .error-card {
-  border: 1px solid #5e5e5e;
-}
-
-@media (prefers-color-scheme: dark) {
-  .no-theme a:hover,
-  .no-theme a:active,
-  .no-theme a:focus {
-    color: rgb(0, 182, 240);
-  }
-
-  .no-theme .pure-button-primary:hover,
-  .no-theme .pure-button-primary:focus,
-  .no-theme .pure-button-secondary:hover,
-  .no-theme .pure-button-secondary:focus {
-    color: #fff !important;
-    border-color: rgb(0, 182, 240) !important;
-    background-color: rgba(0, 182, 240, 1) !important;
-  }
-
-  .no-theme .pure-button-secondary {
-    background-color: #0002;
-    color: #ddd;
-  }
-
-  .no-theme a {
-    color: #adadad;
-    text-decoration: none;
-  }
-
-  body.no-theme {
-    background-color: rgba(35, 35, 35, 1);
-    color: #f0f0f0;
-  }
-
-  .no-theme .pure-form legend {
-    color: #f0f0f0;
-  }
-
-  .no-theme .pure-menu-heading {
-    color: #f0f0f0;
-  }
-
-  .no-theme input,
-  .no-theme select,
-  .no-theme textarea {
-    color: rgba(35, 35, 35, 1);
-  }
-
-  .no-theme .pure-form input[type="file"] {
-    color: #f0f0f0;
-  }
-
-  .no-theme .searchbar input {
-    background-color: inherit;
-    color: inherit;
-  }
-
-  .no-theme footer {
-    color: #adadad;
-  }
-
-  .no-theme footer a {
-    color: #adadad !important;
-  }
-
-  .no-theme .error-card {
-    border: 1px solid #5e5e5e;
-  }
-}
-
-
 /*
  * Miscellanous
  */

assets/css/light.css

@@ -0,0 +1,67 @@
+/* Contains the CSS for the Invidious light theme
+
+--------
+This file should not get loaded by the user as the css here will be used
+to generate theme.css as to support user-agent dark/light theme
+in addition to the class-based swap method without duplicating any styles.
+------
+
+*/
+
+.light-theme a:hover,
+.light-theme a:active,
+.light-theme summary:hover,
+.light-theme a:focus,
+.light-theme summary:focus {
+  color: #075A9E !important;
+}
+
+.light-theme .pure-button-primary:hover,
+.light-theme .pure-button-primary:focus,
+.light-theme .pure-button-secondary:hover,
+.light-theme .pure-button-secondary:focus {
+  color: #fff !important;
+  border-color: rgba(0, 182, 240, 0.75) !important;
+  background-color: rgba(0, 182, 240, 0.75) !important;
+}
+
+.light-theme .pure-button-secondary:not(.low-profile) {
+  color: #335d7a;
+  background-color: #fff2;
+}
+
+.light-theme a {
+  color: #335d7a;
+  text-decoration: none;
+}
+
+/* All links that do not fit with the default color goes here */
+.light-theme a:not([data-id]) > .icon,
+.light-theme .pure-u-lg-1-5 > .h-box > a[href^="/watch?"],
+.light-theme .playlist-restricted > ol > li > a {
+  color: #303030;
+}
+
+.light-theme .pure-menu-heading {
+  color: #565d64;
+}
+
+.light-theme footer {
+  color: #7c7c7c;
+}
+
+.light-theme footer a {
+  color: #7c7c7c !important;
+}
+
+.light-theme .error-card {
+  border: 1px solid black;
+}
+
+.light-theme #filters-box {
+	background: #dfdfdf;
+}
+
+.light-theme .slider-nav {
+    background-color: #ddd;
+}

assets/css/search.css

@@ -95,27 +95,3 @@ fieldset, legend {
 		padding: 15px;
 	}
 }
-
-/* Light theme */
-
-.light-theme #filters-box {
-	background: #dfdfdf;
-}
-
-@media (prefers-color-scheme: light) {
-	.no-theme #filters-box {
-		background: #dfdfdf;
-	}
-}
-
-/* Dark theme */
-
-.dark-theme #filters-box {
-	background: #373737;
-}
-
-@media (prefers-color-scheme: dark) {
-	.no-theme #filters-box {
-		background: #373737;
-	}
-}

src/ext/kemal_static_file_handler.cr

@@ -159,7 +159,9 @@ module Kemal
           redirect_to context, expanded_path + '/'
         end
 
-        return call_next(context) if file_info.nil?
+        return call_next(context) if file_info.nil? ||
+                                     file_path.ends_with?("dark.css") ||
+                                     file_path.ends_with?("light.css")
 
         if is_dir
           if config.is_a?(Hash) && config["dir_listing"] == true

src/invidious/routes/get_theme_css_file.cr

@@ -0,0 +1,52 @@
+# No need to initialize yet another namespace
+#
+# :nodoc:
+module Invidious::Routes::Misc
+  private CSS_THEME_LIGHT    = File.read("assets/css/light.css")
+  private CSS_THEME_UA_LIGHT = CSS_THEME_LIGHT.gsub(".light-theme", ".no-theme")
+
+  private CSS_THEME_DARK    = File.read("assets/css/dark.css")
+  private CSS_THEME_UA_DARK = CSS_THEME_DARK.gsub(".dark-theme", ".no-theme")
+
+  private THEME_LAST_MODIFIED = {
+    File.info("assets/css/light.css").modification_time,
+    File.info("assets/css/dark.css").modification_time,
+  }.min
+
+  def self.theme_css(env)
+    env.response.headers["Content-Type"] = "text/css; charset=utf-8"
+
+    # Replicate cache header behavior of static file handler
+    env.response.headers["Etag"] = %{W/"#{THEME_LAST_MODIFIED.to_unix}"}
+    env.response.headers["Last-Modified"] = HTTP.format_time(THEME_LAST_MODIFIED)
+
+    if cache_request?(env, THEME_LAST_MODIFIED)
+      env.response.status = HTTP::Status::NOT_MODIFIED
+      return
+    end
+
+    # Usually added in `send_file` when static_headers proc is called
+    env.response.headers["Cache-Control"] = "max-age=2629800"
+
+    rendered "theme.css"
+  end
+
+  # Taken from https://github.com/crystal-lang/crystal/blob/1.16.3/src/http/server/handlers/static_file_handler.cr#L236
+  private def self.cache_request?(context : HTTP::Server::Context, last_modified : Time) : Bool
+    # According to RFC 7232:
+    # A recipient must ignore If-Modified-Since if the request contains an If-None-Match header field
+    if if_none_match = context.request.if_none_match
+      match = {"*", context.response.headers["Etag"]}
+      if_none_match.any? { |etag| match.includes?(etag) }
+    elsif if_modified_since = context.request.headers["If-Modified-Since"]?
+      header_time = HTTP.parse_time(if_modified_since)
+      # File mtime probably has a higher resolution than the header value.
+      # An exact comparison might be slightly off, so we add 1s padding.
+      # Static files should generally not be modified in subsecond intervals, so this is perfectly safe.
+      # This might be replaced by a more sophisticated time comparison when it becomes available.
+      !!(header_time && last_modified <= header_time + 1.second)
+    else
+      false
+    end
+  end
+end

src/invidious/routing.cr

@@ -21,6 +21,7 @@ module Invidious::Routing
       get "/privacy", Routes::Misc, :privacy
       get "/licenses", Routes::Misc, :licenses
       get "/redirect", Routes::Misc, :cross_instance_redirect
+      get "/css/theme.css", Routes::Misc, :theme_css
 
       self.register_channel_routes
       self.register_watch_routes

src/invidious/views/template.ecr

@@ -21,6 +21,7 @@
     <link rel="stylesheet" href="/css/grids-responsive-min.css?v=<%= ASSET_COMMIT %>">
     <link rel="stylesheet" href="/css/ionicons.min.css?v=<%= ASSET_COMMIT %>">
     <link rel="stylesheet" href="/css/default.css?v=<%= ASSET_COMMIT %>">
+    <link rel="stylesheet" href="/css/theme.css?v=<%= ASSET_COMMIT %>">
     <link rel="stylesheet" href="/css/carousel.css?v=<%= ASSET_COMMIT %>">
     <script src="/js/_helpers.js?v=<%= ASSET_COMMIT %>"></script>
 </head>

src/invidious/views/theme.css.ecr

@@ -0,0 +1,10 @@
+/*
+This files contains an automatically generated CSS file that contains the styles
+for the dark and light themes of Invidious. Automatically generating this file allows
+supporting both the user-agent color scheme preference and class-based theme preference
+without duplicating the defined styles twice for each theme.
+*/
+<%=CSS_THEME_LIGHT-%>
+@media (prefers-color-scheme: light) {<%= CSS_THEME_UA_LIGHT %>}
+<%=CSS_THEME_DARK%>
+@media (prefers-color-scheme: dark) {<%=CSS_THEME_UA_DARK%>}