Add color scheme (dark and light mode) support

Add 'ui.gtk.color_scheme' config variable with 'system', 'light' and
'dark' string values. Config observer in main.py changes the color to
match the config.

System color scheme is read from freedesktop.org Settings portal via
Dbus.

The setting can be changed with a combo box in the preferences window
via new function connect_gtk_combo_box_text(). If Settings portal cannot
be found, only 'light' and 'dark' options are available in preferences.

share/gpodder/ui/gtk/gpodderpreferences.ui

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.38.2 -->
+<!-- Generated with glade 3.40.0 -->
 <!--*- mode: xml -*-->
 <interface>
   <requires lib="gtk+" version="3.16"/>
@@ -273,6 +273,50 @@
                                 <property name="position">2</property>
                               </packing>
                             </child>
+                            <child>
+                              <object class="GtkBox">
+                                <property name="visible">True</property>
+                                <property name="can-focus">False</property>
+                                <child>
+                                  <object class="GtkLabel" id="label_color_scheme">
+                                    <property name="visible">True</property>
+                                    <property name="can-focus">False</property>
+                                    <property name="margin-end">8</property>
+                                    <property name="label" translatable="yes">Color scheme:</property>
+                                  </object>
+                                  <packing>
+                                    <property name="expand">False</property>
+                                    <property name="fill">True</property>
+                                    <property name="position">0</property>
+                                  </packing>
+                                </child>
+                                <child>
+                                  <object class="GtkComboBoxText" id="combo_color_scheme">
+                                    <property name="visible">True</property>
+                                    <property name="can-focus">False</property>
+                                    <property name="hexpand">True</property>
+                                    <property name="active">0</property>
+                                    <property name="active-id">1</property>
+                                    <items>
+                                      <item id="system" translatable="yes">System</item>
+                                      <item id="light" translatable="yes">Light</item>
+                                      <item id="dark" translatable="yes">Dark</item>
+                                    </items>
+                                  </object>
+                                  <packing>
+                                    <property name="expand">False</property>
+                                    <property name="fill">True</property>
+                                    <property name="pack-type">end</property>
+                                    <property name="position">1</property>
+                                  </packing>
+                                </child>
+                              </object>
+                              <packing>
+                                <property name="expand">False</property>
+                                <property name="fill">True</property>
+                                <property name="position">3</property>
+                              </packing>
+                            </child>
                           </object>
                           <packing>
                             <property name="name">general</property>
@@ -1157,7 +1201,6 @@
                             <property name="can-focus">False</property>
                             <property name="border-width">0</property>
                             <property name="orientation">vertical</property>
-                            <property name="spacing">0</property>
                             <child>
                               <object class="GtkTreeView" id="treeviewExtensions">
                                 <property name="visible">True</property>

src/gpodder/config.py

@@ -182,6 +182,7 @@
             },
 
             'html_shownotes': True,  # enable webkit renderer
+            'color_scheme': 'system',  # system, light, dark
         },
     },
 

src/gpodder/gtkui/app.py

@@ -200,8 +200,50 @@ def do_activate(self):
                 # Handle "subscribe to podcast" events from firefox
                 macosx.register_handlers(self.window)
 
+            # Set dark mode from config key, or from Settings portal if it
+            # exists and color_scheme from config is 'system'
+            if getattr(gpodder.dbus_session_bus, 'fake', False):
+                self.have_settings_portal = False
+                self.set_dark_mode(self.window.config.ui.gtk.color_scheme == 'dark')
+            else:
+                self.read_portal_color_scheme()
+                gpodder.dbus_session_bus.add_signal_receiver(
+                    self.on_portal_setting_changed, "SettingChanged", None,
+                    "org.freedesktop.portal.Desktop", "/org/freedesktop/portal/desktop")
+
         self.window.gPodder.present()
 
+    def set_dark_mode(self, dark):
+        settings = Gtk.Settings.get_default()
+        settings.props.gtk_application_prefer_dark_theme = 1 if dark else 0
+
+    def read_portal_color_scheme(self):
+        gpodder.dbus_session_bus.call_async(
+            "org.freedesktop.portal.Desktop", "/org/freedesktop/portal/desktop",
+            "org.freedesktop.portal.Settings", "ReadOne", "ss",
+            ("org.freedesktop.appearance", "color-scheme"),
+            self.on_portal_settings_read, self.on_portal_settings_read_error)
+
+    def on_portal_settings_read(self, value):
+        self.have_settings_portal = True
+        if self.window.config.ui.gtk.color_scheme == 'system':
+            self.set_dark_mode(value == 1)
+        else:
+            self.set_dark_mode(self.window.config.ui.gtk.color_scheme == 'dark')
+
+    def on_portal_settings_read_error(self, value):
+        self.have_settings_portal = False
+        self.set_dark_mode(self.window.config.ui.gtk.color_scheme == 'dark')
+
+    def on_portal_setting_changed(self, namespace, key, value):
+        if (namespace == 'org.freedesktop.appearance'
+                and key == 'color-scheme'):
+            dark = (value == 1)
+            if self.window.config.ui.gtk.color_scheme == 'system':
+                logger.debug(
+                    f"'color-scheme' changed to {value}, setting dark mode to {dark}")
+                self.set_dark_mode(dark)
+
     def on_menu(self, action, param):
         self.menu_popover.popup()
 
@@ -265,7 +307,8 @@ def on_itemPreferences_activate(self, action, param=None):
                 on_send_full_subscriptions=self.window.on_send_full_subscriptions,
                 on_itemExportChannels_activate=self.window.on_itemExportChannels_activate,
                 on_extension_enabled=self.on_extension_enabled,
-                on_extension_disabled=self.on_extension_disabled)
+                on_extension_disabled=self.on_extension_disabled,
+                have_settings_portal=self.have_settings_portal)
 
     def on_goto_mygpo(self, action, param):
         self.window.mygpo_client.open_website()

src/gpodder/gtkui/config.py

@@ -154,6 +154,13 @@ def _togglebutton_toggled(togglebutton):
             setattr(self, name, togglebutton.get_active())
         togglebutton.connect('toggled', _togglebutton_toggled)
 
+    def connect_gtk_combo_box_text(self, name, combo_text):
+        combo_text.set_active_id(getattr(self, name))
+
+        def _combo_box_text_changed(combo):
+            setattr(self, name, combo.get_active_id())
+        combo_text.connect('changed', _combo_box_text_changed)
+
     def connect_gtk_window(self, window, config_prefix, show_window=False):
         cfg = getattr(self.ui.gtk.state, config_prefix)
 

src/gpodder/gtkui/desktop/preferences.py

@@ -205,6 +205,21 @@ def new(self):
         index = self.video_player_model.get_index(self._config.player.video)
         self.combo_video_player_app.set_active(index)
 
+        self.combo_color_scheme.remove_all()
+        self.combo_color_scheme.prepend('dark', 'Dark')
+        self.combo_color_scheme.prepend('light', 'Light')
+        cs = self._config.ui.gtk.color_scheme
+        if self.have_settings_portal:
+            self.combo_color_scheme.prepend('system', 'System')
+            self.combo_color_scheme.set_active_id(cs)
+        else:
+            if cs == 'system':
+                self.combo_color_scheme.set_active_id('light')
+                self._config.ui.gtk.color_scheme = 'light'
+            else:
+                self.combo_color_scheme.set_active_id(cs)
+        self._config.connect_gtk_combo_box_text('ui.gtk.color_scheme', self.combo_color_scheme)
+
         self.preferred_youtube_format_model = YouTubeVideoFormatListModel(self._config)
         self.combobox_preferred_youtube_format.set_model(self.preferred_youtube_format_model)
         cellrenderer = Gtk.CellRendererText()

src/gpodder/gtkui/main.py

@@ -1486,6 +1486,11 @@ def _on_config_changed(self, name, old_value, new_value):
             self.update_podcast_list_model()
         elif name == 'ui.gtk.episode_list.columns':
             self.update_episode_list_columns_visibility()
+        elif name == 'ui.gtk.color_scheme':
+            if new_value == 'system':
+                self.application.read_portal_color_scheme()
+            else:
+                self.application.set_dark_mode(new_value == 'dark')
         elif name == 'limit.downloads.concurrent_max':
             # Do not allow value to be set below 1
             if new_value < 1: