feat: add ColorAwareApp mixin (resolves #465)

dzgui/views/mixins/colorscheme.py

@@ -0,0 +1,37 @@
+from typing import Any
+
+from dzgui.const.constants import (
+    GIO_SETTINGS_KEY,
+    GIO_SETTINGS_INTERFACE,
+    GIO_SETTINGS_PROP,
+    GIO_SETTINGS_VAL,
+)
+
+import gi
+
+gi.require_version("Gtk", "3.0")
+from gi.repository import Gtk, Gio  # noqa
+
+
+class ColorAwareApp:
+    """
+    Polls the local theme's color scheme settings.
+    Intended to be consumed by Gtk.Applications (or ephemeral widgets like EarlyAlertDialogs)
+    on initialization, prior to being realized. Applying scheme changes too late in the chain
+    may cause a blinking effect.
+    """
+
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        super().__init__(*args, **kwargs)
+        self.interface_settings = Gio.Settings.new(GIO_SETTINGS_INTERFACE)
+        self.interface_settings.connect(
+            "changed::color-scheme", self._on_color_scheme_changed
+        )
+        self.default_settings = Gtk.Settings.get_default()
+        self._on_color_scheme_changed(self.interface_settings, GIO_SETTINGS_PROP)
+
+    def _on_color_scheme_changed(self, settings: Gio.Settings, prop: str) -> None:
+        state = self.interface_settings.get_string(prop) == GIO_SETTINGS_VAL
+        if self.default_settings is None:
+            return
+        self.default_settings.set_property(GIO_SETTINGS_KEY, state)