refactor: introduce thread local THEME variable and distinguish between custom and system theme settings

src/app/core.rs

@@ -40,7 +40,7 @@ pub struct Core {
     /// Scaling factor used by the application
     scale_factor: f32,
 
-    pub theme: Theme,
+    pub system_theme: Theme,
     pub(crate) title: String,
     pub window: Window,
 }
@@ -56,7 +56,7 @@ impl Default for Core {
                 toggled_condensed: true,
             },
             scale_factor: 1.0,
-            theme: theme::theme(),
+            system_theme: theme::theme(),
             title: String::new(),
             window: Window {
                 can_fullscreen: false,

src/app/cosmic.rs

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
 use super::{command, Application, ApplicationExt, Core, Subscription};
-use crate::theme::{self, Theme};
+use crate::theme::{self, Theme, ThemeType, THEME};
 use crate::widget::nav_bar;
 use crate::{keyboard_nav, Element};
 #[cfg(feature = "wayland")]
@@ -36,6 +36,8 @@ pub enum Message {
     ScaleFactor(f32),
     /// Requests theme changes.
     ThemeChange(Theme),
+    /// Notification of system theme changes.
+    SystemThemeChange(Theme),
     /// Toggles visibility of the nav bar.
     ToggleNavBar,
     /// Toggles the condensed status of the nav bar.
@@ -146,14 +148,14 @@ where
                 .map(Message::KeyboardNav)
                 .map(super::Message::Cosmic),
             theme::subscription(0)
-                .map(Message::ThemeChange)
+                .map(Message::SystemThemeChange)
                 .map(super::Message::Cosmic),
             window_events.map(super::Message::Cosmic),
         ])
     }
 
     fn theme(&self) -> Self::Theme {
-        self.app.core().theme.clone()
+        THEME.with(|t| t.borrow().clone())
     }
 
     #[cfg(feature = "wayland")]
@@ -267,12 +269,32 @@ impl<T: Application> Cosmic<T> {
             }
 
             Message::ThemeChange(theme) => {
-                self.app.core_mut().theme = theme;
+                // our system theme is always receiving updates so we should use it instead
+                let theme = if matches!(theme.theme_type, ThemeType::System(_)) {
+                    self.app.core().system_theme.clone()
+                } else {
+                    theme
+                };
+
+                THEME.with(move |t| {
+                    let mut cosmic_theme = t.borrow_mut();
+                    cosmic_theme.set_theme(theme.theme_type);
+                });
             }
 
             Message::ScaleFactor(factor) => {
                 self.app.core_mut().set_scale_factor(factor);
             }
+            Message::SystemThemeChange(theme) => {
+                self.app.core_mut().system_theme = theme.clone();
+                THEME.with(move |t| {
+                    let mut cosmic_theme = t.borrow_mut();
+                    // only apply update if the theme is set to load a system theme
+                    if matches!(cosmic_theme.theme_type, ThemeType::System(_)) {
+                        cosmic_theme.set_theme(theme.theme_type);
+                    }
+                });
+            }
         }
 
         iced::Command::none()

src/app/mod.rs

@@ -33,6 +33,7 @@ pub mod message {
 
 pub use self::core::Core;
 pub use self::settings::Settings;
+use crate::theme::THEME;
 use crate::widget::nav_bar;
 use crate::{Element, ElementExt};
 use apply::Apply;
@@ -58,7 +59,10 @@ pub fn run<App: Application>(settings: Settings, flags: App::Flags) -> iced::Res
     core.set_scale_factor(settings.scale_factor);
     core.set_window_width(settings.size.0);
     core.set_window_height(settings.size.1);
-    core.theme = settings.theme;
+    THEME.with(move |t| {
+        let mut cosmic_theme = t.borrow_mut();
+        cosmic_theme.set_theme(settings.theme.theme_type);
+    });
 
     let mut iced = iced::Settings::with_flags((core, flags));