theme: Use a matching layout theme for any widget theme

Dedicated styling is now possible for themes which have a corresponding style-theme.css file. Adwaita:dark gets one, whereas other themes use the new generic fallback theme.

src/style.rs

@@ -0,0 +1,139 @@
+/* 
+ * Copyright (C) 2000 Red Hat, Inc.
+ * Copyright (C) 2019 Purism, SPC
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.Free
+ */
+
+/*! CSS data loading */
+
+use std::env;
+
+use glib::object::ObjectExt;
+
+/// Gathers stuff defined in C or called by C
+pub mod c {
+    use super::*;
+    use gio;
+    use gtk;
+    use gtk_sys;
+    
+    use gtk::CssProviderExt;
+    use glib::translate::ToGlibPtr;
+
+    /// Loads the layout style based on current theme
+    /// without having to worry about string allocation
+    #[no_mangle]
+    pub extern "C"
+    fn squeek_load_style() -> *const gtk_sys::GtkCssProvider {
+        unsafe { gtk::set_initialized() };
+        let theme = gtk::Settings::get_default()
+            .map(|settings| get_theme_name(&settings));
+        
+        let css_name = path_from_theme(theme);
+
+        let resource_name = if gio::resources_get_info(
+            &css_name,
+            gio::ResourceLookupFlags::NONE
+        ).is_ok() {
+            css_name
+        } else { // use default if this path doesn't exist
+            path_from_theme(None)
+        };
+
+        let provider = gtk::CssProvider::new();
+        provider.load_from_resource(&resource_name);
+        provider.to_glib_full()
+    }
+}
+
+// not Adwaita, but rather fall back to default
+const DEFAULT_THEME_NAME: &str = "";
+
+/// Sugar for logging errors in results
+trait Warn {
+    type Value;
+    fn ok_warn(self, msg: &str) -> Option<Self::Value>;
+}
+
+impl<T, E: std::error::Error> Warn for Result<T, E> {
+    type Value = T;
+    fn ok_warn(self, msg: &str) -> Option<T> {
+        self.map_err(|e| {
+            eprintln!("{}: {}", msg, e);
+            e
+        }).ok()
+    }
+}
+
+struct GtkTheme {
+    name: String,
+    variant: Option<String>,
+}
+
+/// Gets theme as determined by the toolkit
+/// Ported from GTK's gtksettings.c
+fn get_theme_name(settings: &gtk::Settings) -> GtkTheme {
+    let env_theme = env::var("GTK_THEME")
+        .map(|theme| {
+            let mut parts = theme.splitn(2, ":");
+            GtkTheme {
+                // guaranteed at least empty string
+                // as the first result from splitting a string
+                name: parts.next().unwrap().into(),
+                variant: parts.next().map(String::from)
+            }
+        })
+        .map_err(|e| {
+            match &e {
+                env::VarError::NotPresent => {},
+                e => eprintln!("GTK_THEME variable invalid: {}", e),
+            };
+            e
+        }).ok();
+
+    match env_theme {
+        Some(theme) => theme,
+        None => GtkTheme {
+            name: {
+                settings.get_property("gtk-theme-name")
+                    .ok_warn("No theme name")
+                    .and_then(|value| value.get::<String>())
+                    .unwrap_or(DEFAULT_THEME_NAME.into())
+            },
+            variant: {
+                settings.get_property("gtk-application-prefer-dark-theme")
+                    .ok_warn("No settings key")
+                    .and_then(|value| value.get::<bool>())
+                    .and_then(|dark_preferred| match dark_preferred {
+                        true => Some("dark".into()),
+                        false => None,
+                    })
+            },
+        },
+    }
+}
+
+fn path_from_theme(theme: Option<GtkTheme>) -> String {
+    format!(
+        "/sm/puri/squeekboard/style{}.css",
+        match theme {
+            Some(GtkTheme { name, variant: Some(variant) }) => {
+                format!("-{}:{}", name, variant)
+            },
+            Some(GtkTheme { name, variant: None }) => format!("-{}", name),
+            None => "".into(),
+        }
+    )
+}