Use json file based themes instead of code to create them (theme editor + theme mode settings)

common/themes/appearance_configuration.h

@@ -0,0 +1,48 @@
+#ifndef APPEARANCE_CONFIGURATION_H
+#define APPEARANCE_CONFIGURATION_H
+
+#include <QObject>
+#include <QString>
+
+enum class ThemeMode {
+    FollowSystem,
+    Light,
+    Dark,
+    ForcedTheme,
+};
+
+struct ThemeSelection {
+    ThemeMode mode = ThemeMode::FollowSystem;
+    QString lightThemeId = "builtin/light";
+    QString darkThemeId = "builtin/dark";
+    QString fixedThemeId = "builtin/classic";
+};
+
+// Persists theme selection settings to a QSettings INI file under the
+// [Appearance] group. All access is on-demand (no persistent QSettings handle)
+// so the caller does not need to manage a QSettings lifetime.
+class AppearanceConfiguration : public QObject
+{
+    Q_OBJECT
+public:
+    explicit AppearanceConfiguration(const QString &settingsFilePath, QObject *parent = nullptr);
+
+    ThemeSelection selection() const { return sel; }
+
+    void setMode(ThemeMode mode);
+    void setLightThemeId(const QString &id);
+    void setDarkThemeId(const QString &id);
+    void setFixedThemeId(const QString &id);
+
+signals:
+    void selectionChanged();
+
+private:
+    QString path;
+    ThemeSelection sel;
+
+    void load();
+    void write(const QString &key, const QString &value);
+};
+
+#endif // APPEARANCE_CONFIGURATION_H