[Fonts] Wire FontConfig into ThemeManager with appFont and preview (#7535)

* [Fonts] Wire FontConfig into ThemeManager with appFont and preview

* [Fonts] Restore the startup font when a config has no InterfaceDefault

- Capture the untouched application font next to the default palette and use
  it in previewFonts' else branch, so a config without InterfaceDefault
  restores the startup font instead of leaving the last preview applied.
- Drop the unpolish/polish loop from previewFonts: QApplication::setFont
  already notifies every widget, and the loop ran on every editor auto-apply.

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/theme_manager.cpp

@@ -127,8 +127,10 @@ static QString usableDefaultStyle(const QString &style)
 ThemeManager::ThemeManager(QObject *parent) : QObject(parent)
 {
     defaultStyleName = usableDefaultStyle(qApp->style()->objectName());
-    // Capture the untouched application palette before any theme is applied.
+    // Capture the untouched application palette and font before any theme is
+    // applied.
     defaultPalette = qApp->palette();
+    defaultFont = qApp->font();
     ensureThemeDirectoryExists();
 #if (QT_VERSION >= QT_VERSION_CHECK(6, 5, 0))
     connect(QGuiApplication::styleHints(), &QStyleHints::colorSchemeChanged, this, [this] {
@@ -440,6 +442,34 @@ PaletteConfig ThemeManager::loadDefaultPaletteConfig(const QString &themeDirPath
     return cfg;
 }
 
+FontConfig ThemeManager::loadFontConfig(const QString &themeDirPath)
+{
+    if (themeDirPath.isEmpty()) {
+        return {};
+    }
+    return FontConfig::fromThemeDir(themeDirPath);
+}
+
+bool ThemeManager::saveFontConfig(const QString &themeDirPath, const FontConfig &cfg)
+{
+    if (themeDirPath.isEmpty()) {
+        return false;
+    }
+
+    QDir dir(themeDirPath);
+    if (!dir.exists()) {
+        dir.mkpath(".");
+    }
+
+    QFile f(dir.absoluteFilePath(FontConfig::fileName()));
+    if (!f.open(QIODevice::WriteOnly | QIODevice::Text | QIODevice::Truncate)) {
+        return false;
+    }
+
+    QTextStream(&f) << cfg.toToml();
+    return true;
+}
+
 bool ThemeManager::commitPalette(const QString &themeDirPath, const QString &colorScheme, const PaletteConfig &cfg)
 {
     if (!savePaletteConfig(themeDirPath, colorScheme, cfg)) {
@@ -488,6 +518,24 @@ void ThemeManager::previewPalette(const PaletteConfig &cfg, const QString &schem
     applyStyleAndPalette(themeName, themeCfg, cfg, scheme);
 }
 
+void ThemeManager::previewFonts(const FontConfig &cfg)
+{
+    currentFonts = cfg;
+
+    // QApplication::setFont already sends a font change to every widget, so a
+    // repolish pass is not needed for fonts (unlike the palette path).
+    const auto it = cfg.fonts.constFind(AppFont::InterfaceDefault);
+    if (it != cfg.fonts.constEnd()) {
+        qApp->setFont(it.value());
+    } else {
+        // A config without InterfaceDefault means "no override": restore the
+        // startup font instead of leaving the last preview applied.
+        qApp->setFont(defaultFont);
+    }
+
+    emit fontsChanged();
+}
+
 void ThemeManager::applyStyleAndPalette(const QString &themeName,
                                         const ThemeConfig &themeCfg,
                                         const PaletteConfig &palCfg,
@@ -591,6 +639,18 @@ QColor ThemeManager::appColor(AppColor::Role role) const
     return accent;
 }
 
+QFont ThemeManager::appFont(AppFont::Role role) const
+{
+    const auto it = currentFonts.fonts.constFind(role);
+    if (it != currentFonts.fonts.constEnd()) {
+        return it.value();
+    }
+
+    // No per-role scaling: every unset role resolves to the application font,
+    // so with no fonts.toml present the result is identical to before.
+    return qApp->font();
+}
+
 void ThemeManager::themeChangedSlot()
 {
     QString themeName = SettingsCache::instance().getThemeName();
@@ -642,6 +702,24 @@ void ThemeManager::themeChangedSlot()
 
     applyStyleAndPalette(themeName, themeCfg, palette, activeScheme);
 
+    // ── Load fonts: shared per theme, no light/dark split ───────────────────
+    FontConfig fonts = loadFontConfig(dirPath);
+    if (!fonts.hasFonts()) {
+        // The shipped fonts.toml may live in the system theme directory rather
+        // than the resolved (user) theme directory, so built-in themes still
+        // get their curated fonts.
+        const QString sysFontPath = QDir(systemThemesBasePath()).absoluteFilePath(themeName);
+        if (sysFontPath != dirPath) {
+            fonts = loadFontConfig(sysFontPath);
+        }
+    }
+    currentFonts = fonts;
+    const auto fontIt = currentFonts.fonts.constFind(AppFont::InterfaceDefault);
+    if (fontIt != currentFonts.fonts.constEnd()) {
+        qApp->setFont(fontIt.value());
+    }
+    emit fontsChanged();
+
     QStringList resources;
     if (!dirPath.isEmpty()) {
         resources << dir.absolutePath();