core: create qPrefLanguage from SettingsObjectWrapper

Update set/get functions to follow common name scheme:
- get function have same name as in struct preferences
- set function have set_<name>
- signal function have <name>_changed

one class one .h/.cpp is the C++ idiom. Having load/sync of each
variable in 1 functions (in contrast to the distributed way
SettingsObjectWrapper handles it) secures the same storage name
is used. Having the set/get/load/sync functions grouped together
makes it easier to get an overview.

REMARK: this commit only defines the class, it is not active in production

Signed-off-by: Jan Iversen <jani@apache.org>

core/settings/qPrefLanguage.h

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef QPREFLANGUAGE_H
+#define QPREFLANGUAGE_H
+#include "core/pref.h"
+
+#include <QObject>
+
+class qPrefLanguage : public QObject {
+	Q_OBJECT
+	Q_PROPERTY(QString date_format READ date_format WRITE set_date_format NOTIFY date_format_changed);
+	Q_PROPERTY(bool date_format_override READ date_format_override WRITE set_date_format_override NOTIFY date_format_override_changed);
+	Q_PROPERTY(QString date_format_short READ date_format_short WRITE set_date_format_short NOTIFY date_format_short_changed);
+	Q_PROPERTY(QString language READ language WRITE set_language NOTIFY language_changed);
+	Q_PROPERTY(QString lang_locale READ lang_locale WRITE set_lang_locale NOTIFY lang_locale_changed);
+	Q_PROPERTY(QString time_format READ time_format WRITE set_time_format NOTIFY time_format_changed);
+	Q_PROPERTY(bool time_format_override READ time_format_override WRITE set_time_format_override NOTIFY time_format_override_changed);
+	Q_PROPERTY(bool use_system_language READ use_system_language WRITE set_use_system_language NOTIFY use_system_language_changed);
+
+public:
+	qPrefLanguage(QObject *parent = NULL);
+	static qPrefLanguage *instance();
+
+	// Load/Sync local settings (disk) and struct preference
+	void loadSync(bool doSync);
+	void load() { loadSync(false); }
+	void sync() { loadSync(true); }
+
+public:
+	const QString date_format() { return prefs.date_format; }
+	bool date_format_override() { return prefs.date_format_override; }
+	const QString date_format_short() { return prefs.date_format_short; }
+	const QString language() { return prefs.locale.language; }
+	const QString lang_locale() { return prefs.locale.lang_locale; }
+	const QString time_format() { return prefs.time_format; }
+	bool time_format_override() { return prefs.time_format_override; }
+	bool use_system_language() { return prefs.locale.use_system_language; }
+
+public slots:
+	void set_date_format(const QString& value);
+	void set_date_format_override(bool value);
+	void set_date_format_short(const QString& value);
+	void set_language(const QString& value);
+	void set_lang_locale(const QString& value);
+	void set_time_format(const QString& value);
+	void set_time_format_override(bool value);
+	void set_use_system_language(bool value);
+
+signals:
+	void date_format_changed(const QString& value);
+	void date_format_override_changed(bool value);
+	void date_format_short_changed(const QString& value);
+	void language_changed(const QString& value);
+	void lang_locale_changed(const QString& value);
+	void time_format_changed(const QString& value);
+	void time_format_override_changed(bool value);
+	void use_system_language_changed(bool value);
+
+private:
+	void disk_date_format(bool doSync);
+	void disk_date_format_override(bool doSync);
+	void disk_date_format_short(bool doSync);
+	void disk_language(bool doSync);
+	void disk_lang_locale(bool doSync);
+	void disk_time_format(bool doSync);
+	void disk_time_format_override(bool doSync);
+	void disk_use_system_language(bool doSync);
+};
+
+#endif