Improve timezone and language handling

Ensure that changes performed in the Settings UI cause writes to
the appropriate backend setting value.

Ensure that backend setting value changes trigger updates to the
loaded translation catalogue and/or clock.

Note that currently Qt for WebAssembly doesn't support proper
QTimezone enumeration or tzdb.  Thus, we only support UTC or
local timezone (i.e. timezone of the browser, not the device).
Future resolution required, see issue #299 for more info.

Contributes to issue #406

data/SystemSettings.qml

@@ -118,6 +118,24 @@ QtObject {
 		}
 	}
 
+	property DataPoint timeZone: DataPoint {
+		source: "com.victronenergy.settings/Settings/System/TimeZone"
+		onValueChanged: {
+			if (value !== undefined) {
+				ClockTime.systemTimeZone = value
+			}
+		}
+	}
+
+	property DataPoint language: DataPoint {
+		source: "com.victronenergy.settings/Settings/Gui/Language"
+		onValueChanged: {
+			if (value !== undefined) {
+				Language.setCurrentLanguage(value)
+			}
+		}
+	}
+
 	function reset() {
 		// no-op
 	}

pages/settings/PageSettingsDisplay.qml

@@ -99,6 +99,11 @@ Page {
 
 				onOptionClicked: function(index) {
 					Language.current = optionModel.languageAt(index)
+					languageDataPoint.setValue(Language.toString(Language.current))
+				}
+
+				property DataPoint languageDataPoint: DataPoint {
+					source: "com.victronenergy.settings/Settings/Gui/Language"
 				}
 			}
 

pages/settings/PageTzInfo.qml

@@ -61,7 +61,7 @@ Page {
 			ListTextItem {
 				//% "Date/Time UTC"
 				text: qsTrId("settings_tz_date_time_utc")
-				secondaryText: Qt.formatDateTime(ClockTime.currentDateTimeUtc, "yyyy-MM-dd hh:mm")
+				secondaryText: ClockTime.currentTimeUtcText
 			}
 
 			ListButton {

src/clocktime.cpp

@@ -1,5 +1,9 @@
 #include "clocktime.h"
 
+#if !defined(VENUS_WEBASSEMBLY_BUILD)
+#include <QTimeZone>
+#endif
+
 using namespace Victron::VenusOS;
 
 ClockTime::ClockTime(QObject *parent)
@@ -32,13 +36,27 @@ void ClockTime::timerEvent(QTimerEvent *)
 
 void ClockTime::updateTime()
 {
-	m_currentDateTime = QDateTime::currentDateTime();
-	m_currentDateTimeUtc = m_currentDateTime.toUTC();
+	if (m_systemTimeZone.compare(QStringLiteral("/UTC"), Qt::CaseInsensitive) == 0
+			|| m_systemTimeZone.compare(QStringLiteral("UTC"), Qt::CaseInsensitive) == 0) {
+		m_currentDateTime = QDateTime::currentDateTimeUtc();
+	} else {
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+		// Cannot use QTimeZone in Emscripten builds.
+		// We thus cannot convert to the specified timezone offset.
+		// The local time will be the local time of the browser.
+		m_currentDateTime = QDateTime::currentDateTime();
+#else
+		m_currentDateTime = QDateTime::currentDateTime().toTimeZone(QTimeZone(m_systemTimeZone.toUtf8()));
+#endif
+	}
+	m_currentDateTimeUtc = QDateTime::currentDateTimeUtc();
 	m_currentTimeText = m_currentDateTime.toString("hh:mm");
+	m_currentTimeUtcText = m_currentDateTimeUtc.toString("yyyy-MM-dd hh:mm");
 
 	emit currentDateTimeChanged();
 	emit currentDateTimeUtcChanged();
 	emit currentTimeTextChanged();
+	emit currentTimeUtcTextChanged();
 }
 
 void ClockTime::scheduleNextTimeCheck(const QTime &now)
@@ -57,3 +75,17 @@ ClockTime* ClockTime::instance(QObject* parent)
 	return new ClockTime(parent);
 }
 
+QString ClockTime::systemTimeZone() const
+{
+	return m_systemTimeZone;
+}
+
+void ClockTime::setSystemTimeZone(const QString &timezone)
+{
+	if (m_systemTimeZone != timezone) {
+		m_systemTimeZone = timezone;
+		updateTime();
+		emit systemTimeZoneChanged();
+	}
+}
+

src/clocktime.h

@@ -15,12 +15,17 @@ class ClockTime : public QObject
 	Q_PROPERTY(QDateTime currentDateTime MEMBER m_currentDateTime NOTIFY currentDateTimeChanged)
 	Q_PROPERTY(QDateTime currentDateTimeUtc MEMBER m_currentDateTimeUtc NOTIFY currentDateTimeUtcChanged)
 	Q_PROPERTY(QString currentTimeText MEMBER m_currentTimeText NOTIFY currentTimeTextChanged)
+	Q_PROPERTY(QString currentTimeUtcText MEMBER m_currentTimeUtcText NOTIFY currentTimeUtcTextChanged)
+	Q_PROPERTY(QString systemTimeZone READ systemTimeZone WRITE setSystemTimeZone NOTIFY systemTimeZoneChanged)
 
 public:
 	ClockTime(QObject *parent);
 
 	static ClockTime* instance(QObject* parent = nullptr);
 
+	QString systemTimeZone() const;
+	void setSystemTimeZone(const QString &timezone); // "region/city" format.
+
 public Q_SLOTS:
 	QString formatTime(int hour, int minute) const;
 	bool isDateValid(int year, int month, int day) const; // month is 1-12
@@ -29,6 +34,8 @@ public Q_SLOTS:
 	void currentDateTimeChanged();
 	void currentDateTimeUtcChanged();
 	void currentTimeTextChanged();
+	void currentTimeUtcTextChanged();
+	void systemTimeZoneChanged();
 
 protected:
 	void timerEvent(QTimerEvent *) override;
@@ -40,6 +47,8 @@ public Q_SLOTS:
 	QDateTime m_currentDateTime;
 	QDateTime m_currentDateTimeUtc;
 	QString m_currentTimeText;
+	QString m_currentTimeUtcText;
+	QString m_systemTimeZone;
 	int m_timerId = 0;
 };
 

src/language.cpp

@@ -117,6 +117,16 @@ void Language::setCurrentLanguage(QLocale::Language language)
 	}
 }
 
+void Language::setCurrentLanguage(const QString &language)
+{
+	const QLocale::Language lang = QLocale::codeToLanguage(language);
+	if (lang != QLocale::AnyLanguage) {
+		setCurrentLanguage(lang);
+	} else {
+		qCWarning(venusGui) << "Unknown language code specified:" << language;
+	}
+}
+
 bool Language::installTranslatorForLanguage(QLocale::Language language)
 {
 	const bool alreadyLoaded = m_loadedTranslators.contains(language);

src/language.h

@@ -71,6 +71,7 @@ class Language : public QObject
 	Q_INVOKABLE QString toString(QLocale::Language language) const;
 	QLocale::Language getCurrentLanguage() const;
 	void setCurrentLanguage(QLocale::Language language);
+	Q_INVOKABLE void setCurrentLanguage(const QString &language);
 
 Q_SIGNALS:
 	void currentLanguageChanged();