core/clock: fix instability causing timer to fire multiple times

If the signal was fired slightly before the scheduled time, it would
schedule itself again a couple ms in the future.

src/core/clock.cpp

@@ -8,7 +8,7 @@
 #include "util.hpp"
 
 SystemClock::SystemClock(QObject* parent): QObject(parent) {
-	QObject::connect(&this->timer, &QTimer::timeout, this, &SystemClock::update);
+	QObject::connect(&this->timer, &QTimer::timeout, this, &SystemClock::onTimeout);
 	this->update();
 }
 
@@ -30,10 +30,21 @@ void SystemClock::setPrecision(SystemClock::Enum precision) {
 	this->update();
 }
 
-void SystemClock::update() {
-	auto time = QTime::currentTime();
+void SystemClock::onTimeout() {
+	this->setTime(this->nextTime);
+	this->schedule(this->nextTime);
+}
 
+void SystemClock::update() {
 	if (this->mEnabled) {
+		this->setTime(QTime::currentTime());
+		this->schedule(QTime::currentTime());
+	} else {
+		this->timer.stop();
+	}
+}
+
+void SystemClock::setTime(QTime time) {
 	auto secondPrecision = this->mPrecision >= SystemClock::Seconds;
 	auto secondChanged = this->setSeconds(secondPrecision ? time.second() : 0);
 
@@ -44,25 +55,36 @@ void SystemClock::update() {
 	auto hourChanged = this->setHours(hourPrecision ? time.hour() : 0);
 
 	DropEmitter::call(secondChanged, minuteChanged, hourChanged);
+}
 
+void SystemClock::schedule(QTime floor) {
+	auto secondPrecision = this->mPrecision >= SystemClock::Seconds;
+	auto minutePrecision = this->mPrecision >= SystemClock::Minutes;
+	auto hourPrecision = this->mPrecision >= SystemClock::Hours;
+
+setnext:
 	auto nextTime = QTime(
-		    hourPrecision ? time.hour() : 0,
-		    minutePrecision ? time.minute() : 0,
-		    secondPrecision ? time.second() : 0
+	    hourPrecision ? floor.hour() : 0,
+	    minutePrecision ? floor.minute() : 0,
+	    secondPrecision ? floor.second() : 0
 	);
 
 	if (secondPrecision) nextTime = nextTime.addSecs(1);
 	else if (minutePrecision) nextTime = nextTime.addSecs(60);
 	else if (hourPrecision) nextTime = nextTime.addSecs(3600);
 
-		auto delay = time.msecsTo(nextTime);
-		// day rollover
-		if (delay < 0) delay += 86400000;
+	auto delay = QTime::currentTime().msecsTo(nextTime);
+
+	// If off by more than 2 hours we likely wrapped around midnight.
+	if (delay < -7200000) delay += 86400000;
+	else if (delay < 0) {
+		// Otherwise its just the timer being unstable.
+		floor = QTime::currentTime();
+		goto setnext;
+	}
 
 	this->timer.start(delay);
-	} else {
-		this->timer.stop();
-	}
+	this->nextTime = nextTime;
 }
 
 DEFINE_MEMBER_GETSET(SystemClock, hours, setHours);

src/core/clock.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <qdatetime.h>
 #include <qobject.h>
 #include <qqmlintegration.h>
 #include <qtimer.h>
@@ -49,7 +50,7 @@ signals:
 	void secondsChanged();
 
 private slots:
-	void update();
+	void onTimeout();
 
 private:
 	bool mEnabled = true;
@@ -58,6 +59,11 @@ private:
 	quint32 mMinutes = 0;
 	quint32 mSeconds = 0;
 	QTimer timer;
+	QTime nextTime;
+
+	void update();
+	void setTime(QTime time);
+	void schedule(QTime floor);
 
 	DECLARE_PRIVATE_MEMBER(SystemClock, hours, setHours, mHours, hoursChanged);
 	DECLARE_PRIVATE_MEMBER(SystemClock, minutes, setMinutes, mMinutes, minutesChanged);