plugins/nightlight: Make Night Light more robust to QTimer firing slightly earlier

Currently, resetSlowUpdateTimers() will start a timer that will pass
m_next.first as the current time to resetSlowUpdateTimers(). This kind
of works, but there are more code paths where updateTransitionTimings()
can be called.

This change hardens updateTransitionTimings() against the current time
being very close to the start of the next transition by introducing a
time fudge factor.

If we are currently 1 second away from the start of the next transition,
then it is assumed that that transition has been reached, and we need
to calculate the timings of a transition after that.

src/plugins/nightlight/nightlightmanager.cpp

@@ -138,7 +138,7 @@ void NightLightManager::hardReset()
 {
     cancelAllTimers();
 
-    updateTransitionTimings(true);
+    updateTransitionTimings(true, QDateTime::currentDateTime());
     updateTargetTemperature();
 
     if (isEnabled() && !isInhibited()) {
@@ -300,7 +300,7 @@ void NightLightManager::resetAllTimers()
     cancelAllTimers();
     setRunning(isEnabled() && !isInhibited());
     // we do this also for active being false in order to reset the temperature back to the day value
-    updateTransitionTimings(false);
+    updateTransitionTimings(false, QDateTime::currentDateTime());
     updateTargetTemperature();
     resetQuickAdjustTimer(currentTargetTemp());
 }
@@ -356,7 +356,7 @@ void NightLightManager::quickAdjust(int targetTemp)
     }
 }
 
-void NightLightManager::resetSlowUpdateTimers(const QDateTime &todayNow)
+void NightLightManager::resetSlowUpdateTimers()
 {
     m_slowUpdateStartTimer.reset();
 
@@ -371,12 +371,13 @@ void NightLightManager::resetSlowUpdateTimers(const QDateTime &todayNow)
         return;
     }
 
+    const QDateTime todayNow = QDateTime::currentDateTime();
+
     // set up the next slow update
     m_slowUpdateStartTimer = std::make_unique<QTimer>();
     m_slowUpdateStartTimer->setSingleShot(true);
     connect(m_slowUpdateStartTimer.get(), &QTimer::timeout, this, [this]() {
-        const QDateTime nextMilestone = m_next.first; // make a copy so the current time stays the same after updateTransitionTimings() is called
-        resetSlowUpdateTimers(nextMilestone);
+        resetSlowUpdateTimers();
     });
     updateTransitionTimings(false, todayNow);
     updateTargetTemperature();
@@ -459,7 +460,7 @@ void NightLightManager::preview(uint previewTemp)
 void NightLightManager::stopPreview()
 {
     if (m_previewTimer && m_previewTimer->isActive()) {
-        updateTransitionTimings(false);
+        updateTransitionTimings(false, QDateTime::currentDateTime());
         updateTargetTemperature();
         resetQuickAdjustTimer(currentTargetTemp());
     }
@@ -483,14 +484,23 @@ void NightLightManager::updateTransitionTimings(bool force, const QDateTime &tod
     const auto oldPrev = m_prev;
     const auto oldNext = m_next;
 
+    // QTimer is not precise, it can timeout slightly earlier than expected. For example, if the
+    // morning time is 6:00, the timer can fire at 5:59:59. The purpose of this fudge factor is to
+    // make night light think that the morning transition has been reached even though we are not
+    // there yet by a few microseconds or milliseconds.
+    const int granularity = 1;
+
     if (m_mode == NightLightMode::Constant) {
         setDaylight(false);
         m_next = DateTimes();
         m_prev = DateTimes();
     } else if (m_mode == NightLightMode::Timings) {
-        const QDateTime nextMorB = QDateTime(todayNow.date().addDays(m_morning <= todayNow.time()), m_morning);
+        const bool passedMorning = todayNow.time().secsTo(m_morning) <= granularity;
+        const bool passedEvening = todayNow.time().secsTo(m_evening) <= granularity;
+
+        const QDateTime nextMorB = QDateTime(todayNow.date().addDays(passedMorning), m_morning);
         const QDateTime nextMorE = nextMorB.addSecs(m_trTime * 60);
-        const QDateTime nextEveB = QDateTime(todayNow.date().addDays(m_evening <= todayNow.time()), m_evening);
+        const QDateTime nextEveB = QDateTime(todayNow.date().addDays(passedEvening), m_evening);
         const QDateTime nextEveE = nextEveB.addSecs(m_trTime * 60);
 
         if (nextEveB < nextMorB) {
@@ -528,19 +538,21 @@ void NightLightManager::updateTransitionTimings(bool force, const QDateTime &tod
         }
 
         if (force || !checkAutomaticSunTimings()) {
-            // in case this fails, reset them
-            DateTimes morning = getSunTimings(todayNow, lat, lng, true);
-            if (todayNow < morning.first) {
+            const DateTimes morning = getSunTimings(todayNow, lat, lng, true);
+            if (todayNow.secsTo(morning.first) > granularity) {
+                // have not reached the morning yet
                 setDaylight(false);
                 m_prev = getSunTimings(todayNow.addDays(-1), lat, lng, false);
                 m_next = morning;
             } else {
-                DateTimes evening = getSunTimings(todayNow, lat, lng, false);
-                if (todayNow < evening.first) {
+                const DateTimes evening = getSunTimings(todayNow, lat, lng, false);
+                if (todayNow.secsTo(evening.first) > granularity) {
+                    // have not reached the evening yet, it's daylight
                     setDaylight(true);
                     m_prev = morning;
                     m_next = evening;
                 } else {
+                    // we are passed the evening, it's night time
                     setDaylight(false);
                     m_prev = evening;
                     m_next = getSunTimings(todayNow.addDays(1), lat, lng, true);

src/plugins/nightlight/nightlightmanager.h

@@ -250,10 +250,10 @@ private:
     /**
      * Slow shift to daytime target Temperature
      */
-    void resetSlowUpdateTimers(const QDateTime &todayNow = QDateTime::currentDateTime());
+    void resetSlowUpdateTimers();
 
     void updateTargetTemperature();
-    void updateTransitionTimings(bool force, const QDateTime &todayNow = QDateTime::currentDateTime());
+    void updateTransitionTimings(bool force, const QDateTime &todayNow);
     DateTimes getSunTimings(const QDateTime &dateTime, double latitude, double longitude, bool morning) const;
     bool checkAutomaticSunTimings() const;