profile: add local time to profile tooltip

This is a user request: add local time of dive to the tooltip.

Showing a localized time was surprisingly complex. First I had
to add a function that decomposes a timestamp into h/m/s. Then
the QLocale time-string has to be stripped of the timezone.

Fixes #3469.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

CHANGELOG.md

@@ -1,4 +1,4 @@
-
+- profile: show local time of cursor position in tooltip (fixes #3469).
 ---
 * Always add new entries at the very top of this file above other existing entries and this note.
 * Use this layout for new entries: `[Area]: [Details about the change] [reference thread / issue]`

core/string-format.cpp

@@ -304,6 +304,18 @@ QString formatTripTitleWithDives(const dive_trip *trip)
 	       gettextFromC::tr("(%n dive(s))", "", nr);
 }
 
+static QString formatTimeOfDay(timestamp_t when)
+{
+	auto [h, m, s] = utc_time_of_day(when);
+	QLocale loc;
+	QString format = loc.timeFormat(QLocale::LongFormat);
+	// We don't want to show the timezone, as that currently is the
+	// timezone the application is run in, not the timezone of the dive!
+	format.replace("t", "");
+	QTime time(h, m, s);
+	return loc.toString(time, format.trimmed());
+}
+
 #define DIV_UP(x, y) (((x) + (y) - 1) / (y))
 #define translate(x,y) qPrintable(QCoreApplication::translate(x,y))
 
@@ -316,9 +328,11 @@ static QString formatPlotInfoInternal(const dive *d, const plot_info *pi, int id
 	int decimals, cyl;
 	const char *unit;
 	const struct plot_data *entry = pi->entry + idx;
+	timestamp_t when = d->when + entry->sec;
 
 	depthvalue = get_depth_units(entry->depth, NULL, &depth_unit);
-	res = qasprintf_loc("%s: %d:%02d\n", translate("gettextFromC", "@"), FRACTION(entry->sec, 60));
+	res = qasprintf_loc("%s: %d:%02d (%s)\n", translate("gettextFromC", "@"), FRACTION(entry->sec, 60),
+						  qPrintable(formatTimeOfDay(when)));
 	res += qasprintf_loc("%s: %.1f%s\n", translate("gettextFromC", "D"), depthvalue, depth_unit);
 	for (cyl = 0; cyl < pi->nr_cylinders; cyl++) {
 		int mbar = get_plot_pressure(pi, idx, cyl);

core/subsurface-time.h

@@ -9,10 +9,15 @@
 extern "C" {
 #endif
 
+struct time_of_day {
+	int h, m, s;
+};
+
 extern timestamp_t utc_mktime(const struct tm *tm);
 extern void utc_mkdate(timestamp_t, struct tm *tm);
 extern int utc_year(timestamp_t timestamp);
 extern int utc_weekday(timestamp_t timestamp);
+extern struct time_of_day utc_time_of_day(timestamp_t timestamp);
 
 /* parse and format date times of the form YYYY-MM-DD hh:mm:ss */
 extern timestamp_t parse_datetime(const char *s); /* returns 0 on error */

core/time.c

@@ -99,6 +99,37 @@ void utc_mkdate(timestamp_t timestamp, struct tm *tm)
 	tm->tm_mon = m;
 }
 
+/*
+ * Convert 64-bit timestamp to time of day (split into h, m, s)
+ *
+ * On 32-bit machines, only do 64-bit arithmetic for the seconds
+ * part, after that we do everything in 'long'. 64-bit divides
+ * are unnecessary once you're counting minutes (32-bit minutes:
+ * 8000+ years).
+ */
+struct time_of_day utc_time_of_day(timestamp_t timestamp)
+{
+	struct time_of_day res = { 0 };
+	unsigned long val;
+
+	// Midnight at Jan 1, 1970 means "no date"
+	if (!timestamp)
+		return res;
+
+	/* Convert to seconds since 1900 */
+	timestamp += EPOCH_OFFSET;
+
+	/* minutes since 1900 */
+	res.s = timestamp % 60;
+	val = timestamp / 60;
+
+	res.m = val % 60;
+	val /= 60;
+	res.h = val % 24;
+
+	return res;
+}
+
 timestamp_t utc_mktime(const struct tm *tm)
 {
 	static const int mdays[] = {