time: change days_from_civil to days_from_unix_epoch, add date_from_days_after_unix_epoch (#16363)

vlib/time/chrono.c.v

@@ -13,6 +13,6 @@ pub fn portable_timegm(t &C.tm) i64 {
 		year -= years_diff
 		month += 12 * years_diff
 	}
-	days_since_1970 := i64(days_from_civil(year, month + 1, t.tm_mday))
+	days_since_1970 := i64(days_from_unix_epoch(year, month + 1, t.tm_mday))
 	return 60 * (60 * (24 * days_since_1970 + t.tm_hour) + t.tm_min) + t.tm_sec
 }

vlib/time/chrono.v

@@ -1,14 +1,44 @@
 module time
 
-// days_from_civil - return the number of days since the
-// Unix epoch 1970-01-01. A detailed description of the algorithm here
-// is in: http://howardhinnant.github.io/date_algorithms.html
-// Note that it will return negative values for days before 1970-01-01.
-pub fn days_from_civil(oy int, m int, d int) int {
-	y := if m <= 2 { oy - 1 } else { oy }
+// days_from_unix_epoch - return the number of days since the Unix epoch 1970-01-01.
+// A detailed description of the algorithm here is in:
+// http://howardhinnant.github.io/date_algorithms.html
+// Note that function will return negative values for days before 1970-01-01.
+pub fn days_from_unix_epoch(year int, month int, day int) int {
+	y := if month <= 2 { year - 1 } else { year }
 	era := y / 400
-	yoe := y - era * 400 // [0, 399]
-	doy := (153 * (m + (if m > 2 { -3 } else { 9 })) + 2) / 5 + d - 1 // [0, 365]
-	doe := yoe * 365 + yoe / 4 - yoe / 100 + doy // [0, 146096]
-	return era * 146097 + doe - 719468
+	year_of_the_era := y - era * 400 // [0, 399]
+	day_of_year := (153 * (month + (if month > 2 { -3 } else { 9 })) + 2) / 5 + day - 1 // [0, 365]
+	day_of_the_era := year_of_the_era * 365 + year_of_the_era / 4 - year_of_the_era / 100 +
+		day_of_year // [0, 146096]
+	return era * 146097 + day_of_the_era - 719468
+}
+
+// days_from_civil - return the number of days since the
+// Unix epoch 1970-01-01.
+// deprecated: use time.days_from_unix_epoch instead
+[deprecated: 'use time.days_from_unix_epoch instead']
+[deprecated_after: '2022-11-23']
+pub fn days_from_civil(year int, month int, day int) int {
+	return days_from_unix_epoch(year, month, day)
+}
+
+// days_from_unix_epoch - return the number of days since the Unix epoch 1970-01-01.
+// A detailed description of the algorithm here is in:
+// http://howardhinnant.github.io/date_algorithms.html
+// Note that method will return negative values for days before 1970-01-01.
+[inline]
+pub fn (t Time) days_from_unix_epoch() int {
+	return days_from_unix_epoch(t.year, t.month, t.day)
+}
+
+// date_from_days_after_unix_epoch - convert number of `days` after the unix epoch 1970-01-01, to a Time.
+// Only the year, month and day of the returned Time will be set, everything else will be 0.
+pub fn date_from_days_after_unix_epoch(days int) Time {
+	year, month, day := calculate_date_from_offset(i64(days))
+	return Time{
+		year: year
+		month: month
+		day: day
+	}
 }

vlib/time/chrono_test.v

@@ -0,0 +1,35 @@
+module time
+
+fn test_days_from_unix_epoch() {
+	s := '2000-05-10 22:11:03'
+	time_test := parse(s) or {
+		eprintln('> failing format: $s | err: $err')
+		assert false
+		return
+	}
+	one_day_in_seconds := 86400
+
+	assert time_test.days_from_unix_epoch() == 11087
+	assert time_test.days_from_unix_epoch() == int(time_test.unix / one_day_in_seconds)
+	assert days_from_unix_epoch(1970, 1, 1) == 0
+	assert days_from_unix_epoch(1970, 2, 1) == 31
+	assert days_from_unix_epoch(1970, 3, 1) == 59
+	assert days_from_unix_epoch(2022, 11, 10) == 19306
+}
+
+fn test_date_from_days_after_unix_epoch() {
+	assert date_from_days_after_unix_epoch(11087).year == 2000
+	assert date_from_days_after_unix_epoch(11087).month == 5
+	assert date_from_days_after_unix_epoch(11087).day == 10
+	assert date_from_days_after_unix_epoch(1).year == 1970
+	assert date_from_days_after_unix_epoch(1).month == 1
+	assert date_from_days_after_unix_epoch(1).day == 2
+
+	assert date_from_days_after_unix_epoch(31).year == 1970
+	assert date_from_days_after_unix_epoch(31).month == 2
+	assert date_from_days_after_unix_epoch(31).day == 1
+
+	assert date_from_days_after_unix_epoch(59).year == 1970
+	assert date_from_days_after_unix_epoch(59).month == 3
+	assert date_from_days_after_unix_epoch(59).day == 1
+}