time: add new method year_day and the tests for it (#18107)

vlib/time/time.v

@@ -267,6 +267,16 @@ pub fn (t Time) day_of_week() int {
 	return day_of_week(t.year, t.month, t.day)
 }
 
+// year_day returns the current day of the year as an integer.
+// See also #Time.custom_format .
+pub fn (t Time) year_day() int {
+	yday := t.day + time.days_before[t.month - 1]
+	if is_leap_year(t.year) && t.month > 2 {
+		return yday + 1
+	}
+	return yday
+}
+
 // weekday_str returns the current day as a string 3 letter abbreviation.
 pub fn (t Time) weekday_str() string {
 	i := t.day_of_week() - 1

vlib/time/time_test.v

@@ -142,6 +142,25 @@ fn test_day_of_week() {
 	}
 }
 
+fn test_year_day() {
+	// testing if December 31st in a leap year is numbered as 366
+	assert time.parse('2024-12-31 20:00:00')!.year_day() == 366
+
+	// testing December 31st's number in a non leap year
+	assert time.parse('2025-12-31 20:00:00')!.year_day() == 365
+
+	assert time.parse('2024-02-28 20:00:00')!.year_day() == 59
+	assert time.parse('2024-02-29 20:00:00')!.year_day() == 60
+	assert time.parse('2024-03-01 20:00:00')!.year_day() == 61
+	assert time.parse('2024-03-02 20:00:00')!.year_day() == 62
+
+	assert time.parse('2025-02-28 20:00:00')!.year_day() == 59
+	assert time.parse('2025-03-01 20:00:00')!.year_day() == 60
+
+	assert time.parse('2024-01-01 20:00:00')!.year_day() == 1
+	assert time.parse('2025-01-01 20:00:00')!.year_day() == 1
+}
+
 fn test_weekday_str() {
 	day_names := ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
 	for i, name in day_names {