htwkalender-pwa/backend/service/date/dateFormat.go

package date

import "time"

func GetDateFromWeekNumber(year int, weekNumber int, dayName string) (time.Time, error) {
	// Create a time.Date for the first day of the year
	firstDayOfYear := time.Date(year, time.January, 1, 0, 0, 0, 0, time.UTC)

	// Calculate the number of days to add to reach the desired week
	daysToAdd := time.Duration((weekNumber-1)*7) * 24 * time.Hour

	// Find the starting day of the week (e.g., Monday)
	startingDayOfWeek := firstDayOfYear

	// check if the first day of the year is friday or saturday or sunday

	if startingDayOfWeek.Weekday() == time.Friday || startingDayOfWeek.Weekday() == time.Saturday || startingDayOfWeek.Weekday() == time.Sunday {
		for startingDayOfWeek.Weekday() != time.Monday {
			startingDayOfWeek = startingDayOfWeek.Add(24 * time.Hour)
		}
	} else {
		for startingDayOfWeek.Weekday() != time.Monday {
			startingDayOfWeek = startingDayOfWeek.Add(-24 * time.Hour)
		}
	}

	// Calculate the desired date by adding daysToAdd and adjusting for the day name
	desiredDate := startingDayOfWeek.Add(daysToAdd)

	// Find the day of the week
	dayOfWeek := map[string]time.Weekday{
		"Montag":     time.Monday,
		"Dienstag":   time.Tuesday,
		"Mittwoch":   time.Wednesday,
		"Donnerstag": time.Thursday,
		"Freitag":    time.Friday,
		"Samstag":    time.Saturday,
		"Sonntag":    time.Sunday,
	}[dayName]

	// Adjust to the desired day of the week
	for desiredDate.Weekday() != dayOfWeek {
		desiredDate = desiredDate.Add(24 * time.Hour)
	}

	return desiredDate, nil
}