isoweek

The Go package isoweek calculates a starting date and time of ISO 8601 week.

ISO 8601 standard defines the common week number system used in Europe
and many other countries. Monday is the first day of a week.

The Go standard library time package has ISOWeek function
for getting ISO 8601 week number of a given time.Time, but there is no
reverse functionality for getting a date from a week number. This package
implements that.

Invalid input is silently accepted. There is a separate Validate
function if week number validation is needed.

There are also functions for working with Julian day numbers. Using Julian
day numbers is often the easiest and fastest way to do date calculations.

This package does not work with the “traditional” week system used in
US/Canada/Japan/etc. (weeks starting on Sundays). However the Julian day
number functions may be still useful.

Documentation

https://pkg.go.dev/github.com/snabb/isoweek

Examples

Using weeks with Go standard time.Time

A simple example which gets the starting time of the 1st week of 1985:

    t := isoweek.StartTime(1985, 1, time.UTC)
    fmt.Println(t)
    // Output: 1984-12-31 00:00:00 +0000 UTC

The returned time may be within a previous year as can be seen above.

The AddDate function in Go standard library time package can be used
for getting the Time at the end of the week or for iterating through weeks:

    t = t.AddDate(0, 0, 7)
    fmt.Println(t)
    // Output: 1985-01-07 00:00:00 +0000 UTC
    wyear, week := t.ISOWeek()
    fmt.Println(wyear, week)
    // Output: 1985 2

Using weeks, dates and Julian day numbers

The same as above without using Go standard library time package:

    y, m, d := isoweek.StartDate(1985, 1)
    fmt.Println(y, m, d)
    // Output: 1984 December 31
    jdn := isoweek.DateToJulian(y, m, d)
    jdn = jdn + 7 // next week
    y, m, d = isoweek.JulianToDate(jdn)
    fmt.Println(y, m, d)
    // Output: 1985 January 7
    wyear, week := isoweek.FromDate(y, m, d)
    fmt.Println(wyear, week)
    // Output: 1985 2

Repository

https://github.com/snabb/isoweek

License

MIT