ISO8601 duration strings for Go

A package for working with ISO8601 duration strings. See https://en.wikipedia.org/wiki/ISO_8601#Durations for more info.

Some duration string examples:

P3Y6M4DT12H30M5.345S - 3 years, 6 months, 4 days, 12 hours, 30 minutes, 5 seconds, and 345 milliseconds.
P3W - 3 weeks
P1D3H10S - 1 day, 3 hours, and 10 seconds

The package also supports a format extension to include signed durations and/or duration components. Some examples here:

-P1M10D - negative 1 month and 10 days
P1Y-10D - 355 days (1 year less 10 days)

Usage

import (
    "os"

    "github.com/bbetov/isoduration"
)

func main() {
    duration, err := isoduration.Parse("P4W")
    if err != nil {
        println(err)
        os.Exit(1)
    }
    println(duration.String())

    println(duration.StringWeeks())
}

Limitations

The ISO 8601 allows the durations to be specified using a decimal notation, which is not currently supported.

Months are considered to be 30 days.

Years are considered to be 365 days.

TODO

Support PYYYYMMDDThhmmss format
Support P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss] format
Support decimal durations.
Support different signs for the individual components (via a separate function)