date iso8601

# https://en.wikipedia.org/wiki/ISO_8601

date_to_iso8601() {
        date ${1:+-d "$1"} -u +'%Y%m%dT%H%M%SZ'
}

iso8601_to_date() {
        local yyyymmdd="${1%%T*}"
        local hhmmss="${1#*T}"
        hhmmss="${hhmmss%Z*}"
        local mmss="${hhmmss#??}"

        shift
        date -d "${yyyymmdd} ${hhmmss%%????}:${mmss%??}:${mmss#??} +0000" "$@"
}

iso8601_to_date "$(date_to_iso8601 "$(iso8601_to_date "$(date_to_iso8601)")")" -u
date -u