#!/bin/sh
# fix-tar-timestamps --- set mtime of tar file to most recent member mtime
# Author: Noah Friedman <friedman@splode.com>
# Public domain

# $Id: fix-tar-timestamps,v 1.1 2017/05/12 22:09:17 friedman Exp $

# Currently this is only reliable on gnuish systems because it depends on
# the date parsing capabilities of the -d option to GNU `touch'.

recent_gnu_tar_p()
{
    ${TAR-tar} --help 2>&1 | grep '.--full-time' > /dev/null
}

tartv()
{
    case $1 in
            *.gz  | *.tgz ) gzip  -dc "$1" ;;
            *.bz2 | *.tbz ) bzip2 -dc "$1" ;;
            *.xz  | *.txz ) xz    -dc "$1" ;;
            * ) cat "$1" ;;
    esac | ${GTAR-tar} $gtar_opts -tvf -
}

tstamp()
{
    one=
    case $1 in
        -1 ) one='-e 1!d'; shift ;;
    esac

    sed -n $one \
        -e '/^.* \([0-9][0-9]*-[-0-9]* [0-9][:0-9]*\) .*/{s//\1/p;n;}' \
        -e '/^.* \([A-Z][a-z]*\)  *\([0-9][0-9]*\)  *\([0-9][0-9]*:[0-9]*\)  *\([0-9][0-9]*\) .*/{
                s//\4-\1-\2 \3/
                s/-\([0-9]\) /-0\1 /g
                b c
            }' \
        -e '/^.* \([A-Z][a-z]*\)  *\([0-9][0-9]*\)  *\([0-9][0-9]*\) .*/{
                s//\3-\1-\2/
                s/-\([0-9]\)$/-0\1/
                b c
            }' \
        -e 'd' \
        -e ':c
            s/Jan/01/; s/Feb/02/; s/Mar/03/; s/Apr/04/
            s/May/05/; s/Jun/06/; s/Jul/07/; s/Aug/08/
            s/Sep/09/; s/Oct/10/; s/Nov/11/; s/Dec/12/
            p;n;' \
        "$@"
}

main()
{
    case $1 in
        -1 ) fast=t ; shift ;;
    esac

    if recent_gnu_tar_p; then
        gtar_opts='--full-time'
    fi

    for file in "$@"; do
        case $fast in
            t ) ts=`tartv "$file" | tstamp -1` ;;
            * ) ts=`tartv "$file" | tstamp | sort -rn | sed -e 1q` ;;
        esac
        ${GTOUCH-touch} -d "$ts" "$file"
    done
}

main "$@"

# eof