#!/bin/sh

set -euf

usage="Usage: $0 [-i instance] [-p principal] [-a addrend] subcommand [args]"

ATHENA_USER=${ATHENA_USER:-$USER}
principal="$ATHENA_USER/root@ATHENA.MIT.EDU"
addrend="root"
while getopts "i:p:a:h" options; do
    case $options in
        i ) addrend="$OPTARG"; principal="$ATHENA_USER/$OPTARG@ATHENA.MIT.EDU";;
        p ) principal="$OPTARG";;
        a ) addrend="$OPTARG";;
        h ) echo "$usage"; exit 0;;
        \? ) echo "$usage"; exit 1;;
        * ) echo "$usage"; exit 1;;
    esac
done
shift `expr $OPTIND - 1 || :`

export KRB5CCNAME="/tmp/krb5cc_$(id -u).$addrend"
export KRBTKFILE=/dev/null

init () {
    kinit -F -5 -l15m "$principal" "$@"
}

case ${1:-} in
    init)
        shift;
        exec kinit -F -5 -l15m "$principal" "$@"
        ;;
    destroy)
        exec kdestroy -5
        ;;
    shell)
        klist -s || init || exit 1;
        HOST="`hostname` (krb:$addrend)" pagsh -c $SHELL
        ;;
    screen)
        klist -s || init || exit 1;
        HOST="`hostname` (krb:$addrend)" pagsh -c 'exec "$@"' exec "$@"
        ;;
    ssh)
        klist -s || init || exit 1;
        shift
        exec ssh -k -l root "$@"
        ;;
    rlogin)
        klist -s || init || exit 1;
        exec rlogin -x -l root $2
        ;;
    *)
        if [ $# = 0 ]; then
            echo "Usage: $0 init" >&2
            echo "       $0 destroy" >&2
            echo "       $0 shell" >&2
            echo "       $0 ssh [args]" >&2
            echo "       $0 rlogin [args]" >&2
            echo "       $0 [cmd]" >&2
        else
            exec "$@"
        fi
        ;;
esac