#!/bin/sh -e

# fedora's (update-)alternatives --display output doesn't have
# "link <name> is <path>" line, but debian does. so, let's find
# out how they store this information.
#
# debian and friends:
#   https://salsa.debian.org/dpkg-team/dpkg/-/blob/master/utils/update-alternatives.c
#   see calls to altdb_print_line function
#
# fedora and friends:
#   https://github.com/fedora-sysv/chkconfig/blob/master/alternatives.c
#   see calls to parseLine function
#
# conclusion: it is safe to assume that (master) link is on second line

for altdir in \
    /var/lib/dpkg/alternatives \
    /var/lib/alternatives
do
    if [ ! -f "$altdir/${__object_id:?}" ]
    then
        continue
    fi

    link="$( awk 'NR==2' "$altdir/${__object_id:?}" )"

    if [ -n "$link" ]
    then
        break
    fi
done

if [ -z "$link" ]
then
    echo "unable to get link for ${__object_id:?}" >&2
    exit 1
fi

echo "$link"