#!/bin/sh

set -e

# summary of how this script can be called:
#        * <new-preinst> `install'
#        * <new-preinst> `install' <old-version>
#        * <new-preinst> `upgrade' <old-version>
#        * <old-preinst> `abort-upgrade' <new-version>
# for details, see https://www.debian.org/doc/debian-policy/ or
# the debian-policy package

prepare_conffile_transfer() {
    local conffile="$1"
    local lastver="$2"
    local pkgfrom="$3"
    local pkgto="$4"

    if [ "$5" != "--" ]; then
        echo "prepare_conffile_transfer called with the wrong number of arguments" >&2
        return 1
    fi
    for _ in $(seq 1 5); do
        shift
    done

    # If we're installing from scratch or upgrading from a new enough version
    # of the package, then no transfer needs to happen and we can stop here
    if [ -z "$2" ] || dpkg --compare-versions -- "$2" gt "$lastver"; then
        return 0
    fi

    # Depending on the current state of the conffile, we need to perform different
    # steps to transfer it. Moving the conffile to a different location depending
    # on its current state achieves two goals: dpkg will see the conffile is no
    # longer present on disk after $pkgfrom has been upgraded, and so it will no
    # longer associate it with that package (not even as an obsolete conffile);
    # more importanly, $pkgto's postinst, where the transfer process is completed,
    # will be able to figure out the original state of the conffile and make sure
    # it is restored
    if [ -e "$conffile" ]; then
        echo "Preparing transfer of config file $conffile (from $pkgfrom to $pkgto) ..."
        mv -f "$conffile" "$conffile.dpkg-transfer"
    else
        # If the conffile is no longer present on the disk, it means the admin
        # has deleted it, and we should preserve this local modification
        touch "$conffile.dpkg-disappear"
    fi
}

case "$1" in
    install|upgrade)
        prepare_conffile_transfer \
            "/etc/libvirt/virt-login-shell.conf" \
            "6.9.0-2~" \
            "libvirt-clients" \
            "libvirt-login-shell" \
            -- \
            "$@"
    ;;

    abort-upgrade)
    ;;

    *)
        echo "preinst called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac



exit 0