#!/bin/sh

set -e

# wdm versions before 1.28-4 updated display manager list in ${wdmconfig}
# conffile everytime wdm is installed, upgraded or run. That causes unneeded
# queries during upgrade. This was fixed in 1.28-4. This file tries to smooth
# upgrades from previous versions (1.28-2 and above). Checks if the only change
# is display manager line and then checks if change was not blessed by sysadmin,
# reverting automatic changes if so. See Debian bugs #582612 and #606788

# md5sums for pristine wdm-config with DisplayManager*wdmWm stripped
# wdm_1.28-2 (as well as lenny wdm_1.28-3)
pristine_stripped_md5="b903cf9c29cad13e3931ff30e6da7b96"
# Intermediate wdm_1.28-3.5
pristine_stripped_md5_alt="3ec0efa2089101552b0874ff63884292"

# pristine wdm-config DisplayManager*wdmWm string
pristine_string='! DisplayManager*wdmWm:         twm:wmaker:afterstep'

wdmconfig="/etc/X11/wdm/wdm-config"
wdmconfig_tmp="${wdmconfig}.dpkg-tmp"

# Do nothing if this is first installation
if [ -f "$wdmconfig" ]; then
    wdmconfig_stripped_md5=$(grep -v 'DisplayManager\*wdmWm:' "${wdmconfig}" | md5sum  | sed 's/ .*//')

    # First check if "$wdmconfig" matches old pristine files for everything but Displaymanager line.
    if [ "$wdmconfig_stripped_md5" = "$pristine_stripped_md5" ] ||
	[ "$wdmconfig_stripped_md5" = "$pristine_stripped_md5_alt" ]; then
	wdmconfig_dpkg_md5sum=$(dpkg-query -W -f='${Conffiles}' wdm | grep "$wdmconfig" | awk '{print $2}')
	sed -e 's/.*DisplayManager\*wdmWm:.*/'"$pristine_string"'/' "$wdmconfig" > "${wdmconfig_tmp}"
	wdmconfig_new_md5=$(md5sum "${wdmconfig_tmp}" | sed 's/ .*//')

	# Check now if re-created file md5 sum matches that registered by dpkg. Otherwise
	# new file may have been explicitly accepted by sysadmin during upgrade.
	if [ "$wdmconfig_new_md5" = "$wdmconfig_dpkg_md5sum" ]; then
	    echo "Reverting unblessed automatic changes to ${wdmconfig}." >&2
	    mv -f "${wdmconfig_tmp}" "$wdmconfig"
	else
	    rm -f "${wdmconfig_tmp}"
	fi
    fi
fi