#! /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 http://www.debian.org/doc/debian-policy/ or
# the debian-policy package


# This returns true (0) if the conffile belongs to this package, and a modified
# version of it currently exists which needs to be preserved.  If so, the file
# will remain untouched.  In all other cases it will return false (1).  If an
# unmodified verson exists, it will be renamed by appending .dpkg-remove, so
# that it can be restored if the package upgrade fails, or removed in postinst
# if the upgrade completes successfully.
check_conffile()
{
    local f=$1

    # Check that the file hasn't already been removed, and that it hasn't been
    # usurped by some other package (which is unlikely, but would Very Bad for
    # what we are about to do next).
    [ -e "$f" ] || return 1
    dpkg-query -L bit-babbler | grep -F -q -x "$f" || return 1

    local sys_sum=$(md5sum "$f" | sed -e 's/ .*//')
    local pkg_sum=$(dpkg-query -W -f='${Conffiles}' bit-babbler | sed -n -e "\'^ $f ' { s/ obsolete$//; s/.* //; p }")

    # If it's unmodified, move it aside for deletion if the upgrade succeeds.
    if [ "$sys_sum" = "$pkg_sum" ]; then
	mv -f "$f" "${f}.dpkg-remove"
	return 1
    fi

    # Otherwise, we'll migrate it to its new form in postinst.
    return 0
}

check_seedd_conf()
{
    # Just move it out of the way if it's unmodified.  If it is modified, then
    # in postinst we'll generate a custom seedd.conf based upon its content, to
    # replace the one that is shipped in the new package.
    #
    # Because we don't remove the original conffile here before the new files
    # are unpacked, dpkg will remember it as an 'obsolete' conffile until the
    # next package upgrade (by which time it will really have been removed).
    check_conffile '/etc/default/seedd' || return 0
}

check_sysctl_conf()
{
    local oldconf='/etc/sysctl.d/bit-babbler-sysctl.conf'

    # If this one was modified, we also move it aside so that dpkg will forget
    # that it was a conffile, and not keep tracking it as 'obsolete' for purge.
    # This way a purge will do the same thing whether the modified file was
    # created before or after this upgrade (ie. leave it alone).  We will move
    # it back again in the postinst to preserve the local admin's configuration
    # as an override of the packaged version that is now in /usr/lib/sysctl.d
    if check_conffile "$oldconf"; then
	mv -f "$oldconf" "${oldconf}.dpkg-backup"
    fi
}

case "$1" in
    install|upgrade)
	# Version 0.8 adds /etc/bit-babbler/seedd.conf, replacing the previous
	# daemon configuration options which were set in /etc/default/seedd.
	dpkg --compare-versions -- "$2" ge-nl '0.8~' || check_seedd_conf

	# Version 0.9 moves /etc/sysctl.d/bit-babbler-sysctl.conf to the
	# /usr/lib/sysctl.d directory, but we need to preserve the one in
	# /etc exactly as it is, as an override, if it was modified.
	dpkg --compare-versions -- "$2" ge-nl '0.9~' || check_sysctl_conf
    ;;

    abort-upgrade)
    ;;

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



exit 0

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