#!/bin/sh
# This script can be called in the following ways:
#
# Before the package is removed:
# <prerm> remove
#
# Before an upgrade:
# <old-prerm> upgrade <new-version>
# if that fails:
# <new-prerm> failed-upgrade <old-version>
#
#
# Before package is deconfigured while dependency is replaced due to conflict:
# <prerm> deconfigure in-favour <new-package> <version>
# removing <old-package> <version>
#
# Before the package is replaced due to conflict:
# <prerm> remove in-favour <new-package> <version>

set -e

ensure_no_triggers_noawait()
{
admindir=${DPKG_ADMINDIR:-/var/lib/dpkg}
pkgadmindir=$admindir/info

trig_noawait=$(find "$pkgadmindir" -name "*.triggers" -type f | \
xargs -r grep -El "^(interest|activate)-(no)?await" | \
sed -e 's,^.*/\([^/.:]\+\)[^/]\+$,\1,')

# Abort if we cannot possibly downgrade
if [ -n "$trig_noawait" ]; then
cat <<- MSG
dpkg: error: You have packages using the "interest-noawait" and/or
"activate-noawait" trigger directives but the dpkg version that
you're trying to downgrade to doesn't support them. Aborting
downgrade.

List of affected packages:

$trig_noawait
MSG
exit 1
fi

bad_triggers_files=$(find "$admindir/triggers" -type f | \
xargs -r grep -l "/noawait$" || true)
if [ -n "$bad_triggers_files" ]; then
cat <<- MSG
dpkg: error: Some internal trigger files unexpectedly reference
packages tagged with "/noawait" while their corresponding
infodb files doesn't seem to contain any "interest-noawait"
directive. Aborting the downgrade as those tags are not supported
by the version you're trying to downgrade to.

List of internal trigger files that are affected:

$bad_triggers_files
MSG
exit 1
fi
}

downgrade_multiarch_infodb()
{
admindir=${DPKG_ADMINDIR:-/var/lib/dpkg}
pkgadmindir=$admindir/info
triggersdir=$admindir/triggers

coinst_pkgs="`ls "$pkgadmindir" | \
sed -n -e 's/^\([^:]\+:[^.]\+\)\..*$/\1/p' | sort -u | \
cut -d: -f1 | uniq -d`"

# Abort if we cannot possibly downgrade
if [ -n "$coinst_pkgs" ]; then
cat <<- MSG
dpkg: error: You have more than one architecture instance for some
installed 'Multi-Arch: same' packages, to be able to downgrade dpkg
you will need to have only one instance installed per package.

List of co-installed packages:

$coinst_pkgs
MSG
exit 1
fi

bad_dep_pkgs=$(dpkg-query -f '${Package}\t${Depends} ${Recommends} ${Suggests} ${Enhances} ${Conflicts} ${Replaces} ${Breaks}\n' -W | \
grep ":any" | cut -f1 | sort -u)
if [ -n "$bad_dep_pkgs" ]; then
cat <<- MSG
dpkg: error: Some installed packages have multiarch dependencies that
the old dpkg won't parse. You should get rid of them (or downgrade
them to versions without those dependencies) before proceeding with
dpkg's downgrade.

List of affected packages:

$bad_dep_pkgs
MSG
exit 1
fi

dep_fields='Depends|Recommends|Suggests|Enhances|Conflicts|Replaces|Breaks'
if grep -qE "^($dep_fields):.*:any" $admindir/available; then
cat <<- MSG
dpkg: error: Some available packages have multiarch dependencies that
the old dpkg won't parse. You should clear this file before proceeding
with dpkg's downgrade, with:

# dpkg --clear-avail
MSG
exit 1
fi

file_triggers_pkgs="`sed -n -e 's/^[^ ]\+ \([^:]\+\):[^.]\+$/\1/p' \
$triggersdir/File| sort -u`"

if [ -n "$file_triggers_pkgs" ]; then
cat <<-MSG
dpkg: error: The triggers database contains arch-qualified package
names that the old dpkg won't parse. You should get rid of them (or
downgrade them to a non Multi-Arch: same version) before proceeding
with dpkg's downgrade.

List of affected packages:

$file_triggers_pkgs
MSG
exit 1
fi

echo "Downgrading the multiarch dpkg control files database ..."
ls $pkgadmindir | grep : | while read oldfile; do
# We first do a round of hardlinks to the new names, so that the db
# will never be unusable for either of the dpkg versions.
newfile=$(echo $oldfile | sed -e 's/:[^.]\+//')
ln -f "$pkgadmindir/$oldfile" "$pkgadmindir/$newfile"
done
}

case "$1" in
upgrade)
# Allow the downgrade only if no package is using the
# (interest|activate)-noawait trigger directives
if dpkg --compare-versions "$2" lt 1.16.1; then
ensure_no_triggers_noawait
fi
# Downgrade the multiarch db to a “monoarch” db layout
if dpkg --compare-versions "$2" lt 1.16.0~; then
downgrade_multiarch_infodb
fi
;;

remove|failed-upgrade|deconfigure)
;;

*)
echo "$0 called with unknown argument \`$1'" 1>&2
exit 1
;;
esac


exit 0