#!/usr/bin/python3
#

import os
import sys

HOOK_NAME = 'ucs-apt-hook'
FILE_OVERRIDE_HOOK = '/etc/apt/ucs-apt-hook.override'
FILE_ENABLE_DEBUG = '/etc/apt/ucs-apt-hook.enable-debug'
PROTECTED_PACKAGES = [
    'univention-server-master',
    'univention-server-backup',
    'univention-server-slave',
    'univention-server-member',
]
DEBUG = os.path.exists(FILE_ENABLE_DEBUG)


def debug(msg: str) -> None:
    if DEBUG:
        print(f'D: {HOOK_NAME}: {msg}')


def log(msg: str) -> None:
    print(f'W: {HOOK_NAME}: {msg}')


def die(msg: str) -> None:
    print(f'E: {HOOK_NAME}: {msg}')
    sys.exit(1)


INFO_FD = os.environ.get('APT_HOOK_INFO_FD')
if not INFO_FD or INFO_FD == '0' or not INFO_FD.isdigit():
    die('APT_HOOK_INFO_FD not set up correctly')

fd = os.fdopen(int(INFO_FD))
if not fd:
    die(f'could not open APT_HOOK_INFO_FD ({INFO_FD!r})')

line = fd.readline().strip()
debug(f'VERSION: {line!r}')
if line != 'VERSION 2':
    die('expecting hook protocol in version 2')

for line in fd:
    line = line.strip()
    if not line:
        break

for line in fd:
    line = line.strip()
    debug(f'INPUT: {line!r}')
    if not line:
        continue

    try:
        pkg, oldver, direction, newver, action = line.split(' ', 4)
    except ValueError:
        log(f'received unexpected line from apt: {line!r}')
        continue

    if pkg in PROTECTED_PACKAGES:
        if action == '**REMOVE**':
            if not os.path.exists(FILE_OVERRIDE_HOOK):
                for line in f'''
!!! ERROR !!!
An attempt was made to uninstall the {pkg!r} meta package.
This usually leads to a defective UCS system. The trigger for the
uninstallation attempt can be a problem when resolving automatic
package dependencies or a manual uninstallation attempt.

If this message occurred during an app installation/update/uninstall
or a UCS system update, please visit
https://help.univention.de/REPLACEME
for the next steps.
                '''.splitlines():
                    log(line.strip())
                sys.exit(1)