#!/usr/bin/env python3
"""Linux server kit entrypoint. Configuration and worlds are never pack-owned."""
import argparse
import fcntl
import hashlib
import json
import os
from pathlib import Path
import signal
import subprocess
import tomllib
from urllib.request import urlopen


def update(root, platform, url, java):
    # packwiz updates mods, not Minecraft/Loader. Refuse an implicit platform migration.
    with urlopen(url, timeout=30) as response:
        manifest = tomllib.loads(response.read(65536).decode('utf-8'))
    if manifest['versions'] != platform['versions']:
        raise SystemExit('Minecraft/Fabric changed: prepare an explicit migration before updating.')
    tools = root / '.tools'
    for name, digest in platform['sha256'].items():
        if hashlib.sha256((tools / name).read_bytes()).hexdigest() != digest:
            raise SystemExit('Server tool hash mismatch: ' + name)
    subprocess.run([java, '-jar', str(tools / 'packwiz-installer-bootstrap.jar'),
                    '--bootstrap-main-jar', str(tools / 'packwiz-installer.jar'),
                    '--bootstrap-no-update', '-g', '-s', 'server',
                    '--pack-folder', str(root), url], cwd=root, check=True)


def run_minecraft(root, java, memory):
    process = subprocess.Popen([java, '-Xms512M', '-Xmx' + memory, '-jar',
                                str(root / '.tools/fabric-server-launch.jar'), 'nogui'], cwd=root)
    def stop(signum, _frame):
        process.send_signal(signum)
    previous = {s: signal.signal(s, stop) for s in (signal.SIGTERM, signal.SIGINT)}
    try:
        # Keep the update lock until Java has finished saving during shutdown.
        return process.wait()
    finally:
        for signum, handler in previous.items():
            signal.signal(signum, handler)


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('command', choices=('update', 'start'), nargs='?', default='start')
    args = parser.parse_args()
    root = Path(__file__).resolve().parents[1]
    platform = json.loads((root / '.tools/platform.json').read_text())
    java = os.environ.get('SANCTUARY_JAVA', 'java')
    with (root / '.sanctuary-server.lock').open('a') as lock:
        try:
            fcntl.flock(lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except BlockingIOError:
            raise SystemExit('Server is running or an update is already in progress.')
        update(root, platform, os.environ.get('SANCTUARY_PACK_URL', platform['pack_url']), java)
        if args.command == 'start':
            memory = os.environ.get('SANCTUARY_MEMORY', '4G')
            # No shell evaluation of Java options or credentials.
            raise SystemExit(run_minecraft(root, java, memory))


if __name__ == '__main__':
    try:
        main()
    except (OSError, ValueError, KeyError, subprocess.CalledProcessError) as error:
        # Do not print environment values or HTTP response bodies.
        raise SystemExit('Server operation failed (' + type(error).__name__ + ').')