"""OS-backed evaluation lease; released automatically on process exit."""
from __future__ import annotations

import json
import os
import secrets
from pathlib import Path


class EvaluationLock:
    def __init__(self, root: Path):
        self.path = root / '.copienator-finalisation.lock'
        self.stream = None
        self.token = secrets.token_urlsafe(32)

    def __enter__(self):
        from copienator import CliError
        self.stream = self.path.open('a+b')
        try:
            if os.name == 'nt':
                import msvcrt
                self.stream.seek(0)
                if not self.stream.read(1):
                    self.stream.write(b' ')
                    self.stream.flush()
                self.stream.seek(0)
                msvcrt.locking(self.stream.fileno(), msvcrt.LK_NBLCK, 1)
            else:
                import fcntl
                fcntl.flock(self.stream.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
        except OSError:
            self.stream.close()
            self.stream = None
            raise CliError('Cette évaluation est utilisée par un autre traitement ou la finalisation web.') from None
        self.stream.seek(0)
        self.stream.truncate()
        self.stream.write(json.dumps({'pid': os.getpid(), 'token': self.token}).encode())
        self.stream.flush()
        return self

    def __exit__(self, *args):
        if self.stream:
            self.stream.close()
            self.stream = None


def command_lock(args):
    from contextlib import nullcontext
    from copienator import EvaluationWorkspace
    root = getattr(args, 'evaluation', None)
    if root is None and getattr(args, 'target', None):
        try:
            root = EvaluationWorkspace.discover(Path(args.target).resolve()).root
        except Exception:
            return nullcontext()
    if root is None or not Path(root).is_dir():
        return nullcontext()
    root = Path(root).resolve()
    token = os.environ.get('COPIENATOR_FINALISATION_TOKEN')
    if token:
        try:
            data = json.loads((root / '.copienator-finalisation.lock').read_text())
            if secrets.compare_digest(token, data['token']):
                return nullcontext()
        except (OSError, ValueError, KeyError):
            pass
    return EvaluationLock(root)