"""
Process Lock Handler for VPN Server
Ensures only one instance of the server is running
"""

import os
import fcntl
import errno
import atexit
import logging
from typing import Optional

logger = logging.getLogger(__name__)

class ProcessLock:
    def __init__(self, lock_file: str = "/tmp/outline_vpn.lock"):
        self.lock_file = lock_file
        self.lock_fd: Optional[int] = None
        atexit.register(self.release)

    def acquire(self) -> bool:
        """Acquire process lock. Returns True if successful, False if already locked."""
        try:
            # Create or open lock file
            self.lock_fd = os.open(self.lock_file, os.O_CREAT | os.O_RDWR)
            fcntl.flock(self.lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            
            # Write PID to lock file
            os.truncate(self.lock_fd, 0)
            os.write(self.lock_fd, str(os.getpid()).encode())
            
            return True
            
        except (IOError, OSError) as e:
            if e.errno == errno.EWOULDBLOCK:
                # Another instance is running
                logger.warning("Another instance of the VPN server is already running")
            else:
                logger.error(f"Failed to acquire process lock: {e}")
            return False

    def release(self):
        """Release the process lock"""
        if self.lock_fd is not None:
            try:
                fcntl.flock(self.lock_fd, fcntl.LOCK_UN)
                os.close(self.lock_fd)
                os.unlink(self.lock_file)
                self.lock_fd = None
            except (IOError, OSError) as e:
                logger.error(f"Failed to release process lock: {e}")