#!/usr/bin/env python3
"""Port availability checker - test if a local port is in use or available."""
import socket
import sys
from typing import Tuple


def check_port(port: int, host: str = "localhost") -> Tuple[bool, str]:
    """Check if a port is available. Returns (available, message)."""
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(1)
    try:
        result = sock.connect_ex((host, port))
        if result == 0:
            return False, f"Port {port}: IN USE (connection accepted)"
        else:
            return True, f"Port {port}: AVAILABLE (connection refused)"
    except socket.timeout:
        return True, f"Port {port}: AVAILABLE (timeout)"
    except socket.error as e:
        return False, f"Port {port}: ERROR - {e}"
    finally:
        sock.close()


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: python port_check.py <port>", file=sys.stderr)
        sys.exit(1)
    
    try:
        port = int(sys.argv[1])
        if not (1 <= port <= 65536):
            print("Error: Port must be 1-65535", file=sys.stderr)
            sys.exit(1)
    except ValueError:
        print("Error: Port must be an integer", file=sys.stderr)
        sys.exit(1)
    
    available, msg = check_port(port)
    print(msg)
    sys.exit(0 if available else 1)