#!/usr/bin/env python3
"""搜索 V1 工厂协议设备（UDP 4942）。"""

from __future__ import annotations

import argparse
import ipaddress
import json
import secrets
import socket
import struct
import time
from typing import Any

PORT = 4942
REQUEST = 0x5A0EFF00
RESPONSE = 0x5A0EFF01
MAX_DATA = 1024 * 1024


def frame(command: int, payload: bytes) -> bytes:
    return struct.pack("!II", command, len(payload)) + payload


def parse_frame(packet: bytes) -> tuple[int, bytes]:
    if len(packet) < 8:
        raise ValueError("packet shorter than V1 header")
    command, length = struct.unpack("!II", packet[:8])
    if length > MAX_DATA or len(packet) != 8 + length:
        raise ValueError("invalid V1 payload length")
    return command, packet[8:]


def discover(timeout: float, interface: str | None) -> int:
    session = secrets.randbelow(0x7FFFFFFF) + 1
    request = frame(REQUEST, json.dumps({"session": session}).encode("utf-8"))
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
    sock.settimeout(min(0.5, timeout))
    try:
        # Bind the documented client port. If another discovery utility owns
        # it, stop and report the conflict instead of silently using another port.
        sock.bind((interface or "0.0.0.0", PORT))
        sock.sendto(request, ("255.255.255.255", PORT))
        deadline = time.monotonic() + timeout
        seen: set[tuple[str, str]] = set()
        while time.monotonic() < deadline:
            try:
                packet, address = sock.recvfrom(MAX_DATA + 8)
            except socket.timeout:
                continue
            try:
                command, data = parse_frame(packet)
                obj: Any = json.loads(data.decode("utf-8"))
                if command != RESPONSE or not isinstance(obj, dict):
                    continue
                if obj.get("session") != session:
                    continue
                key = (address[0], str(obj.get("sn", "")))
                if key in seen:
                    continue
                seen.add(key)
                print(json.dumps({"source_ip": address[0], "response": obj}, ensure_ascii=False))
            except (ValueError, UnicodeDecodeError, json.JSONDecodeError):
                continue
        return 0
    finally:
        sock.close()


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--timeout", type=float, default=3.0)
    parser.add_argument("--interface", help="optional local IPv4 address to bind")
    args = parser.parse_args()
    if args.timeout <= 0:
        parser.error("--timeout must be positive")
    if args.interface:
        ipaddress.IPv4Address(args.interface)
    return discover(args.timeout, args.interface)


if __name__ == "__main__":
    raise SystemExit(main())