"""proxy_dns 降级路径实测(模拟云通道挂掉)。

验证两条降级链:
  1. 通道失败 -> 直连 fallback_dns 解析成功(全屋 DNS 不断)
  2. 通道失败 + 直连也失败 -> 回 SERVFAIL(客户端立即切备用 DNS)

用法: python3 scripts/test_dns_fallback.py
"""
from __future__ import annotations

import socket
import sys
import threading
import time
from pathlib import Path

sys.path.insert(0, str(Path(__file__).resolve().parent.parent))

from channel.client import ChannelClient, ChannelError  # noqa: E402
from channel.proxy_dns import DnsSplitProxy  # noqa: E402

QUERY = bytes.fromhex(
    "abcd01000001000000000000037777770674616f62616f03636f6d0000010001"
)


class DownClient(ChannelClient):
    """模拟云通道不可用(所有请求抛 ChannelError)。"""

    def __init__(self) -> None:
        super().__init__(host="127.0.0.1", port=1, token="test-stub")

    def send_dns_query(self, raw_query: bytes) -> bytes | None:
        raise ChannelError("simulated channel down")

    def ensure_connected(self) -> None:
        raise ChannelError("simulated channel down")


def ask(port: int, timeout: float = 6.0) -> bytes:
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.settimeout(timeout)
    try:
        s.sendto(QUERY, ("127.0.0.1", port))
        resp, _ = s.recvfrom(4096)
        return resp
    finally:
        s.close()


def rcode(resp: bytes) -> int:
    return resp[3] & 0x0F if len(resp) >= 12 else -1


def case_fallback_ok() -> bool:
    """通道挂 + 直连上游可用 -> 应返回正常解析(RCODE=0)。"""
    proxy = DnsSplitProxy(
        DownClient(), listen_port=18053, school_dns="223.5.5.5",
        internal_suffixes=[], fallback_dns="223.5.5.5",
    )
    threading.Thread(target=proxy.serve, daemon=True).start()
    time.sleep(0.3)
    resp = ask(18053)
    ok = len(resp) > 12 and rcode(resp) == 0 and proxy.fallback_resolved >= 1
    print(
        f"  用例1 通道挂->直连降级: 响应 {len(resp)}B RCODE={rcode(resp)} "
        f"fallback_resolved={proxy.fallback_resolved} -> "
        f"{'PASS' if ok else 'FAIL'}"
    )
    return ok


def case_servfail() -> bool:
    """通道挂 + 直连上游也不可达 -> 应回 SERVFAIL(RCODE=2), 不静默丢弃。"""
    proxy = DnsSplitProxy(
        DownClient(), listen_port=18054, school_dns="192.0.2.1",
        internal_suffixes=[], fallback_dns="192.0.2.1",
    )
    threading.Thread(target=proxy.serve, daemon=True).start()
    time.sleep(0.3)
    resp = ask(18054)
    ok = len(resp) >= 12 and rcode(resp) == 2
    print(
        f"  用例2 通道+直连全挂->SERVFAIL: 响应 {len(resp)}B "
        f"RCODE={rcode(resp)} -> {'PASS' if ok else 'FAIL'}"
    )
    return ok


def main() -> int:
    print("[DNS 降级测试] 模拟云通道不可用")
    r1 = case_fallback_ok()
    r2 = case_servfail()
    print(f"结果: {'全部 PASS' if r1 and r2 else '有 FAIL'}")
    return 0 if (r1 and r2) else 1


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