#!/usr/bin/env python3
"""Deterministic local upstream for the passive proxy lab."""

from __future__ import annotations

import argparse
import json
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer


class FakeModelHandler(BaseHTTPRequestHandler):
    protocol_version = "HTTP/1.1"

    def log_message(self, _format: str, *_args: object) -> None:
        return

    def do_POST(self) -> None:
        length = int(self.headers.get("Content-Length", "0") or "0")
        self.rfile.read(length)
        body = json.dumps(
            {
                "id": "lab-response",
                "object": "chat.completion",
                "choices": [
                    {
                        "index": 0,
                        "message": {
                            "role": "assistant",
                            "content": "The fake upstream received the request.",
                        },
                        "finish_reason": "stop",
                    }
                ],
                "usage": {
                    "prompt_tokens": 0,
                    "completion_tokens": 0,
                    "total_tokens": 0,
                },
            },
            separators=(",", ":"),
        ).encode("utf-8")
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)


def main() -> int:
    parser = argparse.ArgumentParser(description="Fake local model endpoint")
    parser.add_argument("--listen-host", default="127.0.0.1")
    parser.add_argument("--listen-port", type=int, default=18081)
    args = parser.parse_args()
    server = ThreadingHTTPServer((args.listen_host, args.listen_port), FakeModelHandler)
    print(
        f"fake model upstream listening on http://{args.listen_host}:{server.server_port}",
        flush=True,
    )
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        pass
    finally:
        server.server_close()
    return 0


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