"""OpenAI-compatible proxy (MLX server, vLLM, etc.) — SSE passthrough."""

from __future__ import annotations

import json
import logging
from collections.abc import AsyncGenerator

import httpx

logger = logging.getLogger(__name__)


async def stream_chat(
    base_url: str,
    model: str,
    messages: list[dict],
    **kwargs,
) -> AsyncGenerator[str, None]:
    """Proxy OpenAI-compatible chat streaming. SSE passthrough with model field override."""
    payload = {
        "model": model,
        "messages": messages,
        "stream": True,
        **{k: v for k, v in kwargs.items() if v is not None},
    }

    async with httpx.AsyncClient(timeout=120.0) as client:
        async with client.stream(
            "POST",
            f"{base_url}/v1/chat/completions",
            json=payload,
        ) as resp:
            if resp.status_code != 200:
                body = await resp.aread()
                error_msg = body.decode("utf-8", errors="replace")
                yield _error_event(f"Backend error ({resp.status_code}): {error_msg}")
                return

            async for line in resp.aiter_lines():
                if not line.strip():
                    continue
                # Pass through SSE lines as-is (already in OpenAI format)
                if line.startswith("data: "):
                    yield f"{line}\n\n"
                elif line == "data: [DONE]":
                    yield "data: [DONE]\n\n"


async def complete_chat(
    base_url: str,
    model: str,
    messages: list[dict],
    **kwargs,
) -> dict:
    """Non-streaming OpenAI-compatible chat."""
    payload = {
        "model": model,
        "messages": messages,
        "stream": False,
        **{k: v for k, v in kwargs.items() if v is not None},
    }

    async with httpx.AsyncClient(timeout=120.0) as client:
        resp = await client.post(f"{base_url}/v1/chat/completions", json=payload)
        resp.raise_for_status()
        return resp.json()


def _error_event(message: str) -> str:
    error = {
        "id": "chatcmpl-gateway",
        "object": "chat.completion.chunk",
        "model": "error",
        "choices": [
            {
                "index": 0,
                "delta": {"content": f"[Error] {message}"},
                "finish_reason": "stop",
            }
        ],
    }
    return f"data: {json.dumps(error)}\n\ndata: [DONE]\n\n"