main.py

from fastapi import FastAPI, Request
from fastapi.responses import StreamingResponse, JSONResponse
from pydantic import BaseModel
from typing import List, Optional, Union
import requests
import json
import logging

app = FastAPI()

# Logging setup
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger("proxy")

# Configuration
API_URL = "https://api.typegpt.net/v1/chat/completions"
API_KEY = "sk-XzS5hhsa3vpIcRLz3prQirBQXOx2hPydPzSpzdRcE1YddnNm"
BACKEND_MODEL = "pixtral-large-latest"

# Load system prompt mappings
with open("model_map.json", "r", encoding="utf-8") as f:
    MODEL_PROMPTS = json.load(f)

# Request schema
class Message(BaseModel):
    role: str
    content: str

class ChatRequest(BaseModel):
    model: str
    messages: List[Message]
    stream: Optional[bool] = False
    temperature: Optional[float] = 1.0
    top_p: Optional[float] = 1.0
    n: Optional[int] = 1
    stop: Optional[Union[str, List[str]]] = None
    presence_penalty: Optional[float] = 0.0
    frequency_penalty: Optional[float] = 0.0

# Build request to backend with injected system prompt
def build_payload(chat: ChatRequest):
    system_prompt = MODEL_PROMPTS.get(chat.model, "You are a helpful assistant.")
    filtered_messages = [msg for msg in chat.messages if msg.role != "system"]
    payload_messages = [{"role": "system", "content": system_prompt}] + [
        {"role": msg.role, "content": msg.content} for msg in filtered_messages
    ]
    return {
        "model": BACKEND_MODEL,
        "messages": payload_messages,
        "stream": chat.stream,
        "temperature": chat.temperature,
        "top_p": chat.top_p,
        "n": chat.n,
        "stop": chat.stop,
        "presence_penalty": chat.presence_penalty,
        "frequency_penalty": chat.frequency_penalty
    }

# Streaming chunk handler with model replacement and UTF-8 fix
def stream_generator(requested_model: str, payload: dict, headers: dict):
    with requests.post(API_URL, headers=headers, json=payload, stream=True) as r:
        for line in r.iter_lines(decode_unicode=True):
            if not line:
                continue
            if line.startswith("data:"):
                content = line[6:].strip()
                if content == "[DONE]":
                    yield "data: [DONE]\n\n"
                    continue
                try:
                    json_obj = json.loads(content)
                    if json_obj.get("model") == BACKEND_MODEL:
                        json_obj["model"] = requested_model
                    yield "data: " + json.dumps(json_obj, ensure_ascii=False) + "\n\n"
                except json.JSONDecodeError:
                    logger.warning("Invalid JSON in stream chunk: %s", content)
            else:
                logger.debug("Non-data stream line skipped: %s", line)

# Main API endpoint
@app.post("/v1/chat/completions")
async def proxy_chat(request: Request):
    try:
        body = await request.json()
        chat_request = ChatRequest(**body)
        payload = build_payload(chat_request)

        headers = {
            "Authorization": f"Bearer {API_KEY}",
            "Content-Type": "application/json"
        }

        if chat_request.stream:
            return StreamingResponse(
                stream_generator(chat_request.model, payload, headers),
                media_type="text/event-stream; charset=utf-8",
                headers={"Content-Type": "text/event-stream; charset=utf-8"}
            )
        else:
            response = requests.post(API_URL, headers=headers, json=payload)
            data = response.json()
            if "model" in data and data["model"] == BACKEND_MODEL:
                data["model"] = chat_request.model
            return JSONResponse(
                content=data,
                media_type="application/json; charset=utf-8",
                headers={"Content-Type": "application/json; charset=utf-8"}
            )

    except Exception as e:
        logger.error("Error in /v1/chat/completions: %s", str(e))
        return JSONResponse(
            content={"error": "Internal server error."},
            status_code=500
        )