"""FastAPI 网关：对外提供 /chat /health /metrics 接口。

启动：
    uvicorn gateway.api:app --host 0.0.0.0 --port 8000
或：
    python -m gateway.api

依赖：fastapi, uvicorn, pydantic（见 requirements.txt）
"""
from __future__ import annotations

from typing import List, Optional

from pydantic import BaseModel, Field

from router_system.config import load_config
from router_system.router import Router, build_router

# ---- 全局单例 ----
_router: Optional[Router] = None


def get_router() -> Router:
    global _router
    if _router is None:
        _router = build_router()
    return _router


# ---- 请求/响应模型 ----
class QueryRequest(BaseModel):
    query: str = Field(..., min_length=1, max_length=8000, description="用户查询")


class QueryResponse(BaseModel):
    response: str
    domain: str
    difficulty: str
    confidence: float
    upgraded: bool
    quality_score: float
    model_used: str
    route: List[str]
    latency_ms: float
    cache_hit: bool
    cache_level: Optional[str]
    cost_est: float
    error: Optional[str] = None


class HealthResponse(BaseModel):
    status: str
    domains: List[str]
    classifier: str
    judge: str
    fallback: str


# ---- FastAPI 应用 ----
try:
    from fastapi import FastAPI

    app = FastAPI(
        title="Multi-Expert Router API",
        description="多专业小模型 + 路由模型系统（MVP）",
        version="0.1.0",
    )

    @app.get("/health", response_model=HealthResponse, tags=["system"])
    async def health():
        return get_router().health()

    @app.post("/chat", response_model=QueryResponse, tags=["chat"])
    async def chat(req: QueryRequest):
        result = await get_router().route(req.query)
        return QueryResponse(**result.to_dict())

    @app.get("/metrics", tags=["system"])
    async def metrics():
        r = get_router()
        return {
            "router": r.stats.summary(),
            "cache": r.cache.stats(),
        }

except ImportError:
    # fastapi 未安装时，提供 CLI 入口提示
    app = None
    print("[gateway] 未安装 fastapi，请执行: pip install -r requirements.txt")


if __name__ == "__main__":
    import uvicorn
    uvicorn.run("gateway.api:app", host="0.0.0.0", port=8000, reload=False)