"""엔진 게이트웨이 HTTP 클라이언트.

⚠️ 게이트웨이 자체(apps/api/engine_gateway/)는 람다가 직접 만든다. 여기는 *호출부*만.
게이트웨이가 provider 라우팅(claude_api/claude_cli/openai/solar)·캐싱·상주 claude -p 풀을
흡수한다(마스터플랜 §0, R1). 이 백엔드는 ENGINE_URL 로 HTTP 호출만 한다.

계약 (람다와 합의할 게이트웨이 API):
  POST {ENGINE_URL}/v1/generate         — 단발 생성 (평가 deep-loop 등)
  POST {ENGINE_URL}/v1/stream           — SSE 토큰 스트림 (내담자 AI 응답)
  GET  {ENGINE_URL}/health

요청 바디는 3-AI 역할별 system 레이어(L0~L6, 설계서 §1.2)를 게이트웨이에 넘기되,
text 는 *PII 마스킹 후(text_masked)* 만 보낸다 (R7/F-03, 마스킹은 호출 전 가드레일이 완료).
"""

from __future__ import annotations

import asyncio
from typing import Any, AsyncIterator, Optional

import httpx

from .config import settings
from .contracts.engine_gateway import (
    AIRole,
    EngineMessage,
    EngineGatewaySseLineDecoder,
    EngineGatewaySsePacket,
    GenerateRequest,
    GenerateResponse,
    StreamRequest,
)


class EngineError(RuntimeError):
    """게이트웨이 호출 실패. 라우트가 503/502 로 변환."""


class EngineClient:
    """ENGINE_URL 게이트웨이 비동기 클라이언트. 앱 수명주기 동안 1 인스턴스 재사용."""

    def __init__(self, base_url: Optional[str] = None) -> None:
        self.base_url = (base_url or settings.engine_url).rstrip("/")
        self.engine_mode = settings.engine_mode
        self.default_model: Optional[str] = None
        self._client: Optional[httpx.AsyncClient] = None
        self._lock = asyncio.Lock()

    async def startup(self) -> None:
        async with self._lock:
            if self._client is None:
                self._client = self._new_client()

    def _new_client(self) -> httpx.AsyncClient:
        return httpx.AsyncClient(
            base_url=self.base_url,
            timeout=httpx.Timeout(
                settings.engine_timeout,
                connect=settings.engine_connect_timeout,
            ),
        )

    async def shutdown(self) -> None:
        async with self._lock:
            if self._client is not None:
                await self._client.aclose()
                self._client = None

    @staticmethod
    def _model_override(model: Optional[str]) -> Optional[str]:
        value = (model or "").strip()
        if not value or value == "gateway-default":
            return None
        return value

    async def configure(
        self,
        *,
        base_url: str,
        engine_mode: str,
        default_model: Optional[str] = None,
    ) -> None:
        next_url = base_url.rstrip("/")
        next_model = self._model_override(default_model)
        async with self._lock:
            url_changed = next_url != self.base_url
            self.base_url = next_url
            self.engine_mode = engine_mode
            self.default_model = next_model
            if self._client is not None and url_changed:
                old_client = self._client
                self._client = self._new_client()
                await old_client.aclose()

    def _payload(self, req: GenerateRequest) -> dict[str, Any]:
        payload = req.model_dump(exclude_none=True)
        if self.default_model and "model" not in payload:
            payload["model"] = self.default_model
        return payload

    @property
    def client(self) -> httpx.AsyncClient:
        if self._client is None:
            raise EngineError("EngineClient not started — call startup() in lifespan")
        return self._client

    async def health(self) -> bool:
        return bool((await self.health_detail()).get("ok"))

    async def health_detail(self) -> dict[str, Any]:
        try:
            r = await self.client.get("/ready")
            if r.status_code == 404:
                live = await self.client.get("/health")
                return {
                    "ok": live.status_code == 200,
                    "detail": "gateway liveness only; readiness endpoint unavailable",
                    "status_code": live.status_code,
                }
            payload: dict[str, Any] = {}
            try:
                payload = r.json()
            except ValueError:
                payload = {}
            return {
                "ok": r.status_code == 200 and bool(payload.get("ok", False)),
                "detail": str(payload.get("detail") or r.text or "engine readiness failed"),
                "status_code": r.status_code,
                "cached": bool(payload.get("cached", False)),
            }
        except httpx.HTTPError as exc:
            return {
                "ok": False,
                "detail": f"engine readiness transport error: {exc}",
                "status_code": None,
            }

    async def generate(self, req: GenerateRequest) -> GenerateResponse:
        """단발 생성. TODO: 게이트웨이 응답 스키마 확정 후 cost 텔레메트리 turns 적재."""
        try:
            r = await self.client.post("/v1/generate", json=self._payload(req))
            r.raise_for_status()
        except httpx.HTTPStatusError as e:
            raise EngineError(f"engine generate {e.response.status_code}: {e.response.text}") from e
        except httpx.HTTPError as e:
            raise EngineError(f"engine generate transport error: {e}") from e
        return GenerateResponse.model_validate(r.json())

    async def stream(self, req: StreamRequest) -> AsyncIterator[str]:
        """SSE 토큰 스트림 프록시.

        게이트웨이 SSE(`text/event-stream`) 의 원시 non-empty line을 yield한다.
        새 호출부는 raw line 대신 `stream_packets()`를 사용한다.
        """
        try:
            async with self.client.stream(
                "POST", "/v1/stream", json=self._payload(req)
            ) as r:
                r.raise_for_status()
                async for line in r.aiter_lines():
                    if line:
                        yield line
        except httpx.HTTPStatusError as e:
            raise EngineError(f"engine stream {e.response.status_code}") from e
        except httpx.HTTPError as e:
            raise EngineError(f"engine stream transport error: {e}") from e

    async def stream_packets(self, req: StreamRequest) -> AsyncIterator[EngineGatewaySsePacket]:
        """Decode gateway SSE into the shared token/done/error contract.

        Keep wire-format parsing at the gateway client boundary so app services
        do not depend on raw SSE line structure. A future Node.js gateway should
        only need to preserve `app.contracts.engine_gateway`.
        """
        decoder = EngineGatewaySseLineDecoder()
        async for raw in self.stream(req):
            packet = decoder.feed_line(raw)
            if packet is not None:
                yield packet


# 앱 전역 싱글톤 (main lifespan 에서 startup/shutdown)
engine_client = EngineClient()