"""PR-MacMini-Derived-Worker-1 internal endpoint.

Mac mini derived-worker 가 study explanation 가공을 위해 호출.
GPU = RAG context provider (LLM generation X), Mac mini = LLM 가공 공장.
Bearer token 보호 (settings.internal_worker_token).
"""
from __future__ import annotations

import hmac
import logging

from fastapi import APIRouter, Depends, Header, HTTPException, Path, Response, status
from sqlalchemy.ext.asyncio import AsyncSession

from core.config import settings
from core.database import async_session
from models.study_question import StudyQuestion
from services.study.explanation_rag import gather_explanation_context, render_evidence_block
from workers.study_explanation_worker import _render_envelope_prompt

logger = logging.getLogger(__name__)

router = APIRouter()


def _verify_token(authorization: str | None = Header(default=None)) -> None:
    if not settings.internal_worker_token:
        raise HTTPException(status_code=503, detail="internal_worker_token not configured")
    if not authorization or not authorization.lower().startswith("bearer "):
        raise HTTPException(status_code=401, detail="missing Bearer token")
    token = authorization[7:].strip()
    # 상수시간 비교 (R7) — 일반 != 는 첫 불일치에서 단락돼 prefix 길이로 바이트 추정 가능한
    # timing side-channel. 이 토큰이 RAG 정답 포함 endpoint 를 보호하므로 compare_digest 로
    # 통일(search.py 정본과 일치).
    if not hmac.compare_digest(token, settings.internal_worker_token):
        raise HTTPException(status_code=403, detail="invalid token")


async def _session() -> AsyncSession:
    async with async_session() as s:
        yield s


@router.get("/explanation-context/{question_id}")
async def get_explanation_context(
    question_id: int = Path(..., ge=1),
    _auth: None = Depends(_verify_token),
    session: AsyncSession = Depends(_session),
):
    question = await session.get(StudyQuestion, question_id)
    if question is None or question.deleted_at is not None:
        raise HTTPException(status_code=410, detail="question deleted or missing")
    if question.ai_explanation_status == "ready":
        raise HTTPException(status_code=410, detail="explanation already ready")

    ctx = await gather_explanation_context(session, question.user_id, question)
    docs_count = len(ctx.documents)
    qs_count = len(ctx.questions)
    if docs_count == 0 and qs_count == 0:
        return Response(status_code=204)

    doc_block = render_evidence_block(ctx.documents)
    q_block = render_evidence_block(ctx.questions)
    rendered_prompt = _render_envelope_prompt(question, doc_block, q_block)

    logger.info(
        "internal_study_context qid=%s docs=%s questions=%s prompt_len=%s",
        question_id, docs_count, qs_count, len(rendered_prompt),
    )

    return {
        "question_id": question.id,
        "question_correct_choice": question.correct_choice,
        "rendered_prompt": rendered_prompt,
        "evidence_summary": {
            "documents_count": docs_count,
            "questions_count": qs_count,
        },
    }