"""
src/graph/worker_b.py
Worker B: RAG 검색 + 답변 생성 노드

처리 흐름:
  ① 쿼리 추출  (LLM) — 이메일에서 핵심 SAP 질문을 2개 표현으로 확장 (Query Expansion)
  ② Hybrid Retrieval (Dense 0.5 + BM25 0.5) — 쿼리별 top-k 검색 후 중복 제거 병합
  ③ Reranking (bge-reranker-v2-m3) — top-5 재순위화
  ④ 답변 생성  (LLM) — top-5 컨텍스트 기반 RAG 답변

설정 값은 모두 configs.yaml에서 읽음:
  models.worker_b.name          = google/gemini-2.0-flash-lite-001
  rag.dense_weight              = 0.5
  rag.sparse_weight             = 0.5
  rag.top_k_retrieval           = 15
  rag.top_k_rerank              = 5
"""

from __future__ import annotations

import logging
import os

from dotenv import load_dotenv
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI

from src.config import get_config
from src.graph.state import AgentState
from src.rag.retriever import build_hybrid_retriever
from src.rag.reranker import rerank

load_dotenv()
logger = logging.getLogger(__name__)


# ---------------------------------------------------------------------------
# LLM builder (싱글턴)
# ---------------------------------------------------------------------------

_llm: ChatOpenAI | None = None


def _get_llm() -> ChatOpenAI:
    global _llm
    if _llm is not None:
        return _llm

    cfg = get_config()
    api_key = os.getenv("OPENROUTER_API_KEY", "")
    if not api_key:
        raise EnvironmentError("OPENROUTER_API_KEY is not set.")

    wb_cfg = cfg.models.worker_b
    _llm = ChatOpenAI(
        model=wb_cfg.name,
        temperature=wb_cfg.temperature,
        openai_api_key=api_key,
        openai_api_base=cfg.openrouter.base_url,
        default_headers={
            "HTTP-Referer": "https://github.com/daisysooyeon/SAP-ERP-AI-Agent",
            "X-Title": "SAP-ERP-AI-Agent Worker-B",
        },
    )
    return _llm


# ---------------------------------------------------------------------------
# ① 쿼리 추출 + Query Expansion 프롬프트
# ---------------------------------------------------------------------------

_QUERY_EXTRACTION_SYSTEM = """\
You are an expert at extracting and expanding search queries from B2B SAP ERP customer emails.

The email may contain an ERP transaction request (e.g., changing an order) AND a knowledge question about SAP.
Extract ONLY the knowledge/inquiry part, then generate multiple search query variants.

Rules:
1. Analyze the email and identify the core SAP knowledge question (ignore any ERP
   action requests, order/item numbers, quantities, and dates).
2. If a knowledge question exists, set 'has_knowledge_question' to true and generate 2 search query variants:
   - 'query_primary': the most direct restatement of the question. PRESERVE,
     verbatim, every SAP term and feature / screen / field name the customer used
     — do NOT generalize them into generic phrases and do NOT substitute a related
     but different concept. If the question has two distinct parts, keep both.
   - 'query_variant_1': the SAME intent, but MAXIMIZE keyword diversity for hybrid
     (keyword + semantic) retrieval — use alternative SAP terminology, synonyms, or
     the formal SAP feature name for the same concept, rather than only rephrasing
     the grammar.
3. If the email contains NO knowledge question, set 'has_knowledge_question' to false and leave all queries empty ("").

Output MUST be a valid JSON object:
{{
  "has_knowledge_question": true or false,
  "query_primary": "...",
  "query_variant_1": "..."
}}
"""

_QUERY_EXTRACTION_PROMPT = ChatPromptTemplate.from_messages([
    ("system", _QUERY_EXTRACTION_SYSTEM),
    ("human", "Email:\n\n{user_input}"),
])


def _extract_rag_queries(user_input: str) -> list[str]:
    """이메일에서 RAG 검색 쿼리를 최대 2개 추출 (Query Expansion). 질문이 없으면 빈 리스트 반환.

    확장 개수 실험(reports/_expansion_result) 결과: 2개가 3개보다 hit_rate가 같거나 높고
    (후보풀 22%↓로 리랭크 부하도 감소), 1개는 멀티쿼리 이점을 잃어 더 낮았다 → 2개로 고정.
    """
    from langchain_core.output_parsers import JsonOutputParser
    try:
        llm = _get_llm()
        chain = _QUERY_EXTRACTION_PROMPT | llm | JsonOutputParser()
        result = chain.invoke({"user_input": user_input})

        if not result.get("has_knowledge_question"):
            return []

        queries = []
        for key in ("query_primary", "query_variant_1"):
            q = (result.get(key) or "").strip()
            if q:
                queries.append(q)

        logger.info("[worker_b] ① Extracted %d queries: %s", len(queries), queries)
        return queries
    except Exception as e:
        logger.error("[worker_b] Query extraction failed: %s", e)
        return []


# ---------------------------------------------------------------------------
# ④ 답변 생성 프롬프트
# ---------------------------------------------------------------------------

_ANSWER_SYSTEM = """\
You are an SAP ERP expert assistant. Answer the user's question using ONLY the provided context from SAP documentation.

Guidelines:
- Use ANY relevant information in the context to answer as fully as you can. If the context covers the question only partially, answer the parts that ARE supported and briefly state what the documentation does not specify (e.g., "The documentation explains X but does not give the exact transaction code.").
- Only reply EXACTLY "I could not find sufficient information in the SAP documentation to answer this question." when the context contains NOTHING relevant to the question. Do not give up just because the answer is incomplete.
- Do NOT invent facts, figures, transaction codes, or steps that are not present in the context.
- Reproduce every identifier EXACTLY as it appears in the context — SAP Note numbers, business function / feature names (e.g. ALL_CAPS_WITH_UNDERSCORES like Q2C_MULTIPLE_BP_ADDRESSES), transaction codes, table/field/app names. Never abbreviate, truncate, reformat, or guess them; if you are not certain of the exact string, omit it rather than alter it.
- Be concise and accurate, and cite the source document when possible (e.g., "According to TS460...").
"""

_ANSWER_PROMPT = ChatPromptTemplate.from_messages([
    ("system", _ANSWER_SYSTEM),
    ("human", "Question: {query}\n\nContext:\n{context}"),
])


def _generate_answer(query: str, docs: list) -> str:
    """top-k 컨텍스트를 기반으로 LLM 답변 생성."""
    if not docs:
        return "No relevant SAP documentation found for this query."

    # 컨텍스트 조합 (source 정보 포함)
    context_parts = []
    for i, doc in enumerate(docs, 1):
        source = doc.metadata.get("source", "unknown")
        context_parts.append(f"[{i}] (Source: {source})\n{doc.page_content}")
    context = "\n\n".join(context_parts)

    try:
        llm = _get_llm()
        chain = _ANSWER_PROMPT | llm
        result = chain.invoke({"query": query, "context": context})
        answer = result.content.strip()
        logger.info("[worker_b] ④ Answer generated (%d chars)", len(answer))
        return answer
    except Exception as e:
        logger.error("[worker_b] Answer generation failed: %s", e)
        return f"Answer generation failed: {e}"


def _serialize_docs(docs: list) -> list[dict]:
    """LangChain Document 리스트를 JSON 직렬화 가능한 dict 리스트로 변환"""
    return [
        {
            "content":  doc.page_content,
            "source":   doc.metadata.get("source", ""),
            "chunk_id": doc.metadata.get("chunk_id", -1),
            "page":     doc.metadata.get("page", -1),
        }
        for doc in docs
    ]


# ---------------------------------------------------------------------------
# LangGraph 노드
# ---------------------------------------------------------------------------

def worker_b_node(state: AgentState) -> dict:
    """
    LangGraph Worker B 노드.

    Reads:
        state["user_input"]  — 원본 이메일
        state["rag_query"]   — 있으면 쿼리 추출 스킵

    Returns partial AgentState update:
        {
            "rag_query":      str,
            "retrieved_docs": list[dict],  # [{content, source, chunk_id}]
            "rag_answer":     str,
            "error_messages": list[str],
        }
    """
    logger.info("[worker_b] ══════════════ Worker B START ══════════════")

    user_input: str = state.get("user_input", "")
    email_context: dict | None = state.get("email_context")
    errors: list[str] = list(state.get("error_messages", []))

    # 전처리 결과가 "지식 질문 없음"이라고 명확히 신호하면, 비싼 LLM 쿼리 추출 단계를
    # 건너뛴다. preprocess_ok=False이거나 context 자체가 없으면 안전하게 기존 경로로 진행.
    if (email_context
            and email_context.get("preprocess_ok")
            and email_context.get("mentions_question") is False):
        logger.info("[worker_b] Preprocessor: mentions_question=False → skipping RAG stage")
        return {
            "rag_query":      "",
            "retrieved_docs": [],
            "rag_answer":     "",
            "error_messages": errors,
        }

    # 쿼리 추출 입력 선택 (우선순위):
    #   ① question_summary — 전처리가 ERP 액션 노이즈를 제거하고 지식 질문만 정규화한 것.
    #      BOTH 이메일에서 액션과 섞인 질문을 깔끔하게 분리해 검색 정확도를 높인다(검증: 7건 중 3건 회복).
    #   ② cleaned_body    — 인사·서명만 제거한 본문 (question_summary가 없을 때).
    #   ③ user_input      — 전처리 실패 시 원본.
    query_extraction_input = user_input
    if email_context and email_context.get("preprocess_ok"):
        query_extraction_input = (
            email_context.get("question_summary")
            or email_context.get("cleaned_body")
            or user_input
        )

    # ① 쿼리 추출 (Query Expansion: 최대 2개)
    # 재진입(HITL resume·재시도) 시 이전 실행이 저장한 쿼리를 재사용해 LLM 추출을 생략한다.
    # 이때 멀티쿼리를 잃지 않도록 rag_queries(리스트)를 우선 복원하고, 없으면 단일 rag_query로 폴백.
    cached_queries: list[str] = state.get("rag_queries") or []
    cached_query: str = state.get("rag_query", "")
    if cached_queries:
        rag_queries = cached_queries
    elif cached_query:
        rag_queries = [cached_query]
    else:
        rag_queries = _extract_rag_queries(query_extraction_input)

    if not rag_queries:
        logger.warning("[worker_b] No RAG query extracted — skipping retrieval.")
        return {
            "rag_query": "",
            "retrieved_docs": [],
            "rag_answer": "",
            "error_messages": errors,
        }

    rag_query = rag_queries[0]  # 대표 쿼리 (답변 생성 + reranking 기준)

    # ② Hybrid Retrieval — 쿼리별 검색 후 중복 제거 병합
    logger.info("[worker_b] ② Hybrid retrieval (%d queries)", len(rag_queries))
    try:
        retriever = build_hybrid_retriever()
        seen_contents: set[str] = set()
        candidate_docs = []
        for q in rag_queries:
            results = retriever.invoke(q)
            for doc in results:
                if doc.page_content not in seen_contents:
                    seen_contents.add(doc.page_content)
                    candidate_docs.append(doc)
        logger.info("[worker_b] ② Retrieved %d unique candidate docs", len(candidate_docs))
    except Exception as e:
        msg = f"worker_b: retrieval failed — {e}"
        logger.error("[worker_b] %s", msg)
        errors.append(msg)
        return {
            "rag_query": rag_query,
            "retrieved_docs": [],
            "rag_answer": "",
            "error_messages": errors,
        }

    # ③ Reranking (대표 쿼리 기준)
    logger.info("[worker_b] ③ Reranking %d docs …", len(candidate_docs))
    try:
        top_docs = rerank(rag_query, candidate_docs, queries=rag_queries)
        logger.info("[worker_b] ③ Reranked → top %d docs", len(top_docs))
    except Exception as e:
        logger.warning("[worker_b] Reranking failed: %s. Using top-k directly.", e)
        cfg = get_config()
        top_docs = candidate_docs[: cfg.rag.top_k_rerank]

    # state에 저장할 문서 메타 직렬화
    retrieved_docs_serialized = _serialize_docs(top_docs)

    # ④ 답변 생성
    logger.info("[worker_b] ④ Generating answer …")
    rag_answer = _generate_answer(rag_query, top_docs)

    logger.info("[worker_b] ══════════════ Worker B END ══════════════")
    return {
        "rag_query":      rag_query,
        "rag_queries":    rag_queries,
        "retrieved_docs": retrieved_docs_serialized,
        "rag_answer":     rag_answer,
        "error_messages": errors,
    }