import asyncio
import json
import re
import time
from fastapi import APIRouter, Request, Depends
from fastapi.responses import StreamingResponse

from app.models.chat import ChatRequest
from app.models.pipeline import PipelineState
from app.security.rate_limiter import chat_rate_limit
from app.security.jwt_auth import verify_jwt

router = APIRouter()

# Keep-alive interval for SSE when upstream nodes are still working.
# Prevents edge/proxy idle timeouts on long retrieval/generation turns.
_SSE_HEARTBEAT_SECONDS: float = 10.0

# Query pre-processing budgets must stay low to avoid delaying first byte.
_DECONTEXT_TIMEOUT_SECONDS: float = 0.35
_EXPANSION_TIMEOUT_SECONDS: float = 0.60

# Phrases a visitor uses when telling the bot it gave a wrong answer.
# Matched on the lowercased raw message before any LLM call — O(1), zero cost.
_CRITICISM_SIGNALS: frozenset[str] = frozenset({
    "that's wrong", "thats wrong", "you're wrong", "youre wrong",
    "not right", "wrong answer", "you got it wrong", "that is wrong",
    "that's incorrect", "you're incorrect", "thats incorrect", "youre incorrect",
    "fix that", "fix your answer", "actually no", "no that's", "no thats",
    "that was wrong", "your answer was wrong", "wrong information",
    "incorrect information", "that's not right", "thats not right",
})


def _is_criticism(message: str) -> bool:
    lowered = message.lower()
    return any(sig in lowered for sig in _CRITICISM_SIGNALS)


def _filter_sources_by_citations(answer: str, sources: list) -> list:
    """
    Keep only sources explicitly cited in answer text.

    If sources are already pre-filtered upstream (e.g. generate node returned
    only cited sources from original indices), citation numbers may no longer
    match local list positions. In that case, keep the original list unchanged.
    """
    if not answer or not sources:
        return sources

    cited_nums = {int(m) for m in re.findall(r"\[(\d+)\]", answer)}
    if not cited_nums:
        return sources

    max_cited = max(cited_nums)
    if max_cited > len(sources):
        return sources

    return [s for i, s in enumerate(sources, start=1) if i in cited_nums]


async def _generate_follow_ups(
    query: str,
    answer: str,
    sources: list,
    llm_client,
) -> list[str]:
    """
    Generates 3 specific follow-up questions after the main answer is complete.
    Runs after the answer stream finishes — zero added latency before first token.

    Questions MUST:
    - Be grounded in the source documents that were actually retrieved (not hypothetical).
    - Lead the visitor deeper into content the knowledge base ALREADY contains.
    - Never venture into topics not covered by the retrieved sources (no hallucinated follow-ups).
    - Be specific (< 12 words, no generic "tell me more" style).
    """
    # Collect source titles AND types so the LLM knows what was actually retrieved.
    source_info = []
    for s in sources[:4]:
        title = s.title if hasattr(s, "title") else s.get("title", "")
        src_type = s.source_type if hasattr(s, "source_type") else s.get("source_type", "")
        if title:
            source_info.append(f"{title} ({src_type})" if src_type else title)

    sources_str = "\n".join(f"- {si}" for si in source_info) if source_info else "- (no specific sources)"

    prompt = (
        f"Visitor's question: {query}\n\n"
        f"Answer given (excerpt): {answer[:500]}\n\n"
        f"Sources that were retrieved and cited in the answer:\n{sources_str}\n\n"
        "Write exactly 3 follow-up questions the visitor would logically ask NEXT, "
        "based ONLY on what was found in the sources above. "
        "Each question must be clearly answerable from the retrieved sources — "
        "do NOT invent topics that are not present in the sources listed. "
        "Each question must be under 12 words. "
        "Output ONLY the 3 questions, one per line, no numbering or bullet points."
    )
    system = (
        "You write concise follow-up questions for a portfolio chatbot. "
        "CRITICAL RULE: every question you write must be answerable from the source documents listed. "
        "Never invent follow-ups about topics, projects, or facts not mentioned in the retrieved sources. "
        "Never write generic questions like 'tell me more' or 'what else can you tell me'. "
        "Each question must be under 12 words and reference specifics from the answer and sources."
    )

    try:
        stream = llm_client.complete_with_complexity(
            prompt=prompt, system=system, stream=True, complexity="simple"
        )
        raw = ""
        async for token in stream:
            raw += token
        questions = [q.strip() for q in raw.strip().splitlines() if q.strip()][:3]
        return questions
    except Exception:
        return []


async def _update_summary_async(
    conv_store,
    gemini_client,
    session_id: str,
    previous_summary: str | None,
    query: str,
    answer: str,
    processing_api_key: str | None,
) -> None:
    """
    Triggered post-response to update the rolling conversation summary.
    Failures are silently swallowed — summary is best-effort context, not critical.
    """
    try:
        new_summary = await gemini_client.update_conversation_summary(
            previous_summary=previous_summary or "",
            new_turn_q=query,
            new_turn_a=answer[:600],  # cap answer chars sent to Gemini
            processing_api_key=processing_api_key,
        )
        if new_summary:
            conv_store.set_summary(session_id, new_summary)
    except Exception:
        pass


@router.post("")
@chat_rate_limit()
async def chat_endpoint(
    request: Request,
    request_data: ChatRequest,
    token_payload: dict = Depends(verify_jwt),
) -> StreamingResponse:
    """Stream RAG answer as typed SSE events.

    Event sequence for a full RAG request:
        event: status   — guard label, cache miss, gemini routing, retrieve labels
        event: reading  — one per unique source found in Qdrant (before rerank)
        event: sources  — final selected sources array (after rerank)
        event: thinking — CoT scratchpad tokens (70B only)
        event: token    — answer tokens
        event: follow_ups — three suggested follow-up questions

    For cache hits: status → status → token
    For Gemini fast-path: status → status → token
    """
    start_time = time.monotonic()

    pipeline = request.app.state.pipeline
    conv_store = request.app.state.conversation_store
    llm_client = request.app.state.llm_client
    session_id = request_data.session_id

    conversation_history = conv_store.get_recent(session_id)
    conversation_summary = conv_store.get_summary(session_id)
    criticism = _is_criticism(request_data.message)
    if criticism and conversation_history:
        conv_store.mark_last_negative(session_id)

    # Stage 2: decontextualize the query concurrently with Guard when we have a
    # rolling summary. Reference-heavy queries like "tell me more about that project"
    # embed poorly; a self-contained rewrite fixes retrieval without added latency
    # because Gemini Flash runs while Guard is classifying the query.
    gemini_client = getattr(request.app.state, "gemini_client", None)
    decontextualized_query: str | None = None
    decontext_task: asyncio.Task | None = None
    if conversation_summary and gemini_client and gemini_client.is_configured:
        decontext_task = asyncio.create_task(
            gemini_client.decontextualize_query(request_data.message, conversation_summary)
        )

    # Bug 4: concurrent query expansion — starts at request entry so it runs
    # while Guard, Cache, and Gemini-fast-path execute.  Result is ready before
    # the Retrieve node needs it (800 ms budget).  Gemini uses the TOON context
    # to generate canonical name forms (for BM25) and semantic expansions (for
    # dense multi-search).  Falls back to empty if Gemini unavailable or slow.
    expansion_task: asyncio.Task | None = None
    if gemini_client and gemini_client.is_configured:
        expansion_task = asyncio.create_task(
            gemini_client.expand_query(request_data.message)
        )

    # Await decontextualization result before the pipeline begins (retrieve node
    # will use it if present; Guard runs first so the latency is masked).
    if decontext_task is not None:
        try:
            result = await asyncio.wait_for(decontext_task, timeout=_DECONTEXT_TIMEOUT_SECONDS)
            if result and result.strip().lower() != request_data.message.strip().lower():
                decontextualized_query = result.strip()
        except Exception:
            pass  # Decontextualization is best-effort; fall back to raw query.

    # Await expansion result — 800 ms budget so Guard+Cache latency is fully masked.
    expansion_result: dict | None = None
    if expansion_task is not None:
        try:
            expansion_result = await asyncio.wait_for(expansion_task, timeout=_EXPANSION_TIMEOUT_SECONDS)
        except Exception:
            pass  # Expansion is best-effort; retriever falls back to raw query.

    initial_state: PipelineState = {  # type: ignore[assignment]
        "query": request_data.message,
        "session_id": request_data.session_id,
        "query_complexity": "simple",
        # Bug 4: seed expanded_queries with Gemini semantic expansions so the
        # retrieve node issues one dense search per expansion (up to 3 extras).
        # operator.add in PipelineState merges these with any queries added later
        # (e.g. the rag_query from gemini_fast routing to RAG).
        "expanded_queries": (expansion_result or {}).get("semantic_expansions", []),
        "retrieved_chunks": [],
        "reranked_chunks": [],
        "answer": "",
        "sources": [],
        "cached": False,
        "cache_key": None,
        "guard_passed": False,
        "thinking": False,
        "conversation_history": conversation_history,
        "is_criticism": criticism,
        "latency_ms": 0,
        "error": None,
        "interaction_id": None,
        "retrieval_attempts": 0,
        "rewritten_query": None,
        "follow_ups": [],
        "path": None,
        "query_topic": None,
        # Stage 1: follow-up bypass for Gemini fast-path
        "is_followup": request_data.is_followup,
        # Stage 2: progressive history summarisation
        "conversation_summary": conversation_summary or None,
        "decontextualized_query": decontextualized_query,
        # Stage 3: SELF-RAG critic scores (populated by generate node)
        "critic_groundedness": None,
        "critic_completeness": None,
        "critic_specificity": None,
        "critic_quality": None,
        # Fix 1: enumeration classifier — populated by enumerate_query node
        "is_enumeration_query": False,
        # Bug 4: query expansion — canonical name forms for BM25 union search.
        "query_canonical_forms": (expansion_result or {}).get("canonical_forms", []),
    }

    async def sse_generator():
        final_sources = []
        is_cached = False
        final_answer = ""
        interaction_id = None

        try:
            # Emit an early event so clients/proxies receive first bytes quickly.
            yield f"event: status\ndata: {json.dumps({'label': 'Starting response...'})}\n\n"

            # stream_mode=["custom", "updates"] yields (mode, data) tuples:
            #   mode="custom"  → data is whatever writer(payload) was called with
            #   mode="updates" → data is {node_name: state_updates_dict}
            stream_iter = pipeline.astream(
                initial_state,
                stream_mode=["custom", "updates"],
            ).__aiter__()
            next_item_task: asyncio.Task | None = asyncio.create_task(stream_iter.__anext__())

            while True:
                try:
                    mode, data = await asyncio.wait_for(
                        asyncio.shield(next_item_task),
                        timeout=_SSE_HEARTBEAT_SECONDS,
                    )
                except asyncio.TimeoutError:
                    if await request.is_disconnected():
                        if not next_item_task.done():
                            next_item_task.cancel()
                        break
                    yield f"event: ping\ndata: {json.dumps({'ts': int(time.time())})}\n\n"
                    continue
                except StopAsyncIteration:
                    break

                next_item_task = asyncio.create_task(stream_iter.__anext__())

                if await request.is_disconnected():
                    if not next_item_task.done():
                        next_item_task.cancel()
                    break

                if mode == "custom":
                    # Forward writer events as named SSE events.
                    # Each node emits {"type": "<event_name>", ...payload}.
                    event_type = data.get("type", "status")
                    # Strip the "type" key so the client receives a clean payload.
                    payload = {k: v for k, v in data.items() if k != "type"}
                    yield f"event: {event_type}\ndata: {json.dumps(payload)}\n\n"

                elif mode == "updates":
                    # Capture terminal state for the done event; do not re-emit tokens.
                    for _node_name, updates in data.items():
                        if "sources" in updates and updates["sources"]:
                            final_sources = updates["sources"]
                        if "cached" in updates:
                            is_cached = updates["cached"]
                        if "interaction_id" in updates and updates["interaction_id"] is not None:
                            interaction_id = updates["interaction_id"]
                        if "answer" in updates and updates["answer"]:
                            final_answer = updates["answer"]

            elapsed_ms = int((time.monotonic() - start_time) * 1000)

            # Citation-index filtering safety net for paths that return full
            # source lists. No-op when sources are already citation-filtered.
            final_sources = _filter_sources_by_citations(final_answer, final_sources)

            sources_list = [
                s.model_dump() if hasattr(s, "model_dump")
                else s.dict() if hasattr(s, "dict")
                else s
                for s in final_sources
            ]

            # The done event uses plain data: (no event: type) for backward
            # compatibility with widgets that listen on the raw data channel.
            yield (
                f"data: {json.dumps({'done': True, 'sources': sources_list, 'cached': is_cached, 'latency_ms': elapsed_ms, 'interaction_id': interaction_id})}\n\n"
            )

            # ── Follow-up questions ────────────────────────────────────────────
            # Generated after the done event so it never delays answer delivery.
            if final_answer and not await request.is_disconnected():
                follow_ups = await _generate_follow_ups(
                    request_data.message, final_answer, final_sources, llm_client
                )
                if follow_ups:
                    yield f"event: follow_ups\ndata: {json.dumps({'questions': follow_ups})}\n\n"

            # Stage 2: update rolling summary asynchronously — fired after the
            # response is fully delivered so it adds zero latency to the turn.
            if final_answer and gemini_client and gemini_client.is_configured:
                processing_key = getattr(
                    request.app.state, "gemini_processing_api_key", None
                )
                asyncio.create_task(
                    _update_summary_async(
                        conv_store=conv_store,
                        gemini_client=gemini_client,
                        session_id=session_id,
                        previous_summary=conversation_summary,
                        query=request_data.message,
                        answer=final_answer,
                        processing_api_key=processing_key,
                    )
                )

        except Exception as exc:
            yield f"data: {json.dumps({'error': str(exc) or 'Generation failed'})}\n\n"

    return StreamingResponse(
        sse_generator(),
        media_type="text/event-stream",
        headers={
            "Cache-Control": "no-cache",
            "X-Accel-Buffering": "no",
            "Connection": "keep-alive",
        },
    )