import os
import json
from typing import List, Optional

import faiss
import pickle
import redis
from fastapi import FastAPI, HTTPException
from fastapi.responses import RedirectResponse
from pydantic import BaseModel
from sentence_transformers import SentenceTransformer
from transformers import AutoTokenizer, AutoModelForSeq2SeqLM

app = FastAPI(title="Medical Policy RAG Chatbot API")

# --------------------------
# Configuration & Helpers
# --------------------------

REDIS_URL = os.getenv("REDIS_URL", "redis://localhost:6379/0")
redis_client = redis.from_url(REDIS_URL, socket_connect_timeout=1)

# Local fallback for session data if Redis is unavailable
local_cache = {}

INDEX_PATH = os.getenv("FAISS_INDEX_PATH", "data/faiss.index")
METADATA_PATH = os.getenv("METADATA_PATH", "data/metadata.pkl")

EMBEDDING_MODEL = os.getenv("EMBED_MODEL", "intfloat/e5-base-v2")
LLM_MODEL = os.getenv("LLM_MODEL", "google/flan-t5-large")

# Load heavy models once – they are cached in the process memory.

def load_models():
    embedder = SentenceTransformer(EMBEDDING_MODEL)
    tokenizer = AutoTokenizer.from_pretrained(LLM_MODEL)
    llm = AutoModelForSeq2SeqLM.from_pretrained(LLM_MODEL)
    return embedder, tokenizer, llm


def load_index():
    if not os.path.exists(INDEX_PATH) or not os.path.exists(METADATA_PATH):
        raise FileNotFoundError("FAISS index or metadata not found. Run the ingestion pipeline first.")
    index = faiss.read_index(INDEX_PATH)
    with open(METADATA_PATH, "rb") as f:
        docs = pickle.load(f)
    return index, docs

embedder, tokenizer, llm = load_models()
index, documents = load_index()

# --------------------------
# Request / Response models
# --------------------------

class ChatRequest(BaseModel):
    session_id: str
    query: str
    confirm: Optional[bool] = None  # Used for scenario‑based follow‑up

class ChatResponse(BaseModel):
    answer: str
    sources: List[dict] = []
    follow_up: Optional[str] = None

# --------------------------
# Utility functions
# --------------------------

def embed_text(text: str):
    return embedder.encode([text])

def retrieve(query: str, k: int = 5):
    q_emb = embed_text("query: " + query)
    D, I = index.search(q_emb, k)
    retrieved = [documents[i] for i in I[0]]
    return retrieved

def build_prompt(query: str, retrieved: List[dict]):
    context_str = "\n\n".join([doc["text"] for doc in retrieved])
    system = f"""Question: {query}\n\nBased on the context below, write a concise, factual answer.\nIf the answer is unknown, say \"I cannot find this info in the documents.\"\n\nContext:\n{context_str}\n\nAnswer:"""
    return system

def generate_answer(prompt: str) -> str:
    inputs = tokenizer(prompt, return_tensors="pt", truncation=True, max_length=1536).input_ids
    outputs = llm.generate(inputs, max_new_tokens=500, min_length=60, num_beams=4, early_stopping=True)
    return tokenizer.decode(outputs[0], skip_special_tokens=True)

def store_pending(session_id: str, data: dict):
    try:
        redis_client.setex(f"session:{session_id}:pending", 600, json.dumps(data))
    except Exception:
        local_cache[f"session:{session_id}:pending"] = json.dumps(data)

def get_pending(session_id: str) -> Optional[dict]:
    try:
        raw = redis_client.get(f"session:{session_id}:pending")
    except Exception:
        raw = local_cache.get(f"session:{session_id}:pending")

    if raw:
        return json.loads(raw)
    return None

def clear_pending(session_id: str):
    try:
        redis_client.delete(f"session:{session_id}:pending")
    except Exception:
        pass
    local_cache.pop(f"session:{session_id}:pending", None)

# --------------------------
# Core endpoint
# --------------------------

@app.get("/", include_in_schema=False)
def root():
    return RedirectResponse(url="/docs")

@app.post("/chat", response_model=ChatResponse)
def chat(req: ChatRequest):
    # Check if there is a pending confirmation for this session
    pending = get_pending(req.session_id)
    if pending:
        # User is responding to a follow‑up question
        if req.confirm is None:
            raise HTTPException(status_code=400, detail="Missing 'confirm' field for pending follow‑up.")
        if not req.confirm:
            # User declined – abort the flow
            clear_pending(req.session_id)
            return ChatResponse(answer="Okay, let me know if you need anything else.")
        # User confirmed – continue with stored context
        query = pending["original_query"]
        retrieved = pending["retrieved"]
        prompt = pending["prompt"]
        answer = generate_answer(prompt)
        clear_pending(req.session_id)
        return ChatResponse(answer=answer, sources=[{"source": d["source"], "snippet": d["text"][:200]} for d in retrieved])

    # No pending – normal processing
    # Simple keyword detection for scenario‑based flow (can be extended)
    lowered = req.query.lower()
    if "leave" in lowered and "process" in lowered:
        # Ask for confirmation before revealing the full procedure
        retrieved = retrieve(req.query)
        prompt = build_prompt(req.query, retrieved)
        # Store pending state
        store_pending(req.session_id, {
            "original_query": req.query,
            "retrieved": retrieved,
            "prompt": prompt
        })
        return ChatResponse(
            answer="May I proceed to explain the medical leave process?",
            follow_up="Please respond with 'confirm': true or false."
        )

    # Regular RAG path
    retrieved = retrieve(req.query)
    prompt = build_prompt(req.query, retrieved)
    answer = generate_answer(prompt)
    return ChatResponse(
        answer=answer,
        sources=[{"source": d["source"], "snippet": d["text"][:200]} for d in retrieved]
    )