# app.py

import logging
import uuid
import io
from fastapi import FastAPI, UploadFile, File, HTTPException
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel

# Import from our core modules
from core.chunking import semantic_chunker
from core.vector_store import create_faiss_index, deserialize_faiss_index

# Parsing and AI libraries
import fitz
from PIL import Image
import pytesseract
from sentence_transformers import SentenceTransformer
from ctransformers import AutoModel  # NEW: For running quantized GGUF models

# --- 1. INITIAL SETUP & MODEL LOADING ---

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

app = FastAPI(title="Generative Universal Data AI", version="3.0.0")

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"], allow_credentials=True, allow_methods=["*"], allow_headers=["*"]
)

# --- Load Models ---
try:
    logger.info("Loading AI models...")
    # Model for creating vector embeddings (remains the same)
    embedding_model = SentenceTransformer('BAAI/bge-large-en-v1.5')
    
    # NEW: Loading the quantized Phi-2 model using ctransformers
    # This downloads a GGUF model file, optimized for CPU inference.
    # Q4_K_M is a good balance of quality and performance.
    llm = AutoModel.from_pretrained(
        "TheBloke/phi-2-GGUF", 
        model_file="phi-2.Q4_K_M.gguf"
    )
    logger.info("AI models loaded successfully.")
except Exception as e:
    logger.critical(f"Fatal error: Could not load AI models. {e}")
    embedding_model = None
    llm = None

SESSION_DATA = {}

# --- 2. DATA MODELS ---
class QueryRequest(BaseModel): question: str
class UploadResponse(BaseModel): session_id: str; filename: str; chunks_created: int
# Modified response to reflect generative model output
class QueryResponse(BaseModel): answer: str; context: str

# --- 3. HELPER FUNCTIONS --- (No changes here)
def parse_pdf(content: bytes) -> str:
    doc = fitz.open(stream=content, filetype="pdf"); return "".join(page.get_text() for page in doc)
def parse_image(content: bytes) -> str:
    image = Image.open(io.BytesIO(content)); return pytesseract.image_to_string(image)

# --- 4. API ENDPOINTS ---

@app.get("/")
def read_root(): return {"status": "ok", "message": "Welcome to the Generative Universal Data AI"}

@app.post("/upload", response_model=UploadResponse)
async def upload_file(file: UploadFile = File(...)):
    # This endpoint remains largely the same, using the BGE model and semantic chunking
    if not embedding_model: raise HTTPException(status_code=503, detail="Embedding model not available.")
    # ... (the rest of the upload logic is identical to the previous version)
    session_id = str(uuid.uuid4())
    content = await file.read()
    content_type = file.content_type
    if content_type == "application/pdf": text = parse_pdf(content)
    elif content_type and content_type.startswith("image/"): text = parse_image(content)
    else: text = content.decode("utf-8")
    if not text.strip(): raise HTTPException(status_code=400, detail="No text could be extracted.")
    text_chunks = semantic_chunker(text, embedding_model)
    if not text_chunks: raise HTTPException(status_code=400, detail="Document too short to be processed.")
    embeddings = embedding_model.encode(text_chunks, convert_to_numpy=True)
    serialized_index = create_faiss_index(embeddings)
    if not serialized_index: raise HTTPException(status_code=500, detail="Failed to create document index.")
    SESSION_DATA[session_id] = {"chunks": text_chunks, "index": serialized_index}
    logger.info(f"Session {session_id} created with {len(text_chunks)} chunks.")
    return {"session_id": session_id, "filename": file.filename, "chunks_created": len(text_chunks)}

@app.post("/query/{session_id}", response_model=QueryResponse)
async def query_session(session_id: str, request: QueryRequest):
    # --- THIS ENDPOINT IS COMPLETELY REWORKED FOR PHI-2 ---
    if not llm or not embedding_model:
        raise HTTPException(status_code=503, detail="AI models are not available.")
        
    session = SESSION_DATA.get(session_id)
    if not session:
        raise HTTPException(status_code=404, detail="Session not found.")
    
    # Step 1: Retrieve relevant context (same as before)
    query_with_prefix = f"Represent this sentence for searching relevant passages: {request.question}"
    question_embedding = embedding_model.encode([query_with_prefix], convert_to_numpy=True).astype('float32')
    index = deserialize_faiss_index(session["index"])
    if not index: raise HTTPException(status_code=500, detail="Could not load session index.")
    k = min(5, index.ntotal)
    distances, indices = index.search(question_embedding, k)
    context = "\n".join([session["chunks"][i] for i in indices[0]])

    # Step 2: Create a specific prompt for the generative model
    # This template instructs the model on how to behave.
    prompt = f"""
Instruct: Use the following context to answer the question accurately. If the answer is not present in the context, say "The answer is not available in the provided document."

Context:
{context}

Question: {request.question}

Answer:"""

    logger.info("Generating answer with Phi-2...")
    
    # Step 3: Generate the answer
    answer = llm(
        prompt,
        max_new_tokens=256,   # Max length of the answer
        temperature=0.2,      # Lower temperature for more factual answers
        stop=["\n", "Instruct:", "Question:"] # Stop generation at these tokens
    )
    
    # Generative models don't give a confidence 'score' like extractive ones.
    # We simply return the generated text.
    return {"answer": answer.strip(), "context": context}