# 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 AutoModelForCausalLM  # ✅ FIXED import

# --- THIS IS THE FIX FOR TESSERACT ---
# Explicitly tell pytesseract where to find the Tesseract OCR engine.
pytesseract.pytesseract.tesseract_cmd = r'/usr/bin/tesseract'
# ------------------------------------

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

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

app = FastAPI(title="Optimized Universal Data AI", version="3.1.0")

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

# --- Load Optimized Models ---
try:
    logger.info("Loading optimized AI models...")

    # Using a smaller, but still powerful, BGE model
    embedding_model = SentenceTransformer('BAAI/bge-base-en-v1.5')
    
    # Load TinyLlama in GGUF format using ctransformers
    llm = AutoModelForCausalLM.from_pretrained(
        "TheBloke/TinyLlama-1.1B-Chat-v1.0-GGUF",
        model_file="tinyllama-1.1b-chat-v1.0.Q4_K_M.gguf",
        model_type="llama",   # Tell ctransformers the model family
        gpu_layers=0          # For CPU-only environment
    )

    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

class QueryResponse(BaseModel):
    answer: str
    context: str

# --- 3. HELPER FUNCTIONS ---
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 Optimized Universal Data AI"}

@app.post("/upload", response_model=UploadResponse)
async def upload_file(file: UploadFile = File(...)):
    if not embedding_model:
        raise HTTPException(status_code=503, detail="Embedding model not available.")
    
    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)
    elif file.filename.endswith(('.txt', '.md')):
        text = content.decode("utf-8")
    else:
        raise HTTPException(status_code=400, detail=f"Unsupported file type: {content_type}")

    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):
    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.")
    
    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]])

    # Correct prompt format for TinyLlama Chat
    prompt = f"""<|im_start|>user
Use the following context to answer the question.
Context:
{context}

Question: {request.question}<|im_end|>
<|im_start|>assistant
"""

    logger.info("Generating answer with TinyLlama...")
    
    answer = llm(
        prompt,
        max_new_tokens=256,
        temperature=0.3,
        stop=["<|im_end|>"]
    )
    
    return {"answer": answer.strip(), "context": context}