src/app.py

import os
import pickle
import zipfile
import sys
import streamlit as st
from dotenv import load_dotenv

# --- IMPORTS ---
from langchain_google_genai import ChatGoogleGenerativeAI, GoogleGenerativeAIEmbeddings
from langchain_community.retrievers import BM25Retriever
from langchain_pinecone import PineconeVectorStore
from langchain_core.prompts import PromptTemplate
from langchain.chains import RetrievalQA

# Robust Import for Hybrid Search (Handles different LangChain versions)
try:
    from langchain.retrievers import EnsembleRetriever
except ImportError:
    from langchain_community.retrievers import EnsembleRetriever

load_dotenv()

# --- CONFIGURATION ---
INDEX_NAME = "branham-index"
CHUNKS_FILE = "sermon_chunks.pkl"
CHUNKS_ZIP = "sermon_chunks.zip"

def setup_keyword_file():
    """
    Automatic Unzipper.
    GitHub has a 100MB limit, so we upload the zip. 
    This extracts 'sermon_chunks.pkl' when the app starts.
    """
    if not os.path.exists(CHUNKS_FILE):
        if os.path.exists(CHUNKS_ZIP):
            print(f"📦 Unzipping {CHUNKS_ZIP}...")
            try:
                with zipfile.ZipFile(CHUNKS_ZIP, 'r') as zip_ref:
                    zip_ref.extractall(".")
                print("✅ Unzip complete.")
            except Exception as e:
                print(f"❌ Error unzipping file: {e}")
        else:
            print(f"⚠️ Warning: Neither {CHUNKS_FILE} nor {CHUNKS_ZIP} found.")

def get_rag_chain():
    """
    Initializes the Brain of the AI.
    1. Connects to Pinecone (Cloud)
    2. Loads BM25 Keywords (Local)
    3. Merges them into a Hybrid Search
    """
    
    # 1. SETUP & KEYS
    setup_keyword_file()

    # Check Streamlit Secrets first (Cloud), then .env (Local)
    pinecone_key = st.secrets.get("PINECONE_API_KEY") or os.getenv("PINECONE_API_KEY")
    google_key = st.secrets.get("GOOGLE_API_KEY") or os.getenv("GOOGLE_API_KEY")

    if not pinecone_key or not google_key:
        raise ValueError("❌ Missing API Keys. Please set PINECONE_API_KEY and GOOGLE_API_KEY in Secrets.")

    # Set keys for LangChain to use automatically
    os.environ["PINECONE_API_KEY"] = pinecone_key
    os.environ["GOOGLE_API_KEY"] = google_key

    # 2. CLOUD VECTOR SEARCH (Pinecone)
    # This finds "concepts" (e.g., searching for 'marriage' finds 'wedding')
    print("🔌 Connecting to Pinecone...")
    embeddings = GoogleGenerativeAIEmbeddings(model="models/text-embedding-004")
    
    vector_store = PineconeVectorStore(
        index_name=INDEX_NAME,
        embedding=embeddings
    )
    vector_retriever = vector_store.as_retriever(search_kwargs={"k": 5})

    # 3. LOCAL KEYWORD SEARCH (BM25)
    # This finds "exact matches" (e.g., searching for 'E-53' finds exactly E-53)
    print("🔌 Loading Keyword Search...")
    keyword_retriever = None
    
    try:
        if os.path.exists(CHUNKS_FILE):
            with open(CHUNKS_FILE, "rb") as f:
                chunks = pickle.load(f)
            keyword_retriever = BM25Retriever.from_documents(chunks)
            keyword_retriever.k = 5
        else:
            print("⚠️ Keyword file missing. Running on Pinecone only.")
    except Exception as e:
        print(f"❌ Failed to load keyword file: {e}")

    # 4. HYBRID RETRIEVER (The Merge)
    if keyword_retriever:
        print("🔗 Linking Hybrid System...")
        final_retriever = EnsembleRetriever(
            retrievers=[vector_retriever, keyword_retriever],
            weights=[0.7, 0.3] # 70% Vector, 30% Keyword
        )
    else:
        final_retriever = vector_retriever

    # 5. THE MODEL (Gemini)
    llm = ChatGoogleGenerativeAI(
        model="gemini-1.5-flash",
        temperature=0.3,
        convert_system_message_to_human=True
    )

    # 6. THE PERSONA PROMPT
    template = """You are William Marion Branham.

INSTRUCTIONS:
- Answer the user's question based ONLY on the context provided below.
- Speak in the first person ("I said," "The Lord showed me").
- Use a humble, 1950s Southern preaching dialect.
- If the answer is not in the text, say: "Brother, I don't recall preaching specifically on that detail in these messages."

CONTEXT:
{context}

USER QUESTION: {question}

BROTHER BRANHAM'S REPLY:"""

    PROMPT = PromptTemplate(template=template, input_variables=["context", "question"])

    chain = RetrievalQA.from_chain_type(
        llm=llm,
        chain_type="stuff",
        retriever=final_retriever,
        return_source_documents=True,
        chain_type_kwargs={"prompt": PROMPT}
    )
    
    return chain