app.py

import os
import streamlit as st
from huggingface_hub import InferenceClient
from langchain_community.vectorstores import Neo4jVector
from transformers import AutoTokenizer, AutoModel
import torch

# Custom Embedding Class
class CustomHuggingFaceEmbeddings:
    def __init__(self, model_name="sentence-transformers/all-MiniLM-L6-v2"):
        self.tokenizer = AutoTokenizer.from_pretrained(model_name)
        self.model = AutoModel.from_pretrained(model_name)

    def embed_text(self, text):
        inputs = self.tokenizer(text, return_tensors="pt", padding=True, truncation=True)
        with torch.no_grad():
            outputs = self.model(**inputs)
        return outputs.last_hidden_state.mean(dim=1).squeeze().tolist()

    def embed_query(self, text):
        return self.embed_text(text)
    
    def embed_documents(self, text):
        return self.embed_text(text)

# Function to set up the Neo4j Vector Index
@st.cache_resource 
def setup_vector_index():
    return Neo4jVector.from_existing_graph(
        CustomHuggingFaceEmbeddings(),
        url=os.environ['NEO4J_URI'],
        username=os.environ['NEO4J_USERNAME'],
        password=os.environ['NEO4J_PASSWORD'],
        index_name='articles',
        node_label="Article",
        text_node_properties=['topic', 'title', 'abstract'],
        embedding_node_property='embedding',
    )

# Hugging Face API Setup
API_TOKEN = os.environ.get("HUGGINGFACE_API_TOKEN")
MISTRAL_MODEL_NAME = "mistralai/Mistral-7B-Instruct-v0.3"
client = InferenceClient(api_key=API_TOKEN)

# Query Mistral
def query_from_mistral(context: str, user_input: str):
    messages = [
        {"role": "system", "content": f"Use the following context to answer the query:\n{context}"},
        {"role": "user", "content": user_input},
    ]
    completion = client.chat.completions.create(
        model=MISTRAL_MODEL_NAME,
        messages=messages,
        max_tokens=500,
    )
    return completion.choices[0].message["content"]

# extract data from retriever response
def extract_data(documents):
    result = []

    for doc in documents:
        # Extract metadata
        publication_date = doc.metadata.get('publication_date')
        if publication_date:
            publication_date = publication_date.isoformat()
        
        # Extract page content
        page_content = doc.page_content.strip().split("\n")
        topic = page_content[1].strip() if len(page_content) > 1 else "N/A"
        title = page_content[2].strip() if len(page_content) > 2 else "N/A"
        abstract = page_content[3].strip() if len(page_content) > 3 else "N/A"
        
        # Format the extracted data as a string
        doc_data = (
            f"Publication Date: {publication_date}\n"
            f"Topic: {topic}\n"
            f"Title: {title}\n"
            f"Abstract: {abstract}\n"
        )
        result.append(doc_data)
    
    return result

# Main Streamlit Application
def main():
    st.set_page_config(page_title="Vector Chat with Mistral", layout="centered")
    st.title("🤖 Vector Chat with Mistral")
    st.markdown("Chat with **Mistral-7B-Instruct** using context retrieved from a Neo4j vector index.")

    # Initialize the vector index
    vector_index = setup_vector_index()

    if "messages" not in st.session_state:
        st.session_state.messages = []

    with st.form(key="chat_form", clear_on_submit=True):
        user_input = st.text_input("You:", "")
        submit = st.form_submit_button("Send")

    if submit and user_input:
        st.session_state.messages.append({"role": "user", "content": user_input})

        with st.spinner("Fetching response..."):
            try:
                # Retrieve context from the vector index
                context_results = vector_index.similarity_search(user_input, top_k=3)
                context = extract_data(context_results)[0]

                # Get response from Mistral
                response = query_from_mistral(context, user_input)
                st.session_state.messages.append({"role": "bot", "content": response})
            except Exception as e:
                st.error(f"Error: {e}")

    # Display chat history
    for message in st.session_state.messages:
        if message["role"] == "user":
            st.markdown(f"**You:** {message['content']}")
        elif message["role"] == "bot":
            st.markdown(f"**Bot:** {message['content']}")

if __name__ == "__main__":
    main()