app.py

import os
os.environ["CHAINLIT_CONFIG_DIR"] = "/tmp/.chainlit"
os.environ["CHAINLIT_FILES_PATH"] = "/tmp/.chainlit/files"


import chainlit as cl
from langchain.vectorstores import FAISS
from langchain.embeddings import HuggingFaceEmbeddings
from langchain.document_loaders import TextLoader
from langchain.text_splitter import CharacterTextSplitter
from langchain.chains import RetrievalQA
from langchain.prompts import PromptTemplate
from langchain.llms import HuggingFacePipeline
from transformers import AutoModelForCausalLM, AutoTokenizer, pipeline
import torch
import os

# === Step 1: Build or load Vectorstore ===

VECTORSTORE_DIR = "vectorstore"
DATA_PATH = "data/textile_notes.txt"  # Your textile documents path

def build_vectorstore():
    loader = TextLoader(DATA_PATH)
    documents = loader.load()
    splitter = CharacterTextSplitter(chunk_size=500, chunk_overlap=50)
    chunks = splitter.split_documents(documents)
    embeddings = HuggingFaceEmbeddings(model_name="BAAI/bge-small-en-v1.5")

    db = FAISS.from_documents(chunks, embeddings)
    db.save_local(VECTORSTORE_DIR)
    return db

def load_vectorstore():
    embeddings = HuggingFaceEmbeddings(model_name="BAAI/bge-small-en-v1.5")
    return FAISS.load_local(VECTORSTORE_DIR, embeddings)

# === Step 2: Load LLM and create QA chain ===

def load_qa_chain():
    # Load local vectorstore if exists else build it
    if os.path.exists(VECTORSTORE_DIR):
        vectorstore = load_vectorstore()
    else:
        vectorstore = build_vectorstore()

    # Load open-source Mistral 7B Instruct model (small & free-ish)
    tokenizer = AutoTokenizer.from_pretrained("mistralai/Mistral-7B-Instruct-v0.1")
    model = AutoModelForCausalLM.from_pretrained(
        "mistralai/Mistral-7B-Instruct-v0.1",
        torch_dtype=torch.float16,
        device_map="auto"
    )

    pipe = pipeline(
        "text-generation",
        model=model,
        tokenizer=tokenizer,
        max_new_tokens=512,
        do_sample=True,
        temperature=0.7,
    )
    llm = HuggingFacePipeline(pipeline=pipe)

    # Prompt template for friendly, user-focused answers
    prompt_template = """
Answer the question using ONLY the context below.
Be clear, helpful, and friendly.

Context:
{context}

Question:
{question}
"""

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

    qa_chain = RetrievalQA.from_chain_type(
        llm=llm,
        chain_type="stuff",
        retriever=vectorstore.as_retriever(search_kwargs={"k": 4}),
        chain_type_kwargs={"prompt": prompt},
        return_source_documents=True,
    )

    return qa_chain

# === Chainlit event handlers ===

@cl.on_chat_start
async def on_chat_start():
    qa = load_qa_chain()
    cl.user_session.set("qa_chain", qa)
    await cl.Message("👋 Hi! Ask me anything about textile — I'll answer using our custom documents.").send()

@cl.on_message
async def on_message(message: cl.Message):
    qa = cl.user_session.get("qa_chain")
    answer = qa.run(message.content)
    await cl.Message(answer).send()