chatbot_rag.py

from langchain_community.vectorstores import Chroma
from langchain_community.embeddings import HuggingFaceEmbeddings
from langchain_community.llms import HuggingFacePipeline
from transformers import AutoTokenizer, AutoModelForCausalLM, pipeline
from langchain.prompts import PromptTemplate
from langchain_core.runnables import RunnablePassthrough
from langchain_core.output_parsers import StrOutputParser
import re
import os
import traceback
from huggingface_hub import login


token = os.getenv("HF_TOKEN")
print("🔑 HF_TOKEN available?", token is not None)
if token:
    login(token=token)
else:
    print("❌ No HF_TOKEN found in environment")


def build_qa():
    """Builds and returns the RAG QA pipeline (rag_chain style)."""
    print("🚀 Starting QA pipeline...")

    # 1. Embeddings
    print("🔹 Loading embeddings...")
    embeddings = HuggingFaceEmbeddings(
        model_name="sentence-transformers/all-MiniLM-L6-v2"
    )

    # 2. Load vector DB
    print("🔹 Loading Chroma DB...")
    vectorstore = Chroma(
        persist_directory="db",
        collection_name="rag-docs",
        embedding_function=embeddings,
    )
    print("📂 Docs in DB:", vectorstore._collection.count())

    # 3. Load LLM (Phi-3.5-mini-instruct)
    print("🔹 Loading LLM...") 
    model_id = "microsoft/Phi-3.5-mini-instruct"

    tokenizer = AutoTokenizer.from_pretrained(model_id)
    model = AutoModelForCausalLM.from_pretrained(
        model_id,
        device_map="auto",       
        torch_dtype="auto",      
        trust_remote_code=True
    )
    model.config.use_cache = False

    pipe = pipeline(
        "text-generation",
        model=model,
        tokenizer=tokenizer,
        max_new_tokens=80,       # shorter answers
        temperature=0.2,         # deterministic
        do_sample=False,
        repetition_penalty=1.2,
        eos_token_id=tokenizer.eos_token_id,
        return_full_text=False
    )

    llm = HuggingFacePipeline(pipeline=pipe)

    # 4. Retriever
    retriever = vectorstore.as_retriever(search_kwargs={"k": 3})

    # 5. Prompt
    prompt = PromptTemplate( 
        input_variables=["context", "question"], 
        template="""Answer the question using the context below.
        Respond in ONE short factual sentence only.
        If you don't know, say "I don't know."
        
        Context:
        {context}
        
        Question:
        {question}
        
        Answer:""",
    )

    # 6. Helper
    def format_docs(docs):
        texts = [doc.page_content.strip() for doc in docs if doc.page_content]
        return "\n".join(texts)

    def hf_to_str(x):
        if isinstance(x, list) and "generated_text" in x[0]:
            text = x[0]["generated_text"]
        else:
            text = str(x)
        text = re.sub(r"\s+", " ", text).strip()
        # ✅ Only keep first sentence
        return re.split(r"(?<=[.!?])\s+", text)[0]

    # 7. Chain
    rag_chain = (
        {
            "context": retriever | format_docs,
            "question": RunnablePassthrough(),
        }
        | prompt
        | llm
        | (lambda x: hf_to_str(x))
        | StrOutputParser()
    )

    print("✅ QA pipeline ready.")
    return rag_chain


# Build once
try:
    qa_pipeline = build_qa()
    print("✅ qa_pipeline built successfully:", type(qa_pipeline))
except Exception as e:
    qa_pipeline = None
    print("❌ Failed to build QA pipeline")
    print("Error message:", str(e))
    traceback.print_exc()


def get_answer(query: str) -> str:
    """Run a query against the QA pipeline and return the answer text."""
    if qa_pipeline is None:
        return "⚠️ QA pipeline not initialized."
    try:
        result = qa_pipeline.invoke(query)
        return result
    except Exception as e:
        return f"❌ QA run failed: {e}"