Streamlit UI: upload, chat, citations

Wiring up the UI is what turns code into a product anyone can use. Two hours and you have a real app.

You wrote the engine. Now you bolt on the steering wheel, the seat, the dashboard.

UI pieces:

• Sidebar PDF uploader (calls ingest)
• Chat input and history
• Streaming responses
• Source citations expander

import streamlit as st
from rag import index_pdf, answer

st.title("PDF Chatbot")

with st.sidebar:
    uploaded = st.file_uploader("Upload PDF", type=["pdf"])
    if uploaded:
        path = f"data/{uploaded.name}"
        with open(path, "wb") as f:
            f.write(uploaded.read())
        n = index_pdf(path)
        st.success(f"Indexed {n} chunks from {uploaded.name}")

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

for msg in st.session_state.messages:
    with st.chat_message(msg["role"]):
        st.markdown(msg["content"])

if prompt := st.chat_input("Ask about your PDFs"):
    st.session_state.messages.append({"role": "user", "content": prompt})
    with st.chat_message("user"):
        st.markdown(prompt)

    with st.chat_message("assistant"):
        placeholder = st.empty()
        text = ""
        for delta in answer(prompt):
            text += delta
            placeholder.markdown(text + "_")
        placeholder.markdown(text)
        st.session_state.messages.append({"role": "assistant", "content": text})

That is the whole app.