src/app.py

# app.py
import os
import json
import streamlit as st
import requests
from requests.exceptions import RequestException

BACKEND_URL = os.getenv("BACKEND_URL", "http://127.0.0.1:8000/chat")
DEFAULT_SYSTEM_PROMPT = "You are a helpful assistant."

# Some example OpenRouter model IDs; adjust as needed
PRESET_MODELS = [
    "openai/gpt-4o-mini",
    "openai/gpt-4o",
    "meta-llama/llama-3.1-8b-instruct:free",
    "anthropic/claude-3.5-sonnet",
    "google/gemini-1.5-flash",
    "mistralai/mistral-medium",
    "cohere/command-r-plus",
    "custom",  # sentinel for custom entry
]

st.set_page_config(page_title="OpenRouter Chat", page_icon="💬", layout="centered")

# Session state initialization
if "messages" not in st.session_state:
    st.session_state.messages = [{"role": "system", "content": DEFAULT_SYSTEM_PROMPT}]
if "api_key" not in st.session_state:
    st.session_state.api_key = ""  # kept only in browser memory
if "model_choice" not in st.session_state:
    st.session_state.model_choice = PRESET_MODELS[0]
if "custom_model" not in st.session_state:
    st.session_state.custom_model = ""
if "temperature" not in st.session_state:
    st.session_state.temperature = 0.7
if "max_tokens" not in st.session_state:
    st.session_state.max_tokens = 0

st.title("💬 OpenRouter Chat")

with st.expander("Settings", expanded=False):
    # API key in browser memory only
    st.caption("API key is stored only in your browser session and sent with each request.")
    api_key = st.text_input("OpenRouter API Key", type="password", value=st.session_state.api_key)
    st.session_state.api_key = api_key

    # System prompt editor
    current_system = next((m for m in st.session_state.messages if m["role"] == "system"), None)
    sys_prompt = st.text_area("System Message", value=current_system["content"] if current_system else DEFAULT_SYSTEM_PROMPT, height=120)

    # Model selector
    model_choice = st.selectbox("Model (preset)", PRESET_MODELS, index=PRESET_MODELS.index(st.session_state.model_choice) if st.session_state.model_choice in PRESET_MODELS else 0)
    st.session_state.model_choice = model_choice
    custom_model = ""
    if model_choice == "custom":
        custom_model = st.text_input("Custom model id (OpenRouter id)", value=st.session_state.custom_model)
        st.session_state.custom_model = custom_model

    # Sampling params
    temperature = st.slider("Temperature", 0.0, 1.5, st.session_state.temperature, 0.1)
    max_tokens = st.number_input("Max tokens (0 = auto)", min_value=0, value=st.session_state.max_tokens)

    col1, col2 = st.columns(2)
    with col1:
        apply_clicked = st.button("Apply settings")
    with col2:
        reset_chat = st.button("Reset conversation")

    if apply_clicked:
        # Update system message at index 0 or insert if missing
        if st.session_state.messages and st.session_state.messages[0]["role"] == "system":
            st.session_state.messages[0]["content"] = sys_prompt
        else:
            st.session_state.messages.insert(0, {"role": "system", "content": sys_prompt})
        st.session_state.temperature = float(temperature)
        st.session_state.max_tokens = int(max_tokens)
        st.success("Settings applied.")
    if reset_chat:
        st.session_state.messages = [{"role": "system", "content": sys_prompt}]
        st.experimental_rerun()

# Resolve model to use
def get_selected_model():
    if st.session_state.model_choice == "custom":
        return st.session_state.custom_model.strip() or PRESET_MODELS[0]
    return st.session_state.model_choice

# Show chat history (exclude system)
for m in st.session_state.messages:
    if m["role"] == "user":
        with st.chat_message("user"):
            st.markdown(m["content"])
    elif m["role"] == "assistant":
        with st.chat_message("assistant"):
            st.markdown(m["content"])

prompt = st.chat_input("Type your message")

def stream_chat(messages, model, temperature, max_tokens, api_key):
    payload = {
        "messages": messages,
        "model": model,
        "temperature": temperature,
    }
    if max_tokens and max_tokens > 0:
        payload["max_tokens"] = int(max_tokens)

    headers = {}
    # Pass API key via header; never persisted server-side
    if api_key:
        headers["X-OpenRouter-Api-Key"] = api_key
    # Optional attribution header
    headers["HTTP-Referer"] = "http://localhost:8501"

    try:
        with requests.post(BACKEND_URL, json=payload, headers=headers, stream=True, timeout=300) as r:
            r.raise_for_status()
            for line in r.iter_lines(decode_unicode=True):
                if not line:
                    continue
                if line.startswith("data: "):
                    data = line[len("data: "):]
                    if data.strip() == "done":
                        break
                    try:
                        obj = json.loads(data)
                        if "content" in obj:
                            yield obj["content"]
                    except json.JSONDecodeError:
                        continue
    except RequestException as e:
        yield f"\n[Connection error: {e}]"

if prompt:
    if not get_selected_model():
        st.error("Please select or enter a model.")
    else:
        # Append user message
        st.session_state.messages.append({"role": "user", "content": prompt})
        with st.chat_message("assistant"):
            ai_area = st.empty()
            streamed = ""
            for chunk in stream_chat(
                st.session_state.messages,
                model=get_selected_model(),
                temperature=st.session_state.temperature,
                max_tokens=st.session_state.max_tokens,
                api_key=st.session_state.api_key,
            ):
                streamed += chunk
                ai_area.markdown(streamed)
        st.session_state.messages.append({"role": "assistant", "content": streamed})

# Sidebar quick actions
with st.sidebar:
    if st.button("Clear chat"):
        sys_msg = next((m for m in st.session_state.messages if m["role"] == "system"), None)
        content = sys_msg["content"] if sys_msg else DEFAULT_SYSTEM_PROMPT
        st.session_state.messages = [{"role": "system", "content": content}]
        st.experimental_rerun()