app.py

import os
import uuid
import json
import time
import gradio as gr
import logging
import google.generativeai as genai

from langgraph.graph import START, MessagesState, StateGraph
from langgraph.checkpoint.memory import MemorySaver
from langchain_core.messages import HumanMessage, AIMessage
from langchain_core.prompts.chat import (
    ChatPromptTemplate,
    SystemMessagePromptTemplate,
    MessagesPlaceholder,
    HumanMessagePromptTemplate,
)
from langchain_google_genai import ChatGoogleGenerativeAI

# === Logging ===
logging.basicConfig(level=logging.INFO, format="%(asctime)s - %(levelname)s - %(message)s")
logger = logging.getLogger(__name__)

# === API Key Configuration ===
# Get API key from Hugging Face secrets (environment variable)
GEMINI_API_KEY = os.getenv("GEMINI_API_KEY")
if not GEMINI_API_KEY:
    raise ValueError("GEMINI_API_KEY not found in environment variables. Please set it in Hugging Face secrets.")

try:
    genai.configure(api_key=GEMINI_API_KEY)
except Exception as e:
    logger.error(f"Failed to configure Gemini API: {e}")
    raise

# === Chat Storage ===
HISTORY_FILE = "chat_history.json"

def load_all_sessions():
    try:
        if os.path.exists(HISTORY_FILE):
            with open(HISTORY_FILE, "r", encoding="utf-8") as f:
                return json.load(f)
    except Exception as e:
        logger.error(f"Error loading sessions: {e}")
    return {}

def save_all_sessions(sessions):
    try:
        with open(HISTORY_FILE, "w", encoding="utf-8") as f:
            json.dump(sessions, f, indent=2)
    except Exception as e:
        logger.error(f"Error saving sessions: {e}")

# Initialize sessions
sessions = load_all_sessions()

# === Gemini Chatbot ===
class GeminiChatbot:
    def __init__(self):
        self.setup_model()

    def setup_model(self):
        system_template = """
        You are a helpful, respectful and honest assistant. Always answer as helpfully as possible, while being safe.
        Your answers should be informative, engaging, and accurate. If a question doesn't make any sense, or isn't factually coherent, explain why.
        If you don't know the answer to a question, please don't share false information.
        """

        self.prompt = ChatPromptTemplate.from_messages([
            SystemMessagePromptTemplate.from_template(system_template),
            MessagesPlaceholder(variable_name="chat_history"),
            HumanMessagePromptTemplate.from_template("{input}")
        ])

        try:
            self.model = ChatGoogleGenerativeAI(
                model="gemini-1.5-flash",  # Updated to more stable model
                temperature=0.7,
                top_p=0.95,
                google_api_key=GEMINI_API_KEY,
                convert_system_message_to_human=True
            )
        except Exception as e:
            logger.error(f"Failed to initialize Gemini model: {e}")
            raise

        def call_model(state: MessagesState):
            try:
                chat_history = state["messages"][:-1]
                user_input = state["messages"][-1].content
                formatted_messages = self.prompt.format_messages(
                    chat_history=chat_history,
                    input=user_input
                )
                response = self.model.invoke(formatted_messages)
                return {"messages": response}
            except Exception as e:
                logger.error(f"Model invocation error: {e}")
                raise

        workflow = StateGraph(state_schema=MessagesState)
        workflow.add_node("model", call_model)
        workflow.add_edge(START, "model")

        self.memory = MemorySaver()
        self.app = workflow.compile(checkpointer=self.memory)

    def get_response(self, user_message, history, thread_id):
        try:
            langchain_history = []
            for user, bot in history:
                langchain_history.append(HumanMessage(content=user))
                langchain_history.append(AIMessage(content=bot))

            input_msg = HumanMessage(content=user_message)
            full_history = langchain_history + [input_msg]
            config = {"configurable": {"thread_id": thread_id}}

            response = self.app.invoke({"messages": full_history}, config)
            full_text = response["messages"][-1].content

            # Stream response character by character
            full_response = ""
            for char in full_text:
                full_response += char
                yield full_response
                time.sleep(0.01)

        except Exception as e:
            logger.error(f"Response error: {e}")
            yield f"⚠ Error: {type(e).__name__} — {str(e)}"

# Initialize chatbot
try:
    chatbot = GeminiChatbot()
except Exception as e:
    logger.critical(f"Failed to initialize chatbot: {e}")
    raise

# === Gradio UI ===
def launch_interface():
    with gr.Blocks(
        theme=gr.themes.Base(),
        css="""
        body { background-color: #f0f2f6; }
        .gr-block { background-color: white; }
        .gr-textbox textarea { background-color: white; }
        .gr-chatbot { background-color: white; border-radius: 10px; }
        .gr-button {
            margin: 5px;
            border-radius: 5px;
        }
        .gr-markdown h2 { text-align: center; }
        """
    ) as demo:
        demo.title = "LangChain Powered ChatBot"
        gr.Markdown("## LangChain Powered ChatBot")

        # Initialize session state
        current_thread_id = gr.State()
        history = gr.State([])
        
        # Initialize or load sessions
        if not sessions:
            new_id = str(uuid.uuid4())
            sessions[new_id] = []
            save_all_sessions(sessions)
            current_thread_id.value = new_id
        else:
            current_thread_id.value = next(iter(sessions))

        def get_dropdown_choices():
            choices = []
            for session_id in sessions:
                if sessions[session_id]:  # Only show non-empty sessions
                    first_msg = sessions[session_id][0][0][:20]  # First message snippet
                    choices.append((f"Chat: {first_msg}...", session_id))
            choices.append(("+ New Chat", current_thread_id.value))
            return choices

        # UI Components
        with gr.Row():
            new_chat_btn = gr.Button("+ New Chat", variant="primary")
            session_selector = gr.Dropdown(
                label="Your Chats",
                choices=get_dropdown_choices(),
                value=current_thread_id.value,
                interactive=True
            )

        chatbot_ui = gr.Chatbot(label="Conversation", height=400)

        with gr.Row():
            msg = gr.Textbox(placeholder="Type your message...", container=False, scale=9)
            send_btn = gr.Button("Send", variant="primary", scale=1)

        clear_btn = gr.Button("Clear Current Chat")

        def start_new_chat():
            new_id = str(uuid.uuid4())
            sessions[new_id] = []
            save_all_sessions(sessions)
            current_thread_id.value = new_id
            return [], gr.Dropdown.update(choices=get_dropdown_choices(), value=new_id)

        def switch_chat(session_id):
            if session_id == current_thread_id.value:
                return current_thread_id.value, sessions.get(session_id, [])
            current_thread_id.value = session_id
            return session_id, sessions.get(session_id, [])

        def respond(message, chat_history, thread_id):
            if not message.strip():
                yield chat_history
                return
                
            chat_history.append((message, ""))
            yield chat_history
            
            full_response = ""
            for chunk in chatbot.get_response(message, chat_history[:-1], thread_id):
                full_response = chunk
                chat_history[-1] = (message, full_response)
                yield chat_history
            
            sessions[thread_id] = chat_history
            save_all_sessions(sessions)
            
            # Update dropdown if this was first message
            if len(chat_history) == 1:
                yield chat_history, gr.Dropdown.update(choices=get_dropdown_choices())
            else:
                yield chat_history

        def clear_chat(thread_id):
            sessions[thread_id] = []
            save_all_sessions(sessions)
            return []

        # Event handlers
        new_chat_btn.click(
            start_new_chat,
            outputs=[chatbot_ui, session_selector]
        )
        
        session_selector.change(
            switch_chat,
            inputs=session_selector,
            outputs=[current_thread_id, chatbot_ui]
        )
        
        send_btn.click(
            respond,
            inputs=[msg, chatbot_ui, current_thread_id],
            outputs=[chatbot_ui, session_selector]
        ).then(lambda: "", None, msg)
        
        msg.submit(
            respond,
            inputs=[msg, chatbot_ui, current_thread_id],
            outputs=[chatbot_ui, session_selector]
        ).then(lambda: "", None, msg)
        
        clear_btn.click(
            clear_chat,
            inputs=[current_thread_id],
            outputs=[chatbot_ui]
        )

    return demo

# Run the app
if __name__ == "__main__":
    try:
        demo = launch_interface()
        demo.launch(server_name="0.0.0.0", server_port=7860)
    except Exception as e:
        logger.critical(f"Application failed to start: {e}")