app.py

import os
import uuid
import json
import time
import gradio as gr
import logging
from dotenv import load_dotenv
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
from langchain_core.messages import BaseMessage


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

GEMINI_API_KEY = os.getenv("GEMINI_API_KEY")
if not GEMINI_API_KEY:
    raise ValueError("Missing GEMINI_API_KEY")
genai.configure(api_key=GEMINI_API_KEY)

HISTORY_FILE = "chat_history.json"

# === Persistent Storage ===
def load_all_sessions():
    if os.path.exists(HISTORY_FILE):
        with open(HISTORY_FILE, "r", encoding="utf-8") as f:
            return json.load(f)
    return {}

def save_all_sessions(sessions):
    with open(HISTORY_FILE, "w", encoding="utf-8") as f:
        json.dump(sessions, f, indent=2)

# === Chatbot Class ===
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 instead of answering something not correct.
        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}")
        ])

        self.model = ChatGoogleGenerativeAI(
            model="gemini-2.0-flash",
            temperature=0.7,
            top_p=0.95,
            google_api_key=GEMINI_API_KEY,
            convert_system_message_to_human=True
        )

        def call_model(state: MessagesState):
            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}

        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:
            # Convert string history into LangChain message objects
            langchain_history = []
            for user, bot in history:
                langchain_history.append(HumanMessage(content=user))
                langchain_history.append(AIMessage(content=bot))

            # Add the new user message
            input_message = HumanMessage(content=user_message)
            full_history = langchain_history + [input_message]

            full_response = ""
            config = {"configurable": {"thread_id": thread_id}}

            # Invoke the model with full conversation
            response = self.app.invoke({"messages": full_history}, config)
            complete_response = response["messages"][-1].content

            for char in complete_response:
                full_response += char
                yield full_response
                time.sleep(0.01)

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


# === Gradio UI ===
chatbot = GeminiChatbot()
sessions = load_all_sessions()


def launch_interface():
    with gr.Blocks(
            theme=gr.themes.Base(),
            css="""
        body {
            background-color: black;
        }
        .gr-block.gr-textbox textarea {
            background-color: #2f2f2f;
            color: white;
        }
        .gr-chatbot {
            background-color: #2f2f2f;
            color: white;
        }
        .gr-button, .gr-dropdown {
            margin: 5px auto;
            display: block;
            width: 50%;
        }
        .gr-markdown h2 {
            text-align: center;
            color: white;
        }
        """
    ) as demo:
        demo.title = "LangChain Powered ChatBot"
        gr.Markdown("## LangChain Powered ChatBot")

        current_thread_id = gr.State()
        session_names = gr.State()
        history = gr.State([])

        # Initialize with first session or create new
        if not sessions:
            new_id = str(uuid.uuid4())
            sessions[new_id] = []
            save_all_sessions(sessions)
            current_thread_id.value = new_id
            session_names.value = [f"NEW: {new_id}"]
        else:
            current_thread_id.value = next(iter(sessions.keys()))
            session_names.value = [f"PREVIOUS: {k}" for k in sessions.keys()]

        def get_dropdown_choices():
            """Get current dropdown choices including active sessions and new chat"""
            choices = []
            for session_id in sessions:
                if sessions[session_id]:  # Only show sessions with history
                    choices.append(f"PREVIOUS: {session_id}")
            choices.append(f"NEW: {current_thread_id.value}")
            return choices

        with gr.Column():
            new_chat_btn = gr.Button("New Chat", variant="primary")
            session_selector = gr.Dropdown(
                label="Chats",
                choices=get_dropdown_choices(),
                value=f"NEW: {current_thread_id.value}",
                interactive=True
            )

        chatbot_ui = gr.Chatbot(label="Conversation", height=320)

        with gr.Row():
            msg = gr.Textbox(placeholder="Ask a question...", container=False, scale=9)
            send = gr.Button("Send", variant="primary", scale=1)

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

        def start_new_chat():
            new_id = str(uuid.uuid4())
            sessions[new_id] = []
            save_all_sessions(sessions)

            # Format for dropdown
            display_name = f"NEW: {new_id}"
            updated_choices = [f"PREVIOUS: {k}" for k in sessions if sessions[k]] + [display_name]

            return (
                new_id,  # thread ID state
                [],  # history
                gr.update(choices=updated_choices, value=display_name),  # update dropdown
                display_name  # visible value
            )



        def switch_chat(selected_display_id):
            """Switch between different chat sessions"""
            if not selected_display_id:
                return current_thread_id.value, [], ""

            true_id = selected_display_id.split(": ", 1)[-1]
            chat_history = sessions.get(true_id, [])
            return true_id, chat_history, selected_display_id

        def respond(message, history, thread_id):
            """Generate response and update chat history"""
            if not message.strip():
                yield history
                return

            # Add user message to history
            history.append((message, ""))
            yield history

            # Stream response
            full_response = ""
            for chunk in chatbot.get_response(message, history[:-1], thread_id):
                full_response = chunk
                history[-1] = (message, full_response)
                yield history

            # Save updated session
            sessions[thread_id] = history
            save_all_sessions(sessions)

        def clear_current(thread_id):
            """Clear current chat history"""
            sessions[thread_id] = []
            save_all_sessions(sessions)
            return []

        new_chat_btn.click(
            start_new_chat,
            outputs=[current_thread_id, chatbot_ui, session_selector, session_selector]
        )

        session_selector.change(
            switch_chat,
            inputs=session_selector,
            outputs=[current_thread_id, chatbot_ui, session_selector]
        )

        send.click(
            respond,
            inputs=[msg, chatbot_ui, current_thread_id],
            outputs=[chatbot_ui]
        ).then(
            lambda: "", None, msg  # Clear input after sending
        )

        msg.submit(
            respond,
            inputs=[msg, chatbot_ui, current_thread_id],
            outputs=[chatbot_ui]
        ).then(
            lambda: "", None, msg  # Clear input after sending
        )

        clear.click(
            clear_current,
            inputs=[current_thread_id],
            outputs=[chatbot_ui]
        )

    return demo



# === Run App ===
if __name__ == "__main__":
    try:
        demo = launch_interface()
        demo.launch(share=True)
    except Exception as e:
        logger.critical(f"App failed: {e}")