app.py

import gradio as gr
from huggingface_hub import InferenceClient
from transformers import AutoTokenizer  # Import the tokenizer
from langchain.memory import ConversationBufferMemory
from langchain.schema import HumanMessage, AIMessage

# Use the appropriate tokenizer for your model.
tokenizer = AutoTokenizer.from_pretrained("HuggingFaceH4/zephyr-7b-beta")
client = InferenceClient("HuggingFaceH4/zephyr-7b-beta")

# Define a maximum context length (tokens).  Check your model's documentation!
MAX_CONTEXT_LENGTH = 4096  # Example: Adjust this based on your model!

# Read the default prompt from a file
with open("prompt.txt", "r") as file:
    nvc_prompt_template = file.read()

# Initialize LangChain Conversation Memory
memory = ConversationBufferMemory(memory_key="chat_history", return_messages=True)

def count_tokens(text: str) -> int:
    """Counts the number of tokens in a given string."""
    return len(tokenizer.encode(text))

def truncate_memory(memory, system_message: str, max_length: int):
    """
    Truncates the conversation memory messages to fit within the maximum token limit.
    
    Args:
        memory: The LangChain conversation memory object.
        system_message: The system message.
        max_length: The maximum number of tokens allowed.
        
    Returns:
        A list of messages (as dicts with role and content) that fit within the token limit.
    """
    truncated_messages = []
    system_tokens = count_tokens(system_message)
    current_length = system_tokens

    # Iterate backwards through the memory (newest to oldest)
    for msg in reversed(memory.chat_memory.messages):
        tokens = count_tokens(msg.content)
        if current_length + tokens <= max_length:
            role = "user" if isinstance(msg, HumanMessage) else "assistant"
            truncated_messages.insert(0, {"role": role, "content": msg.content})
            current_length += tokens
        else:
            break

    return truncated_messages

def respond(
    message,
    history: list[tuple[str, str]],  # Required by Gradio but we now use LangChain memory
    system_message,
    max_tokens,
    temperature,
    top_p,
):
    """
    Responds to a user message while maintaining conversation history via LangChain memory.
    It builds the prompt with a system message and the (truncated) conversation history,
    streams the response from the client, and finally updates the memory with the new response.
    """
    # Use your prompt template as the system message.
    formatted_system_message = nvc_prompt_template

    # Prepare and add the new user message (with your special tokens) to memory.
    new_user_message = f"<|user|>\n{message}</s>"
    memory.chat_memory.add_message(HumanMessage(content=new_user_message))

    # Truncate memory to ensure the context fits within the maximum token length (reserve space for generation).
    truncated_history = truncate_memory(
        memory, formatted_system_message, MAX_CONTEXT_LENGTH - max_tokens - 100
    )
    # Ensure the current user message is present at the end.
    if not truncated_history or truncated_history[-1]["content"] != new_user_message:
        truncated_history.append({"role": "user", "content": new_user_message})

    # Build the full message list: system prompt + conversation history.
    messages = [{"role": "system", "content": formatted_system_message}] + truncated_history

    response = ""
    try:
        for chunk in client.chat_completion(
            messages,
            max_tokens=max_tokens,
            stream=True,
            temperature=temperature,
            top_p=top_p,
        ):
            token = chunk.choices[0].delta.content
            response += token
            yield response
    except Exception as e:
        print(f"An error occurred: {e}")
        yield "I'm sorry, I encountered an error. Please try again."

    # Once the full response is generated, add it to the LangChain memory.
    memory.chat_memory.add_message(AIMessage(content=f"<|assistant|>\n{response}</s>"))

# --- Gradio Interface ---
demo = gr.ChatInterface(
    respond,
    additional_inputs=[
        gr.Textbox(value=nvc_prompt_template, label="System message", visible=True),
        gr.Slider(minimum=1, maximum=2048, value=512, step=1, label="Max new tokens"),
        gr.Slider(minimum=0.1, maximum=4.0, value=0.7, step=0.1, label="Temperature"),
        gr.Slider(minimum=0.1, maximum=1.0, value=0.95, step=0.05, label="Top-p (nucleus sampling)"),
    ],
)

if __name__ == "__main__":
    demo.launch()