app.py

import os
import torch
import gradio as gr
from PIL import Image
import tempfile
import shutil
from functools import partial 
import traceback # <--- ADDED THIS LINE: Import the traceback module

from diffusers import StableDiffusionPipeline
from huggingface_hub import InferenceClient

# LangChain imports
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.tools import tool
from langchain_community.tools import DuckDuckGoSearchRun
from langchain_community.llms import HuggingFaceHub
from langchain.agents import AgentExecutor, create_react_agent
from langchain.schema import HumanMessage, AIMessage

# --- 1. Load Stable Diffusion Pipeline (happens once at startup) ---
HF_TOKEN = os.environ.get("HF_TOKEN") # Using HF_TOKEN for consistency with HuggingFaceHub LLM

# Define the model ID for image generation
IMAGE_GEN_MODEL_ID = "segmind/tiny-sd" # Using the smaller model as it loaded successfully

print(f"Loading Stable Diffusion Pipeline directly on GPU: {IMAGE_GEN_MODEL_ID}...")
try:
    pipe = StableDiffusionPipeline.from_pretrained(
        IMAGE_GEN_MODEL_ID,
        torch_dtype=torch.float16, # Use float16 for less VRAM usage on T4
        use_safetensors=False, # Set to False for models that don't have safetensors (like tiny-sd)
        token=HF_TOKEN # Pass token for potential faster model download
    )
    pipe.to("cuda") # Move the model to the GPU
    print(f"Stable Diffusion Pipeline ({IMAGE_GEN_MODEL_ID}) loaded successfully on GPU.")
except Exception as e:
    print("❌ Error loading Stable Diffusion Pipeline:")
    traceback.print_exc()
    pipe = None # Indicate failure to load

# --- 2. Define Custom Image Generation Tool for LangChain ---
# Use @tool decorator to make a function a LangChain tool
@tool
def image_generator(prompt: str) -> str:
    """
    Generates an image from a detailed text prompt using a Stable Diffusion pipeline.
    The input MUST be a detailed text description for the image to generate.
    """
    if pipe is None:
        return "Error: Image generation pipeline failed to load. Please check Space logs during startup."
    
    print(f"\n--- Agent is calling image_generator with prompt: '{prompt}' ---")
    try:
        with torch.no_grad():
            pil_image = pipe(prompt, guidance_scale=7.5, height=512, width=512).images[0]
        
        # Save the PIL image to a temporary file, Gradio will handle displaying this path
        # NOTE: LangChain tools typically return strings. For image display, we'll return
        # the path, and handle its display in the Gradio UI directly based on content.
        temp_dir = tempfile.mkdtemp()
        image_path = os.path.join(temp_dir, "generated_image.png")
        pil_image.save(image_path)
        
        print(f"Image saved to temporary path: {image_path}")
        # Return a special string prefix so Gradio knows it's an image path
        return f"__IMAGE_PATH__:{image_path}" 
    except Exception as e:
        print("Error in image_generator tool execution:")
        traceback.print_exc()
        return f"Error generating image: {str(e)}"

# --- 3. Define other Tools for LangChain ---
search = DuckDuckGoSearchRun()

# --- 4. Define the LangChain Agent ---
# Ensure models are loaded successfully before proceeding
if pipe is None:
    raise RuntimeError("Cannot start agent as image generation pipeline failed to load. Check logs.")

# Instantiate the LLM for the agent
llm = HuggingFaceHub(
    repo_id="HuggingFaceH4/zephyr-7b-beta",
    huggingfacehub_api_token=HF_TOKEN, # Use HF_TOKEN directly as required by HuggingFaceHub LLM
    model_kwargs={"temperature": 0.5, "max_new_tokens": 512}
)

# Create the tools list
tools = [image_generator, search]

# Define the agent prompt
# This prompt guides the LLM on how to use the tools
prompt_template = ChatPromptTemplate.from_messages(
    [
        ("system", """You are a powerful AI assistant that can generate images and search the web.
You have access to the following tools: {tools}
Available tools: {tool_names} # <--- THIS LINE IS CRUCIAL AND MUST BE PRESENT.

When you need to generate an image, use the `image_generator` tool. Its input must be a very detailed, descriptive text string.
When you need factual information or context, use the `search` tool.

Always follow these steps:
1. Think step-by-step: Analyze the user's request and determine if you need to search or generate an image.
2. If you need to search, use the `search` tool.
3. If you need to generate an image, ensure you have enough detail. If not, ask for more or use search.
4. When you have enough information, use the `image_generator` tool.
5. Provide your final answer. If you generated an image, include the image in your final answer.
"""),
        MessagesPlaceholder(variable_name="chat_history"),
        ("human", "{input}"),
        MessagesPlaceholder(variable_name="agent_scratchpad"), # This placeholder must be present
    ]
)

# Create the agent
agent = create_react_agent(llm, tools, prompt_template)

# Create the agent executor
agent_executor = AgentExecutor(agent=agent, tools=tools, verbose=True, handle_parsing_errors=True)

# --- 5. Gradio UI Integration ---

# Function to run the agent and display output
def run_agent_in_gradio(message, history):
    # Convert Gradio history to LangChain chat_history format
    chat_history = []
    for human_msg, ai_msg in history:
        chat_history.append(HumanMessage(content=human_msg))
        chat_history.append(AIMessage(content=ai_msg))

    try:
        # THIS LINE IS CRUCIAL AND MUST INCLUDE "agent_scratchpad": []
        response = agent_executor.invoke(
            {"input": message, "chat_history": chat_history, "agent_scratchpad": []} 
        )
        agent_output = response["output"]

        # Check if the output is an image path from our custom tool
        if agent_output.startswith("__IMAGE_PATH__:") :
            image_path = agent_output.replace("__IMAGE_PATH__:", "")
            # Return the Gradio Image component directly
            return gr.Image(value=image_path, label="Generated Image")
        else:
            # Return regular text
            return agent_output

    except Exception as e:
        print(f"Error running agent: {e}")
        traceback.print_exc() 
        return f"❌ Agent encountered an error: {str(e)}"
        
# Gradio ChatInterface setup
demo = gr.ChatInterface(
    fn=run_agent_in_gradio,
    chatbot=gr.Chatbot(label="AI Agent"),
    textbox=gr.Textbox(placeholder="Ask me to generate an image or search the web...", container=False, scale=7),
    title="Intelligent Image Generator & Web Search Agent (LangChain)",
    description="This agent can generate images based on prompts or search the web for information first."
)

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