app.py

from fastapi import FastAPI
from langgraph.graph import StateGraph
from typing import TypedDict, Annotated, List
from langgraph.graph.message import add_messages
from pydantic import BaseModel

# Initialize FastAPI app
app = FastAPI(title="LangGraph Agent API")

class State(TypedDict):
    messages: Annotated[list[str], add_messages]
    current_step: str

class AgentInput(BaseModel):
    messages: List[str]

def collect_info(state: State) -> dict:
    print("\n--> In collect_info")
    print(f"Messages before: {state['messages']}")
    
    messages = state["messages"] + ["Information collected"]
    print(f"Messages after: {messages}")
    
    return {
        "messages": messages,
        "current_step": "process"
    }

def process_info(state: State) -> dict:
    print("\n--> In process_info")
    print(f"Messages before: {state['messages']}")
    
    messages = state["messages"] + ["Information processed"]
    print(f"Messages after: {messages}")
    
    return {
        "messages": messages,
        "current_step": "end"
    }

# Create and setup graph
workflow = StateGraph(State)

# Add nodes
workflow.add_node("collect", collect_info)
workflow.add_node("process", process_info)

# Add edges
workflow.add_edge("collect", "process")

# Set entry and finish points
workflow.set_entry_point("collect")
workflow.set_finish_point("process")

# Compile the workflow
agent = workflow.compile()


@app.post("/run-agent")
async def run_agent(input_data: AgentInput):
    """
    Run the agent with the provided input messages.
    """
    initial_state = State(messages=input_data.messages, current_step="collect")
    final_state = agent.invoke(initial_state)
    return {"messages": final_state["messages"]}

@app.get("/")
async def root():
    """
    Root endpoint that returns basic API information.
    """
    return {"message": "LangGraph Agent API is running", "endpoints": ["Navigate to https://jstoppa-langgraph-basic-example-api.hf.space/docs#/default/run_agent_run_agent_post to run the example"]}

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=7860)