application/services/langgraph_service.py

from typing import List
from langchain.agents import AgentExecutor, create_openai_tools_agent
from langchain.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.tools import BaseTool
from langchain_openai import ChatOpenAI

def create_agent(

    llm: ChatOpenAI,

    tools: List[BaseTool],

    system_prompt: str

) -> AgentExecutor:
    """Create an agent executor with given tools and a system prompt."""
    prompt = ChatPromptTemplate.from_messages(
        [
            ("system", system_prompt),
            MessagesPlaceholder(variable_name="messages"),
            MessagesPlaceholder(variable_name="agent_scratchpad"),
        ]
    )
    agent = create_openai_tools_agent(llm, tools, prompt)
    executor = AgentExecutor(agent=agent, tools=tools)
    return executor