LangGraph

// index.ts
import { Tool } from "@langchain/core/tools";
import { ChatOpenAI } from "@langchain/openai";
import { MemorySaver } from "@langchain/langgraph";
import { HumanMessage } from "@langchain/core/messages";
import { createReactAgent } from "@langchain/langgraph/prebuilt";
import * as dotenv from "dotenv";
dotenv.config();

// ----------------------
// Custom Weather Tool
// ----------------------
class WeatherTool extends Tool {
  name = "get_weather";
  description =
    "Fetches current weather data for a given city. Use this when asked about weather.";

  async _call(city: string): Promise<string> {
    try {
      const url = `${process.env.WEATHER_API_URL}?q=${encodeURIComponent(
        city,
      )}&appid=${process.env.WEATHER_API_KEY}&units=metric`;

      const res = await fetch(url);
      if (!res.ok) return `Weather API error: ${res.statusText}`;
      const data = await res.json();

      const weather = data.weather?.[0]?.description ?? "No description";
      const temp = data.main?.temp ?? "N/A";
      const feels_like = data.main?.feels_like ?? "N/A";

      return `Weather in ${city}: ${weather}, Temp: ${temp}°C, Feels like: ${feels_like}°C`;
    } catch (err) {
      return `Error: ${(err as Error).message}`;
    }
  }
}

// ----------------------
// Setup LLM Agent
// ----------------------
const weatherTool = new WeatherTool();
const agentModel = new ChatOpenAI({ temperature: 0 });
const memory = new MemorySaver();

const agent = createReactAgent({
  llm: agentModel,
  tools: [weatherTool],
  checkpointSaver: memory,
});

// ----------------------
// Use the Agent
// ----------------------
const run = async () => {
  const first = await agent.invoke(
    { messages: [new HumanMessage("What is the weather in San Francisco?")] },
    { configurable: { thread_id: "42" } },
  );

  console.log(
    "
[SF]",
    first.messages[first.messages.length - 1].content,
  );

  const second = await agent.invoke(
    { messages: [new HumanMessage("what about New York?")] },
    { configurable: { thread_id: "42" } },
  );

  console.log(
    "
[NY]",
    second.messages[second.messages.length - 1].content,
  );
};

run();