// What does LangChain actually do?
// Teaching excerpts; see the explanation and boundaries on the episode page.

// Define the tool contract
import { createAgent, tool, modelCallLimitMiddleware } from "langchain";
import { z } from "zod";

const orderStatus = tool(
  ({ orderId }) => readMyOrder(orderId),
  {
    name: "order_status",
    description: "Read my order status",
    schema: z.object({ orderId: z.string() }),
  }
);

// Keep data access in your server function
const demoOrders = new Map([
  ["42", { owner: "demo-user", status: "In the kitchen" }],
  ["43", { owner: "another-user", status: "Out for delivery" }],
]);
function readMyOrder(orderId, signedInUser = "demo-user") {
  const order = demoOrders.get(orderId);
  if (!order || order.owner !== signedInUser) {
    throw new Error("Order unavailable");
  }
  return order.status;
}

// Connect the model and bound the loop
const agent = createAgent({
  model,
  tools: [orderStatus],
  middleware: [
    modelCallLimitMiddleware({ runLimit: 3, exitBehavior: "error" }),
  ],
});
const result = await agent.invoke({
  messages: [{ role: "user", content: "Where is order 42?" }],
});
const answer = result.messages.at(-1).content;

// Choose the smallest useful flow
// Chat-model invocation without an agent loop.
const reply = await model.invoke("Say hello.");