// How do you stop a LangChain agent from retrying?
// Teaching excerpts; see the explanation and boundaries on the episode page.

// Use the native tool-call limiter
import { createAgent, tool, toolCallLimitMiddleware, ToolCallLimitExceededError as LimitError } from 'langchain';
import { z } from 'zod';

export function makeSupportAgent(model, read) {
  const lookup = tool(({ ticket }) => read(ticket), {
    name: 'lookup', description: 'Read the status of my support ticket',
    schema: z.object({ ticket: z.string() }),
  });
  return createAgent({
    model, tools: [lookup],
    middleware: [toolCallLimitMiddleware({
      runLimit: 3, exitBehavior: 'error',
    })],
  });
}

// Return an incomplete result at the application boundary
// LimitError is imported above.
export async function runSupport(agent, request) {
  try {
    const result = await agent.invoke(request);
    return { status: 'answered', message: result.messages.at(-1).content };
  } catch (error) {
    if (!(error instanceof LimitError)) throw error;
    return { status: 'incomplete', reason: 'tool_limit' };
  }
}

// Predict the result before running the fixture
// Sequential failure fixture
{ status: "incomplete", reason: "tool_limit" }

// Successful first lookup fixture
{ status: "answered", message: "Ticket 42 is open" }