create-cen-app/my-cen-app/frontend/tests/utils/mailcatcher.ts

create an client-engineering-style app

import type { APIRequestContext } from "@playwright/test";

type Email = {
  id: number;
  recipients: string[];
  subject: string;
};

async function findEmail({
  request,
  filter,
}: {
  request: APIRequestContext;
  filter?: (email: Email) => boolean;
}) {
  const response = await request.get("http://localhost:1080/messages");

  let emails = await response.json();

  if (filter) {
    emails = emails.filter(filter);
  }

  const email = emails[emails.length - 1];

  if (email) {
    return email as Email;
  }

  return null;
}

export function findLastEmail({
  request,
  filter,
  timeout = 5000,
}: {
  request: APIRequestContext;
  filter?: (email: Email) => boolean;
  timeout?: number;
}) {
  const timeoutPromise = new Promise<never>((_, reject) =>
    setTimeout(
      () => reject(new Error("Timeout while trying to get latest email")),
      timeout,
    ),
  );

  const checkEmails = async () => {
    while (true) {
      const emailData = await findEmail({ request, filter });

      if (emailData) {
        return emailData;
      }
      // Wait for 100ms before checking again
      await new Promise((resolve) => setTimeout(resolve, 100));
    }
  };

  return Promise.race([timeoutPromise, checkEmails()]);
}