/**
 * Newsletter signup — posts the visitor's email to a configured serverless
 * endpoint. No credential is ever sent: the serverless function authenticates
 * with an API token it reads from platform env/secrets at deploy time.
 *
 * Pure-ish by design (no DOM, injectable fetch), so every behaviour is unit
 * testable in Node; the browser wiring at the bottom is guarded accordingly.
 */
import { NEWSLETTER_ENDPOINT } from "./newsletter-config.js";

/** User-safe message shown when the signup cannot be completed. */
export const NEWSLETTER_ERROR_MESSAGE =
  "Sorry, the newsletter signup isn't available right now. Please try again later.";

/** Confirmation message shown after a successful signup. */
export const NEWSLETTER_SUCCESS_MESSAGE = "Thanks for subscribing!";

/** Simple email shape check; the HTML5 `type="email"` input is the primary gate. */
export function isValidEmail(value) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(String(value).trim());
}

/**
 * Read the trimmed email value from a form.
 * Works with a real DOM form and with the minimal fake form used in tests.
 *
 * @param {{querySelectorAll(selector: string): ArrayLike<{name: string, value: string}>}} form
 * @returns {string}
 */
export function readFormEmail(form) {
  for (const el of form.querySelectorAll("[name]")) {
    if (el.name === "email") return el.value.trim();
  }
  return "";
}

/**
 * POST the email to the serverless endpoint with no credential in the request
 * — no auth header, no token in the body or URL. The serverless function reads
 * its API token from platform env/secrets, never from the client. A clearly
 * invalid email fails fast with a user-safe error and no network call. Any
 * non-2xx response and any network failure map to the same generic message, so
 * the endpoint internals, any status code, and any raw response body are never
 * surfaced to the visitor.
 *
 * @param {string} email
 * @param {{endpoint?: string, fetchImpl?: typeof fetch}} [options]
 * @returns {Promise<{ok: boolean, message: string}>}
 */
export async function submitNewsletterSignup(
  email,
  { endpoint = NEWSLETTER_ENDPOINT, fetchImpl = fetch } = {},
) {
  if (!isValidEmail(email)) {
    return { ok: false, message: NEWSLETTER_ERROR_MESSAGE };
  }

  let response;
  try {
    response = await fetchImpl(endpoint, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ email }),
    });
  } catch {
    return { ok: false, message: NEWSLETTER_ERROR_MESSAGE };
  }

  if (!response.ok) {
    return { ok: false, message: NEWSLETTER_ERROR_MESSAGE };
  }
  return { ok: true, message: NEWSLETTER_SUCCESS_MESSAGE };
}

/**
 * Handle a newsletter form submit: validate the email, POST it, and surface
 * the result (confirmation or user-safe error) through `setStatus`.
 *
 * @param {HTMLFormElement} form
 * @param {{endpoint?: string, fetchImpl?: typeof fetch, setStatus?: (message: string, kind: "success"|"error") => void}} [options]
 * @returns {Promise<{ok: boolean, message: string}>}
 */
export async function handleNewsletterSubmit(
  form,
  {
    endpoint = NEWSLETTER_ENDPOINT,
    fetchImpl = fetch,
    setStatus = defaultSetStatus,
  } = {},
) {
  const email = readFormEmail(form);
  if (!isValidEmail(email)) {
    setStatus(NEWSLETTER_ERROR_MESSAGE, "error");
    return { ok: false, message: NEWSLETTER_ERROR_MESSAGE };
  }

  const result = await submitNewsletterSignup(email, { endpoint, fetchImpl });
  setStatus(result.message, result.ok ? "success" : "error");
  return result;
}

/** Default status renderer — puts the message into `#newsletter-status`. */
function defaultSetStatus(message, kind) {
  const el = document.getElementById("newsletter-status");
  if (el) {
    el.textContent = message;
    el.dataset.kind = kind;
  }
}

/**
 * Wire the submit handler onto a newsletter form.
 * @param {HTMLFormElement} form
 */
export function initNewsletterForm(form, options = {}) {
  form.addEventListener("submit", (event) => {
    event.preventDefault();
    handleNewsletterSubmit(form, options);
  });
}

// Browser-only wiring — guarded so this module stays importable in Node tests.
if (typeof window !== "undefined" && typeof document !== "undefined") {
  const form = document.getElementById("newsletter-form");
  if (form) initNewsletterForm(form);
}