// Server-only — syncs newsletter opt-ins to Brevo's Contacts API. Brevo
// owns everything downstream of that (list membership, unsubscribe links,
// and whatever Welcome Flow automation is configured on the list in
// Brevo's own UI — that automation isn't manageable via their public API
// at all, only contacts/lists are). This app never sends marketing mail
// itself; it only ever hands Brevo the contact + consent.
const BREVO_API_URL = "https://api.brevo.com/v3/contacts";

export type BrevoSyncResult = { ok: true } | { ok: false; reason: string };

export type NewsletterOptInSource = "checkout" | "newsletter-page" | "newsletter-modal" | "newsletter-hero" | "challenge";

// `source` becomes a Brevo contact attribute so campaigns/segments can
// tell a checkout opt-in apart from the standalone signup forms without
// needing separate lists.
export async function upsertNewsletterContact(
  email: string,
  source: NewsletterOptInSource,
): Promise<BrevoSyncResult> {
  const apiKey = process.env.BREVO_API_KEY;
  const listId = process.env.BREVO_LIST_ID;
  if (!apiKey || !listId) {
    return { ok: false, reason: "BREVO_API_KEY/BREVO_LIST_ID nicht konfiguriert." };
  }

  try {
    const res = await fetch(BREVO_API_URL, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        "api-key": apiKey,
      },
      body: JSON.stringify({
        email,
        listIds: [Number(listId)],
        updateEnabled: true,
        attributes: { OPT_IN_SOURCE: source },
      }),
      signal: AbortSignal.timeout(8000),
    });
    // 204 for both a fresh contact and an existing one (updateEnabled
    // above merges the list membership onto the existing contact instead
    // of erroring).
    if (res.ok || res.status === 204) return { ok: true };
    const body = await res.json().catch(() => null);
    return { ok: false, reason: body?.message ?? `Brevo antwortete mit ${res.status}` };
  } catch (err) {
    return { ok: false, reason: err instanceof Error ? err.message : "Brevo ist gerade nicht erreichbar." };
  }
}