redefined-designs/backend/src/favoriteAlerts.ts

import { pool } from './db';
import { sendMail } from './mailer';
import { renderTemplate, greeting, TemplateKey } from './emailTemplates';
import { getSettings } from './adminSettings';
import { loadStoredTemplate } from './routes/adminEmailTemplates';

// Shown to the customer when they opt in, and stored verbatim against their
// consent so the record says what they actually agreed to — the same pattern
// the marketing consent already uses.
export const FAVORITE_ALERTS_CONSENT_TEXT =
  'Email me when an item I have favorited is sold to someone else, so I know it is no longer available.';

export interface FavoriteRecipient {
  email: string;
  // Nullable because customers who registered while names were optional have
  // none — the same reason the greeting needs a fallback at all.
  first_name: string | null;
  last_name: string | null;
  item_name: string;
}

// Gathered separately from sending because deleting an item cascades its
// favorites away: the recipients have to be read *before* the row goes, while
// the send has to happen *after*, so nobody is told about a withdrawal that
// then failed.
export async function collectFavoriteRecipients(
  itemIds: number[],
  excludeCustomerId: number | null,
  onlyUnsold = false
): Promise<FavoriteRecipient[]> {
  if (!itemIds.length) return [];

  const { rows } = await pool.query<FavoriteRecipient>(
    `SELECT c.email, c.first_name, c.last_name, i.name AS item_name
     FROM favorites f
     JOIN customers c ON c.id = f.customer_id
     JOIN items i ON i.id = f.item_id
     WHERE f.item_id = ANY($1::int[])
       AND c.favorite_alerts = true
       AND c.disabled_at IS NULL
       AND ($2::int IS NULL OR c.id <> $2::int)
       AND ($3::boolean = false OR i.status <> 'sold')`,
    [itemIds, excludeCustomerId, onlyUnsold]
  );
  return rows;
}

// One message per item per person, never batched: each is about a specific
// thing the customer asked to hear about. Sent independently so one bad
// address cannot stop the rest — and whatever prompted this has already
// happened regardless of whether the mail goes out.
async function send(recipients: FavoriteRecipient[], key: TemplateKey): Promise<void> {
  if (!recipients.length) return;

  // Loaded once for the batch rather than per recipient: the copy is the same
  // for everyone, only the item name differs.
  const stored = await loadStoredTemplate(key);
  const siteUrl = process.env.PUBLIC_URL ?? '';
  const { greetingFormat, greetingFallback } = await getSettings();

  for (const recipient of recipients) {
    const { subject, html } = renderTemplate(key, stored, {
      greeting: greeting(recipient.first_name, greetingFormat, greetingFallback, recipient.last_name),
      firstName: recipient.first_name ?? '',
      lastName: recipient.last_name ?? '',
      itemName: recipient.item_name,
      siteUrl
    });
    sendMail(recipient.email, subject, html)
      .catch(err => console.error('favorite alert failed', err));
  }
}


// Called *after* the sale has been committed, never inside the transaction.
// Emailing about a sale that then rolled back would be worse than a late
// notification, and the transaction should not be held open for SMTP.
//
// `buyerId` is excluded: telling customers the item they just bought is no
// longer available reads as a bug.
export async function notifyFavoritersOfSale(itemIds: number[], buyerId: number | null): Promise<void> {
  const recipients = await collectFavoriteRecipients(itemIds, buyerId);
  await send(recipients, 'favoriteSold');
}

// Sent when an item is withdrawn from sale rather than sold. Recipients must be
// collected before the delete, since the favorites rows cascade with the item.
// Async now that the copy is loaded from the database before rendering. It was
// previously synchronous in dispatch — the sends were fire-and-forget, but they
// were *started* before the caller returned. Leaving it fire-and-forget would
// mean the response can beat the mail out of the door, which is a behaviour
// change nobody asked for and which the withdrawal test caught.
export async function notifyFavoritersOfRemoval(recipients: FavoriteRecipient[]): Promise<void> {
  await send(recipients, 'favoriteWithdrawn');
}