async function checkProduct(product, deps) {
  const {
    fetchAndExtractPrice, fetchAndExtractPriceViaBrowser,
    sendMail, recordCheckSuccess, recordCheckFailure, now,
  } = deps;
  let result = await fetchAndExtractPrice(product.url);

  if ((result.error || result.price == null) && fetchAndExtractPriceViaBrowser) {
    result = await fetchAndExtractPriceViaBrowser(product.url);
  }

  if (result.error) {
    console.error(`[check] fetch_error "${product.name}" (${product.url}): ${result.error.message}`);
    recordCheckFailure(product.id, 'fetch_error');
    return { status: 'fetch_error' };
  }
  if (result.price == null) {
    console.error(`[check] not_found "${product.name}" (${product.url}): geen prijs gevonden op de pagina`);
    recordCheckFailure(product.id, 'not_found');
    return { status: 'not_found' };
  }

  const isBaseline = product.last_price == null;
  const changed = !isBaseline && result.price !== product.last_price;

  if (changed) {
    try {
      await sendMail({
        name: product.name,
        url: product.url,
        oldPrice: product.last_price,
        newPrice: result.price,
      });
    } catch (err) {
      console.error(`[check] mail_error "${product.name}" (${product.url}): ${err && err.message}`);
      recordCheckFailure(product.id, 'mail_error');
      return { status: 'mail_error' };
    }
  }

  recordCheckSuccess(product.id, { price: result.price, checkedAt: now() });
  return { status: 'ok', changed };
}

async function checkAllProducts(products, deps) {
  const results = [];
  for (const product of products) {
    try {
      const result = await checkProduct(product, deps);
      results.push({ productId: product.id, ...result });
    } catch (err) {
      console.error(`[check] error "${product.name}" (${product.url}): ${err && err.message}`);
      results.push({ productId: product.id, status: 'error', error: err });
    }
  }
  return results;
}

module.exports = { checkProduct, checkAllProducts };