(() => {
  const form = document.getElementById('checkout-form');
  const button = document.getElementById('checkout-button');
  const qtyInput = document.getElementById('quantity');
  const message = document.getElementById('message');

  if (!form || !button || !qtyInput) {
    return;
  }

  const setMessage = (text, isError = true) => {
    if (!message) {
      return;
    }
    message.textContent = text;
    message.style.color = isError ? '#dc2626' : '#16a34a';
  };

  form.addEventListener('submit', async (event) => {
    event.preventDefault();

    const quantity = Number.parseInt(qtyInput.value, 10);
    if (!Number.isFinite(quantity) || quantity <= 0) {
      setMessage('Enter a quantity of at least 1.');
      qtyInput.focus();
      return;
    }

    try {
      button.disabled = true;
      setMessage('Contacting Stripe…', false);

      const response = await fetch('/api/checkout', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
        },
        body: JSON.stringify({ quantity }),
      });

      if (!response.ok) {
        const errorText = await response.text();
        throw new Error(errorText || 'Checkout request failed.');
      }

      const data = await response.json();
      if (!data || !data.url) {
        throw new Error('Checkout response missing redirect URL.');
      }

      setMessage('Redirecting to Stripe…', false);
      window.location.href = data.url;
    } catch (err) {
      console.error('Checkout failed', err);
      setMessage('Unable to start checkout. Please try again.');
      button.disabled = false;
    }
  });
})();