first commit. all the code has been initialized by Codex

script.js

@@ -0,0 +1,82 @@
+const form = document.getElementById('rsvp-form');
+const statusNode = document.getElementById('form-status');
+const attendanceFields = document.getElementById('attendance-fields');
+const attendanceInputs = Array.from(document.querySelectorAll('input[name="attendance"]'));
+const successModal = document.getElementById('success-modal');
+const successOkButton = document.getElementById('success-ok');
+const closeModalNodes = Array.from(document.querySelectorAll('[data-close-modal]'));
+
+function updateAttendanceFields() {
+  const selected = document.querySelector('input[name="attendance"]:checked');
+  const attending = selected?.value === 'si';
+
+  attendanceFields.classList.toggle('attendance-fields--hidden', !attending);
+
+  attendanceFields.querySelectorAll('input, select, textarea').forEach((field) => {
+    field.disabled = !attending;
+    if (!attending && field.tagName === 'TEXTAREA') field.value = '';
+    if (!attending && field.tagName === 'SELECT') field.value = '0';
+  });
+}
+
+function openSuccessModal() {
+  if (!successModal) return;
+  successModal.classList.add('success-modal--open');
+  successModal.setAttribute('aria-hidden', 'false');
+  document.body.classList.add('modal-open');
+  successOkButton?.focus();
+}
+
+function closeSuccessModal() {
+  if (!successModal) return;
+  successModal.classList.remove('success-modal--open');
+  successModal.setAttribute('aria-hidden', 'true');
+  document.body.classList.remove('modal-open');
+}
+
+attendanceInputs.forEach((input) => input.addEventListener('change', updateAttendanceFields));
+closeModalNodes.forEach((node) => node.addEventListener('click', closeSuccessModal));
+successOkButton?.addEventListener('click', closeSuccessModal);
+document.addEventListener('keydown', (event) => {
+  if (event.key === 'Escape' && successModal?.classList.contains('success-modal--open')) {
+    closeSuccessModal();
+  }
+});
+updateAttendanceFields();
+
+function encode(data) {
+  return new URLSearchParams(data).toString();
+}
+
+form?.addEventListener('submit', async (event) => {
+  event.preventDefault();
+
+  if (!form.reportValidity()) return;
+
+  const submitButton = form.querySelector('button[type="submit"]');
+  const formData = new FormData(form);
+
+  submitButton.disabled = true;
+  statusNode.textContent = 'Invio in corso...';
+
+  try {
+    const response = await fetch('/', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+      body: encode(formData)
+    });
+
+    if (!response.ok) {
+      throw new Error('Submission failed');
+    }
+
+    form.reset();
+    updateAttendanceFields();
+    statusNode.textContent = '';
+    openSuccessModal();
+  } catch (error) {
+    statusNode.textContent = 'C’è stato un problema nell’invio. Riprova tra poco.';
+  } finally {
+    submitButton.disabled = false;
+  }
+});