Cara handle state di stateless env buat nested sub modals.

stateful.php

<?php

// initial state
$state = (object) [
  'count' => 0,
  'showModal' => false,
  'showSubModal' => false,
  ...$_GET
];

// generic utility function -- mestinya ditaruh di file lain
function render_state() {
  global $state;
  return '?' . http_build_query((array) $state);
}

// action
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
  switch ($_POST['action']) {
    case 'increment':
      $state->count++;
      break;
    case 'decrement':
      $state->count--;
      break;
    case 'openModal':
      $state->showModal = true;
      break;
    case 'closeModal':
      $state->showModal = false;
      break;
    case 'openSubModal':
      $state->showSubModal = true;
      break;
    case 'closeSubModal':
      $state->showSubModal = false;
      break;
  }
  header('Location: ' . render_state());
  exit;
}

?>
<form action="<?= render_state() ?>" method="post">
  <p>Count: <?= $state->count ?></p>
  <button name="action" value="increment">+</button>
  <button name="action" value="decrement">-</button>
</form>

<form action="<?= render_state() ?>" method="post">
  <button name="action" value="openModal">Open Modal</button>
</form>

<?php if ($state->showModal): ?>
  <div>
    Modal content here.
    <form action="<?= render_state() ?>" method="post">
      <button name="action" value="openSubModal">Open Sub Modal</button>
      <button name="action" value="closeModal">Close Modal</button>
    </form>
  </div>
<?php endif ?>

<?php if ($state->showSubModal): ?>
  <div>
    Sub Modal content here.
    <form action="<?= render_state() ?>" method="post">
      <button name="action" value="closeSubModal">Close Sub Modal</button>
    </form>
  </div>
<?php endif ?>