class ComponentElement

class ComponentElement extends RenderElementBase {
  use DoTrustedCallbackTrait;
  
  /**
   * Expands a component into an inline template with an attachment.
   *
   * @param array $element
   *   The element to process. See main class documentation for properties.
   *
   * @return array
   *   The form element.
   *
   * @throws \Drupal\Core\Render\Component\Exception\InvalidComponentDataException
   */
  public function preRenderComponent(array $element) : array {
    $props = $element['#props'];
    $props_alter_callbacks = $element['#propsAlter'];
    // This callback can be used to prepare the context. For instance to replace
    // tokens in the props.
    $props = array_reduce($props_alter_callbacks, fn(array $carry, callable $callback) => $this->doTrustedCallback($callback, [
      $carry,
    ], '%s is not trusted'), $props);
    $inline_template = $this->generateComponentTemplate($element['#component'], $element['#slots'], $element['#slotsAlter'], $props);
    $element['inline-template'] = [
      '#type' => 'inline_template',
      '#template' => $inline_template,
      '#context' => $props,
    ];
    return $element;
  }
  
  /**
   * Generates the template to render the component.
   *
   * @param string $id
   *   The component id.
   * @param array $slots
   *   The contents of any potential embed blocks.
   * @param array $slots_alter_callbacks
   *   The potential callables for altering slots.
   * @param array $context
   *   Inline template context.
   *
   * @return string
   *   The template.
   *
   * @throws \Drupal\Core\Render\Component\Exception\InvalidComponentDataException
   *   When slots are not render arrays.
   */
  private function generateComponentTemplate(string $id, array $slots, array $slots_alter_callbacks, array &$context) : string {
    $template = '{# This template was dynamically generated by single-directory components #}' . PHP_EOL;
    $template .= sprintf('{%% embed \'%s\' %%}', $id);
    $template .= PHP_EOL;
    foreach ($slots as $slot_name => $slot_value) {
      if (\is_scalar($slot_value)) {
        $slot_value = [
          "#plain_text" => (string) $slot_value,
        ];
      }
      if (!Element::isRenderArray($slot_value)) {
        $message = sprintf('Unable to render component "%s". A render array or a scalar is expected for the slot "%s" when using the render element with the "#slots" property', $id, $slot_name);
        throw new InvalidComponentDataException($message);
      }
      $context[$slot_name] = array_reduce($slots_alter_callbacks, fn(array $carry, callable $callback) => $this->doTrustedCallback($callback, [
        $carry,
        $context,
      ], '%s is not trusted'), $slot_value);
      $template .= "  {% block {$slot_name} %}" . PHP_EOL . "    {{ {$slot_name} }}" . PHP_EOL . "  {% endblock %}" . PHP_EOL;
    }
    $template .= '{% endembed %}' . PHP_EOL;
    return $template;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getInfo() : array {
    return [
      '#pre_render' => [
        [
          $this,
          'preRenderComponent',
        ],
      ],
      '#component' => '',
      '#props' => [],
      '#slots' => [],
      '#propsAlter' => [],
      '#slotsAlter' => [],
    ];
  }

}