class ViewDuplicateForm

class ViewDuplicateForm extends ViewFormBase {
    
    /**
     * {@inheritdoc}
     */
    protected function prepareEntity() {
        // Do not prepare the entity while it is being added.
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        parent::form($form, $form_state);
        $form['#title'] = $this->t('Duplicate of @label', [
            '@label' => $this->entity
                ->label(),
        ]);
        $form['label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('View name'),
            '#required' => TRUE,
            '#size' => 32,
            '#maxlength' => 255,
            '#default_value' => $this->t('Duplicate of @label', [
                '@label' => $this->entity
                    ->label(),
            ]),
        ];
        $form['id'] = [
            '#type' => 'machine_name',
            '#maxlength' => 128,
            '#machine_name' => [
                'exists' => '\\Drupal\\views\\Views::getView',
                'source' => [
                    'label',
                ],
            ],
            '#default_value' => '',
            '#description' => $this->t('A unique machine-readable name for this View. It must only contain lowercase letters, numbers, and underscores.'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function actions(array $form, FormStateInterface $form_state) {
        $actions['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Duplicate'),
        ];
        return $actions;
    }
    
    /**
     * Form submission handler for the 'clone' action.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   A reference to a keyed array containing the current state of the form.
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->entity = $this->entity
            ->createDuplicate();
        $this->entity
            ->set('label', $form_state->getValue('label'));
        $this->entity
            ->set('id', $form_state->getValue('id'));
        $this->entity
            ->save();
        // Redirect the user to the view admin form.
        $form_state->setRedirectUrl($this->entity
            ->toUrl('edit-form'));
    }

}