class FileTestForm

class FileTestForm implements FormInterface {
    use FileTestFormTrait;
    use StringTranslationTrait;
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return '_file_test_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form = $this->baseForm($form, $form_state);
        $form['file_test_upload'] = [
            '#type' => 'file',
            '#title' => $this->t('Upload a file'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        // Process the upload and perform validation. Note: we're using the
        // form value for the $replace parameter.
        if (!$form_state->isValueEmpty('file_subdir')) {
            $destination = 'temporary://' . $form_state->getValue('file_subdir');
            \Drupal::service('file_system')->prepareDirectory($destination, FileSystemInterface::CREATE_DIRECTORY);
        }
        else {
            $destination = FALSE;
        }
        // Setup validators.
        $validators = [];
        if ($form_state->getValue('is_image_file')) {
            $validators['FileIsImage'] = [];
        }
        $allow = $form_state->getValue('allow_all_extensions');
        if ($allow === 'empty_array') {
            $validators['FileExtension'] = [];
        }
        elseif ($allow === 'empty_string') {
            $validators['FileExtension'] = [
                'extensions' => '',
            ];
        }
        elseif (!$form_state->isValueEmpty('extensions')) {
            $validators['FileExtension'] = [
                'extensions' => $form_state->getValue('extensions'),
            ];
        }
        // The test for \Drupal::service('file_system')->moveUploadedFile()
        // triggering a warning is unavoidable. We're interested in what happens
        // afterwards in file_save_upload().
        if (\Drupal::state()->get('file_test.disable_error_collection')) {
            define('SIMPLETEST_COLLECT_ERRORS', FALSE);
        }
        $file = file_save_upload('file_test_upload', $validators, $destination, 0, static::fileExistsFromName($form_state->getValue('file_test_replace')));
        if ($file) {
            $form_state->setValue('file_test_upload', $file);
            \Drupal::messenger()->addStatus($this->t('File @filepath was uploaded.', [
                '@filepath' => $file->getFileUri(),
            ]));
            \Drupal::messenger()->addStatus($this->t('File name is @filename.', [
                '@filename' => $file->getFilename(),
            ]));
            \Drupal::messenger()->addStatus($this->t('File MIME type is @mimetype.', [
                '@mimetype' => $file->getMimeType(),
            ]));
            \Drupal::messenger()->addStatus($this->t('You WIN!'));
        }
        elseif ($file === FALSE) {
            \Drupal::messenger()->addError($this->t('Epic upload FAIL!'));
        }
    }
    
    /**
     * Get a FileExists enum from its name.
     */
    protected static function fileExistsFromName(string $name) : FileExists {
        return match ($name) {    FileExists::Replace->name => FileExists::Replace,
            FileExists::Error->name => FileExists::Error,
            default => FileExists::Rename,
        
        };
    }

}