class BooleanItem

class BooleanItem extends FieldItemBase implements OptionsProviderInterface {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultFieldSettings() {
        return [
            'on_label' => new TranslatableMarkup('On'),
            'off_label' => new TranslatableMarkup('Off'),
        ] + parent::defaultFieldSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
        $properties['value'] = DataDefinition::create('boolean')->setLabel(t('Boolean value'))
            ->setRequired(TRUE);
        return $properties;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function schema(FieldStorageDefinitionInterface $field_definition) {
        return [
            'columns' => [
                'value' => [
                    'type' => 'int',
                    'size' => 'tiny',
                ],
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
        $element = [];
        $element['on_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('"On" label'),
            '#default_value' => $this->getSetting('on_label'),
            '#required' => TRUE,
        ];
        $element['off_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('"Off" label'),
            '#default_value' => $this->getSetting('off_label'),
            '#required' => TRUE,
        ];
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPossibleValues(?AccountInterface $account = NULL) {
        return [
            0,
            1,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPossibleOptions(?AccountInterface $account = NULL) {
        return [
            0 => $this->getSetting('off_label'),
            1 => $this->getSetting('on_label'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSettableValues(?AccountInterface $account = NULL) {
        return [
            0,
            1,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSettableOptions(?AccountInterface $account = NULL) {
        return $this->getPossibleOptions($account);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
        $values['value'] = mt_rand(0, 1);
        return $values;
    }

}