class NumericItemBase

abstract class NumericItemBase extends FieldItemBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultFieldSettings() {
        return [
            'min' => '',
            'max' => '',
            'prefix' => '',
            'suffix' => '',
        ] + parent::defaultFieldSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
        $element = [];
        $settings = $this->getSettings();
        $element['min'] = [
            '#type' => 'number',
            '#title' => t('Minimum'),
            '#default_value' => $settings['min'],
            '#description' => t('The minimum value that should be allowed in this field. Leave blank for no minimum.'),
        ];
        $element['max'] = [
            '#type' => 'number',
            '#title' => t('Maximum'),
            '#default_value' => $settings['max'],
            '#description' => t('The maximum value that should be allowed in this field. Leave blank for no maximum.'),
        ];
        $element['prefix'] = [
            '#type' => 'textfield',
            '#title' => t('Prefix'),
            '#default_value' => $settings['prefix'],
            '#size' => 60,
            '#description' => t("Define a string that should be prefixed to the value, like '\$ ' or '€ '. Leave blank for none. Separate singular and plural values with a pipe ('pound|pounds')."),
        ];
        $element['suffix'] = [
            '#type' => 'textfield',
            '#title' => t('Suffix'),
            '#default_value' => $settings['suffix'],
            '#size' => 60,
            '#description' => t("Define a string that should be suffixed to the value, like ' m', ' kb/s'. Leave blank for none. Separate singular and plural values with a pipe ('pound|pounds')."),
        ];
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isEmpty() {
        if (empty($this->value) && (string) $this->value !== '0') {
            return TRUE;
        }
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConstraints() {
        $constraint_manager = \Drupal::typedDataManager()->getValidationConstraintManager();
        $constraints = parent::getConstraints();
        $settings = $this->getSettings();
        $label = $this->getFieldDefinition()
            ->getLabel();
        if (isset($settings['min']) && $settings['min'] !== '') {
            $min = $settings['min'];
            $constraints[] = $constraint_manager->create('ComplexData', [
                'value' => [
                    'Range' => [
                        'min' => $min,
                        'minMessage' => t('%name: the value may be no less than %min.', [
                            '%name' => $label,
                            '%min' => $min,
                        ]),
                    ],
                ],
            ]);
        }
        if (isset($settings['max']) && $settings['max'] !== '') {
            $max = $settings['max'];
            $constraints[] = $constraint_manager->create('ComplexData', [
                'value' => [
                    'Range' => [
                        'max' => $max,
                        'maxMessage' => t('%name: the value may be no greater than %max.', [
                            '%name' => $label,
                            '%max' => $max,
                        ]),
                    ],
                ],
            ]);
        }
        return $constraints;
    }
    
    /**
     * Helper method to truncate a decimal number to a given number of decimals.
     *
     * @param float $decimal
     *   Decimal number to truncate.
     * @param int $num
     *   Number of digits the output will have.
     *
     * @return float
     *   Decimal number truncated.
     */
    protected static function truncateDecimal($decimal, $num) {
        return floor($decimal * pow(10, $num)) / pow(10, $num);
    }

}