trait DateTimeRangeTrait

trait DateTimeRangeTrait {
    
    /**
     * Get the default settings for a date and time range display.
     *
     * @return array
     *   An array containing default settings.
     */
    protected static function dateTimeRangeDefaultSettings() : array {
        return [
            'from_to' => DateTimeRangeConstantsInterface::BOTH,
            'separator' => '-',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $elements = [];
        $separator = $this->getSetting('separator');
        foreach ($items as $delta => $item) {
            if (!empty($item->start_date) && !empty($item->end_date)) {
                
                /** @var \Drupal\Core\Datetime\DrupalDateTime $start_date */
                $start_date = $item->start_date;
                
                /** @var \Drupal\Core\Datetime\DrupalDateTime $end_date */
                $end_date = $item->end_date;
                if ($start_date->getTimestamp() !== $end_date->getTimestamp()) {
                    $elements[$delta] = $this->renderStartEndWithIsoAttribute($start_date, $separator, $end_date);
                }
                else {
                    $elements[$delta] = $this->buildDateWithIsoAttribute($start_date);
                    if (!empty($item->_attributes)) {
                        $elements[$delta]['#attributes'] += $item->_attributes;
                        // Unset field item attributes since they have been included in the
                        // formatter output and should not be rendered in the field template.
                        unset($item->_attributes);
                    }
                }
            }
        }
        return $elements;
    }
    
    /**
     * Configuration form for date time range.
     *
     * @param array $form
     *   The form array.
     *
     * @return array
     *   Modified form array.
     */
    protected function dateTimeRangeSettingsForm(array $form) : array {
        $form['from_to'] = [
            '#type' => 'select',
            '#title' => $this->t('Display'),
            '#options' => $this->getFromToOptions(),
            '#default_value' => $this->getSetting('from_to'),
        ];
        $field_name = $this->fieldDefinition
            ->getName();
        $form['separator'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Date separator'),
            '#description' => $this->t('The string to separate the start and end dates'),
            '#default_value' => $this->getSetting('separator'),
            '#states' => [
                'visible' => [
                    'select[name="fields[' . $field_name . '][settings_edit_form][settings][from_to]"]' => [
                        'value' => DateTimeRangeConstantsInterface::BOTH,
                    ],
                ],
            ],
        ];
        return $form;
    }
    
    /**
     * Gets the date time range settings summary.
     *
     * @return array
     *   An array of summary messages.
     */
    protected function dateTimeRangeSettingsSummary() : array {
        $summary = [];
        if ($from_to = $this->getSetting('from_to')) {
            $from_to_options = $this->getFromToOptions();
            if (isset($from_to_options[$from_to])) {
                $summary[] = $from_to_options[$from_to];
            }
        }
        if (($separator = $this->getSetting('separator')) && $this->getSetting('from_to') === DateTimeRangeConstantsInterface::BOTH) {
            $summary[] = $this->t('Separator: %separator', [
                '%separator' => $separator,
            ]);
        }
        return $summary;
    }
    
    /**
     * Returns a list of possible values for the 'from_to' setting.
     *
     * @return array
     *   A list of 'from_to' options.
     */
    protected function getFromToOptions() : array {
        return [
            DateTimeRangeConstantsInterface::BOTH => $this->t('Display both start and end dates'),
            DateTimeRangeConstantsInterface::START_DATE => $this->t('Display start date only'),
            DateTimeRangeConstantsInterface::END_DATE => $this->t('Display end date only'),
        ];
    }
    
    /**
     * Gets whether the start date should be displayed.
     *
     * @return bool
     *   True if the start date should be displayed. False otherwise.
     */
    protected function startDateIsDisplayed() : bool {
        switch ($this->getSetting('from_to')) {
            case DateTimeRangeConstantsInterface::BOTH:
            case DateTimeRangeConstantsInterface::START_DATE:
                return TRUE;
        }
        return FALSE;
    }
    
    /**
     * Gets whether the end date should be displayed.
     *
     * @return bool
     *   True if the end date should be displayed. False otherwise.
     */
    protected function endDateIsDisplayed() : bool {
        switch ($this->getSetting('from_to')) {
            case DateTimeRangeConstantsInterface::BOTH:
            case DateTimeRangeConstantsInterface::END_DATE:
                return TRUE;
        }
        return FALSE;
    }
    
    /**
     * Creates a render array given start/end dates.
     *
     * @param \Drupal\Core\Datetime\DrupalDateTime $start_date
     *   The start date to be rendered.
     * @param string $separator
     *   The separator string.
     * @param \Drupal\Core\Datetime\DrupalDateTime $end_date
     *   The end date to be rendered.
     *
     * @return array
     *   A renderable array for a single date time range.
     */
    protected function renderStartEnd(DrupalDateTime $start_date, string $separator, DrupalDateTime $end_date) : array {
        $element = [];
        if ($this->startDateIsDisplayed()) {
            $element[DateTimeRangeConstantsInterface::START_DATE] = $this->buildDate($start_date);
        }
        if ($this->startDateIsDisplayed() && $this->endDateIsDisplayed()) {
            $element['separator'] = [
                '#plain_text' => ' ' . $separator . ' ',
            ];
        }
        if ($this->endDateIsDisplayed()) {
            $element[DateTimeRangeConstantsInterface::END_DATE] = $this->buildDate($end_date);
        }
        return $element;
    }
    
    /**
     * Creates a render array with ISO attributes given start/end dates.
     *
     * @param \Drupal\Core\Datetime\DrupalDateTime $start_date
     *   The start date to be rendered.
     * @param string $separator
     *   The separator string.
     * @param \Drupal\Core\Datetime\DrupalDateTime $end_date
     *   The end date to be rendered.
     *
     * @return array
     *   A renderable array for a single date time range.
     */
    protected function renderStartEndWithIsoAttribute(DrupalDateTime $start_date, string $separator, DrupalDateTime $end_date) : array {
        $element = [];
        if ($this->startDateIsDisplayed()) {
            $element[DateTimeRangeConstantsInterface::START_DATE] = $this->buildDateWithIsoAttribute($start_date);
        }
        if ($this->startDateIsDisplayed() && $this->endDateIsDisplayed()) {
            $element['separator'] = [
                '#plain_text' => ' ' . $separator . ' ',
            ];
        }
        if ($this->endDateIsDisplayed()) {
            $element[DateTimeRangeConstantsInterface::END_DATE] = $this->buildDateWithIsoAttribute($end_date);
        }
        return $element;
    }

}