class TimestampFormatter

class TimestampFormatter extends FormatterBase {
    
    /**
     * Used to specify a date format that is customizable by user.
     *
     * @var string
     */
    protected const CUSTOM_DATE_FORMAT = 'custom';
    
    /**
     * Constructs a new TimestampFormatter.
     *
     * @param string $plugin_id
     *   The plugin ID for the formatter.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The definition of the field to which the formatter is associated.
     * @param array $settings
     *   The formatter settings.
     * @param string $label
     *   The formatter label display setting.
     * @param string $view_mode
     *   The view mode.
     * @param array $third_party_settings
     *   Third party settings.
     * @param \Drupal\Core\Datetime\DateFormatterInterface $dateFormatter
     *   The date formatter service.
     * @param \Drupal\Core\Entity\EntityStorageInterface $dateFormatStorage
     *   The date format storage.
     * @param \Drupal\Component\Datetime\TimeInterface $time
     *   The time service.
     */
    public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatterInterface $dateFormatter, EntityStorageInterface $dateFormatStorage, TimeInterface $time) {
        parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['view_mode'], $configuration['third_party_settings'], $container->get('date.formatter'), $container->get('entity_type.manager')
            ->getStorage('date_format'), $container->get('datetime.time'));
    }
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        return [
            'date_format' => 'medium',
            'custom_date_format' => '',
            'timezone' => '',
            'tooltip' => [
                'date_format' => 'long',
                'custom_date_format' => '',
            ],
            'time_diff' => [
                'enabled' => FALSE,
                'future_format' => '@interval hence',
                'past_format' => '@interval ago',
                'granularity' => 2,
                'refresh' => 60,
            ],
        ] + parent::defaultSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form = parent::settingsForm($form, $form_state);
        $date_formats = [];
        $requestTime = $this->time
            ->getRequestTime();
        foreach ($this->dateFormatStorage
            ->loadMultiple() as $machine_name => $value) {
            $date_formats[$machine_name] = $this->t('@name format: @date', [
                '@name' => $value->label(),
                '@date' => $this->dateFormatter
                    ->format($requestTime, $machine_name),
            ]);
        }
        $date_formats[static::CUSTOM_DATE_FORMAT] = $this->t('Custom');
        $time_diff = $this->getSetting('time_diff');
        $form['time_diff']['#tree'] = TRUE;
        $form['time_diff']['enabled'] = [
            '#type' => 'checkbox',
            '#title' => $this->t("Display as a time difference (e.g. '6 months ago')"),
            '#default_value' => $time_diff['enabled'],
        ];
        $states = $this->buildStates([
            'time_diff',
            'enabled',
        ], [
            'checked' => TRUE,
        ]);
        $form['time_diff']['future_format'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Future format'),
            '#description' => $this->t("Use the <code>@interval</code> placeholder to represent the formatted time difference interval. E.g. <code>@interval hence</code> will be displayed as <em>2 hours 5 minutes hence</em>."),
            '#default_value' => $time_diff['future_format'],
            '#states' => $states,
        ];
        $form['time_diff']['past_format'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Past format'),
            '#description' => $this->t("Use the <code>@interval</code> placeholder to represent the formatted time difference interval. E.g. <code>@interval ago</code> will be displayed as <em>2 hours 5 minutes ago</em>."),
            '#default_value' => $time_diff['past_format'],
            '#states' => $states,
        ];
        $form['time_diff']['granularity'] = [
            '#type' => 'select',
            '#title' => $this->t('Time units'),
            '#description' => $this->t("How many time units will be used in formatting the time difference. For example, if '1' is selected then the displayed time difference will only contain a single time unit such as '2 years' or '5 minutes' never '2 years 3 months' or '5 minutes 8 seconds'."),
            '#default_value' => $time_diff['granularity'],
            '#options' => array_combine(range(1, 7), range(1, 7)),
            '#states' => $states,
        ];
        $form['time_diff']['refresh'] = [
            '#type' => 'select',
            '#title' => $this->t('Refresh interval'),
            '#description' => $this->t('How often to refresh the displayed time difference. The time difference is refreshed on client-side, by JavaScript, without reloading the page.'),
            '#default_value' => $time_diff['refresh'],
            '#options' => $this->getRefreshIntervals(),
            '#states' => $states,
        ];
        $form['time_diff']['description'] = [
            '#type' => 'item',
            '#title' => $this->t('Fallback configuration'),
            '#description' => $this->t('The configuration below is used as a fallback when JavaScript is not available on the page.'),
            '#states' => $states,
        ];
        $form['date_format'] = [
            '#type' => 'select',
            '#title' => $this->t('Date format'),
            '#options' => $date_formats,
            '#default_value' => $this->getSetting('date_format'),
        ];
        $form['custom_date_format'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Custom date format'),
            '#description' => $this->t('See <a href="https://www.php.net/manual/datetime.format.php#refsect1-datetime.format-parameters" target="_blank">the documentation for PHP date formats</a>.'),
            '#default_value' => $this->getSetting('custom_date_format'),
            '#states' => $this->buildStates([
                'date_format',
            ], [
                'value' => static::CUSTOM_DATE_FORMAT,
            ]),
        ];
        $form['timezone'] = [
            '#type' => 'select',
            '#title' => $this->t('Time zone'),
            '#options' => [
                '' => $this->t('- Default site/user time zone -'),
            ] + TimeZoneFormHelper::getOptionsListByRegion(),
            '#default_value' => $this->getSetting('timezone'),
        ];
        $tooltip = $this->getSetting('tooltip');
        $form['tooltip']['#tree'] = TRUE;
        $form['tooltip']['date_format'] = [
            '#type' => 'select',
            '#title' => $this->t('Tooltip date format'),
            '#description' => $this->t('Select the date format to be used for the title and displayed on mouse hover.'),
            '#options' => $date_formats,
            '#default_value' => $tooltip['date_format'],
            '#empty_option' => $this->t('- No tooltip -'),
        ];
        $form['tooltip']['custom_date_format'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Tooltip custom date format'),
            '#description' => $this->t('See <a href="http://php.net/manual/function.date.php" target="_blank">the documentation for PHP date formats</a>.'),
            '#default_value' => $tooltip['custom_date_format'],
            '#states' => $this->buildStates([
                'tooltip',
                'date_format',
            ], [
                'value' => static::CUSTOM_DATE_FORMAT,
            ]),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = parent::settingsSummary();
        $time_diff = $this->getSetting('time_diff');
        $date_format = $this->getSetting('date_format');
        $date_format = $date_format === static::CUSTOM_DATE_FORMAT ? $this->getSetting('custom_date_format') : $date_format;
        if ($time_diff['enabled']) {
            $summary[] = $this->t('Displayed as a time difference');
            $options = [
                'granularity' => $time_diff['granularity'],
            ];
            $timestamp = strtotime('1 year 1 month 1 week 1 day 1 hour 1 minute');
            $interval = $this->dateFormatter
                ->formatTimeDiffUntil($timestamp, $options);
            $display = new FormattableMarkup($time_diff['future_format'], [
                '@interval' => $interval,
            ]);
            $summary[] = $this->t('Future date: %display', [
                '%display' => $display,
            ]);
            $timestamp = strtotime('-1 year -1 month -1 week -1 day -1 hour -1 minute');
            $interval = $this->dateFormatter
                ->formatTimeDiffSince($timestamp, $options);
            $display = new FormattableMarkup($time_diff['past_format'], [
                '@interval' => $interval,
            ]);
            $summary[] = $this->t('Past date: %display', [
                '%display' => $display,
            ]);
            if ($time_diff['refresh']) {
                $refresh_intervals = $this->getRefreshIntervals();
                $summary[] = $this->t('Refresh every @interval', [
                    '@interval' => $refresh_intervals[$time_diff['refresh']],
                ]);
            }
            $summary[] = $this->t('Disabled JavaScript format: @date_format', [
                '@date_format' => $date_format,
            ]);
        }
        else {
            $summary[] = $this->t('Date format: @date_format', [
                '@date_format' => $date_format,
            ]);
        }
        $tooltip = $this->getSetting('tooltip');
        if (!empty($tooltip['date_format'])) {
            $tooltip_date_format = $tooltip['date_format'];
            $tooltip_date_format = $tooltip_date_format === static::CUSTOM_DATE_FORMAT ? $tooltip['custom_date_format'] : $tooltip_date_format;
            $summary[] = $this->t('Tooltip date format: @date_format', [
                '@date_format' => $tooltip_date_format,
            ]);
        }
        if ($timezone = $this->getSetting('timezone')) {
            $summary[] = $this->t('Time zone: @timezone', [
                '@timezone' => $timezone,
            ]);
        }
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $elements = [];
        $date_format = $this->getSetting('date_format');
        $custom_date_format = $this->getSetting('custom_date_format');
        $timezone = $this->getSetting('timezone') ?: NULL;
        $tooltip = $this->getSetting('tooltip');
        $time_diff = $this->getSetting('time_diff');
        foreach ($items as $delta => $item) {
            $elements[$delta] = [
                '#theme' => 'time',
                '#attributes' => [
                    // The representation of the date/time as RFC3339 "date-time".
                    // @see https://www.ietf.org/rfc/rfc3339.txt
'datetime' => $this->dateFormatter
                        ->format($item->value, static::CUSTOM_DATE_FORMAT, \DateTimeInterface::RFC3339, $timezone),
                ],
                '#text' => $this->dateFormatter
                    ->format($item->value, $date_format, $custom_date_format, $timezone, $langcode),
                '#cache' => [
                    'contexts' => [
                        'timezone',
                    ],
                ],
            ];
            if (!empty($tooltip['date_format'])) {
                // Show a tooltip on mouse hover as title. When the time is displayed as
                // time difference, it helps the user to read the exact date.
                $elements[$delta]['#attributes']['title'] = $this->dateFormatter
                    ->format($item->value, $tooltip['date_format'], $tooltip['custom_date_format'], $timezone, $langcode);
            }
            if ($time_diff['enabled']) {
                $elements[$delta]['#attached']['library'][] = 'core/drupal.time-diff';
                $settings = [
                    'format' => [
                        'future' => $time_diff['future_format'],
                        'past' => $time_diff['past_format'],
                    ],
                    'granularity' => $time_diff['granularity'],
                    'refresh' => $time_diff['refresh'],
                ];
                $elements[$delta]['#attributes']['data-drupal-time-diff'] = Json::encode($settings);
            }
        }
        return $elements;
    }
    
    /**
     * Builds the #states key for form elements.
     *
     * @param string[] $path
     *   The remote element path.
     * @param array $conditions
     *   The conditions to be checked.
     *
     * @return array[]
     *   The #states array.
     */
    protected function buildStates(array $path, array $conditions) : array {
        $path = '[' . implode('][', $path) . ']';
        return [
            'visible' => [
                [
                    ":input[name='fields[{$this->fieldDefinition->getName()}][settings_edit_form][settings]{$path}']" => $conditions,
                ],
            ],
        ];
    }
    
    /**
     * Returns the refresh interval options for the time difference display.
     *
     * @return \Drupal\Component\Render\MarkupInterface[]
     *   A list of refresh time intervals.
     */
    protected function getRefreshIntervals() : array {
        return [
            0 => $this->t('No refresh'),
            1 => $this->t('1 second'),
            15 => $this->t('@count seconds', [
                '@count' => 15,
            ]),
            60 => $this->t('1 minute'),
            300 => $this->t('@count minutes', [
                '@count' => 5,
            ]),
            600 => $this->t('@count minutes', [
                '@count' => 10,
            ]),
        ];
    }

}