class OpmlFields

class OpmlFields extends RowPluginBase {
    
    /**
     * Does the row plugin support to add fields to its output.
     *
     * @var bool
     */
    protected $usesFields = TRUE;
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['text_field'] = [
            'default' => '',
        ];
        $options['created_field'] = [
            'default' => '',
        ];
        $options['type_field'] = [
            'default' => '',
        ];
        $options['description_field'] = [
            'default' => '',
        ];
        $options['html_url_field'] = [
            'default' => '',
        ];
        $options['language_field'] = [
            'default' => '',
        ];
        $options['xml_url_field'] = [
            'default' => '',
        ];
        $options['url_field'] = [
            'default' => '',
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $initial_labels = [
            '' => $this->t('- None -'),
        ];
        $view_fields_labels = $this->displayHandler
            ->getFieldLabels();
        $view_fields_labels = array_merge($initial_labels, $view_fields_labels);
        $types = [
            'rss' => $this->t('RSS'),
            'link' => $this->t('Link'),
            'include' => $this->t('Include'),
        ];
        $types = array_merge($initial_labels, $types);
        $form['type_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Type attribute'),
            '#description' => $this->t('The type of this row.'),
            '#options' => $types,
            '#default_value' => $this->options['type_field'],
        ];
        $form['text_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Text attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML text attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['text_field'],
            '#required' => TRUE,
        ];
        $form['created_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Created attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML created attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['created_field'],
        ];
        $form['description_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Description attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML description attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['description_field'],
            '#states' => [
                'visible' => [
                    ':input[name="row_options[type_field]"]' => [
                        'value' => 'rss',
                    ],
                ],
            ],
        ];
        $form['html_url_field'] = [
            '#type' => 'select',
            '#title' => $this->t('HTML URL attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML htmlUrl attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['html_url_field'],
            '#states' => [
                'visible' => [
                    ':input[name="row_options[type_field]"]' => [
                        'value' => 'rss',
                    ],
                ],
            ],
        ];
        $form['language_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Language attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML language attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['language_field'],
            '#states' => [
                'visible' => [
                    ':input[name="row_options[type_field]"]' => [
                        'value' => 'rss',
                    ],
                ],
            ],
        ];
        $form['xml_url_field'] = [
            '#type' => 'select',
            '#title' => $this->t('XML URL attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML XML URL attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['xml_url_field'],
            '#states' => [
                'visible' => [
                    ':input[name="row_options[type_field]"]' => [
                        'value' => 'rss',
                    ],
                ],
            ],
        ];
        $form['url_field'] = [
            '#type' => 'select',
            '#title' => $this->t('URL attribute'),
            '#description' => $this->t('The field that is going to be used as the OPML URL attribute for each row.'),
            '#options' => $view_fields_labels,
            '#default_value' => $this->options['url_field'],
            '#states' => [
                'visible' => [
                    ':input[name="row_options[type_field]"]' => [
                        [
                            'value' => 'link',
                        ],
                        [
                            'value' => 'include',
                        ],
                    ],
                ],
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate() {
        $errors = parent::validate();
        if (empty($this->options['text_field'])) {
            $errors[] = $this->t('Row style plugin requires specifying which views field to use for OPML text attribute.');
        }
        if (!empty($this->options['type_field'])) {
            if ($this->options['type_field'] == 'rss') {
                if (empty($this->options['xml_url_field'])) {
                    $errors[] = $this->t('Row style plugin requires specifying which views field to use for XML URL attribute.');
                }
            }
            elseif (in_array($this->options['type_field'], [
                'link',
                'include',
            ])) {
                if (empty($this->options['url_field'])) {
                    $errors[] = $this->t('Row style plugin requires specifying which views field to use for URL attribute.');
                }
            }
        }
        return $errors;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render($row) {
        // Create the OPML item array.
        $item = [];
        $row_index = $this->view->row_index;
        $item['text'] = $this->getField($row_index, $this->options['text_field']);
        $item['created'] = $this->getField($row_index, $this->options['created_field']);
        if ($this->options['type_field']) {
            $item['type'] = $this->options['type_field'];
            if ($item['type'] == 'rss') {
                $item['description'] = $this->getField($row_index, $this->options['description_field']);
                $item['language'] = $this->getField($row_index, $this->options['language_field']);
                $item['xmlUrl'] = $this->getField($row_index, $this->options['xml_url_field']);
                $item['htmlUrl'] = $this->getField($row_index, $this->options['html_url_field']);
            }
            else {
                $item['url'] = $this->getField($row_index, $this->options['url_field']);
            }
        }
        // Remove empty attributes.
        $item = array_filter($item);
        $build = [
            '#theme' => $this->themeFunctions(),
            '#view' => $this->view,
            '#options' => $this->options,
            '#row' => $item,
            '#field_alias' => isset($this->field_alias) ? $this->field_alias : '',
        ];
        return $build;
    }
    
    /**
     * Retrieves a views field value from the style plugin.
     *
     * @param $index
     *   The index count of the row as expected by views_plugin_style::getField().
     * @param $field_id
     *   The ID assigned to the required field in the display.
     *
     * @return string
     *   The rendered field value.
     */
    public function getField($index, $field_id) {
        if (empty($this->view->style_plugin) || !is_object($this->view->style_plugin) || empty($field_id)) {
            return '';
        }
        return (string) $this->view->style_plugin
            ->getField($index, $field_id);
    }

}