class DataFieldRow

class DataFieldRow extends RowPluginBase {
    
    /**
     * {@inheritdoc}
     */
    protected $usesFields = TRUE;
    
    /**
     * Stores an array of prepared field aliases from options.
     *
     * @var array
     */
    protected $replacementAliases = [];
    
    /**
     * Stores an array of options to determine if the raw field output is used.
     *
     * @var array
     */
    protected $rawOutputOptions = [];
    
    /**
     * {@inheritdoc}
     */
    public function init(ViewExecutable $view, DisplayPluginBase $display, array &$options = NULL) {
        parent::init($view, $display, $options);
        if (!empty($this->options['field_options'])) {
            $options = (array) $this->options['field_options'];
            // Prepare a trimmed version of replacement aliases.
            $aliases = static::extractFromOptionsArray('alias', $options);
            $this->replacementAliases = array_filter(array_map('trim', $aliases));
            // Prepare an array of raw output field options.
            $this->rawOutputOptions = static::extractFromOptionsArray('raw_output', $options);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['field_options'] = [
            'default' => [],
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['field_options'] = [
            '#type' => 'table',
            '#header' => [
                $this->t('Field'),
                $this->t('Alias'),
                $this->t('Raw output'),
            ],
            '#empty' => $this->t('You have no fields. Add some to your view.'),
            '#tree' => TRUE,
        ];
        $options = $this->options['field_options'];
        if ($fields = $this->view->display_handler
            ->getOption('fields')) {
            foreach ($fields as $id => $field) {
                // Don't show the field if it has been excluded.
                if (!empty($field['exclude'])) {
                    continue;
                }
                $form['field_options'][$id]['field'] = [
                    '#markup' => $id,
                ];
                $form['field_options'][$id]['alias'] = [
                    '#title' => $this->t('Alias for @id', [
                        '@id' => $id,
                    ]),
                    '#title_display' => 'invisible',
                    '#type' => 'textfield',
                    '#default_value' => isset($options[$id]['alias']) ? $options[$id]['alias'] : '',
                    '#element_validate' => [
                        [
                            $this,
                            'validateAliasName',
                        ],
                    ],
                ];
                $form['field_options'][$id]['raw_output'] = [
                    '#title' => $this->t('Raw output for @id', [
                        '@id' => $id,
                    ]),
                    '#title_display' => 'invisible',
                    '#type' => 'checkbox',
                    '#default_value' => isset($options[$id]['raw_output']) ? $options[$id]['raw_output'] : '',
                ];
            }
        }
    }
    
    /**
     * Form element validation handler for \Drupal\rest\Plugin\views\row\DataFieldRow::buildOptionsForm().
     */
    public function validateAliasName($element, FormStateInterface $form_state) {
        if (preg_match('@[^A-Za-z0-9_-]+@', $element['#value'])) {
            $form_state->setError($element, $this->t('The machine-readable name must contain only letters, numbers, dashes and underscores.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateOptionsForm(&$form, FormStateInterface $form_state) {
        // Collect an array of aliases to validate.
        $aliases = static::extractFromOptionsArray('alias', $form_state->getValue([
            'row_options',
            'field_options',
        ]));
        // If array filter returns empty, no values have been entered. Unique keys
        // should only be validated if we have some.
        if (($filtered = array_filter($aliases)) && array_unique($filtered) !== $filtered) {
            $form_state->setErrorByName('aliases', $this->t('All field aliases must be unique'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function render($row) {
        $output = [];
        foreach ($this->view->field as $id => $field) {
            // If the raw output option has been set, just get the raw value.
            if (!empty($this->rawOutputOptions[$id])) {
                $value = $field->getValue($row);
            }
            else {
                // Advanced render for token replacement.
                $markup = $field->advancedRender($row);
                // Post render to support uncacheable fields.
                $field->postRender($row, $markup);
                $value = $field->last_render;
            }
            // Omit excluded fields from the rendered output.
            if (empty($field->options['exclude'])) {
                $output[$this->getFieldKeyAlias($id)] = $value;
            }
        }
        return $output;
    }
    
    /**
     * Return an alias for a field ID, as set in the options form.
     *
     * @param string $id
     *   The field id to lookup an alias for.
     *
     * @return string
     *   The matches user entered alias, or the original ID if nothing is found.
     */
    public function getFieldKeyAlias($id) {
        if (isset($this->replacementAliases[$id])) {
            return $this->replacementAliases[$id];
        }
        return $id;
    }
    
    /**
     * Extracts a set of option values from a nested options array.
     *
     * @param string $key
     *   The key to extract from each array item.
     * @param array $options
     *   The options array to return values from.
     *
     * @return array
     *   A regular one dimensional array of values.
     */
    protected static function extractFromOptionsArray($key, $options) {
        return array_map(function ($item) use ($key) {
            return isset($item[$key]) ? $item[$key] : NULL;
        }, $options);
    }

}