class QueryParameter

class QueryParameter extends ArgumentDefaultPluginBase implements CacheableDependencyInterface {
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['query_param'] = [
            'default' => '',
        ];
        $options['fallback'] = [
            'default' => '',
        ];
        $options['multiple'] = [
            'default' => 'and',
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['query_param'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Query parameter'),
            '#description' => $this->t('The query parameter to use.'),
            '#default_value' => $this->options['query_param'],
        ];
        $form['fallback'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Fallback value'),
            '#description' => $this->t('The fallback value to use when the above query parameter is not present.'),
            '#default_value' => $this->options['fallback'],
        ];
        $form['multiple'] = [
            '#type' => 'radios',
            '#title' => $this->t('Multiple values'),
            '#description' => $this->t('Conjunction to use when handling multiple values. E.g. "?value[0]=a&value[1]=b".'),
            '#default_value' => $this->options['multiple'],
            '#options' => [
                'and' => $this->t('AND'),
                'or' => $this->t('OR'),
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getArgument() {
        $current_request = $this->view
            ->getRequest();
        // Convert a[b][c][d] into ['a', 'b', 'c', 'd'].
        $path = array_filter(preg_split('#(\\[|\\]\\[|\\])#', $this->options['query_param']));
        if ($current_request->query
            ->has($path[0])) {
            $query = $current_request->query
                ->all();
            $param = NestedArray::getValue($query, $path);
            if (is_array($param)) {
                $conjunction = $this->options['multiple'] == 'and' ? ',' : '+';
                $param = implode($conjunction, $param);
            }
            return $param;
        }
        else {
            // Otherwise, use the fixed fallback value.
            return $this->options['fallback'];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheMaxAge() {
        return Cache::PERMANENT;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        return [
            'url',
        ];
    }

}