class SortPluginBase

abstract class SortPluginBase extends HandlerBase implements CacheableDependencyInterface {
    
    /**
     * Determine if a sort can be exposed.
     */
    public function canExpose() {
        return TRUE;
    }
    
    /**
     * Called to add the sort to a query.
     */
    public function query() {
        $this->ensureMyTable();
        // Add the field.
        $this->query
            ->addOrderBy($this->tableAlias, $this->realField, $this->options['order']);
    }
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['order'] = [
            'default' => 'ASC',
        ];
        $options['exposed'] = [
            'default' => FALSE,
        ];
        $options['expose'] = [
            'contains' => [
                'label' => [
                    'default' => '',
                ],
            ],
        ];
        return $options;
    }
    
    /**
     * Display whether or not the sort order is ascending or descending
     */
    public function adminSummary() {
        if (!empty($this->options['exposed'])) {
            return $this->t('Exposed');
        }
        switch ($this->options['order']) {
            case 'ASC':
            case 'asc':
            default:
                return $this->t('asc');
            case 'DESC':
            case 'desc':
                return $this->t('desc');
        }
    }
    
    /**
     * Basic options for all sort criteria
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        if ($this->canExpose()) {
            $this->showExposeButton($form, $form_state);
        }
        $form['op_val_start'] = [
            '#value' => '<div class="clearfix">',
        ];
        $this->showSortForm($form, $form_state);
        $form['op_val_end'] = [
            '#value' => '</div>',
        ];
        if ($this->canExpose()) {
            $this->showExposeForm($form, $form_state);
        }
    }
    
    /**
     * Shortcut to display the expose/hide button.
     */
    public function showExposeButton(&$form, FormStateInterface $form_state) {
        $form['expose_button'] = [
            '#prefix' => '<div class="views-expose clearfix">',
            '#suffix' => '</div>',
            // Should always come first
'#weight' => -1000,
        ];
        // Add a checkbox for JS users, which will have behavior attached to it
        // so it can replace the button.
        $form['expose_button']['checkbox'] = [
            '#theme_wrappers' => [
                'container',
            ],
            '#attributes' => [
                'class' => [
                    'js-only',
                ],
            ],
        ];
        $form['expose_button']['checkbox']['checkbox'] = [
            '#title' => $this->t('Expose this sort to visitors, to allow them to change it'),
            '#type' => 'checkbox',
        ];
        // Then add the button itself.
        if (empty($this->options['exposed'])) {
            $form['expose_button']['markup'] = [
                '#markup' => '<div class="description exposed-description" style="float: left; margin-right:10px">' . $this->t('This sort is not exposed. Expose it to allow the users to change it.') . '</div>',
            ];
            $form['expose_button']['button'] = [
                '#limit_validation_errors' => [],
                '#type' => 'submit',
                '#value' => $this->t('Expose sort'),
                '#submit' => [
                    [
                        $this,
                        'displayExposedForm',
                    ],
                ],
            ];
            $form['expose_button']['checkbox']['checkbox']['#default_value'] = 0;
        }
        else {
            $form['expose_button']['markup'] = [
                '#markup' => '<div class="description exposed-description">' . $this->t('This sort is exposed. If you hide it, users will not be able to change it.') . '</div>',
            ];
            $form['expose_button']['button'] = [
                '#limit_validation_errors' => [],
                '#type' => 'submit',
                '#value' => $this->t('Hide sort'),
                '#submit' => [
                    [
                        $this,
                        'displayExposedForm',
                    ],
                ],
            ];
            $form['expose_button']['checkbox']['checkbox']['#default_value'] = 1;
        }
    }
    
    /**
     * Simple validate handler
     */
    public function validateOptionsForm(&$form, FormStateInterface $form_state) {
        $this->sortValidate($form, $form_state);
        if (!empty($this->options['exposed'])) {
            $this->validateExposeForm($form, $form_state);
        }
    }
    
    /**
     * Simple submit handler
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        // Do not store this values.
        $form_state->unsetValue('expose_button');
        $this->sortSubmit($form, $form_state);
        if (!empty($this->options['exposed'])) {
            $this->submitExposeForm($form, $form_state);
        }
    }
    
    /**
     * Shortcut to display the value form.
     */
    protected function showSortForm(&$form, FormStateInterface $form_state) {
        $options = $this->sortOptions();
        if (!empty($options)) {
            $form['order'] = [
                '#title' => $this->t('Order', [], [
                    'context' => 'Sort order',
                ]),
                '#type' => 'radios',
                '#options' => $options,
                '#default_value' => $this->options['order'],
            ];
        }
    }
    protected function sortValidate(&$form, FormStateInterface $form_state) {
    }
    public function sortSubmit(&$form, FormStateInterface $form_state) {
    }
    
    /**
     * Provide a list of options for the default sort form.
     * Should be overridden by classes that don't override sort_form
     */
    protected function sortOptions() {
        return [
            'ASC' => $this->t('Sort ascending'),
            'DESC' => $this->t('Sort descending'),
        ];
    }
    public function buildExposeForm(&$form, FormStateInterface $form_state) {
        // #flatten will move everything from $form['expose'][$key] to $form[$key]
        // prior to rendering. That's why the preRender for it needs to run first,
        // so that when the next preRender (the one for fieldsets) runs, it gets
        // the flattened data.
        array_unshift($form['#pre_render'], [
            get_class($this),
            'preRenderFlattenData',
        ]);
        $form['expose']['#flatten'] = TRUE;
        $form['expose']['label'] = [
            '#type' => 'textfield',
            '#default_value' => $this->options['expose']['label'],
            '#title' => $this->t('Label'),
            '#required' => TRUE,
            '#size' => 40,
            '#weight' => -1,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function trustedCallbacks() {
        $callbacks = parent::trustedCallbacks();
        $callbacks[] = 'preRenderFlattenData';
        return $callbacks;
    }
    
    /**
     * Provide default options for exposed sorts.
     */
    public function defaultExposeOptions() {
        $this->options['expose'] = [
            'label' => $this->definition['title'],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheMaxAge() {
        // The result of a sort does not depend on outside information, so by
        // default it is cacheable.
        return Cache::PERMANENT;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        $cache_contexts = [];
        // Exposed sorts use GET parameters, so it depends on the current URL.
        if ($this->isExposed()) {
            $cache_contexts[] = 'url.query_args:sort_by';
        }
        return $cache_contexts;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheTags() {
        return [];
    }

}