class CommentAccessControlHandler

class CommentAccessControlHandler extends EntityAccessControlHandler {
    
    /**
     * {@inheritdoc}
     */
    protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
        
        /** @var \Drupal\comment\CommentInterface|\Drupal\user\EntityOwnerInterface $entity */
        $comment_admin = $account->hasPermission('administer comments');
        if ($operation == 'approve') {
            return AccessResult::allowedIf($comment_admin && !$entity->isPublished())
                ->cachePerPermissions()
                ->addCacheableDependency($entity);
        }
        if ($comment_admin) {
            $access = AccessResult::allowed()->cachePerPermissions();
            return $operation != 'view' ? $access : $access->andIf($entity->getCommentedEntity()
                ->access($operation, $account, TRUE));
        }
        switch ($operation) {
            case 'view':
                $access_result = AccessResult::allowedIf($account->hasPermission('access comments') && $entity->isPublished())
                    ->cachePerPermissions()
                    ->addCacheableDependency($entity)
                    ->andIf($entity->getCommentedEntity()
                    ->access($operation, $account, TRUE));
                if (!$access_result->isAllowed()) {
                    $access_result->setReason("The 'access comments' permission is required and the comment must be published.");
                }
                return $access_result;
            case 'update':
                $access_result = AccessResult::allowedIf($account->id() && $account->id() == $entity->getOwnerId() && $entity->isPublished() && $account->hasPermission('edit own comments'))
                    ->cachePerPermissions()
                    ->cachePerUser()
                    ->addCacheableDependency($entity);
                if (!$access_result->isAllowed()) {
                    $access_result->setReason("The 'edit own comments' permission is required, the user must be the comment author, and the comment must be published.");
                }
                return $access_result;
            default:
                // No opinion.
                return AccessResult::neutral()->cachePerPermissions();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
        return AccessResult::allowedIfHasPermission($account, 'post comments');
    }
    
    /**
     * {@inheritdoc}
     */
    protected function checkFieldAccess($operation, FieldDefinitionInterface $field_definition, AccountInterface $account, FieldItemListInterface $items = NULL) {
        if ($operation == 'edit') {
            // Only users with the "administer comments" permission can edit
            // administrative fields.
            $administrative_fields = [
                'uid',
                'status',
                'created',
                'date',
            ];
            if (in_array($field_definition->getName(), $administrative_fields, TRUE)) {
                return AccessResult::allowedIfHasPermission($account, 'administer comments');
            }
            // No user can change read-only fields.
            $read_only_fields = [
                'hostname',
                'changed',
                'cid',
                'thread',
            ];
            // These fields can be edited during comment creation.
            $create_only_fields = [
                'comment_type',
                'uuid',
                'entity_id',
                'entity_type',
                'field_name',
                'pid',
            ];
            if ($items && ($entity = $items->getEntity()) && $entity->isNew() && in_array($field_definition->getName(), $create_only_fields, TRUE)) {
                // We are creating a new comment, user can edit create only fields.
                return AccessResult::allowedIfHasPermission($account, 'post comments')->addCacheableDependency($entity);
            }
            // We are editing an existing comment - create only fields are now read
            // only.
            $read_only_fields = array_merge($read_only_fields, $create_only_fields);
            if (in_array($field_definition->getName(), $read_only_fields, TRUE)) {
                return AccessResult::forbidden();
            }
            // If the field is configured to accept anonymous contact details - admins
            // can edit name, homepage and mail. Anonymous users can also fill in the
            // fields on comment creation.
            if (in_array($field_definition->getName(), [
                'name',
                'mail',
                'homepage',
            ], TRUE)) {
                if (!$items) {
                    // We cannot make a decision about access to edit these fields if we
                    // don't have any items and therefore cannot determine the Comment
                    // entity. In this case we err on the side of caution and prevent edit
                    // access.
                    return AccessResult::forbidden();
                }
                $is_name = $field_definition->getName() === 'name';
                
                /** @var \Drupal\comment\CommentInterface $entity */
                $entity = $items->getEntity();
                $commented_entity = $entity->getCommentedEntity();
                $anonymous_contact = $commented_entity->get($entity->getFieldName())
                    ->getFieldDefinition()
                    ->getSetting('anonymous');
                $admin_access = AccessResult::allowedIfHasPermission($account, 'administer comments');
                $anonymous_access = AccessResult::allowedIf($entity->isNew() && $account->isAnonymous() && ($anonymous_contact != CommentInterface::ANONYMOUS_MAYNOT_CONTACT || $is_name) && $account->hasPermission('post comments'))
                    ->cachePerPermissions()
                    ->addCacheableDependency($entity)
                    ->addCacheableDependency($field_definition->getConfig($commented_entity->bundle()))
                    ->addCacheableDependency($commented_entity);
                return $admin_access->orIf($anonymous_access);
            }
        }
        if ($operation == 'view') {
            // Nobody has access to the hostname.
            if ($field_definition->getName() == 'hostname') {
                return AccessResult::forbidden();
            }
            // The mail field is hidden from non-admins.
            if ($field_definition->getName() == 'mail') {
                return AccessResult::allowedIfHasPermission($account, 'administer comments');
            }
        }
        return parent::checkFieldAccess($operation, $field_definition, $account, $items);
    }

}