class ViewsQueryAlter

class ViewsQueryAlter implements ContainerInjectionInterface {
    
    /**
     * The entity type manager service.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $entityFieldManager;
    
    /**
     * The workspace manager service.
     *
     * @var \Drupal\workspaces\WorkspaceManagerInterface
     */
    protected $workspaceManager;
    
    /**
     * The views data.
     *
     * @var \Drupal\views\ViewsData
     */
    protected $viewsData;
    
    /**
     * A plugin manager which handles instances of views join plugins.
     *
     * @var \Drupal\views\Plugin\ViewsHandlerManager
     */
    protected $viewsJoinPluginManager;
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Constructs a new ViewsQueryAlter instance.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager service.
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
     *   The entity field manager.
     * @param \Drupal\workspaces\WorkspaceManagerInterface $workspace_manager
     *   The workspace manager service.
     * @param \Drupal\views\ViewsData $views_data
     *   The views data.
     * @param \Drupal\views\Plugin\ViewsHandlerManager $views_join_plugin_manager
     *   The views join plugin manager.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $entity_field_manager, WorkspaceManagerInterface $workspace_manager, ViewsData $views_data, ViewsHandlerManager $views_join_plugin_manager, LanguageManagerInterface $language_manager) {
        $this->entityTypeManager = $entity_type_manager;
        $this->entityFieldManager = $entity_field_manager;
        $this->workspaceManager = $workspace_manager;
        $this->viewsData = $views_data;
        $this->viewsJoinPluginManager = $views_join_plugin_manager;
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('entity_field.manager'), $container->get('workspaces.manager'), $container->get('views.views_data'), $container->get('plugin.manager.views.join'), $container->get('language_manager'));
    }
    
    /**
     * Implements a hook bridge for hook_views_query_alter().
     *
     * @see hook_views_query_alter()
     */
    public function alterQuery(ViewExecutable $view, QueryPluginBase $query) {
        // Don't alter any views queries if we're not in a workspace context.
        if (!$this->workspaceManager
            ->hasActiveWorkspace()) {
            return;
        }
        // Don't alter any non-sql views queries.
        if (!$query instanceof Sql) {
            return;
        }
        // Find out what entity types are represented in this query.
        $entity_type_ids = [];
        foreach ($query->relationships as $info) {
            $table_data = $this->viewsData
                ->get($info['base']);
            if (empty($table_data['table']['entity type'])) {
                continue;
            }
            $entity_type_id = $table_data['table']['entity type'];
            // This construct ensures each entity type exists only once.
            $entity_type_ids[$entity_type_id] = $entity_type_id;
        }
        $entity_type_definitions = $this->entityTypeManager
            ->getDefinitions();
        foreach ($entity_type_ids as $entity_type_id) {
            if ($this->workspaceManager
                ->isEntityTypeSupported($entity_type_definitions[$entity_type_id])) {
                $this->alterQueryForEntityType($query, $entity_type_definitions[$entity_type_id]);
            }
        }
    }
    
    /**
     * Alters the entity type tables for a Views query.
     *
     * This should only be called after determining that this entity type is
     * involved in the query, and that a non-default workspace is in use.
     *
     * @param \Drupal\views\Plugin\views\query\Sql $query
     *   The query plugin object for the query.
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type definition.
     */
    protected function alterQueryForEntityType(Sql $query, EntityTypeInterface $entity_type) {
        
        /** @var \Drupal\Core\Entity\Sql\DefaultTableMapping $table_mapping */
        $table_mapping = $this->entityTypeManager
            ->getStorage($entity_type->id())
            ->getTableMapping();
        $field_storage_definitions = $this->entityFieldManager
            ->getFieldStorageDefinitions($entity_type->id());
        $dedicated_field_storage_definitions = array_filter($field_storage_definitions, function ($definition) use ($table_mapping) {
            return $table_mapping->requiresDedicatedTableStorage($definition);
        });
        $dedicated_field_data_tables = array_map(function ($definition) use ($table_mapping) {
            return $table_mapping->getDedicatedDataTableName($definition);
        }, $dedicated_field_storage_definitions);
        $move_workspace_tables = [];
        $table_queue =& $query->getTableQueue();
        foreach ($table_queue as $alias => &$table_info) {
            // If we reach the workspace_association array item before any candidates,
            // then we do not need to move it.
            if ($table_info['table'] == 'workspace_association') {
                break;
            }
            // Any dedicated field table is a candidate.
            if ($field_name = array_search($table_info['table'], $dedicated_field_data_tables, TRUE)) {
                $relationship = $table_info['relationship'];
                // There can be reverse relationships used. If so, Workspaces can't do
                // anything with them. Detect this and skip.
                if ($table_info['join']->field != 'entity_id') {
                    continue;
                }
                // Get the dedicated revision table name.
                $new_table_name = $table_mapping->getDedicatedRevisionTableName($field_storage_definitions[$field_name]);
                // Now add the workspace_association table.
                $workspace_association_table = $this->ensureWorkspaceAssociationTable($entity_type->id(), $query, $relationship);
                // Update the join to use our COALESCE.
                $revision_field = $entity_type->getKey('revision');
                $table_info['join']->leftFormula = "COALESCE({$workspace_association_table}.target_entity_revision_id, {$relationship}.{$revision_field})";
                // Update the join and the table info to our new table name, and to join
                // on the revision key.
                $table_info['table'] = $new_table_name;
                $table_info['join']->table = $new_table_name;
                $table_info['join']->field = 'revision_id';
                // Finally, if we added the workspace_association table we have to move
                // it in the table queue so that it comes before this field.
                if (empty($move_workspace_tables[$workspace_association_table])) {
                    $move_workspace_tables[$workspace_association_table] = $alias;
                }
            }
        }
        // JOINs must be in order. i.e, any tables you mention in the ON clause of a
        // JOIN must appear prior to that JOIN. Since we're modifying a JOIN in
        // place, and adding a new table, we must ensure that the new table appears
        // prior to this one. So we recorded at what index we saw that table, and
        // then use array_splice() to move the workspace_association table join to
        // the correct position.
        foreach ($move_workspace_tables as $workspace_association_table => $alias) {
            $this->moveEntityTable($query, $workspace_association_table, $alias);
        }
        $base_entity_table = $entity_type->isTranslatable() ? $entity_type->getDataTable() : $entity_type->getBaseTable();
        $base_fields = array_diff($table_mapping->getFieldNames($entity_type->getBaseTable()), [
            $entity_type->getKey('langcode'),
        ]);
        $revisionable_fields = array_diff($table_mapping->getFieldNames($entity_type->getRevisionDataTable()), $base_fields);
        // Go through and look to see if we have to modify fields and filters.
        foreach ($query->fields as &$field_info) {
            // Some fields don't actually have tables, meaning they're formulae and
            // whatnot. At this time we are going to ignore those.
            if (empty($field_info['table'])) {
                continue;
            }
            // Dereference the alias into the actual table.
            $table = $table_queue[$field_info['table']]['table'];
            if ($table == $base_entity_table && in_array($field_info['field'], $revisionable_fields)) {
                $relationship = $table_queue[$field_info['table']]['alias'];
                $alias = $this->ensureRevisionTable($entity_type, $query, $relationship);
                if ($alias) {
                    // Change the base table to use the revision table instead.
                    $field_info['table'] = $alias;
                }
            }
        }
        $relationships = [];
        // Build a list of all relationships that might be for our table.
        foreach ($query->relationships as $relationship => $info) {
            if ($info['base'] == $base_entity_table) {
                $relationships[] = $relationship;
            }
        }
        // Now we have to go through our where clauses and modify any of our fields.
        foreach ($query->where as &$clauses) {
            foreach ($clauses['conditions'] as &$where_info) {
                // Build a matrix of our possible relationships against fields we need
                // to switch.
                foreach ($relationships as $relationship) {
                    foreach ($revisionable_fields as $field) {
                        if (is_string($where_info['field']) && $where_info['field'] == "{$relationship}.{$field}") {
                            $alias = $this->ensureRevisionTable($entity_type, $query, $relationship);
                            if ($alias) {
                                // Change the base table to use the revision table instead.
                                $where_info['field'] = "{$alias}.{$field}";
                            }
                        }
                    }
                }
            }
        }
        // @todo Handle $query->orderby, $query->groupby, $query->having and
        //   $query->count_field in https://www.drupal.org/node/2968165.
    }
    
    /**
     * Adds the 'workspace_association' table to a views query.
     *
     * @param string $entity_type_id
     *   The ID of the entity type to join.
     * @param \Drupal\views\Plugin\views\query\Sql $query
     *   The query plugin object for the query.
     * @param string $relationship
     *   The primary table alias this table is related to.
     *
     * @return string
     *   The alias of the 'workspace_association' table.
     */
    protected function ensureWorkspaceAssociationTable($entity_type_id, Sql $query, $relationship) {
        if (isset($query->tables[$relationship]['workspace_association'])) {
            return $query->tables[$relationship]['workspace_association']['alias'];
        }
        $table_data = $this->viewsData
            ->get($query->relationships[$relationship]['base']);
        // Construct the join.
        $definition = [
            'table' => 'workspace_association',
            'field' => 'target_entity_id',
            'left_table' => $relationship,
            'left_field' => $table_data['table']['base']['field'],
            'extra' => [
                [
                    'field' => 'target_entity_type_id',
                    'value' => $entity_type_id,
                ],
                [
                    'field' => 'workspace',
                    'value' => $this->workspaceManager
                        ->getActiveWorkspace()
                        ->id(),
                ],
            ],
            'type' => 'LEFT',
        ];
        $join = $this->viewsJoinPluginManager
            ->createInstance('standard', $definition);
        $join->adjusted = TRUE;
        return $query->queueTable('workspace_association', $relationship, $join);
    }
    
    /**
     * Adds the revision table of an entity type to a query object.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type definition.
     * @param \Drupal\views\Plugin\views\query\Sql $query
     *   The query plugin object for the query.
     * @param string $relationship
     *   The name of the relationship.
     *
     * @return string
     *   The alias of the relationship.
     */
    protected function ensureRevisionTable(EntityTypeInterface $entity_type, Sql $query, $relationship) {
        // Get the alias for the 'workspace_association' table we chain off of in
        // the COALESCE.
        $workspace_association_table = $this->ensureWorkspaceAssociationTable($entity_type->id(), $query, $relationship);
        // Get the name of the revision table and revision key.
        $base_revision_table = $entity_type->isTranslatable() ? $entity_type->getRevisionDataTable() : $entity_type->getRevisionTable();
        $revision_field = $entity_type->getKey('revision');
        // If the table was already added and has a join against the same field on
        // the revision table, reuse that rather than adding a new join.
        if (isset($query->tables[$relationship][$base_revision_table])) {
            $table_queue =& $query->getTableQueue();
            $alias = $query->tables[$relationship][$base_revision_table]['alias'];
            if (isset($table_queue[$alias]['join']->field) && $table_queue[$alias]['join']->field == $revision_field) {
                // If this table previously existed, but was not added by us, we need
                // to modify the join and make sure that 'workspace_association' comes
                // first.
                if (empty($table_queue[$alias]['join']->workspace_adjusted)) {
                    $table_queue[$alias]['join'] = $this->getRevisionTableJoin($relationship, $base_revision_table, $revision_field, $workspace_association_table, $entity_type);
                    // We also have to ensure that our 'workspace_association' comes before
                    // this.
                    $this->moveEntityTable($query, $workspace_association_table, $alias);
                }
                return $alias;
            }
        }
        // Construct a new join.
        $join = $this->getRevisionTableJoin($relationship, $base_revision_table, $revision_field, $workspace_association_table, $entity_type);
        return $query->queueTable($base_revision_table, $relationship, $join);
    }
    
    /**
     * Fetches a join for a revision table using the workspace_association table.
     *
     * @param string $relationship
     *   The relationship to use in the view.
     * @param string $table
     *   The table name.
     * @param string $field
     *   The field to join on.
     * @param string $workspace_association_table
     *   The alias of the 'workspace_association' table joined to the main entity
     *   table.
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type that is being queried.
     *
     * @return \Drupal\views\Plugin\views\join\JoinPluginInterface
     *   An adjusted views join object to add to the query.
     *
     * @throws \Drupal\Component\Plugin\Exception\PluginException
     */
    protected function getRevisionTableJoin($relationship, $table, $field, $workspace_association_table, EntityTypeInterface $entity_type) {
        $definition = [
            'table' => $table,
            'field' => $field,
            // Making this explicitly NULL allows the left table to be a formula.
'left_table' => NULL,
            'left_field' => "COALESCE({$workspace_association_table}.target_entity_revision_id, {$relationship}.{$field})",
        ];
        if ($entity_type->isTranslatable() && $this->languageManager
            ->isMultilingual()) {
            $langcode_field = $entity_type->getKey('langcode');
            $definition['extra'] = "{$table}.{$langcode_field} = {$relationship}.{$langcode_field}";
        }
        
        /** @var \Drupal\views\Plugin\views\join\JoinPluginInterface $join */
        $join = $this->viewsJoinPluginManager
            ->createInstance('standard', $definition);
        $join->adjusted = TRUE;
        $join->workspace_adjusted = TRUE;
        return $join;
    }
    
    /**
     * Moves a 'workspace_association' table to appear before the given alias.
     *
     * Because Workspace chains possibly pre-existing tables onto the
     * 'workspace_association' table, we have to ensure that the
     * 'workspace_association' table appears in the query before the alias it's
     * chained on or the SQL is invalid.
     *
     * @param \Drupal\views\Plugin\views\query\Sql $query
     *   The SQL query object.
     * @param string $workspace_association_table
     *   The alias of the 'workspace_association' table.
     * @param string $alias
     *   The alias of the table it needs to appear before.
     */
    protected function moveEntityTable(Sql $query, $workspace_association_table, $alias) {
        $table_queue =& $query->getTableQueue();
        $keys = array_keys($table_queue);
        $current_index = array_search($workspace_association_table, $keys);
        $index = array_search($alias, $keys);
        // If it's already before our table, we don't need to move it, as we could
        // accidentally move it forward.
        if ($current_index < $index) {
            return;
        }
        $splice = [
            $workspace_association_table => $table_queue[$workspace_association_table],
        ];
        unset($table_queue[$workspace_association_table]);
        // Now move the item to the proper location in the array. Don't use
        // array_splice() because that breaks indices.
        $table_queue = array_slice($table_queue, 0, $index, TRUE) + $splice + array_slice($table_queue, $index, NULL, TRUE);
    }

}