Search Feature: How does it work?

function search($search_for, $type, $user, $page = 1, $per_page = 30) {
      $page = (integer) $page;
      $per_page = (integer) $per_page;

      $search_index_table = TABLE_PREFIX . 'search_index';

      $offset = ($page - 1) * $per_page;

      // Search in projects
      if($type == 'ProjectObject') {
        $type_filter = ProjectUsers::getVisibleTypesFilter($user, array(PROJECT_STATUS_ACTIVE, PROJECT_STATUS_PAUSED, PROJECT_STATUS_COMPLETED, PROJECT_STATUS_CANCELED));
        if(empty($type_filter)) {
          return array(null, new Pager(1, 0, $per_page));
        } // if

        $project_objects_table = TABLE_PREFIX . 'project_objects';

        //$total_items = (integer) array_var(db_execute_one("SELECT COUNT($project_objects_table.id) AS 'row_count' FROM $project_objects_table, $search_index_table WHERE $type_filter AND MATCH ($search_index_table.content) AGAINST (? IN BOOLEAN MODE) AND $project_objects_table.id = $search_index_table.object_id AND $search_index_table.type = ? AND state >= ? AND visibility >= ?", $search_for, $type, STATE_VISIBLE, $user->getVisibility()), 'row_count');
        $total_items = (integer) array_var(db_execute_one("SELECT COUNT($project_objects_table.id) AS 'row_count' FROM $project_objects_table, $search_index_table WHERE $type_filter AND MATCH ($search_index_table.content) AGAINST (?) AND $project_objects_table.id = $search_index_table.object_id AND $search_index_table.type = ? AND state >= ? AND visibility >= ?", $search_for, $type, STATE_VISIBLE, $user->getVisibility()), 'row_count');
        if($total_items) {
          // $items = ProjectObjects::findBySQL("SELECT $project_objects_table.* FROM $project_objects_table, $search_index_table WHERE $type_filter AND MATCH ($search_index_table.content) AGAINST (? IN BOOLEAN MODE) AND $project_objects_table.id = $search_index_table.object_id AND $search_index_table.type = ? AND state >= ? AND visibility >= ? LIMIT $offset, $per_page", array($search_for, $type, STATE_VISIBLE, $user->getVisibility()));
          $items = ProjectObjects::findBySQL("SELECT $project_objects_table.*, MATCH ($search_index_table.content) AGAINST (?) as score  FROM $project_objects_table, $search_index_table WHERE $type_filter AND MATCH ($search_index_table.content) AGAINST (?) AND $project_objects_table.id = $search_index_table.object_id AND $search_index_table.type = ? AND state >= ? AND visibility >= ? ORDER BY score DESC, $project_objects_table.updated_on DESC, $project_objects_table.name LIMIT $offset, $per_page", array($search_for, $search_for, $type, STATE_VISIBLE, $user->getVisibility()));
        } else {
          $items = null;
        } // if

        return array($items, new Pager($page, $total_items, $per_page));

      // Search for projects
      } elseif($type == 'Project') {
        $project_ids = Projects::findProjectIdsByUser($user, null, true);
        if(!is_foreachable($project_ids)) {
          return array(null, new Pager(1, 0, $per_page));
        } // if

        $projects_table = TABLE_PREFIX . 'projects';

        //$total_items = (integer) array_var(db_execute_one("SELECT COUNT($projects_table.id) AS 'row_count' FROM $projects_table, $search_index_table WHERE $projects_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (? IN BOOLEAN MODE) AND $projects_table.id = $search_index_table.object_id AND $search_index_table.type = ?", $project_ids, $search_for, 'Project'), 'row_count');
        $total_items = (integer) array_var(db_execute_one("SELECT COUNT($projects_table.id) AS 'row_count' FROM $projects_table, $search_index_table WHERE $projects_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (?) AND $projects_table.id = $search_index_table.object_id AND $search_index_table.type = ?", $project_ids, $search_for, 'Project'), 'row_count');
        if($total_items) {
		  //$items = Projects::findBySQL("SELECT * FROM $projects_table, $search_index_table WHERE $projects_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (? IN BOOLEAN MODE) AND $projects_table.id = $search_index_table.object_id AND $search_index_table.type = ? LIMIT $offset, $per_page", array($project_ids, $search_for, 'Project'));
          $items = Projects::findBySQL("SELECT *, MATCH ($search_index_table.content) AGAINST (?) as score FROM $projects_table, $search_index_table WHERE $projects_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (?) AND $projects_table.id = $search_index_table.object_id AND $search_index_table.type = ? ORDER BY score DESC, updated_on DESC, name ASC LIMIT $offset, $per_page", array($search_for, $project_ids, $search_for, 'Project'));
        } else {
          $items = null;
        } // if

        return array($items, new Pager($page, $total_items, $per_page));

      // Search for users
      } elseif($type == 'User') {
        $user_ids = $user->visibleUserIds();
        if(!is_foreachable($user_ids)) {
          return array(null, new Pager(1, 0, $per_page));
        } // if
        $users_table = TABLE_PREFIX . 'users';

        $total_items = (integer) array_var(db_execute_one("SELECT COUNT($users_table.id) AS 'row_count' FROM $users_table, $search_index_table WHERE $users_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (?) AND $users_table.id = $search_index_table.object_id AND $search_index_table.type = ?", $user_ids, $search_for, 'User'), 'row_count');
        if($total_items) {
          $items = Users::findBySQL("SELECT * FROM $users_table, $search_index_table WHERE $users_table.id IN (?) AND MATCH ($search_index_table.content) AGAINST (?) AND $users_table.id = $search_index_table.object_id AND $search_index_table.type = ? LIMIT $offset, $per_page", array($user_ids, $search_for, 'User'));
        } else {
          $items = null;
        } // if

        return array($items, new Pager($page, $total_items, $per_page));

      // Unknown search type
      } else {
        return array(null, new Pager(1, 0, $per_page));
      } // if
    } // search