public static function getAuthorisedViewLevels($userId)
	{
		// Get all groups that the user is mapped to recursively.
		$groups = self::getGroupsByUser($userId);

		// Only load the view levels once.
		if (empty(self::$viewLevels))
		{
			// Build the view levels array.
			$levels = Viewlevel::all()
				->rows();

			foreach ($levels as $level)
			{
				self::$viewLevels[$level->get('id')] = (array) json_decode($level->get('rules'));
			}
		}

		// Initialise the authorised array.
		$authorised = array(1);

		// Find the authorised levels.
		foreach (self::$viewLevels as $level => $rule)
		{
			foreach ($rule as $id)
			{
				if (($id < 0) && (($id * -1) == $userId))
				{
					$authorised[] = $level;
					break;
				}
				// Check to see if the group is mapped to the level.
				elseif (($id >= 0) && in_array($id, $groups))
				{
					$authorised[] = $level;
					break;
				}
			}
		}

		return $authorised;
	}