silverstripe-fulltextsearch/code/search/SearchVariantSubsites.php

<?php

class SearchVariantSubsites extends SearchVariant {

	function appliesToEnvironment() {
		return class_exists('Subsite');
	}

	function appliesTo($class, $includeSubclasses) {
		// Include all DataExtensions that contain a SubsiteID.
		// TODO: refactor subsites to inherit a common interface, so we can run introspection once only.
		return SearchIntrospection::has_extension($class, 'SiteTreeSubsites', $includeSubclasses) ||
			SearchIntrospection::has_extension($class, 'GroupSubsites', $includeSubclasses) ||
			SearchIntrospection::has_extension($class, 'FileSubsites', $includeSubclasses) ||
			SearchIntrospection::has_extension($class, 'SiteConfigSubsites', $includeSubclasses);
	}

	function currentState() {
		 return (string)Subsite::currentSubsiteID();
	}

	function reindexStates() {
		static $ids = null;

		if ($ids === null) {
			$ids = array('0');
			foreach (DataObject::get('Subsite') as $subsite) $ids[] = (string)$subsite->ID;
		}

		return $ids;
	}

	function activateState($state) {
		// We always just set the $_GET variable rather than store in Session - this always works, has highest priority
		// in Subsite::currentSubsiteID() and doesn't persist unlike Subsite::changeSubsite
		$_GET['SubsiteID'] = $state;
		Permission::flush_permission_cache();
	}

	function alterDefinition($base, $index) {
		$self = get_class($this);
		
		$index->filterFields['_subsite'] = array(
			'name' => '_subsite',
			'field' => '_subsite',
			'fullfield' => '_subsite',
			'base' => $base,
			'origin' => $base,
			'type' => 'Int',
			'lookup_chain' => array(array('call' => 'variant', 'variant' => $self, 'method' => 'currentState'))
		);
	}

	function alterQuery($query, $index) {
		$subsite = Subsite::currentSubsiteID();
		$query->filter('_subsite', array($subsite, SearchQuery::$missing));
	}

	static $subsites = null;

	/**
	 * We need _really_ complicated logic to find just the changed subsites (because we use versions there's no explicit
	 * deletes, just new versions with different members) so just always use all of them
	 */
	function extractManipulationWriteState(&$writes) {
		$self = get_class($this);

		foreach ($writes as $key => $write) {
			if (!$this->appliesTo($write['class'], true)) continue;

			if (self::$subsites === null) {
				$query = new SQLQuery('"ID"', '"Subsite"');
				self::$subsites = array_merge(array('0'), $query->execute()->column());
			}

			$next = array();

			foreach ($write['statefulids'] as $i => $statefulid) {
				foreach (self::$subsites as $subsiteID) {
					$next[] = array('id' => $statefulid['id'], 'state' => array_merge($statefulid['state'], array($self => (string)$subsiteID)));
				}
			}

			$writes[$key]['statefulids'] = $next;
		}
	}

}