<?php
/**
 * EGroupware API - Interapplicaton links
 *
 * Links have two ends each pointing to an entry, each entry is a double:
 * 	 - app   app-name or directory-name of an egw application, eg. 'infolog'
 * 	 - id    this is the id, eg. an integer or a tupple like '0:INBOX:1234'
 *
 * @link http://www.egroupware.org
 * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
 * @copyright 2001-2016 by RalfBecker@outdoor-training.de
 * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
 * @package api
 * @subpackage link
 * @version $Id$
 */

namespace EGroupware\Api;

/**
 * Generalized linking between entries of EGroupware apps
 *
 * Please note: this class can NOT and does not need to be initialised, all methods are static
 *
 * To participate in the linking an applications has to implement the following hooks:
 *
 * 	/**
 *	 * Hook called by link-class to include app in the appregistry of the linkage
 *	 *
 *	 * @param array|string $location location and other parameters (not used)
 *	 * @return array with method-names
 *	 *%
 *	function search_link($location)
 *	{
 *		return array(
 *			'query' => 'app.class.link_query',		// method to search app for a pattern: array link_query(string $pattern, array $options)
 *			'title' => 'app.class.link_title',		// method to return title of an entry of app: string/false/null link_title(int/string $id)
 *			'titles' => 'app.class.link_titles',	// method to return multiple titles: array link_title(array $ids)
 *			'view'  => array(						// get parameters to view an entry of app
 *				'menuaction' => 'app.class.method',
 *			),
 *			'types' => array(				// Optional list of sub-types to filter (eg organisations), app to handle different queries
 *				'type_key' => array(
 *					'name'	=>	'Human Reference',
 *					'icon'	=>	'app/icon'	// Optional icon to use for that sub-type
 *				)
 *			),
 *			'view_id' => 'app_id',					// name of get parameter of the id
 *          'view_popup' => '400x300',				// size of popup (XxY), if view is in popup
 *			'view_list'  => 'app.class.method'		// deprecated use 'list' instead
 *          'list' => array(						// Method to be called to display a list of links, method should check $_GET['search'] to filter
 *          	'menuaction' => 'app.class.method',
 *          ),
 *          'list_popup' => '400x300'
 *			'add' => array(							// get parameter to add an empty entry to app
 *				'menuaction' => 'app.class.method',
 *			),
 *			'add_app'    => 'link_app',				// name of get parameter to add links to other app
 *			'add_id'     => 'link_id',				// --------------------- " ------------------- id
 *			'add_popup' => '400x300',				  // size of popup (XxY), if add is in popup
 *			'no_quick_add' => false,          // App does not want to be in quick add selectbox, defaults to false
 *			'notify' => 'app.class.method',			// method to be called if an other applications links or unlinks with app: notify(array $data)
 * 			'file_access' => 'app.class.method',	// method to be called to check file access rights of a given user, see links_stream_wrapper class
 *													// bool|int file_access(string $id,int $check,string $rel_path=null,int $user=null)
 *                                                  // bool, if result does NOT depend on $rel_path and can be cached, int=0|1, if it depends on $rel_path
 * 			'file_access_user' => false,			// true if file_access method supports 4th parameter $user, if app is NOT supporting it
 *                                                  // Link::file_access() returns false for $user != current user!
 *			'file_dir'	=> 'app/sub',				// sub file dir for uploaded files/links
 *			'find_extra'  => array('name_preg' => '/^(?!.picture.jpg)$/')	// extra options to Vfs::find, to eg. remove some files from the list of attachments
 *			'edit' => array(
 *				'menuaction' => 'app.class.method',
 *			),
 *			'edit_id' => 'app_id',
 *			'edit_popup' => '400x300',
 *			'name' => 'Some name',					// Name to use instead of app-name
 *			'icon' => 'app/icon',					// Optional icon to use instead of app-icon
 *          'entry' => 'Contact',					// Optional name for single entry of app, eg. "contact" used instead of appname
 *          'entries' => 'Contacts',				// Optional name for multiple entries of app, eg. "contacts" used instead of appname
 *			'modification_time' => array(			// Optional location of entry's last modification
 *				'column' => {string} table.column	// Table & column name
 *				'type'   => {string} longint        // Data type for the column, if it's not a timestamp
 *			),
 *          'mime' => array(						// Optional register mime-types application can open
 *          	'text/something' => array(
 *          		'mime_url'  => $attr,			// either mime_url or mime_data is required for server-side processing!
 *          		'mime_data' => $attr,			// md5-hash returned from Link::set_data() to retrieve content (only server-side)
 *          		'menuaction' => 'app.class.method',	// method to call
 *          		'mime_popup' => '400x300',		// optional size of popup
 *          		'mime_target' => '_self',		// optional target, default _blank
 *          		// other get-parameters to set in url
 *          	),
 *          	// further mime types supported ...
 *          ),
 *			'fetch'	=>	'app.class.method',			// method to return entry data for a given id. the method called should support id, and expected mime-type
 *													// basically you should return something like array(id, title, mimetype, body, linked-files)
 *
 *          'push_data' => <callable> | "key" | ["key1", ...]    // keys of ACL relevant and privacy save data needed for push of changes to client
 *                                                  // or callable to do the cleaning eg. used in calendar
 *
 *			'additional' => array(					// allow one app to register sub-types,
 *				'app-sub' => array(					// different from 'types' approach above
 *					// every value defined above
 *				)
 *			)
 *	}
 * All entries are optional, thought you only get conected functionality, if you implement them ...
 *
 * The BO-layer implements some extra features on top of the so-layer:
 * 1) It handles links to not already existing entries. This is used by the eTemplate link-widget, which allows to
 *    setup links even for new / not already existing entries, before they get saved.
 * 	  In that case you have to set the first id to 0 for the link-static function and pass the array returned in that id
 * 	  (not the return-value) after saveing your new entry again to the link static function.
 * 2) Attaching files: they are saved in the vfs and not the link-table (!).
 *    Attached files are stored under $vfs_basedir='/infolog' in the vfs!
 * 3) It manages the link-registry, in which apps can register themselfs by implementing some hooks
 * 4) It notifies apps, who registered for that service, about changes in the links their entries
 *
 * Modification times in links (and deleted timestamp) are always in server-time!
 * (We dont convert them here, as most apps ignore them anyway)
 */
class Link extends Link\Storage
{
	/**
	 * appname used for returned attached files (!= 'filemanager'!)
	 */
	const VFS_APPNAME = 'file';		// pseudo-appname for own file-attachments in vfs, this is NOT the vfs-app

	/**
	 * Appname used of files stored via Link::set_data()
	 */
	const DATA_APPNAME = 'egw-data';

	/**
	 * appname used for linking existing files to VFS
	 */
	const VFS_LINK = 'link';

	/**
	 * Baseurl for the attachments in the vfs
	 */
	const VFS_BASEURL = 'vfs://default/apps';
	/**
	 * Turns on debug-messages
	 */
	const DEBUG = false;

	/**
	 * Flag to mark an app+id as not cacheable
	 */
	const NO_CACHE_FLAG = "NO CACHE";

	/**
	 * other apps can participate in the linking by implementing a 'search_link' hook, which
	 * has to return an array in the format of an app_register entry below
	 *
	 * @var array
	 */
	static $app_register = array(
		'api-accounts' => array(    // user need run-rights for home
									'app'     => 'api',
									'name'    => 'Accounts',
									'icon'    => 'addressbook/accounts',
									'query'   => 'EGroupware\\Api\\Accounts::link_query',
									'title'   => 'EGroupware\\Api\\Accounts::title',
									'view'    => array('menuaction' => 'addressbook.addressbook_ui.view',
													   'ajax'       => 'true'),
									'view_id' => 'account_id'
		),
		'api'          => array(
			// handling of text or pdf files by browser in a popup window
			'mime' => array(
				'application/pdf' => array(
					'mime_popup' => '1024x1024',
					'mime_target' => '_blank',
				),
				'/^text\\/(plain|html|diff)/' => array(	// text/(mimetypes which can be opened as recognised popups)
					'mime_popup' => '800x1024',
					'mime_target' => '_blank',
				),
				'/^image\\//' => array(	// image
					'mime_popup' => '800x640',
					'mime_target' => '_blank',
				),
			),
		),
	);

	/**
	 * Max. number of titles stored in session (older once get removed)
	 */
	const TITLE_CACHE_SIZE = 500;
	/**
	 * Caches link titles for a better performance
	 *
	 * @var array
	 */
	private static $title_cache = array();

	/**
	 * Max. number of titles stored in session (older once get removed)
	 */
	const FILE_ACCESS_CACHE_SIZE = 1000;
	/**
	 * Cache file access permissions
	 *
	 * @var array
	 */
	private static $file_access_cache = array();

	/**
	 * Private constructor to forbid instanciated use
	 *
	 */
	private function __construct()
	{

	}

	/**
	 * initialize our static vars
	 *
	 * @param boolean $clear_all do not use session AND not permission check for app-registry
	 */
	static function init_static($clear_all=false)
	{
		// FireFox 36 can not display pdf with it's internal viewer in an iframe used by mobile theme/template for popups
		// same is true for all mobile devices
		if (Header\UserAgent::type() == 'firefox' && $GLOBALS['egw_info']['user']['preferences']['common']['theme'] == 'mobile' ||
			Header\UserAgent::mobile())
		{
			unset(self::$app_register['api']['mime']['application/pdf']);
		}
		// other apps can participate in the linking by implementing a search_link hook, which
		// has to return an array in the format of an app_register entry
		// for performance reasons, we do it only once / cache it in the session
		if ($clear_all || !($search_link_hooks = Cache::getSession(__CLASS__, 'search_link_hooks')))
		{
			$search_link_hooks = Hooks::process('search_link',array(), $clear_all || !empty($GLOBALS['egw_info']['flags']['async-service']));
			Cache::setSession(__CLASS__, 'search_link_hooks', $search_link_hooks);
		}
		if (is_array($search_link_hooks))
		{
			foreach($search_link_hooks as $app => $data)
			{
				// allow apps to register additional types
				if (isset($data['additional']))
				{
					foreach($data['additional'] as $name => $values)
					{
						$values['app'] = $app;	// store name of registring app, to be able to check access
						self::$app_register[$name] = $values;
					}
					unset($data['additional']);
				}
				// support deprecated view_list attribute instead of new index attribute
				if (isset($data['view_list']) && !isset($data['list']))
				{
					$data['list'] = array('menuaction' => $data['view_list']);
				}
				elseif(isset($data['list']) && !isset($data['view_list']))
				{
					$data['view_list'] = $data['list']['menuaction'];
				}
				if (is_array($data))
				{
					self::$app_register[$app] = $data;
				}
			}
		}
		// disable ability to link to accounts for non-admins, if account-selection is disabled
		if ($GLOBALS['egw_info']['user']['preferences']['common']['account_selection'] == 'none' &&
			!isset($GLOBALS['egw_info']['user']['apps']['admin']))
		{
			unset(self::$app_register['api-accounts']);
		}
		if (!(self::$title_cache = Cache::getSession(__CLASS__, 'link_title_cache')))
		{
			self::$title_cache = array();
		}
		if (!(self::$file_access_cache = Cache::getSession(__CLASS__, 'link_file_access_cache')))
		{
			self::$file_access_cache = array();
		}

		// register self::save_session_cache to run on shutdown
		Egw::on_shutdown(array(__CLASS__, 'save_session_cache'));

		//error_log(__METHOD__.'() items in title-cache: '.count(self::$title_cache).' file-access-cache: '.count(self::$file_access_cache));
	}

	/**
	 * Get clientside relevant attributes from app registry in json format
	 *
	 * Only transferring relevant information cuts approx. half of the size.
	 * Also only transferring information relevant to apps user has access too.
	 * Important eg. for mime-registry, to not use calendar for opening iCal files, if user has no calendar!
	 * As app can store additonal types, we have to check the registring app $data['app'] too!
	 *
	 * @return string json encoded object with app: object pairs with attributes "(view|add|edit)(|_id|_popup)"
	 */
	public static function json_registry()
	{
		$to_json = array();
		foreach(self::$app_register as $app => $data)
		{
			if (isset($GLOBALS['egw_info']['user']['apps'][$app]) ||
				isset($data['app']) && isset($GLOBALS['egw_info']['user']['apps'][$data['app']]))
			{
				$to_json[$app] = array_intersect_key($data, array_flip(array(
					'view','view_id','view_popup',
					'add','add_app','add_id','add_popup','no_quick_add',
					'edit','edit_id','edit_popup',
					'list','list_popup',
					'search',
					'name','icon','query',
					'mime','entry','entries'
				)));
			}
		}
		return json_encode($to_json);
	}

	/**
	 * Called by Egw::shutdown to store the title-cache in session and run notifications
	 *
	 * Would probably better called shutdown as well.
	 */
	static function save_session_cache()
	{
		if (isset($GLOBALS['egw']->session))	// eg. cron-jobs use it too, without any session
		{
			//error_log(__METHOD__.'() items in title-cache: '.count(self::$title_cache).' file-access-cache: '.count(self::$file_access_cache));

			if (count(self::$title_cache) > self::TITLE_CACHE_SIZE)
			{
				self::$title_cache = array_slice(self::$title_cache, -self::TITLE_CACHE_SIZE);
			}
			Cache::setSession(__CLASS__, 'link_title_cache', self::$title_cache);

			if (count(self::$file_access_cache) > self::FILE_ACCESS_CACHE_SIZE)
			{
				self::$file_access_cache = array_slice(self::$file_access_cache, -self::FILE_ACCESS_CACHE_SIZE);
			}
			Cache::setSession(__CLASS__, 'link_file_access_cache', self::$file_access_cache);
		}
	}

	/**
	 * creats a link between $app1,$id1 and $app2,$id2 - $id1 does NOT need to exist yet
	 *
	 * Does NOT check if link already exists.
	 * File-attachments return a negative link-id !!!
	 *
	 * @param string $app1 app of $id1
	 * @param string|array &$id1 id of item to linkto or 0 if item not yet created or array with links
	 * 	of not created item or $file-array if $app1 == self::VFS_APPNAME (see below).
	 * 	If $id==0 it will be set on return to an array with the links for the new item.
	 * @param string|array $app2 app of 2.linkend or array with links ($id2 not used)
	 * @param string $id2 ='' id of 2. item of $file-array if $app2 == self::VFS_APPNAME or self::DATA_APPNAME
	 * 	$file array with informations about the file in format of the etemplate file-type
	 * 	$file['name'] name of the file (no directory)
	 * 	$file['type'] mime-type of the file
	 * 	$file['tmp_name'] name of the uploaded file (incl. directory) for self::VFS_APPNAME or
	 *  $file['egw_data'] id of Link::set_data() call for self::DATA_APPNAME
	 * @param string $remark ='' Remark to be saved with the link (defaults to '')
	 * @param int $owner =0 Owner of the link (defaults to user)
	 * @param int $lastmod =0 timestamp of last modification (defaults to now=time())
	 * @param int $no_notify =0 &1 dont notify $app1, &2 dont notify $app2
	 * @return int/boolean False (for db or param-error) or on success link_id (Please not the return-value of $id1)
	 */
	static function link( $app1,&$id1,$app2,$id2='',$remark='',$owner=0,$lastmod=0,$no_notify=0 )
	{
		if (self::DEBUG)
		{
			echo "<p>Link::link('$app1',$id1,'".print_r($app2,true)."',".print_r($id2,true).",'$remark',$owner,$lastmod)</p>\n";
		}
		if (!$app1 || !$app2 || $app1 == $app2 && $id1 == $id2)
		{
			return False;
		}
		if (is_array($app2) && !$id2)
		{
			reset($app2);
			$link_id = True;
			while ($link_id && $link = current($app2))
			{
				if (!is_array($link))	// check for unlink-marker
				{
					//echo "<b>link='$link' is no array</b><br>\n";
					next($app2);
					continue;
				}
				if (is_array($id1) || !$id1)		// create link only in $id1 array
				{
					self::link($app1, $id1, $link['app'], $link['id'], $link['remark'],$link['owner'],$link['lastmod']);
					next($app2);
					continue;
				}
				switch ($link['app'])
				{
					case self::DATA_APPNAME:
						if (!($link['id']['tmp_name'] = self::get_data($link['id']['egw_data'], true)))
						{
							$link_id = false;
							break;
						}
						// fall through
					case self::VFS_APPNAME:
						$link_id = self::attach_file($app1,$id1,$link['id'],$link['remark']);
						break;

					case self::VFS_LINK:
						$link_id = self::link_file($app1,$id1, $link['id'],$link['remark']);
						break;

					default:
						$link_id = Link\Storage::link($app1,$id1,$link['app'],$link['id'],
							$link['remark'],$link['owner'],$link['lastmod']);
						// notify both sides
						if (!($no_notify&2)) self::notify('link',$link['app'],$link['id'],$app1,$id1,$link_id);
						if (!($no_notify&1)) self::notify('link',$app1,$id1,$link['app'],$link['id'],$link_id);
						break;
				}
				next($app2);
			}
			return $link_id;
		}
		if (is_array($id1) || !$id1)		// create link only in $id1 array
		{
			if (!is_array($id1))
			{
				$id1 = array( );
			}
			$link_id = self::temp_link_id($app2,$id2);

			$id1[$link_id] = array(
				'app'     => $app2,
				'id'      => $id2,
				'title'   => is_array($id2) ? $id2['title'] ?? $id2['name'] : null,
				'remark'  => $remark,
				'owner'   => $owner,
				'link_id' => $link_id,
				'lastmod' => time()
			);
			if (self::DEBUG)
			{
				_debug_array($id1);
			}
			return $link_id;
		}
		if ($app1 == self::VFS_LINK)
		{
			return self::link_file($app2,$id2,$id1,$remark);
		}
		elseif ($app2 == self::VFS_LINK)
		{
			return self::link_file($app1,$id1,$id2,$remark);
		}
		if ($app1 == self::VFS_APPNAME)
		{
			return self::attach_file($app2,$id2,$id1,$remark);
		}
		elseif ($app2 == self::VFS_APPNAME)
		{
			return self::attach_file($app1,$id1,$id2,$remark);
		}
		$link_id = Link\Storage::link($app1,$id1,$app2,$id2,$remark,$owner);

		if (!($no_notify&2)) self::notify('link',$app2,$id2,$app1,$id1,$link_id);
		if (!($no_notify&1)) self::notify('link',$app1,$id1,$app2,$id2,$link_id);

		return $link_id;
	}

	/**
	 * generate temporary link_id used as array-key
	 *
	 * @param string $app app-name
	 * @param mixed $id
	 * @return string
	 */
	static function temp_link_id($app,$id)
	{
		return $app.':'.(!in_array($app, array(self::VFS_APPNAME,self::VFS_LINK, self::DATA_APPNAME)) || !is_array($id) ? $id : $id['name']);
	}

	/**
	 * returns array of links to $app,$id (reimplemented to deal with not yet created items)
	 *
	 * @param string $app appname
	 * @param string|array $id id(s) in $app
	 * @param string $only_app ='' if set return only links from $only_app (eg. only addressbook-entries) or NOT from if $only_app[0]=='!'
	 * @param string $order ='link_lastmod DESC' defaults to newest links first
	 * @param boolean $cache_titles =false should all titles be queryed and cached (allows to query each link app only once!)
	 * 	This option also removes links not viewable by current user from the result!
	 * @param boolean $deleted =false Include links that have been flagged as deleted, waiting for purge of linked record.
	 * @param int $limit =null number of entries to return, only affects links, attachments are allways reported!
	 * @return array id => links pairs if $id is an array or just the links (only_app: ids) or empty array if no matching links found
	 */
	static function get_links($app, $id, $only_app = '', $order = 'link_lastmod DESC, link_id DESC', $cache_titles = false, $deleted = false, $limit = null)
	{
		if (self::DEBUG) echo "<p>Link::get_links(app='$app',id='$id',only_app='$only_app',order='$order',deleted='$deleted')</p>\n";

		if (is_array($id) || !$id)
		{
			$ids = array();
			if (is_array($id))
			{
				if (($not_only = $only_app[0] == '!'))
				{
					$only_app = substr(1,$only_app);
				}
				foreach (array_reverse($id) as $link)
				{
					if (is_array($link)  // check for unlink-marker
						&&  !($only_app && $not_only == ($link['app'] == $only_app)))
					{
						$ids[$link['link_id']] = $only_app ? $link['id'] : $link;
					}
				}
			}
			return $ids;
		}
		$ids = Link\Storage::get_links($app, $id, $only_app, $order, $deleted, $limit);
		$limit_exceeded = self::$limit_exceeded;
		if (empty($only_app) || $only_app == self::VFS_APPNAME ||
		    ($only_app[0] == '!' && $only_app != '!'.self::VFS_APPNAME))
		{
			if (($vfs_ids = self::list_attached($app,$id)))
			{
				$ids += $vfs_ids;
				self::$row_count += count($vfs_ids);
			}
		}
		//echo "ids=<pre>"; print_r($ids); echo "</pre>\n";
		if ($cache_titles)
		{
			// aggregate links by app
			$app_ids = array();
			foreach($ids as $link)
			{
				$app_ids[$only_app ? $only_app : $link['app']][] = is_array($link) ? $link['id'] : $link;
			}
			foreach($app_ids as $appname => $a_ids)
			{
				self::titles($appname,array_unique($a_ids));
			}
			// remove links, current user has no access, from result
			foreach($ids as $key => $link)
			{
				if(!self::title(is_array($link) ? $link['app'] : $only_app, is_array($link) ? $link['id'] : $link))
				{
					unset($ids[$key]);
					self::$row_count--;
				}
			}
			reset($ids);
		}
		self::$limit_exceeded = $limit_exceeded;
		return $ids;
	}

	/**
	 * Query the links of multiple entries of one application
	 *
	 * @ToDo also query the attachments in a single query, eg. via a directory listing of /apps/$app
	 * @param string $app
	 * @param array $ids
	 * @param boolean $cache_titles =true should all titles be queryed and cached (allows to query each link app only once!)
	 * @param string $only_app if set return only links from $only_app (eg. only addressbook-entries) or NOT from if $only_app[0]=='!'
	 * @param string $order ='link_lastmod DESC' defaults to newest links first
	 * @param boolean $deleted =false Include links that have been flagged as deleted, waiting for purge of linked record.
	 * @return array of $id => array($links) pairs
	 */
	static function get_links_multiple($app,array $ids,$cache_titles=true,$only_app='',$order='link_lastmod DESC', $deleted=false )
	{
		if (self::DEBUG) echo "<p>".__METHOD__."('$app',".print_r($ids,true).",$cache_titles,'$only_app','$order')</p>\n";

		if (!$ids)
		{
			return array();		// no ids are linked to nothing
		}
		$links = Link\Storage::get_links($app,$ids,$only_app,$order,$deleted);

		if (empty($only_app) || $only_app == self::VFS_APPNAME ||
		    ($only_app[0] == '!' && $only_app != '!'.self::VFS_APPNAME))
		{
			// todo do that in a single query, eg. directory listing, too
			foreach($ids as $id)
			{
				if (!isset($links[$id]))
				{
					$links[$id] = array();
				}
				if (($vfs_ids = self::list_attached($app,$id)))
				{
					$links[$id] += $vfs_ids;
				}
			}
		}
		if ($cache_titles)
		{
			// agregate links by app
			$app_ids = array();
			foreach($links as &$targets)
			{
				foreach($targets as $link)
				{
					if (is_array($link)) $app_ids[$link['app']][] = $link['id'];
				}
			}
			foreach($app_ids as $a_app => $a_ids)
			{
				self::titles($a_app,array_unique($a_ids));
			}
		}
		return $links;
	}

	/**
	 * Read one link specified by it's link_id or by the two end-points
	 *
	 * If $id is an array (links not yet created) only link_ids are allowed.
	 *
	 * @param int|string $app_link_id > 0 link_id of link or app-name of link
	 * @param string|array $id ='' id if $app_link_id is an appname or array with links, if 1. entry not yet created
	 * @param string $app2 ='' second app
	 * @param string $id2 ='' id in $app2
	 * @return array with link-data or False
	 */
	static function get_link($app_link_id,$id='',$app2='',$id2='')
	{
		if (self::DEBUG)
		{
			echo '<p>'.__METHOD__."($app_link_id,$id,$app2,$id2)</p>\n"; echo function_backtrace();
		}
		if (is_array($id))
		{
			if (strpos($app_link_id,':') === false) $app_link_id = self::temp_link_id($app2,$id2);	// create link_id of temporary link, if not given

			if (isset($id[$app_link_id]) && is_array($id[$app_link_id]))	// check for unlinked-marker
			{
				return $id[$app_link_id];
			}
			return False;
		}
		if ((int)$app_link_id < 0 || $app_link_id == self::VFS_APPNAME || $app2 == self::VFS_APPNAME)
		{
			if ((int)$app_link_id < 0)	// vfs link_id ?
			{
				return self::fileinfo2link(-$app_link_id);
			}
			if ($app_link_id == self::VFS_APPNAME)
			{
				return self::info_attached($app2,$id2,$id);
			}
			return self::info_attached($app_link_id,$id,$id2);
		}
		return Link\Storage::get_link($app_link_id,$id,$app2,$id2);
	}

	/**
	 * Remove link with $link_id or all links matching given $app,$id
	 *
	 * Note: if $link_id != '' and $id is an array: unlink removes links from that array only
	 * 	unlink has to be called with &$id to see the result (depricated) or unlink2 has to be used !!!
	 *
	 * @param string $link_id link-id to remove if > 0
	 * @param string $app ='' appname of first endpoint
	 * @param string|array $id ='' id in $app or array with links, if 1. entry not yet created
	 * @param int $owner =0 account_id to delete all links of a given owner, or 0
	 * @param string $app2 ='' app of second endpoint
	 * @param string $id2 ='' id in $app2
	 * @param boolean $hold_for_purge Don't really delete the link, just mark it as deleted and wait for final delete
	 * @return int the number of links deleted
	 */
	static function unlink($link_id,$app='',$id='',$owner=0,$app2='',$id2='',$hold_for_purge=false)
	{
		return self::unlink2($link_id,$app,$id,$owner,$app2,$id2,$hold_for_purge);
	}

	/**
	 * Remove link with $link_id or all links matching given $app,$id
	 *
	 * @param $link_id link-id to remove if > 0
	 * @param string $app ='' appname of first endpoint
	 * @param string|array &$id='' id in $app or array with links, if 1. entry not yet created
	 * @param int $owner =0 account_id to delete all links of a given owner, or 0
	 * @param string $app2 ='' app of second endpoint, or !file (other !app are not yet supported!)
	 * @param string $id2 ='' id in $app2
	 * @param boolean $hold_for_purge Don't really delete the link, just mark it as deleted and wait for final delete
	 * @return int|boolean the number of links deleted
	 */
	static function unlink2($link_id,$app,&$id,$owner=0,$app2='',$id2='',$hold_for_purge=false)
	{
		if (self::DEBUG)
		{
			echo "<p>Link::unlink('$link_id','$app',".array2string($id).",'$owner','$app2','$id2', $hold_for_purge)</p>\n";
		}
		if ((int)$link_id < 0)	// vfs-link?
		{
			return self::delete_attached(-$link_id);
		}
		elseif ($app === self::VFS_APPNAME)
		{
			return self::delete_attached($app2,$id2,$id);
		}
		elseif ($app2 === self::VFS_APPNAME)
		{
			return self::delete_attached($app,$id,$id2);
		}
		if (!is_array($id))
		{
			if (!$link_id && !$app2 && !$id2 && $app2 != '!'.self::VFS_APPNAME)
			{
				// in case "someone" interested in all changes (used eg. for push)
				Hooks::process([
					'location' => 'notify-all',
					'type'     => 'delete',
					'app'      => $app,
					'id'       => $id,
				], null, true);

				self::delete_attached($app,$id);	// deleting all attachments
				self::delete_cache($app,$id);
			}

			// Log in history
			if($link_id && (!$app || !$app2))
			{
				// Need to load it first
				$link = self::get_link($link_id);
				$app = $link['link_app1'];
				$id = $link['link_id1'];
				$app2 = $link['link_app2'];
				$id2 = $link['link_id2'];
			}
			// only history-log and notify, if there were any links deleted
			if (($deleted = Link\Storage::unlink($link_id,$app,$id,$owner,$app2 != '!'.self::VFS_APPNAME ? $app2 : '',$id2,$hold_for_purge)))
			{
				if ($app && $app2)
				{
					Storage\History::static_add($app,$id,$GLOBALS['egw_info']['user']['account_id'],'~link~','',$app2.':'.$id2);
					Storage\History::static_add($app2,$id2,$GLOBALS['egw_info']['user']['account_id'],'~link~','',$app.':'.$id);
				}
				// only notify on real links, not the one cached for writing or fileattachments
				self::notify_unlink($deleted);
			}
			return count($deleted);
		}
		if (!$link_id) $link_id = self::temp_link_id($app2,$id2);	// create link_id of temporary link, if not given

		if (isset($id[$link_id]))
		{
			$id[$link_id] = False;	// set the unlink marker

			if (self::DEBUG)
			{
				_debug_array($id);
			}
			return True;
		}
		return False;
	}

	/**
	 * get list/array of link-aware apps the user has rights to use
	 *
	 * @param string $must_support capability the apps need to support, eg. 'add', default ''=list all apps
	 * @return array with app => title pairs
	 */
	static function app_list($must_support='')
	{
		$apps = array();
		foreach(self::$app_register as $type => $reg)
		{
			if ($must_support && !isset($reg[$must_support])) continue;

			list($app) = explode('-', $type);
			if (!empty($GLOBALS['egw_info']['user']['apps'][$app]))
			{
				$apps[$type] = lang(self::get_registry($type, 'name'));
			}
		}
		return $apps;
	}

	/**
	 * Default number of returned rows for Link::query()
	 */
	const DEFAULT_NUM_ROWS = 100;

	/**
	 * Searches for a $pattern in the entries of $app
	 *
	 * @param string $app app to search
	 * @param string $pattern pattern to search
	 * @param array& $options passed to callback: type, start, num_rows, filter, exclude; on return value for "total"
	 * @return array with $id => $title pairs of matching entries of app
	 */
	static function query($app, $pattern, &$options = array())
	{
		if ($app == '' || !is_array($reg = self::$app_register[$app]) || !isset($reg['query']))
		{
			return array();
		}
		$method = $reg['query'];

		if (self::DEBUG)
		{
			echo "<p>Link::query('$app','$pattern') => '$method'</p>\n";
			echo "Options: "; _debug_array($options);
		}
		// limit number of returned rows by default to 100, if no limit is set
		if(!isset($options['num_rows']))
		{
			$options['num_rows'] = max((int)$GLOBALS['egw_info']['user']['preference']['common']['maxmatchs'], self::DEFAULT_NUM_ROWS);
		}

		if (isset($options['order']) && !preg_match(preg_match('/^[a-z0-9_]+$/', $options['order'])))
		{
			unset($options['order'], $options['sort']);
		}

		$result = self::exec($method, array($pattern, &$options));

		if (!isset($options['total']))
		{
		       $options['total'] = count($result);
		}
		if (isset($options['exclude']))
		{
			$result = array_diff_key($result, array_flip($options['exclude']));
		}
		if (is_array($result) && (isset($options['start']) || (isset($options['num_rows']) && count($result) > $options['num_rows'])))
		{
			$result = array_slice($result, $options['start'], (isset($options['num_rows']) ? $options['num_rows'] : count($result)), true);
		}

		return $result;
	}

	/**
	 * returns the title (short description) of entry $id and $app
	 *
	 * @param string $app appname
	 * @param string $id id in $app
	 * @param array $link =null link-data for file-attachments
	 * @return string/boolean string with title, null if $id does not exist in $app or false if no perms to view it
	 */
	static function title($app,$id,$link=null)
	{
		if (!$id) return '';

		$title =& self::get_cache($app,$id);
		if (isset($title) && !empty($title) && !is_array($id))
		{
			if (self::DEBUG) echo '<p>'.__METHOD__."('$app','$id')='$title' (from cache)</p>\n";
			return $title;
		}
		if ($app == self::VFS_APPNAME)
		{
			if (is_array($id) && $link)
			{
				$link = $id;
				$title = Vfs::decodePath($link['name']);
			}
			else
			{
				$title = $id;
			}
			/* disabling mime-type and size in link-title of attachments, as it clutters the UI
			   and users dont need it most of the time. These details can allways be views in filemanager.
			if (is_array($link))
			{
				$title .= ': '.$link['type'] . ' '.Vfs::hsize($link['size']);
			}*/
			if (self::DEBUG) echo '<p>'.__METHOD__."('$app','$id')='$title' (file)</p>\n";
			return $title;
		}
		if ($app == '' || !is_array($reg = self::$app_register[$app]) || !isset($reg['title']))
		{
			if (self::DEBUG) echo "<p>".__METHOD__."('$app','$id') something is wrong!!!</p>\n";
			return false; //array(); // not sure why it should return an array on failure, as the description states boolean/string
		}
		$method = $reg['title'];

		if (true) $title = self::exec($method, array($id));

		if ($id && is_null($title))	// $app,$id has been deleted ==> unlink all links to it
		{
			static $unlinking = array();
			// check if we are already trying to unlink the entry, to avoid an infinite recursion
			if (!isset($unlinking[$app]) || !isset($unlinking[$app][$id]))
			{
				$unlinking[$app][$id] = true;
				self::unlink(0,$app,$id);
				unset($unlinking[$app][$id]);
			}
			if (self::DEBUG) echo '<p>'.__METHOD__."('$app','$id') unlinked, as $method returned null</p>\n";
			return False;
		}
		if (self::DEBUG) echo '<p>'.__METHOD__."('$app','$id')='$title' (from $method)</p>\n";

		return $title;
	}

	/**
	 * Maximum number of titles to query from an application at once (to NOT trash mysql)
	 */
	const MAX_TITLES_QUERY = 100;

	/**
	 * Query the titles off multiple id's of one app
	 *
	 * Apps can implement that hook, if they have a quicker (eg. less DB queries) method to query the title of multiple entries.
	 * If it's not implemented, we call the regular title method multiple times.
	 *
	 * @param string $app
	 * @param array $ids
	 */
	static function titles($app,array $ids)
	{
		if (self::DEBUG)
		{
			echo "<p>".__METHOD__."($app,".implode(',',$ids).")</p>\n";
		}
		$titles = $ids_to_query = array();
		foreach($ids as $id)
		{
			$title =& self::get_cache($app,$id);
			if (!isset($title))
			{
				if (isset(self::$app_register[$app]['titles']))
				{
					$ids_to_query[] = $id;	// titles method --> collect links to query at once
				}
				else
				{
					try {
						$title = self::title($app, $id);    // no titles method --> fallback to query each link separate
					}
					catch (\Throwable $e) {
						$title = lang('Error').': '.$e->getMessage();
					}
				}
			}
			$titles[$id] = $title;
		}
		if ($ids_to_query)
		{
			for ($n = 0; ($ids = array_slice($ids_to_query,$n*self::MAX_TITLES_QUERY,self::MAX_TITLES_QUERY)); ++$n)
			{
				foreach(self::exec(self::$app_register[$app]['titles'], array($ids)) as $id => $t)
				{
					$title =& self::get_cache($app,$id);
					$titles[$id] = $title = $t;
				}
			}
		}
		return $titles;
	}

	/**
	 * Add new entry to $app, evtl. already linked to $to_app, $to_id
	 *
	 * @param string $app appname of entry to create
	 * @param string $to_app ='' appname to link the new entry to
	 * @param string $to_id =''id in $to_app
	 * @return array/boolean with name-value pairs for link to add-methode of $app or false if add not supported
	 */
	static function add($app,$to_app='',$to_id='')
	{
		//echo "<p>Link::add('$app','$to_app','$to_id') app_register[$app] ="; _debug_array($app_register[$app]);
		if ($app == '' || !is_array($reg = self::$app_register[$app]) || !isset($reg['add']))
		{
			return false;
		}
		$params = $reg['add'];

		if ($reg['add_app'] && $to_app && $reg['add_id'] && $to_id)
		{
			$params[$reg['add_app']] = $to_app;
			$params[$reg['add_id']] = $to_id;
		}
		return $params;
	}

	/**
	 * Edit entry $id of $app
	 *
	 * @param string $app appname of entry
	 * @param string $id id in $app
	 * @param string &$popup=null on return popup size eg. '600x400' or null
	 * @return array|boolean with name-value pairs for link to edit-methode of $app or false if edit not supported
	 */
	static function edit($app,$id,&$popup=null)
	{
		//echo "<p>Link::add('$app','$to_app','$to_id') app_register[$app] ="; _debug_array($app_register[$app]);
		if (empty($app) || empty($id) || !is_array($reg = self::$app_register[$app]) || !isset($reg['edit']))
		{
			if ($reg && isset($reg['view']))
			{
				$popup = $reg['view_popup'];
				return self::view($app,$id);	// fallback to view
			}
			return false;
		}
		$params = $reg['edit'];
		$params[$reg['edit_id']] = $id;

		$popup = $reg['edit_popup'];

		return $params;
	}

	/**
	 * view entry $id of $app
	 *
	 * @param string $app appname
	 * @param string $id id in $app
	 * @param array $link =null link-data for file-attachments
	 * @return array with name-value pairs for link to view-methode of $app to view $id
	 */
	static function view($app,$id,$link=null)
	{
		if ($app == self::VFS_APPNAME && !empty($id) && is_array($link))
		{
			//return Vfs::download_url(self::vfs_path($link['app2'],$link['id2'],$link['id'],true));
			return self::mime_open(self::vfs_path($link['app2'],$link['id2'],$link['id'],true), $link['type']);
		}
		if ($app == '' || !is_array($reg = self::$app_register[$app]) || !isset($reg['view']) || !isset($reg['view_id']))
		{
			return array();
		}
		$view = $reg['view'];

		$names = explode(':',$reg['view_id']);
		if (count($names) > 1)
		{
			$id = explode(':',$id);
			foreach($names as $n => $name)
			{
				$view[$name] = $id[$n];
			}
		}
		elseif(is_array($view))
		{
			$view[$reg['view_id']] = $id;
		}
		return $view;
	}

	/**
	 * Get mime-type information from app-registry
	 *
	 * Only return information from apps the user has access too (incl. registered sub-types of that apps).
	 *
	 * We prefer full matches over wildcards like "text/*" written as regexp "/^text\\//".
	 *
	 * @param string $type
	 * @param ?string $_app check only $_app, if given
	 * @return array with values for keys 'menuaction', 'mime_id' (path) or 'mime_url' and options 'mime_popup' and other values to pass one
	 */
	static function get_mime_info($type, string $_app=null)
	{
		foreach($_app ? [$_app => self::$app_register[$_app] ?? []] : self::$app_register as $app => $registry)
		{
			if (isset($registry['mime']) &&
				(isset($GLOBALS['egw_info']['user']['apps'][$app]) ||
				isset($registry['app']) && isset($GLOBALS['egw_info']['user']['apps'][$registry['app']])))
			{
				foreach($registry['mime'] as $mime => $data)
				{
					if ($mime == $type) return $data;
					if ($mime[0] == '/' && preg_match($mime.'i', $type))
					{
						$wildcard_mime = $data;
					}
				}
			}
		}
		return isset($wildcard_mime) ? $wildcard_mime : null;
	}

	/**
	 * Get handler (link-data) for given path and mime-type
	 *
	 * @param string $path vfs path
	 * @param string $type =null default to Vfs::mime_content_type($path)
	 * @param string &$popup=null on return popup size or null
	 * @return string|array string with EGw relative link, array with get-parameters for '/index.php' or null (directory and not filemanager access)
	 */
	static function mime_open($path, $type=null, &$popup=null)
	{
		if (is_null($type)) $type = Vfs::mime_content_type($path);

		if (($data = self::get_mime_info($type)))
		{
			if (isset($data['mime_url']))
			{
				$data[$data['mime_url']] = Vfs::PREFIX.$path;
				unset($data['mime_url']);
			}
			elseif (isset($data['mime_id']))
			{
				$data[$data['mime_id']] = $path;
				unset($data['mime_id']);
			}
			elseif(isset($data['mime_popup']))
			{
				$popup = $data['mime_popup'];
			}
			else
			{
				throw new Exception\AssertionFailed("Missing 'mime_id' or 'mime_url' for mime-type '$type'!");
			}
			unset($data['mime_popup']);
		}
		else
		{
			$data = Vfs::download_url($path);
		}
		return $data;
	}

	/**
	 * Check if $app uses a popup for $action
	 *
	 * @param string $app app-name
	 * @param string $action ='view' name of the action, atm. 'view' or 'add'
	 * @param array $link =null link-data for file-attachments
	 * @return boolean|string false if no popup is used or $app is not registered, otherwise string with the prefered popup size (eg. '640x400)
	 */
	static function is_popup($app, $action='view', $link=null)
	{
		$popup = self::get_registry($app,$action.'_popup');

		// for files/attachments check mime-registry
		if ($app == self::VFS_APPNAME && is_array($link) && !empty($link['type']))
		{
			$path = self::vfs_path($link['app2'], $link['id2'], $link['id'], true);
			$p = null;
			if (self::mime_open($path, $link['type'], $p))
			{
				$popup = $p;
			}
		}
		//error_log(__METHOD__."('$app', '$action', ".array2string($link).') returning '.array2string($popup));
		return $popup;
	}

	/**
	 * Check if $app is in the registry and has an entry for $name
	 *
	 * @param string $app app-name
	 * @param string $name name / key in the registry, eg. 'view'
	 * @param boolean|array|string|int $url_id format entries like "add", "edit", "view" for actions "url" incl. an ID
	 *  array to add arbitrary parameter eg. ['some_id' => '$id']
	 * @return boolean|string false if $app is not registered, otherwise string with the value for $name
	 */
	static function get_registry($app, $name, $url_id=false)
	{
		$reg = self::$app_register[$app] ?? null;

		if (!isset($reg)) return false;

		if (!isset($reg[$name]))	// some defaults
		{
			switch($name)
			{
				case 'name':
					$reg[$name] = $app;
					break;
				case 'entry':
					$reg[$name] = $app;
					break;
				case 'icon':
					if (isset($GLOBALS['egw_info']['apps'][$app]['icon']))
					{
						$reg[$name] = ($GLOBALS['egw_info']['apps'][$app]['icon_app'] ? $GLOBALS['egw_info']['apps'][$app]['icon_app'] : $app).
							'/'.$GLOBALS['egw_info']['apps'][$app]['icon'];
					}
					else
					{
						$reg[$name] = $app.'/navbar';
					}
					break;
				case 'quick_add':
					$reg[$name] = true;
			}
		}

		// format as action url
		if ($url_id && isset($reg[$name]) && is_array($reg[$name]))
		{
			$params = $reg[$name];
			if (isset($reg[$name.'_id']))
			{
				$params[$reg[$name.'_id']] = $url_id === true ? '$id' : $url_id;
			}
			if (is_array($url_id))
			{
				$params += $url_id;
			}
			foreach($params as $name => $value)
			{
				$str .= (!empty($str) ? '&' : '').$name.'='.$value;
			}
			return $str;
		}

		return $reg[$name] ?? false;
	}

	/**
	 * path to the attached files of $app/$ip or the directory for $app if no $id,$file given
	 *
	 * All link-files are based in the vfs-subdir '/apps/'.$app
	 *
	 * @param string $app appname
	 * @param string $id ='' id in $app
	 * @param string $file ='' filename
	 * @param boolean $just_the_path =false return url or just the vfs path
	 * @return string/array path or array with path and relatives, depending on $relatives
	 */
	static function vfs_path($app,$id='',$file='',$just_the_path=false)
	{
		$path = self::VFS_BASEURL;

		if ($app)
		{
			if( isset(self::$app_register[$app]) ) {
				$reg = self::$app_register[$app];

				if( isset($reg['file_dir']) ) {
					$app = $reg['file_dir'];
				}
			}

			$path .= '/'.$app;

			if ($id)
			{
				$path .= '/'.$id;

				if ($file)
				{
					$path .= '/'.$file;
				}
			}
		}
		if ($just_the_path)
		{
			$path = parse_url($path,PHP_URL_PATH);
		}
		else
		{
			$path = Vfs::resolve_url($path);
		}
		//error_log(__METHOD__."($app,$id,$file,$just_the_path)=$path");
		return $path;
	}

	/**
	 * Put a file to the corrosponding place in the VFS and set the attributes
	 *
	 * Does NO is_uploaded_file check, calling application is responsible for doing that for uploaded files!
	 *
	 * @param string $app appname to linke the file to
	 * @param string $id id in $app
	 * @param array $file informations about the file in format of the etemplate file-type
	 * 	$file['name'] name of the file (optional incl. a directory)
	 * 	$file['type'] mine-type of the file
	 * 	$file['tmp_name'] name of the uploaded file (incl. directory) or resource of opened file
	 * @param string $comment ='' comment to add to the link
	 * @return int negative id of egw_sqlfs table as negative link-id's are for vfs attachments
	 */
	static function attach_file($app,$id,$file,$comment='')
	{
		// check if $file['name'] specifies a subdirectory, in which case use and, if necessary, create it
		if (is_array($file) && strpos($file['name'], '/') && strpos($file['name'], '..') === false)
		{
			$entry_dir = self::vfs_path($app, $id, Vfs::dirname($file['name']));
			$file['name'] = Vfs::basename($file['name']);
		}
		else
		{
			$entry_dir = self::vfs_path($app,$id);
		}
		if (self::DEBUG)
		{
			echo "<p>attach_file: app='$app', id='$id', tmp_name='$file[tmp_name]', name='$file[name]', size='$file[size]', type='$file[type]', path='$file[path]', ip='$file[ip]', comment='$comment', entry_dir='$entry_dir'</p>\n";
		}
		if (file_exists($entry_dir) || ($Ok = mkdir($entry_dir,0,true)))
		{
			$Ok = Vfs::copy_uploaded($file, $p=Vfs::parse_url($entry_dir, PHP_URL_PATH), $comment, false);	// no is_uploaded_file() check!
			if (!$Ok) error_log(__METHOD__."('$app', '$id', ".array2string($file).", '$comment') called Vfs::copy_uploaded(".json_encode($file).", '$p', '$comment', false)=".array2string($Ok));
		}
		else
		{
			error_log(__METHOD__."($app,$id,".array2string($file).",$comment) Can't mkdir $entry_dir!");
		}
		return $Ok ? -$Ok['ino'] : false;
	}

	/**
	 * Links the entry to an existing file in the VFS
	 *
	 * @param string $app appname to link the file to
	 * @param string $id id in $app
	 * @param string $file VFS path to link to
	 * @return boolean true on success, false on failure
	 */
	static function link_file($app,$id,$file)
	{
		// Don't try to link into app dir if there is no id
		if(!$id) return;

		if (!Vfs::stat($file))
		{
			error_log(__METHOD__. ' (Link target ' . Vfs::decodePath($file) . ' not found!');
			return false;
		}

		$entry_dir = self::vfs_path($app, $id);
		if (!file_exists($entry_dir) && !mkdir($entry_dir, 0, true))
		{
			error_log(__METHOD__."($app,$id,".array2string($file).") Can't mkdir $entry_dir!");
			return false;
		}

		return Vfs::symlink($file, Vfs::concat($entry_dir, Vfs::basename($file)));
	}
	/**
	 * deletes a single or all attached files of an entry (for all there's no acl check, as the entry probably not exists any more!)
	 *
	 * @param int|string $app > 0: file_id of an attchemnt or $app/$id entry which linked to
	 * @param string $id ='' id in app
	 * @param string $fname ='' filename
	 * @return boolean|array false on error ($app or $id not found), array with path as key and boolean result of delete
	 */
	static function delete_attached($app,$id='',$fname='')
	{
		if ((int)$app > 0)	// is file_id
		{
			$url = Vfs::resolve_url(Vfs\Sqlfs\StreamWrapper::id2path($app));
		}
		else
		{
			if (empty($app) || empty($id))
			{
				return False;	// dont delete more than all attachments of an entry
			}
			$url = self::vfs_path($app,$id,$fname);

			if (!$fname || !$id)	// we delete the whole entry (or all entries), which probably not exist anymore
			{
				$current_is_root = Vfs::$is_root;
				Vfs::$is_root = true;
			}
		}
		if (self::DEBUG)
		{
			echo '<p>'.__METHOD__."('$app','$id','$fname') url=$url</p>\n";
		}
		// Log in history - Need to load it first
		if((int)$app > 0)
		{
			$link = self::get_link(-$app);
			if($link['app2'] && $link['id2'])
			{
				Storage\History::static_add($link['app2'],$link['id2'],$GLOBALS['egw_info']['user']['account_id'],'~file~','', Vfs::basename($url));
			}
		}
		try {
			if (($Ok = !file_exists($url) || Vfs::remove($url,true)) && ((int)$app > 0 || $fname))
			{
				// try removing the dir, in case it's empty
				if (($dir = Vfs::dirname($url))) @Vfs::rmdir($dir);
			}
		}
		catch (\Exception $e) {
			// ignore SQL error caused by only virtual directories with non-integer (hash) fs_id
			$Ok = false;
		}
		if (!is_null($current_is_root))
		{
			Vfs::$is_root = $current_is_root;
		}
		return $Ok;
	}

	/**
	 * converts the infos vfs has about a file into a link
	 *
	 * @param string $app appname
	 * @param string $id id in app
	 * @param string $filename filename
	 * @return array 'kind' of link-array
	 */
	static function info_attached($app,$id,$filename)
	{
		$path = self::vfs_path($app,$id,$filename,true);
		if (!($stat = Vfs::stat($path,STREAM_URL_STAT_QUIET)))
		{
			return false;
		}
		return self::fileinfo2link($stat,$path);
	}

	/**
	 * converts a fileinfo (row in the vfs-db-table) in a link
	 *
	 * @param array|int $fileinfo a row from the vfs-db-table (eg. returned by the vfs ls static function) or a file_id of that table
	 * @return array a 'kind' of link-array
	 */
	static function fileinfo2link($fileinfo,$url=null)
	{
		if (!is_array($fileinfo))
		{
			$url = Vfs\Sqlfs\StreamWrapper::id2path($fileinfo);
			if (!($fileinfo = Vfs::stat($url,STREAM_URL_STAT_QUIET)))
			{
				return false;
			}
		}

		$up = explode('/',$url[0] == '/' ? $url : parse_url($url,PHP_URL_PATH));	// /apps/$app/$id
		$app = null;

		foreach( self::$app_register as $tapp => $reg ) {
			if( isset($reg['file_dir']) ) {
				$lup = $up;

				unset($lup[0]);
				unset($lup[1]);
				reset($lup);

				$fdp = explode('/',$reg['file_dir'][0] == '/' ?
					$reg['file_dir'] : parse_url($reg['file_dir'],PHP_URL_PATH));

				$found = true;

				foreach( $fdp as $part ) {
					if( current($lup) == $part ) {
						if( next($lup) === false ) {
							$found = false;
							break;
						}
					}
					else {
						$found = false;
						break;
					}
				}

				if( $found ) {
					$id	= current($lup);
					$app = $tapp;
					break;
				}
			}
		}

		if( $app === null ) {
			list(,,$app,$id) = $up;
		}

		return array(
			'app'       => self::VFS_APPNAME,
			'id'        => $fileinfo['name'],
			'app2'      => $app,
			'id2'       => $id,
			'remark'    => '',					// only list_attached currently sets the remark
			'owner'     => $fileinfo['uid'],
			'link_id'   => -$fileinfo['ino'],
			'lastmod'   => $fileinfo['mtime'],
			'size'      => $fileinfo['size'],
			'type'      => $fileinfo['mime'],
		);
	}

	/**
	 * lists all attachments to $app/$id
	 *
	 * @param string $app appname
	 * @param string $id id in app
	 * @return array with link_id => 'kind' of link-array pairs
	 */
	static function list_attached($app, $id, $file = '')
	{
		$path = self::vfs_path($app, $id, $file);
		//error_log(__METHOD__."($app,$id) url=$url");

		if (!($extra = self::get_registry($app,'find_extra'))) $extra = array();

		// always use regular links stream wrapper here: extended one is unnecessary (slow) for just listing attachments
		if ($app !== 'invoices' && substr($path,0,13) == 'stylite.links') $path = substr($path,8);

		$attached = array();
		if (($url2stats = Vfs::find($path,array('need_mime'=>true,'type'=>'F','url'=>true)+$extra,true)))
		{
			$props = Vfs::propfind(array_keys($url2stats));	// get the comments
			foreach($url2stats as $url => &$fileinfo)
			{
				$link = self::fileinfo2link($fileinfo,$url);
				if ($props && isset($props[$url]))
				{
					foreach($props[$url] as $prop)
					{
						if ($prop['ns'] == Vfs::DEFAULT_PROP_NAMESPACE && $prop['name'] == 'comment')
						{
							$link['remark'] = $prop['val'];
						}
					}
				}
				$attached[$link['link_id']] = $link;
			}
		}
		return $attached;
	}

	/**
	 * reverse static function of htmlspecialchars()
	 *
	 * @param string $str string to decode
	 * @return string decoded string
	 */
	static private function decode_htmlspecialchars($str)
	{
		return str_replace(array('&amp;','&quot;','&lt;','&gt;'),array('&','"','<','>'),$str);
	}

	/**
	 * Key for old link title in $data param to Link::notify
	 */
	const OLD_LINK_TITLE = 'old_link_title';

	/**
	 * notify other apps about changed content in $app,$id
	 *
	 * To give other apps the possebility to update a title, you can also specify
	 * a changed old link-title in $data[Link::OLD_LINK_TITLE].
	 *
	 * @param string $app name of app in which the updated happend
	 * @param string $id id in $app of the updated entry
	 * @param array $data =null updated data of changed entry, as the read-method of the BO-layer would supply it
	 * @param string $type ="unknown" type of update: "add", "edit", "update" or default "unknown"
	 */
	static function notify_update($app,$id,$data=null,$type='unknown')
	{
		self::delete_cache($app,$id);
		//error_log(__METHOD__."('$app', $id, $data)");
		foreach(self::get_links($app,$id,'!'.self::VFS_APPNAME) as $link_id => $link)
		{
			self::notify('update',$link['app'],$link['id'],$app,$id,$link_id,$data);
		}
		if (!empty($data[Link::OLD_LINK_TITLE]) && Json\Response::isJSONResponse())
		{
			// Update client side with new title
			Json\Response::get()->apply('egw.link_title_callback',array(array($app => array($id => self::title($app, $id)))));
		}

		// in case "someone" interested in all changes (used eg. for push)
		Hooks::process([
			'location' => 'notify-all',
			'type'     => !empty($data[Link::OLD_LINK_TITLE]) ? 'update' : $type,
			'app'      => $app,
			'id'       => $id,
			'data'     => $data,
		], null, true);
	}

	/**
	 * Stores notifications to run after regular processing is done
	 *
	 * @var array
	 */
	private static $notifies = array();

	/**
	 * notify an application about a new or deleted links to own entries or updates in the content of the linked entry
	 *
	 * Please note: not all apps supply update notifications
	 *
	 * @internal
	 * @param string $type 'link' for new links, 'unlink' for unlinked entries, 'update' of content in linked entries
	 * @param string $notify_app app to notify
	 * @param string $notify_id id in $notify_app
	 * @param string $target_app name of app whos entry changed, linked or deleted
	 * @param string $target_id id in $target_app
	 * @param array $data =null data of entry in app2 (optional)
	 */
	static private function notify($type,$notify_app,$notify_id,$target_app,$target_id,$link_id,$data=null)
	{
		//error_log(__METHOD__."('$type', '$notify_app', $notify_id, '$target_app', $target_id, $link_id, $data)");
		if ($link_id && isset(self::$app_register[$notify_app]) && isset(self::$app_register[$notify_app]['notify']))
		{
			if (!self::$notifies)
			{
				Egw::on_shutdown(array(__CLASS__, 'run_notifies'));
			}
			self::$notifies[] = array(
				'method'     => self::$app_register[$notify_app]['notify'],
				'type'       => $type,
				'id'         => $notify_id,
				'target_app' => $target_app,
				'target_id'  => $target_id,
				'link_id'    => $link_id,
				'data'       => $data,
			);
		}
	}

	/**
	 * Run notifications called by Egw::on_shutdown(), after regular processing is finished
	 */
	static public function run_notifies()
	{
		//error_log(__METHOD__."() count(self::\$notifies)=".count(self::$notifies));
		while(self::$notifies)
		{
			$args = array_shift(self::$notifies);
			$method = $args['method'];
			unset($args['method']);
			//error_log(__METHOD__."() calling $method(".array2string($args).')');
			self::exec($method, array($args));
		}
	}

	/**
	 * notifies about unlinked links
	 *
	 * @internal
	 * @param array &$links unlinked links from the database
	 */
	static private function notify_unlink(&$links)
	{
		foreach($links as $link)
		{
			// we notify both sides of the link, as the unlink command NOT clearly knows which side initiated the unlink
			self::notify('unlink',$link['link_app1'],$link['link_id1'],$link['link_app2'],$link['link_id2'],$link['link_id']);
			self::notify('unlink',$link['link_app2'],$link['link_id2'],$link['link_app1'],$link['link_id1'],$link['link_id']);
		}
	}

	/**
	 * Get a reference to the cached value for $app/$id for $type
	 *
	 * @param string $app
	 * @param string|int $id
	 * @param string $type ='title' 'title' or 'file_access'
	 * @return int|string can be null, if cache not yet set
	 */
	private static function &get_cache($app,$id,$type = 'title')
	{
		switch($type)
		{
			case 'title':
				if ($app === self::VFS_APPNAME)
				{
					$ret = null;	// do not cache file titles, they are just the names
					return $ret;
				}
				return self::$title_cache[$app.':'.$id];
			case 'file_access':
				return self::$file_access_cache[$app.':'.$id];
			default:
				throw new Exception\WrongParameter("Unknown type '$type'!");
		}
	}

	/**
	 * Set title and optional file_access cache for $app,$id
	 *
	 * Allows applications to set values for title and file access, eg. in their search method,
	 * to not be called again. This offloads the need to cache from the app to the link class.
	 * If there's no caching, items get read multiple times from the database!
	 *
	 * @param string $app
	 * @param int|string $id
	 * @param string $title title string or null
	 * @param int $file_access =null Acl::READ, Acl::EDIT or both or'ed together
	 */
	public static function set_cache($app,$id,$title,$file_access=null)
	{
		//error_log(__METHOD__."($app,$id,$title,$file_access)");
		// do not cache file titles, they are just the names
		if (!is_null($title) && $app != self::VFS_APPNAME)
		{
			self::$title_cache[$app.':'.$id] = $title;
		}
		if (!is_null($file_access))
		{
			self::$file_access_cache[$app.':'.$id] = $file_access;
		}
	}

	/**
	 * Delete the diverse caches for $app/$id
	 *
	 * @param string $app app-name or null to delete the whole cache
	 * @param int|string $id id or null to delete only file_access cache of given app (keeps title cache, if app implements file_access!)
	 */
	private static function delete_cache($app,$id)
	{
		unset(self::$title_cache[$app.':'.$id]);
		unset(self::$file_access_cache[$app.':'.$id]);
	}

	/**
	 * Store function call and parameters in session and return id to retrieve it result
	 *
	 * @param string $mime_type
	 * @param string $method
	 * @param array $params
	 * @param boolean $ignore_mime =false true: return id, even if nothing registered for given mime-type
	 * @return string|null md5 hash of stored data of server-side supported mime-type or null otherwise
	 */
	public static function set_data($mime_type, $method, array $params, $ignore_mime=false)
	{
		if (!$ignore_mime && (!($info = self::get_mime_info($mime_type)) || empty($info['mime_data'])))
		{
			return null;
		}
		array_unshift($params, $method);
		$id = md5(serialize($params));
		//error_log(__METHOD__."('$mime_type', '$method', ...) params=".array2string($params)." --> json=".array2string(serialize($params)).' --> id='.array2string($id));
		Cache::setSession(__CLASS__, $id, $params);
		return $id;
	}

	/**
	 * Call stored function with parameters and return result
	 *
	 * @param string $id
	 * @param boolean $return_resource =false false: return string, true: return resource
	 * @return mixed null if id is not found or invalid
	 * @throws Exception\WrongParameter
	 */
	public static function get_data($id, $return_resource=false)
	{
		$data = Cache::getSession(__CLASS__, $id);

		if (!isset($data) || empty($data[0]))
		{
			throw new Exception\WrongParameter(__METHOD__."('$id')");
		}
		$method = array_shift($data);
		$ret = self::exec($method, $data);

		if (is_resource($ret)) fseek($ret, 0);

		if ($return_resource != is_resource($ret))
		{
			if ($return_resource && ($fp = fopen('php://temp', 'w')))
			{
				fwrite($fp, $ret);
				fseek($fp, 0);
				$ret = $fp;
			}
			if (!$return_resource)
			{
				$fp = $ret;
				$ret = '';
				while(!feof($fp))
				{
					$ret .= fread($fp, 8192);
				}
				fclose($fp);
			}
		}
		//error_log(__METHOD__."('$id') returning ".gettype($ret).'='.array2string($ret));
		return $ret;
	}

	/**
	 * Check the file access perms for $app/id and given user $user
	 *
	 * If $user given and != current user AND app does not set file_access_user=true,
	 * always return false, as there's no way to check access for an other user!
	 *
	 * @ToDo $rel_path is not yet implemented, as no app use it currently
	 * @param string $app
	 * @param string|int $id id of entry
	 * @param int $required =Acl::READ Acl::{READ|EDIT}
	 * @param string $rel_path =null
	 * @param int $user =null default null = current user
	 * @return boolean true if access granted, false otherwise
	 */
	static function file_access($app,$id,$required=Acl::READ,$rel_path=null,$user=null)
	{
		// are we called for an other user
		if ($user && $user != $GLOBALS['egw_info']['user']['account_id'])
		{
			// check if app supports file_access WITH 4th $user parameter --> return false if not
			if (!self::get_registry($app,'file_access_user') || !($method = self::get_registry($app,'file_access')))
			{
				$ret = false;
				$err = "(no file_access_user)";
			}
			else
			{
				$ret = self::exec($method, array($id, $required, $rel_path, $user));
				$err = "(from $method)";
			}
			//error_log(__METHOD__."('$app',$id,$required,'$rel_path',$user) returning $err ".array2string($ret));
			return $ret;
		}

		$ret = $cache =& self::get_cache($app, $id,'file_access');

		if(!isset($ret) || $ret == self::NO_CACHE_FLAG || $required == Acl::EDIT && !($ret & $required))
		{
			if(($method = self::get_registry($app, 'file_access')))
			{
				$ret = self::exec($method, array($id, $required, $rel_path));
				// bool return value means cacheable, non-bool, means not cacheable, because of $rel_path
				if(is_bool($ret) && $cache !== self::NO_CACHE_FLAG)
				{
					$cache |= $ret ? $required | Acl::READ : 0;
				}
				else
				{
					// Do not cache anything for this app+id or any non boolean (false) will override
					$cache = self::NO_CACHE_FLAG;
				}
				$ret = $ret ? $required|Acl::READ : 0;
			}
			else
			{
				$ret = $cache |= self::title($app,$id) ? Acl::READ|Acl::EDIT : 0;
			}
			//error_log(__METHOD__."($app,$id,$required,$rel_path) got $ret --> ".($ret & $required ? 'true' : 'false'));
		}
		//else error_log(__METHOD__."($app,$id,$required,$rel_path) using cached value $cache --> ".($cache & $required ? 'true' : 'false'));
		return !!($ret & $required);
	}

	/**
	 * Execute a static method or $app.$class.$method string with given arguments
	 *
	 * In case of a non-static method as shared instance of the class is used.
	 * This is a replacement for global ExecMethod(2) functions.
	 *
	 * @param callable|string $method "$app.$class.$method" or static method
	 * @param array $params array with arguments incl. references
	 * @return mixed
	 */
	protected static function exec($method, array $params=array())
	{
		static $objs = array();

		// static methods or callables can be called directly
		if (is_callable($method))
		{
			return call_user_func_array($method, $params);
		}

		list($app, $class, $m) = $parts = explode('.', $method);
		if (count($parts) != 3) throw Api\Exception\WrongParameter("Wrong dot-delimited method string '$method'!");

		if (!isset($objs[$class]))
		{
			if (!class_exists($class))
			{
				require_once EGW_INCLUDE_ROOT.'/'.$app.'/inc/class.'.$class.'.inc.php';
			}
			$objs[$class] = new $class;
		}
		// php5.6+: return $objs[$class]->$m(...$params);
		return call_user_func_array(array($objs[$class], $m), $params);
	}
}
Link::init_static();