initial sabre upgrade (needs lots of work - to wit: authentication, redo the browser interface, and rework event export/import)

8 files changed, 2228 insertions, 0 deletions

diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php b/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php
new file mode 100644
index 000000000..d58b4a46e
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php
@@ -0,0 +1,226 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+use Sabre\VObject;
+use Sabre\CalDAV;
+
+/**
+ * Abstract Calendaring backend. Extend this class to create your own backends.
+ *
+ * Checkout the BackendInterface for all the methods that must be implemented.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+abstract class AbstractBackend implements BackendInterface {
+
+    /**
+     * Updates properties for a calendar.
+     *
+     * The list of mutations is stored in a Sabre\DAV\PropPatch object.
+     * To do the actual updates, you must tell this object which properties
+     * you're going to process with the handle() method.
+     *
+     * Calling the handle method is like telling the PropPatch object "I
+     * promise I can handle updating this property".
+     *
+     * Read the PropPatch documenation for more info and examples.
+     *
+     * @param string $path
+     * @param \Sabre\DAV\PropPatch $propPatch
+     * @return void
+     */
+    function updateCalendar($calendarId, \Sabre\DAV\PropPatch $propPatch) {
+
+    }
+
+    /**
+     * Returns a list of calendar objects.
+     *
+     * This method should work identical to getCalendarObject, but instead
+     * return all the calendar objects in the list as an array.
+     *
+     * If the backend supports this, it may allow for some speed-ups.
+     *
+     * @param mixed $calendarId
+     * @param array $uris
+     * @return array
+     */
+    function getMultipleCalendarObjects($calendarId, array $uris) {
+
+        return array_map(function($uri) use ($calendarId) {
+            return $this->getCalendarObject($calendarId, $uri);
+        }, $uris);
+
+    }
+
+    /**
+     * Performs a calendar-query on the contents of this calendar.
+     *
+     * The calendar-query is defined in RFC4791 : CalDAV. Using the
+     * calendar-query it is possible for a client to request a specific set of
+     * object, based on contents of iCalendar properties, date-ranges and
+     * iCalendar component types (VTODO, VEVENT).
+     *
+     * This method should just return a list of (relative) urls that match this
+     * query.
+     *
+     * The list of filters are specified as an array. The exact array is
+     * documented by \Sabre\CalDAV\CalendarQueryParser.
+     *
+     * Note that it is extremely likely that getCalendarObject for every path
+     * returned from this method will be called almost immediately after. You
+     * may want to anticipate this to speed up these requests.
+     *
+     * This method provides a default implementation, which parses *all* the
+     * iCalendar objects in the specified calendar.
+     *
+     * This default may well be good enough for personal use, and calendars
+     * that aren't very large. But if you anticipate high usage, big calendars
+     * or high loads, you are strongly adviced to optimize certain paths.
+     *
+     * The best way to do so is override this method and to optimize
+     * specifically for 'common filters'.
+     *
+     * Requests that are extremely common are:
+     *   * requests for just VEVENTS
+     *   * requests for just VTODO
+     *   * requests with a time-range-filter on either VEVENT or VTODO.
+     *
+     * ..and combinations of these requests. It may not be worth it to try to
+     * handle every possible situation and just rely on the (relatively
+     * easy to use) CalendarQueryValidator to handle the rest.
+     *
+     * Note that especially time-range-filters may be difficult to parse. A
+     * time-range filter specified on a VEVENT must for instance also handle
+     * recurrence rules correctly.
+     * A good example of how to interprete all these filters can also simply
+     * be found in \Sabre\CalDAV\CalendarQueryFilter. This class is as correct
+     * as possible, so it gives you a good idea on what type of stuff you need
+     * to think of.
+     *
+     * @param mixed $calendarId
+     * @param array $filters
+     * @return array
+     */
+    function calendarQuery($calendarId, array $filters) {
+
+        $result = [];
+        $objects = $this->getCalendarObjects($calendarId);
+
+        foreach ($objects as $object) {
+
+            if ($this->validateFilterForObject($object, $filters)) {
+                $result[] = $object['uri'];
+            }
+
+        }
+
+        return $result;
+
+    }
+
+    /**
+     * This method validates if a filter (as passed to calendarQuery) matches
+     * the given object.
+     *
+     * @param array $object
+     * @param array $filters
+     * @return bool
+     */
+    protected function validateFilterForObject(array $object, array $filters) {
+
+        // Unfortunately, setting the 'calendardata' here is optional. If
+        // it was excluded, we actually need another call to get this as
+        // well.
+        if (!isset($object['calendardata'])) {
+            $object = $this->getCalendarObject($object['calendarid'], $object['uri']);
+        }
+
+        $vObject = VObject\Reader::read($object['calendardata']);
+
+        $validator = new CalDAV\CalendarQueryValidator();
+        $result = $validator->validate($vObject, $filters);
+
+        // Destroy circular references so PHP will GC the object.
+        $vObject->destroy();
+
+        return $result;
+
+    }
+
+    /**
+     * Searches through all of a users calendars and calendar objects to find
+     * an object with a specific UID.
+     *
+     * This method should return the path to this object, relative to the
+     * calendar home, so this path usually only contains two parts:
+     *
+     * calendarpath/objectpath.ics
+     *
+     * If the uid is not found, return null.
+     *
+     * This method should only consider * objects that the principal owns, so
+     * any calendars owned by other principals that also appear in this
+     * collection should be ignored.
+     *
+     * @param string $principalUri
+     * @param string $uid
+     * @return string|null
+     */
+    function getCalendarObjectByUID($principalUri, $uid) {
+
+        // Note: this is a super slow naive implementation of this method. You
+        // are highly recommended to optimize it, if your backend allows it.
+        foreach ($this->getCalendarsForUser($principalUri) as $calendar) {
+
+            // We must ignore calendars owned by other principals.
+            if ($calendar['principaluri'] !== $principalUri) {
+                continue;
+            }
+
+            // Ignore calendars that are shared.
+            if (isset($calendar['{http://sabredav.org/ns}owner-principal']) && $calendar['{http://sabredav.org/ns}owner-principal'] !== $principalUri) {
+                continue;
+            }
+
+            $results = $this->calendarQuery(
+                $calendar['id'],
+                [
+                    'name'         => 'VCALENDAR',
+                    'prop-filters' => [],
+                    'comp-filters' => [
+                        [
+                            'name'           => 'VEVENT',
+                            'is-not-defined' => false,
+                            'time-range'     => null,
+                            'comp-filters'   => [],
+                            'prop-filters'   => [
+                                [
+                                    'name'           => 'UID',
+                                    'is-not-defined' => false,
+                                    'time-range'     => null,
+                                    'text-match'     => [
+                                        'value'            => $uid,
+                                        'negate-condition' => false,
+                                        'collation'        => 'i;octet',
+                                    ],
+                                    'param-filters' => [],
+                                ],
+                            ]
+                        ]
+                    ],
+                ]
+            );
+            if ($results) {
+                // We have a match
+                return $calendar['uri'] . '/' . $results[0];
+            }
+
+        }
+
+    }
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/BackendInterface.php b/vendor/sabre/dav/lib/CalDAV/Backend/BackendInterface.php
new file mode 100644
index 000000000..7513fb60d
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/BackendInterface.php
@@ -0,0 +1,268 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+/**
+ * Every CalDAV backend must at least implement this interface.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface BackendInterface {
+
+    /**
+     * Returns a list of calendars for a principal.
+     *
+     * Every project is an array with the following keys:
+     *  * id, a unique id that will be used by other functions to modify the
+     *    calendar. This can be the same as the uri or a database key.
+     *  * uri, which is the basename of the uri with which the calendar is
+     *    accessed.
+     *  * principaluri. The owner of the calendar. Almost always the same as
+     *    principalUri passed to this method.
+     *
+     * Furthermore it can contain webdav properties in clark notation. A very
+     * common one is '{DAV:}displayname'.
+     *
+     * Many clients also require:
+     * {urn:ietf:params:xml:ns:caldav}supported-calendar-component-set
+     * For this property, you can just return an instance of
+     * Sabre\CalDAV\Property\SupportedCalendarComponentSet.
+     *
+     * If you return {http://sabredav.org/ns}read-only and set the value to 1,
+     * ACL will automatically be put in read-only mode.
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getCalendarsForUser($principalUri);
+
+    /**
+     * Creates a new calendar for a principal.
+     *
+     * If the creation was a success, an id must be returned that can be used to
+     * reference this calendar in other methods, such as updateCalendar.
+     *
+     * @param string $principalUri
+     * @param string $calendarUri
+     * @param array $properties
+     * @return void
+     */
+    function createCalendar($principalUri, $calendarUri, array $properties);
+
+    /**
+     * Updates properties for a calendar.
+     *
+     * The list of mutations is stored in a Sabre\DAV\PropPatch object.
+     * To do the actual updates, you must tell this object which properties
+     * you're going to process with the handle() method.
+     *
+     * Calling the handle method is like telling the PropPatch object "I
+     * promise I can handle updating this property".
+     *
+     * Read the PropPatch documentation for more info and examples.
+     *
+     * @param string $path
+     * @param \Sabre\DAV\PropPatch $propPatch
+     * @return void
+     */
+    function updateCalendar($calendarId, \Sabre\DAV\PropPatch $propPatch);
+
+    /**
+     * Delete a calendar and all its objects
+     *
+     * @param mixed $calendarId
+     * @return void
+     */
+    function deleteCalendar($calendarId);
+
+    /**
+     * Returns all calendar objects within a calendar.
+     *
+     * Every item contains an array with the following keys:
+     *   * calendardata - The iCalendar-compatible calendar data
+     *   * uri - a unique key which will be used to construct the uri. This can
+     *     be any arbitrary string, but making sure it ends with '.ics' is a
+     *     good idea. This is only the basename, or filename, not the full
+     *     path.
+     *   * lastmodified - a timestamp of the last modification time
+     *   * etag - An arbitrary string, surrounded by double-quotes. (e.g.:
+     *   '"abcdef"')
+     *   * size - The size of the calendar objects, in bytes.
+     *   * component - optional, a string containing the type of object, such
+     *     as 'vevent' or 'vtodo'. If specified, this will be used to populate
+     *     the Content-Type header.
+     *
+     * Note that the etag is optional, but it's highly encouraged to return for
+     * speed reasons.
+     *
+     * The calendardata is also optional. If it's not returned
+     * 'getCalendarObject' will be called later, which *is* expected to return
+     * calendardata.
+     *
+     * If neither etag or size are specified, the calendardata will be
+     * used/fetched to determine these numbers. If both are specified the
+     * amount of times this is needed is reduced by a great degree.
+     *
+     * @param mixed $calendarId
+     * @return array
+     */
+    function getCalendarObjects($calendarId);
+
+    /**
+     * Returns information from a single calendar object, based on it's object
+     * uri.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * The returned array must have the same keys as getCalendarObjects. The
+     * 'calendardata' object is required here though, while it's not required
+     * for getCalendarObjects.
+     *
+     * This method must return null if the object did not exist.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @return array|null
+     */
+    function getCalendarObject($calendarId, $objectUri);
+
+    /**
+     * Returns a list of calendar objects.
+     *
+     * This method should work identical to getCalendarObject, but instead
+     * return all the calendar objects in the list as an array.
+     *
+     * If the backend supports this, it may allow for some speed-ups.
+     *
+     * @param mixed $calendarId
+     * @param array $uris
+     * @return array
+     */
+    function getMultipleCalendarObjects($calendarId, array $uris);
+
+    /**
+     * Creates a new calendar object.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * It is possible to return an etag from this function, which will be used
+     * in the response to this PUT request. Note that the ETag must be
+     * surrounded by double-quotes.
+     *
+     * However, you should only really return this ETag if you don't mangle the
+     * calendar-data. If the result of a subsequent GET to this object is not
+     * the exact same as this request body, you should omit the ETag.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @param string $calendarData
+     * @return string|null
+     */
+    function createCalendarObject($calendarId, $objectUri, $calendarData);
+
+    /**
+     * Updates an existing calendarobject, based on it's uri.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * It is possible return an etag from this function, which will be used in
+     * the response to this PUT request. Note that the ETag must be surrounded
+     * by double-quotes.
+     *
+     * However, you should only really return this ETag if you don't mangle the
+     * calendar-data. If the result of a subsequent GET to this object is not
+     * the exact same as this request body, you should omit the ETag.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @param string $calendarData
+     * @return string|null
+     */
+    function updateCalendarObject($calendarId, $objectUri, $calendarData);
+
+    /**
+     * Deletes an existing calendar object.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @return void
+     */
+    function deleteCalendarObject($calendarId, $objectUri);
+
+    /**
+     * Performs a calendar-query on the contents of this calendar.
+     *
+     * The calendar-query is defined in RFC4791 : CalDAV. Using the
+     * calendar-query it is possible for a client to request a specific set of
+     * object, based on contents of iCalendar properties, date-ranges and
+     * iCalendar component types (VTODO, VEVENT).
+     *
+     * This method should just return a list of (relative) urls that match this
+     * query.
+     *
+     * The list of filters are specified as an array. The exact array is
+     * documented by Sabre\CalDAV\CalendarQueryParser.
+     *
+     * Note that it is extremely likely that getCalendarObject for every path
+     * returned from this method will be called almost immediately after. You
+     * may want to anticipate this to speed up these requests.
+     *
+     * This method provides a default implementation, which parses *all* the
+     * iCalendar objects in the specified calendar.
+     *
+     * This default may well be good enough for personal use, and calendars
+     * that aren't very large. But if you anticipate high usage, big calendars
+     * or high loads, you are strongly adviced to optimize certain paths.
+     *
+     * The best way to do so is override this method and to optimize
+     * specifically for 'common filters'.
+     *
+     * Requests that are extremely common are:
+     *   * requests for just VEVENTS
+     *   * requests for just VTODO
+     *   * requests with a time-range-filter on either VEVENT or VTODO.
+     *
+     * ..and combinations of these requests. It may not be worth it to try to
+     * handle every possible situation and just rely on the (relatively
+     * easy to use) CalendarQueryValidator to handle the rest.
+     *
+     * Note that especially time-range-filters may be difficult to parse. A
+     * time-range filter specified on a VEVENT must for instance also handle
+     * recurrence rules correctly.
+     * A good example of how to interprete all these filters can also simply
+     * be found in Sabre\CalDAV\CalendarQueryFilter. This class is as correct
+     * as possible, so it gives you a good idea on what type of stuff you need
+     * to think of.
+     *
+     * @param mixed $calendarId
+     * @param array $filters
+     * @return array
+     */
+    function calendarQuery($calendarId, array $filters);
+
+    /**
+     * Searches through all of a users calendars and calendar objects to find
+     * an object with a specific UID.
+     *
+     * This method should return the path to this object, relative to the
+     * calendar home, so this path usually only contains two parts:
+     *
+     * calendarpath/objectpath.ics
+     *
+     * If the uid is not found, return null.
+     *
+     * This method should only consider * objects that the principal owns, so
+     * any calendars owned by other principals that also appear in this
+     * collection should be ignored.
+     *
+     * @param string $principalUri
+     * @param string $uid
+     * @return string|null
+     */
+    function getCalendarObjectByUID($principalUri, $uid);
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/NotificationSupport.php b/vendor/sabre/dav/lib/CalDAV/Backend/NotificationSupport.php
new file mode 100644
index 000000000..19b9b22a7
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/NotificationSupport.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+use Sabre\CalDAV\Xml\Notification\NotificationInterface;
+
+/**
+ * Adds caldav notification support to a backend.
+ *
+ * Note: This feature is experimental, and may change in between different
+ * SabreDAV versions.
+ *
+ * Notifications are defined at:
+ * http://svn.calendarserver.org/repository/calendarserver/CalendarServer/trunk/doc/Extensions/caldav-notifications.txt
+ *
+ * These notifications are basically a list of server-generated notifications
+ * displayed to the user. Users can dismiss notifications by deleting them.
+ *
+ * The primary usecase is to allow for calendar-sharing.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface NotificationSupport extends BackendInterface {
+
+    /**
+     * Returns a list of notifications for a given principal url.
+     *
+     * @param string $principalUri
+     * @return NotificationInterface[]
+     */
+    function getNotificationsForPrincipal($principalUri);
+
+    /**
+     * This deletes a specific notifcation.
+     *
+     * This may be called by a client once it deems a notification handled.
+     *
+     * @param string $principalUri
+     * @param NotificationInterface $notification
+     * @return void
+     */
+    function deleteNotification($principalUri, NotificationInterface $notification);
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/PDO.php b/vendor/sabre/dav/lib/CalDAV/Backend/PDO.php
new file mode 100644
index 000000000..76b69dc6e
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/PDO.php
@@ -0,0 +1,1210 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+use Sabre\VObject;
+use Sabre\CalDAV;
+use Sabre\DAV;
+use Sabre\DAV\Exception\Forbidden;
+
+/**
+ * PDO CalDAV backend
+ *
+ * This backend is used to store calendar-data in a PDO database, such as
+ * sqlite or MySQL
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+class PDO extends AbstractBackend implements SyncSupport, SubscriptionSupport, SchedulingSupport {
+
+    /**
+     * We need to specify a max date, because we need to stop *somewhere*
+     *
+     * On 32 bit system the maximum for a signed integer is 2147483647, so
+     * MAX_DATE cannot be higher than date('Y-m-d', 2147483647) which results
+     * in 2038-01-19 to avoid problems when the date is converted
+     * to a unix timestamp.
+     */
+    const MAX_DATE = '2038-01-01';
+
+    /**
+     * pdo
+     *
+     * @var \PDO
+     */
+    protected $pdo;
+
+    /**
+     * The table name that will be used for calendars
+     *
+     * @var string
+     */
+    public $calendarTableName = 'calendars';
+
+    /**
+     * The table name that will be used for calendar objects
+     *
+     * @var string
+     */
+    public $calendarObjectTableName = 'calendarobjects';
+
+    /**
+     * The table name that will be used for tracking changes in calendars.
+     *
+     * @var string
+     */
+    public $calendarChangesTableName = 'calendarchanges';
+
+    /**
+     * The table name that will be used inbox items.
+     *
+     * @var string
+     */
+    public $schedulingObjectTableName = 'schedulingobjects';
+
+    /**
+     * The table name that will be used for calendar subscriptions.
+     *
+     * @var string
+     */
+    public $calendarSubscriptionsTableName = 'calendarsubscriptions';
+
+    /**
+     * List of CalDAV properties, and how they map to database fieldnames
+     * Add your own properties by simply adding on to this array.
+     *
+     * Note that only string-based properties are supported here.
+     *
+     * @var array
+     */
+    public $propertyMap = [
+        '{DAV:}displayname'                                   => 'displayname',
+        '{urn:ietf:params:xml:ns:caldav}calendar-description' => 'description',
+        '{urn:ietf:params:xml:ns:caldav}calendar-timezone'    => 'timezone',
+        '{http://apple.com/ns/ical/}calendar-order'           => 'calendarorder',
+        '{http://apple.com/ns/ical/}calendar-color'           => 'calendarcolor',
+    ];
+
+    /**
+     * List of subscription properties, and how they map to database fieldnames.
+     *
+     * @var array
+     */
+    public $subscriptionPropertyMap = [
+        '{DAV:}displayname'                                           => 'displayname',
+        '{http://apple.com/ns/ical/}refreshrate'                      => 'refreshrate',
+        '{http://apple.com/ns/ical/}calendar-order'                   => 'calendarorder',
+        '{http://apple.com/ns/ical/}calendar-color'                   => 'calendarcolor',
+        '{http://calendarserver.org/ns/}subscribed-strip-todos'       => 'striptodos',
+        '{http://calendarserver.org/ns/}subscribed-strip-alarms'      => 'stripalarms',
+        '{http://calendarserver.org/ns/}subscribed-strip-attachments' => 'stripattachments',
+    ];
+
+    /**
+     * Creates the backend
+     *
+     * @param \PDO $pdo
+     */
+    function __construct(\PDO $pdo) {
+
+        $this->pdo = $pdo;
+
+    }
+
+    /**
+     * Returns a list of calendars for a principal.
+     *
+     * Every project is an array with the following keys:
+     *  * id, a unique id that will be used by other functions to modify the
+     *    calendar. This can be the same as the uri or a database key.
+     *  * uri. This is just the 'base uri' or 'filename' of the calendar.
+     *  * principaluri. The owner of the calendar. Almost always the same as
+     *    principalUri passed to this method.
+     *
+     * Furthermore it can contain webdav properties in clark notation. A very
+     * common one is '{DAV:}displayname'.
+     *
+     * Many clients also require:
+     * {urn:ietf:params:xml:ns:caldav}supported-calendar-component-set
+     * For this property, you can just return an instance of
+     * Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet.
+     *
+     * If you return {http://sabredav.org/ns}read-only and set the value to 1,
+     * ACL will automatically be put in read-only mode.
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getCalendarsForUser($principalUri) {
+
+        $fields = array_values($this->propertyMap);
+        $fields[] = 'id';
+        $fields[] = 'uri';
+        $fields[] = 'synctoken';
+        $fields[] = 'components';
+        $fields[] = 'principaluri';
+        $fields[] = 'transparent';
+
+        // Making fields a comma-delimited list
+        $fields = implode(', ', $fields);
+        $stmt = $this->pdo->prepare("SELECT " . $fields . " FROM " . $this->calendarTableName . " WHERE principaluri = ? ORDER BY calendarorder ASC");
+        $stmt->execute([$principalUri]);
+
+        $calendars = [];
+        while ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+
+            $components = [];
+            if ($row['components']) {
+                $components = explode(',', $row['components']);
+            }
+
+            $calendar = [
+                'id'                                                                 => $row['id'],
+                'uri'                                                                => $row['uri'],
+                'principaluri'                                                       => $row['principaluri'],
+                '{' . CalDAV\Plugin::NS_CALENDARSERVER . '}getctag'                  => 'http://sabre.io/ns/sync/' . ($row['synctoken'] ? $row['synctoken'] : '0'),
+                '{http://sabredav.org/ns}sync-token'                                 => $row['synctoken'] ? $row['synctoken'] : '0',
+                '{' . CalDAV\Plugin::NS_CALDAV . '}supported-calendar-component-set' => new CalDAV\Xml\Property\SupportedCalendarComponentSet($components),
+                '{' . CalDAV\Plugin::NS_CALDAV . '}schedule-calendar-transp'         => new CalDAV\Xml\Property\ScheduleCalendarTransp($row['transparent'] ? 'transparent' : 'opaque'),
+            ];
+
+
+            foreach ($this->propertyMap as $xmlName => $dbName) {
+                $calendar[$xmlName] = $row[$dbName];
+            }
+
+            $calendars[] = $calendar;
+
+        }
+
+        return $calendars;
+
+    }
+
+    /**
+     * Creates a new calendar for a principal.
+     *
+     * If the creation was a success, an id must be returned that can be used
+     * to reference this calendar in other methods, such as updateCalendar.
+     *
+     * @param string $principalUri
+     * @param string $calendarUri
+     * @param array $properties
+     * @return string
+     */
+    function createCalendar($principalUri, $calendarUri, array $properties) {
+
+        $fieldNames = [
+            'principaluri',
+            'uri',
+            'synctoken',
+            'transparent',
+        ];
+        $values = [
+            ':principaluri' => $principalUri,
+            ':uri'          => $calendarUri,
+            ':synctoken'    => 1,
+            ':transparent'  => 0,
+        ];
+
+        // Default value
+        $sccs = '{urn:ietf:params:xml:ns:caldav}supported-calendar-component-set';
+        $fieldNames[] = 'components';
+        if (!isset($properties[$sccs])) {
+            $values[':components'] = 'VEVENT,VTODO';
+        } else {
+            if (!($properties[$sccs] instanceof CalDAV\Xml\Property\SupportedCalendarComponentSet)) {
+                throw new DAV\Exception('The ' . $sccs . ' property must be of type: \Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet');
+            }
+            $values[':components'] = implode(',', $properties[$sccs]->getValue());
+        }
+        $transp = '{' . CalDAV\Plugin::NS_CALDAV . '}schedule-calendar-transp';
+        if (isset($properties[$transp])) {
+            $values[':transparent'] = $properties[$transp]->getValue() === 'transparent';
+        }
+
+        foreach ($this->propertyMap as $xmlName => $dbName) {
+            if (isset($properties[$xmlName])) {
+
+                $values[':' . $dbName] = $properties[$xmlName];
+                $fieldNames[] = $dbName;
+            }
+        }
+
+        $stmt = $this->pdo->prepare("INSERT INTO " . $this->calendarTableName . " (" . implode(', ', $fieldNames) . ") VALUES (" . implode(', ', array_keys($values)) . ")");
+        $stmt->execute($values);
+
+        return $this->pdo->lastInsertId();
+
+    }
+
+    /**
+     * Updates properties for a calendar.
+     *
+     * The list of mutations is stored in a Sabre\DAV\PropPatch object.
+     * To do the actual updates, you must tell this object which properties
+     * you're going to process with the handle() method.
+     *
+     * Calling the handle method is like telling the PropPatch object "I
+     * promise I can handle updating this property".
+     *
+     * Read the PropPatch documenation for more info and examples.
+     *
+     * @param string $calendarId
+     * @param \Sabre\DAV\PropPatch $propPatch
+     * @return void
+     */
+    function updateCalendar($calendarId, \Sabre\DAV\PropPatch $propPatch) {
+
+        $supportedProperties = array_keys($this->propertyMap);
+        $supportedProperties[] = '{' . CalDAV\Plugin::NS_CALDAV . '}schedule-calendar-transp';
+
+        $propPatch->handle($supportedProperties, function($mutations) use ($calendarId) {
+            $newValues = [];
+            foreach ($mutations as $propertyName => $propertyValue) {
+
+                switch ($propertyName) {
+                    case '{' . CalDAV\Plugin::NS_CALDAV . '}schedule-calendar-transp' :
+                        $fieldName = 'transparent';
+                        $newValues[$fieldName] = $propertyValue->getValue() === 'transparent';
+                        break;
+                    default :
+                        $fieldName = $this->propertyMap[$propertyName];
+                        $newValues[$fieldName] = $propertyValue;
+                        break;
+                }
+
+            }
+            $valuesSql = [];
+            foreach ($newValues as $fieldName => $value) {
+                $valuesSql[] = $fieldName . ' = ?';
+            }
+
+            $stmt = $this->pdo->prepare("UPDATE " . $this->calendarTableName . " SET " . implode(', ', $valuesSql) . " WHERE id = ?");
+            $newValues['id'] = $calendarId;
+            $stmt->execute(array_values($newValues));
+
+            $this->addChange($calendarId, "", 2);
+
+            return true;
+
+        });
+
+    }
+
+    /**
+     * Delete a calendar and all it's objects
+     *
+     * @param string $calendarId
+     * @return void
+     */
+    function deleteCalendar($calendarId) {
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->calendarObjectTableName . ' WHERE calendarid = ?');
+        $stmt->execute([$calendarId]);
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->calendarTableName . ' WHERE id = ?');
+        $stmt->execute([$calendarId]);
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->calendarChangesTableName . ' WHERE calendarid = ?');
+        $stmt->execute([$calendarId]);
+
+    }
+
+    /**
+     * Returns all calendar objects within a calendar.
+     *
+     * Every item contains an array with the following keys:
+     *   * calendardata - The iCalendar-compatible calendar data
+     *   * uri - a unique key which will be used to construct the uri. This can
+     *     be any arbitrary string, but making sure it ends with '.ics' is a
+     *     good idea. This is only the basename, or filename, not the full
+     *     path.
+     *   * lastmodified - a timestamp of the last modification time
+     *   * etag - An arbitrary string, surrounded by double-quotes. (e.g.:
+     *   '  "abcdef"')
+     *   * size - The size of the calendar objects, in bytes.
+     *   * component - optional, a string containing the type of object, such
+     *     as 'vevent' or 'vtodo'. If specified, this will be used to populate
+     *     the Content-Type header.
+     *
+     * Note that the etag is optional, but it's highly encouraged to return for
+     * speed reasons.
+     *
+     * The calendardata is also optional. If it's not returned
+     * 'getCalendarObject' will be called later, which *is* expected to return
+     * calendardata.
+     *
+     * If neither etag or size are specified, the calendardata will be
+     * used/fetched to determine these numbers. If both are specified the
+     * amount of times this is needed is reduced by a great degree.
+     *
+     * @param string $calendarId
+     * @return array
+     */
+    function getCalendarObjects($calendarId) {
+
+        $stmt = $this->pdo->prepare('SELECT id, uri, lastmodified, etag, calendarid, size, componenttype FROM ' . $this->calendarObjectTableName . ' WHERE calendarid = ?');
+        $stmt->execute([$calendarId]);
+
+        $result = [];
+        foreach ($stmt->fetchAll(\PDO::FETCH_ASSOC) as $row) {
+            $result[] = [
+                'id'           => $row['id'],
+                'uri'          => $row['uri'],
+                'lastmodified' => $row['lastmodified'],
+                'etag'         => '"' . $row['etag'] . '"',
+                'calendarid'   => $row['calendarid'],
+                'size'         => (int)$row['size'],
+                'component'    => strtolower($row['componenttype']),
+            ];
+        }
+
+        return $result;
+
+    }
+
+    /**
+     * Returns information from a single calendar object, based on it's object
+     * uri.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * The returned array must have the same keys as getCalendarObjects. The
+     * 'calendardata' object is required here though, while it's not required
+     * for getCalendarObjects.
+     *
+     * This method must return null if the object did not exist.
+     *
+     * @param string $calendarId
+     * @param string $objectUri
+     * @return array|null
+     */
+    function getCalendarObject($calendarId, $objectUri) {
+
+        $stmt = $this->pdo->prepare('SELECT id, uri, lastmodified, etag, calendarid, size, calendardata, componenttype FROM ' . $this->calendarObjectTableName . ' WHERE calendarid = ? AND uri = ?');
+        $stmt->execute([$calendarId, $objectUri]);
+        $row = $stmt->fetch(\PDO::FETCH_ASSOC);
+
+        if (!$row) return null;
+
+        return [
+            'id'            => $row['id'],
+            'uri'           => $row['uri'],
+            'lastmodified'  => $row['lastmodified'],
+            'etag'          => '"' . $row['etag'] . '"',
+            'calendarid'    => $row['calendarid'],
+            'size'          => (int)$row['size'],
+            'calendardata'  => $row['calendardata'],
+            'component'     => strtolower($row['componenttype']),
+         ];
+
+    }
+
+    /**
+     * Returns a list of calendar objects.
+     *
+     * This method should work identical to getCalendarObject, but instead
+     * return all the calendar objects in the list as an array.
+     *
+     * If the backend supports this, it may allow for some speed-ups.
+     *
+     * @param mixed $calendarId
+     * @param array $uris
+     * @return array
+     */
+    function getMultipleCalendarObjects($calendarId, array $uris) {
+
+        $query = 'SELECT id, uri, lastmodified, etag, calendarid, size, calendardata, componenttype FROM ' . $this->calendarObjectTableName . ' WHERE calendarid = ? AND uri IN (';
+        // Inserting a whole bunch of question marks
+        $query .= implode(',', array_fill(0, count($uris), '?'));
+        $query .= ')';
+
+        $stmt = $this->pdo->prepare($query);
+        $stmt->execute(array_merge([$calendarId], $uris));
+
+        $result = [];
+        while ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+
+            $result[] = [
+                'id'           => $row['id'],
+                'uri'          => $row['uri'],
+                'lastmodified' => $row['lastmodified'],
+                'etag'         => '"' . $row['etag'] . '"',
+                'calendarid'   => $row['calendarid'],
+                'size'         => (int)$row['size'],
+                'calendardata' => $row['calendardata'],
+                'component'    => strtolower($row['componenttype']),
+            ];
+
+        }
+        return $result;
+
+    }
+
+
+    /**
+     * Creates a new calendar object.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * It is possible return an etag from this function, which will be used in
+     * the response to this PUT request. Note that the ETag must be surrounded
+     * by double-quotes.
+     *
+     * However, you should only really return this ETag if you don't mangle the
+     * calendar-data. If the result of a subsequent GET to this object is not
+     * the exact same as this request body, you should omit the ETag.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @param string $calendarData
+     * @return string|null
+     */
+    function createCalendarObject($calendarId, $objectUri, $calendarData) {
+
+        $extraData = $this->getDenormalizedData($calendarData);
+
+        $stmt = $this->pdo->prepare('INSERT INTO ' . $this->calendarObjectTableName . ' (calendarid, uri, calendardata, lastmodified, etag, size, componenttype, firstoccurence, lastoccurence, uid) VALUES (?,?,?,?,?,?,?,?,?,?)');
+        $stmt->execute([
+            $calendarId,
+            $objectUri,
+            $calendarData,
+            time(),
+            $extraData['etag'],
+            $extraData['size'],
+            $extraData['componentType'],
+            $extraData['firstOccurence'],
+            $extraData['lastOccurence'],
+            $extraData['uid'],
+        ]);
+        $this->addChange($calendarId, $objectUri, 1);
+
+        return '"' . $extraData['etag'] . '"';
+
+    }
+
+    /**
+     * Updates an existing calendarobject, based on it's uri.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * It is possible return an etag from this function, which will be used in
+     * the response to this PUT request. Note that the ETag must be surrounded
+     * by double-quotes.
+     *
+     * However, you should only really return this ETag if you don't mangle the
+     * calendar-data. If the result of a subsequent GET to this object is not
+     * the exact same as this request body, you should omit the ETag.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @param string $calendarData
+     * @return string|null
+     */
+    function updateCalendarObject($calendarId, $objectUri, $calendarData) {
+
+        $extraData = $this->getDenormalizedData($calendarData);
+
+        $stmt = $this->pdo->prepare('UPDATE ' . $this->calendarObjectTableName . ' SET calendardata = ?, lastmodified = ?, etag = ?, size = ?, componenttype = ?, firstoccurence = ?, lastoccurence = ?, uid = ? WHERE calendarid = ? AND uri = ?');
+        $stmt->execute([$calendarData, time(), $extraData['etag'], $extraData['size'], $extraData['componentType'], $extraData['firstOccurence'], $extraData['lastOccurence'], $extraData['uid'], $calendarId, $objectUri]);
+
+        $this->addChange($calendarId, $objectUri, 2);
+
+        return '"' . $extraData['etag'] . '"';
+
+    }
+
+    /**
+     * Parses some information from calendar objects, used for optimized
+     * calendar-queries.
+     *
+     * Returns an array with the following keys:
+     *   * etag - An md5 checksum of the object without the quotes.
+     *   * size - Size of the object in bytes
+     *   * componentType - VEVENT, VTODO or VJOURNAL
+     *   * firstOccurence
+     *   * lastOccurence
+     *   * uid - value of the UID property
+     *
+     * @param string $calendarData
+     * @return array
+     */
+    protected function getDenormalizedData($calendarData) {
+
+        $vObject = VObject\Reader::read($calendarData);
+        $componentType = null;
+        $component = null;
+        $firstOccurence = null;
+        $lastOccurence = null;
+        $uid = null;
+        foreach ($vObject->getComponents() as $component) {
+            if ($component->name !== 'VTIMEZONE') {
+                $componentType = $component->name;
+                $uid = (string)$component->UID;
+                break;
+            }
+        }
+        if (!$componentType) {
+            throw new \Sabre\DAV\Exception\BadRequest('Calendar objects must have a VJOURNAL, VEVENT or VTODO component');
+        }
+        if ($componentType === 'VEVENT') {
+            $firstOccurence = $component->DTSTART->getDateTime()->getTimeStamp();
+            // Finding the last occurence is a bit harder
+            if (!isset($component->RRULE)) {
+                if (isset($component->DTEND)) {
+                    $lastOccurence = $component->DTEND->getDateTime()->getTimeStamp();
+                } elseif (isset($component->DURATION)) {
+                    $endDate = clone $component->DTSTART->getDateTime();
+                    $endDate = $endDate->add(VObject\DateTimeParser::parse($component->DURATION->getValue()));
+                    $lastOccurence = $endDate->getTimeStamp();
+                } elseif (!$component->DTSTART->hasTime()) {
+                    $endDate = clone $component->DTSTART->getDateTime();
+                    $endDate = $endDate->modify('+1 day');
+                    $lastOccurence = $endDate->getTimeStamp();
+                } else {
+                    $lastOccurence = $firstOccurence;
+                }
+            } else {
+                $it = new VObject\Recur\EventIterator($vObject, (string)$component->UID);
+                $maxDate = new \DateTime(self::MAX_DATE);
+                if ($it->isInfinite()) {
+                    $lastOccurence = $maxDate->getTimeStamp();
+                } else {
+                    $end = $it->getDtEnd();
+                    while ($it->valid() && $end < $maxDate) {
+                        $end = $it->getDtEnd();
+                        $it->next();
+
+                    }
+                    $lastOccurence = $end->getTimeStamp();
+                }
+
+            }
+        }
+
+        // Destroy circular references to PHP will GC the object.
+        $vObject->destroy();
+
+        return [
+            'etag'           => md5($calendarData),
+            'size'           => strlen($calendarData),
+            'componentType'  => $componentType,
+            'firstOccurence' => $firstOccurence,
+            'lastOccurence'  => $lastOccurence,
+            'uid'            => $uid,
+        ];
+
+    }
+
+    /**
+     * Deletes an existing calendar object.
+     *
+     * The object uri is only the basename, or filename and not a full path.
+     *
+     * @param string $calendarId
+     * @param string $objectUri
+     * @return void
+     */
+    function deleteCalendarObject($calendarId, $objectUri) {
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->calendarObjectTableName . ' WHERE calendarid = ? AND uri = ?');
+        $stmt->execute([$calendarId, $objectUri]);
+
+        $this->addChange($calendarId, $objectUri, 3);
+
+    }
+
+    /**
+     * Performs a calendar-query on the contents of this calendar.
+     *
+     * The calendar-query is defined in RFC4791 : CalDAV. Using the
+     * calendar-query it is possible for a client to request a specific set of
+     * object, based on contents of iCalendar properties, date-ranges and
+     * iCalendar component types (VTODO, VEVENT).
+     *
+     * This method should just return a list of (relative) urls that match this
+     * query.
+     *
+     * The list of filters are specified as an array. The exact array is
+     * documented by \Sabre\CalDAV\CalendarQueryParser.
+     *
+     * Note that it is extremely likely that getCalendarObject for every path
+     * returned from this method will be called almost immediately after. You
+     * may want to anticipate this to speed up these requests.
+     *
+     * This method provides a default implementation, which parses *all* the
+     * iCalendar objects in the specified calendar.
+     *
+     * This default may well be good enough for personal use, and calendars
+     * that aren't very large. But if you anticipate high usage, big calendars
+     * or high loads, you are strongly adviced to optimize certain paths.
+     *
+     * The best way to do so is override this method and to optimize
+     * specifically for 'common filters'.
+     *
+     * Requests that are extremely common are:
+     *   * requests for just VEVENTS
+     *   * requests for just VTODO
+     *   * requests with a time-range-filter on a VEVENT.
+     *
+     * ..and combinations of these requests. It may not be worth it to try to
+     * handle every possible situation and just rely on the (relatively
+     * easy to use) CalendarQueryValidator to handle the rest.
+     *
+     * Note that especially time-range-filters may be difficult to parse. A
+     * time-range filter specified on a VEVENT must for instance also handle
+     * recurrence rules correctly.
+     * A good example of how to interprete all these filters can also simply
+     * be found in \Sabre\CalDAV\CalendarQueryFilter. This class is as correct
+     * as possible, so it gives you a good idea on what type of stuff you need
+     * to think of.
+     *
+     * This specific implementation (for the PDO) backend optimizes filters on
+     * specific components, and VEVENT time-ranges.
+     *
+     * @param string $calendarId
+     * @param array $filters
+     * @return array
+     */
+    function calendarQuery($calendarId, array $filters) {
+
+        $componentType = null;
+        $requirePostFilter = true;
+        $timeRange = null;
+
+        // if no filters were specified, we don't need to filter after a query
+        if (!$filters['prop-filters'] && !$filters['comp-filters']) {
+            $requirePostFilter = false;
+        }
+
+        // Figuring out if there's a component filter
+        if (count($filters['comp-filters']) > 0 && !$filters['comp-filters'][0]['is-not-defined']) {
+            $componentType = $filters['comp-filters'][0]['name'];
+
+            // Checking if we need post-filters
+            if (!$filters['prop-filters'] && !$filters['comp-filters'][0]['comp-filters'] && !$filters['comp-filters'][0]['time-range'] && !$filters['comp-filters'][0]['prop-filters']) {
+                $requirePostFilter = false;
+            }
+            // There was a time-range filter
+            if ($componentType == 'VEVENT' && isset($filters['comp-filters'][0]['time-range'])) {
+                $timeRange = $filters['comp-filters'][0]['time-range'];
+
+                // If start time OR the end time is not specified, we can do a
+                // 100% accurate mysql query.
+                if (!$filters['prop-filters'] && !$filters['comp-filters'][0]['comp-filters'] && !$filters['comp-filters'][0]['prop-filters'] && (!$timeRange['start'] || !$timeRange['end'])) {
+                    $requirePostFilter = false;
+                }
+            }
+
+        }
+
+        if ($requirePostFilter) {
+            $query = "SELECT uri, calendardata FROM " . $this->calendarObjectTableName . " WHERE calendarid = :calendarid";
+        } else {
+            $query = "SELECT uri FROM " . $this->calendarObjectTableName . " WHERE calendarid = :calendarid";
+        }
+
+        $values = [
+            'calendarid' => $calendarId,
+        ];
+
+        if ($componentType) {
+            $query .= " AND componenttype = :componenttype";
+            $values['componenttype'] = $componentType;
+        }
+
+        if ($timeRange && $timeRange['start']) {
+            $query .= " AND lastoccurence > :startdate";
+            $values['startdate'] = $timeRange['start']->getTimeStamp();
+        }
+        if ($timeRange && $timeRange['end']) {
+            $query .= " AND firstoccurence < :enddate";
+            $values['enddate'] = $timeRange['end']->getTimeStamp();
+        }
+
+        $stmt = $this->pdo->prepare($query);
+        $stmt->execute($values);
+
+        $result = [];
+        while ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+            if ($requirePostFilter) {
+                if (!$this->validateFilterForObject($row, $filters)) {
+                    continue;
+                }
+            }
+            $result[] = $row['uri'];
+
+        }
+
+        return $result;
+
+    }
+
+    /**
+     * Searches through all of a users calendars and calendar objects to find
+     * an object with a specific UID.
+     *
+     * This method should return the path to this object, relative to the
+     * calendar home, so this path usually only contains two parts:
+     *
+     * calendarpath/objectpath.ics
+     *
+     * If the uid is not found, return null.
+     *
+     * This method should only consider * objects that the principal owns, so
+     * any calendars owned by other principals that also appear in this
+     * collection should be ignored.
+     *
+     * @param string $principalUri
+     * @param string $uid
+     * @return string|null
+     */
+    function getCalendarObjectByUID($principalUri, $uid) {
+
+        $query = <<<SQL
+SELECT
+    calendars.uri AS calendaruri, calendarobjects.uri as objecturi
+FROM
+    $this->calendarObjectTableName AS calendarobjects
+LEFT JOIN
+    $this->calendarTableName AS calendars
+    ON calendarobjects.calendarid = calendars.id
+WHERE
+    calendars.principaluri = ?
+    AND
+    calendarobjects.uid = ?
+SQL;
+
+        $stmt = $this->pdo->prepare($query);
+        $stmt->execute([$principalUri, $uid]);
+
+        if ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+            return $row['calendaruri'] . '/' . $row['objecturi'];
+        }
+
+    }
+
+    /**
+     * The getChanges method returns all the changes that have happened, since
+     * the specified syncToken in the specified calendar.
+     *
+     * This function should return an array, such as the following:
+     *
+     * [
+     *   'syncToken' => 'The current synctoken',
+     *   'added'   => [
+     *      'new.txt',
+     *   ],
+     *   'modified'   => [
+     *      'modified.txt',
+     *   ],
+     *   'deleted' => [
+     *      'foo.php.bak',
+     *      'old.txt'
+     *   ]
+     * ];
+     *
+     * The returned syncToken property should reflect the *current* syncToken
+     * of the calendar, as reported in the {http://sabredav.org/ns}sync-token
+     * property this is needed here too, to ensure the operation is atomic.
+     *
+     * If the $syncToken argument is specified as null, this is an initial
+     * sync, and all members should be reported.
+     *
+     * The modified property is an array of nodenames that have changed since
+     * the last token.
+     *
+     * The deleted property is an array with nodenames, that have been deleted
+     * from collection.
+     *
+     * The $syncLevel argument is basically the 'depth' of the report. If it's
+     * 1, you only have to report changes that happened only directly in
+     * immediate descendants. If it's 2, it should also include changes from
+     * the nodes below the child collections. (grandchildren)
+     *
+     * The $limit argument allows a client to specify how many results should
+     * be returned at most. If the limit is not specified, it should be treated
+     * as infinite.
+     *
+     * If the limit (infinite or not) is higher than you're willing to return,
+     * you should throw a Sabre\DAV\Exception\TooMuchMatches() exception.
+     *
+     * If the syncToken is expired (due to data cleanup) or unknown, you must
+     * return null.
+     *
+     * The limit is 'suggestive'. You are free to ignore it.
+     *
+     * @param string $calendarId
+     * @param string $syncToken
+     * @param int $syncLevel
+     * @param int $limit
+     * @return array
+     */
+    function getChangesForCalendar($calendarId, $syncToken, $syncLevel, $limit = null) {
+
+        // Current synctoken
+        $stmt = $this->pdo->prepare('SELECT synctoken FROM ' . $this->calendarTableName . ' WHERE id = ?');
+        $stmt->execute([ $calendarId ]);
+        $currentToken = $stmt->fetchColumn(0);
+
+        if (is_null($currentToken)) return null;
+
+        $result = [
+            'syncToken' => $currentToken,
+            'added'     => [],
+            'modified'  => [],
+            'deleted'   => [],
+        ];
+
+        if ($syncToken) {
+
+            $query = "SELECT uri, operation FROM " . $this->calendarChangesTableName . " WHERE synctoken >= ? AND synctoken < ? AND calendarid = ? ORDER BY synctoken";
+            if ($limit > 0) $query .= " LIMIT " . (int)$limit;
+
+            // Fetching all changes
+            $stmt = $this->pdo->prepare($query);
+            $stmt->execute([$syncToken, $currentToken, $calendarId]);
+
+            $changes = [];
+
+            // This loop ensures that any duplicates are overwritten, only the
+            // last change on a node is relevant.
+            while ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+
+                $changes[$row['uri']] = $row['operation'];
+
+            }
+
+            foreach ($changes as $uri => $operation) {
+
+                switch ($operation) {
+                    case 1 :
+                        $result['added'][] = $uri;
+                        break;
+                    case 2 :
+                        $result['modified'][] = $uri;
+                        break;
+                    case 3 :
+                        $result['deleted'][] = $uri;
+                        break;
+                }
+
+            }
+        } else {
+            // No synctoken supplied, this is the initial sync.
+            $query = "SELECT uri FROM " . $this->calendarObjectTableName . " WHERE calendarid = ?";
+            $stmt = $this->pdo->prepare($query);
+            $stmt->execute([$calendarId]);
+
+            $result['added'] = $stmt->fetchAll(\PDO::FETCH_COLUMN);
+        }
+        return $result;
+
+    }
+
+    /**
+     * Adds a change record to the calendarchanges table.
+     *
+     * @param mixed $calendarId
+     * @param string $objectUri
+     * @param int $operation 1 = add, 2 = modify, 3 = delete.
+     * @return void
+     */
+    protected function addChange($calendarId, $objectUri, $operation) {
+
+        $stmt = $this->pdo->prepare('INSERT INTO ' . $this->calendarChangesTableName . ' (uri, synctoken, calendarid, operation) SELECT ?, synctoken, ?, ? FROM ' . $this->calendarTableName . ' WHERE id = ?');
+        $stmt->execute([
+            $objectUri,
+            $calendarId,
+            $operation,
+            $calendarId
+        ]);
+        $stmt = $this->pdo->prepare('UPDATE ' . $this->calendarTableName . ' SET synctoken = synctoken + 1 WHERE id = ?');
+        $stmt->execute([
+            $calendarId
+        ]);
+
+    }
+
+    /**
+     * Returns a list of subscriptions for a principal.
+     *
+     * Every subscription is an array with the following keys:
+     *  * id, a unique id that will be used by other functions to modify the
+     *    subscription. This can be the same as the uri or a database key.
+     *  * uri. This is just the 'base uri' or 'filename' of the subscription.
+     *  * principaluri. The owner of the subscription. Almost always the same as
+     *    principalUri passed to this method.
+     *  * source. Url to the actual feed
+     *
+     * Furthermore, all the subscription info must be returned too:
+     *
+     * 1. {DAV:}displayname
+     * 2. {http://apple.com/ns/ical/}refreshrate
+     * 3. {http://calendarserver.org/ns/}subscribed-strip-todos (omit if todos
+     *    should not be stripped).
+     * 4. {http://calendarserver.org/ns/}subscribed-strip-alarms (omit if alarms
+     *    should not be stripped).
+     * 5. {http://calendarserver.org/ns/}subscribed-strip-attachments (omit if
+     *    attachments should not be stripped).
+     * 7. {http://apple.com/ns/ical/}calendar-color
+     * 8. {http://apple.com/ns/ical/}calendar-order
+     * 9. {urn:ietf:params:xml:ns:caldav}supported-calendar-component-set
+     *    (should just be an instance of
+     *    Sabre\CalDAV\Property\SupportedCalendarComponentSet, with a bunch of
+     *    default components).
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getSubscriptionsForUser($principalUri) {
+
+        $fields = array_values($this->subscriptionPropertyMap);
+        $fields[] = 'id';
+        $fields[] = 'uri';
+        $fields[] = 'source';
+        $fields[] = 'principaluri';
+        $fields[] = 'lastmodified';
+
+        // Making fields a comma-delimited list
+        $fields = implode(', ', $fields);
+        $stmt = $this->pdo->prepare("SELECT " . $fields . " FROM " . $this->calendarSubscriptionsTableName . " WHERE principaluri = ? ORDER BY calendarorder ASC");
+        $stmt->execute([$principalUri]);
+
+        $subscriptions = [];
+        while ($row = $stmt->fetch(\PDO::FETCH_ASSOC)) {
+
+            $subscription = [
+                'id'           => $row['id'],
+                'uri'          => $row['uri'],
+                'principaluri' => $row['principaluri'],
+                'source'       => $row['source'],
+                'lastmodified' => $row['lastmodified'],
+
+                '{' . CalDAV\Plugin::NS_CALDAV . '}supported-calendar-component-set' => new CalDAV\Xml\Property\SupportedCalendarComponentSet(['VTODO', 'VEVENT']),
+            ];
+
+            foreach ($this->subscriptionPropertyMap as $xmlName => $dbName) {
+                if (!is_null($row[$dbName])) {
+                    $subscription[$xmlName] = $row[$dbName];
+                }
+            }
+
+            $subscriptions[] = $subscription;
+
+        }
+
+        return $subscriptions;
+
+    }
+
+    /**
+     * Creates a new subscription for a principal.
+     *
+     * If the creation was a success, an id must be returned that can be used to reference
+     * this subscription in other methods, such as updateSubscription.
+     *
+     * @param string $principalUri
+     * @param string $uri
+     * @param array $properties
+     * @return mixed
+     */
+    function createSubscription($principalUri, $uri, array $properties) {
+
+        $fieldNames = [
+            'principaluri',
+            'uri',
+            'source',
+            'lastmodified',
+        ];
+
+        if (!isset($properties['{http://calendarserver.org/ns/}source'])) {
+            throw new Forbidden('The {http://calendarserver.org/ns/}source property is required when creating subscriptions');
+        }
+
+        $values = [
+            ':principaluri' => $principalUri,
+            ':uri'          => $uri,
+            ':source'       => $properties['{http://calendarserver.org/ns/}source']->getHref(),
+            ':lastmodified' => time(),
+        ];
+
+        foreach ($this->subscriptionPropertyMap as $xmlName => $dbName) {
+            if (isset($properties[$xmlName])) {
+
+                $values[':' . $dbName] = $properties[$xmlName];
+                $fieldNames[] = $dbName;
+            }
+        }
+
+        $stmt = $this->pdo->prepare("INSERT INTO " . $this->calendarSubscriptionsTableName . " (" . implode(', ', $fieldNames) . ") VALUES (" . implode(', ', array_keys($values)) . ")");
+        $stmt->execute($values);
+
+        return $this->pdo->lastInsertId();
+
+    }
+
+    /**
+     * Updates a subscription
+     *
+     * The list of mutations is stored in a Sabre\DAV\PropPatch object.
+     * To do the actual updates, you must tell this object which properties
+     * you're going to process with the handle() method.
+     *
+     * Calling the handle method is like telling the PropPatch object "I
+     * promise I can handle updating this property".
+     *
+     * Read the PropPatch documenation for more info and examples.
+     *
+     * @param mixed $subscriptionId
+     * @param \Sabre\DAV\PropPatch $propPatch
+     * @return void
+     */
+    function updateSubscription($subscriptionId, DAV\PropPatch $propPatch) {
+
+        $supportedProperties = array_keys($this->subscriptionPropertyMap);
+        $supportedProperties[] = '{http://calendarserver.org/ns/}source';
+
+        $propPatch->handle($supportedProperties, function($mutations) use ($subscriptionId) {
+
+            $newValues = [];
+
+            foreach ($mutations as $propertyName => $propertyValue) {
+
+                if ($propertyName === '{http://calendarserver.org/ns/}source') {
+                    $newValues['source'] = $propertyValue->getHref();
+                } else {
+                    $fieldName = $this->subscriptionPropertyMap[$propertyName];
+                    $newValues[$fieldName] = $propertyValue;
+                }
+
+            }
+
+            // Now we're generating the sql query.
+            $valuesSql = [];
+            foreach ($newValues as $fieldName => $value) {
+                $valuesSql[] = $fieldName . ' = ?';
+            }
+
+            $stmt = $this->pdo->prepare("UPDATE " . $this->calendarSubscriptionsTableName . " SET " . implode(', ', $valuesSql) . ", lastmodified = ? WHERE id = ?");
+            $newValues['lastmodified'] = time();
+            $newValues['id'] = $subscriptionId;
+            $stmt->execute(array_values($newValues));
+
+            return true;
+
+        });
+
+    }
+
+    /**
+     * Deletes a subscription
+     *
+     * @param mixed $subscriptionId
+     * @return void
+     */
+    function deleteSubscription($subscriptionId) {
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->calendarSubscriptionsTableName . ' WHERE id = ?');
+        $stmt->execute([$subscriptionId]);
+
+    }
+
+    /**
+     * Returns a single scheduling object.
+     *
+     * The returned array should contain the following elements:
+     *   * uri - A unique basename for the object. This will be used to
+     *           construct a full uri.
+     *   * calendardata - The iCalendar object
+     *   * lastmodified - The last modification date. Can be an int for a unix
+     *                    timestamp, or a PHP DateTime object.
+     *   * etag - A unique token that must change if the object changed.
+     *   * size - The size of the object, in bytes.
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @return array
+     */
+    function getSchedulingObject($principalUri, $objectUri) {
+
+        $stmt = $this->pdo->prepare('SELECT uri, calendardata, lastmodified, etag, size FROM ' . $this->schedulingObjectTableName . ' WHERE principaluri = ? AND uri = ?');
+        $stmt->execute([$principalUri, $objectUri]);
+        $row = $stmt->fetch(\PDO::FETCH_ASSOC);
+
+        if (!$row) return null;
+
+        return [
+            'uri'          => $row['uri'],
+            'calendardata' => $row['calendardata'],
+            'lastmodified' => $row['lastmodified'],
+            'etag'         => '"' . $row['etag'] . '"',
+            'size'         => (int)$row['size'],
+         ];
+
+    }
+
+    /**
+     * Returns all scheduling objects for the inbox collection.
+     *
+     * These objects should be returned as an array. Every item in the array
+     * should follow the same structure as returned from getSchedulingObject.
+     *
+     * The main difference is that 'calendardata' is optional.
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getSchedulingObjects($principalUri) {
+
+        $stmt = $this->pdo->prepare('SELECT id, calendardata, uri, lastmodified, etag, size FROM ' . $this->schedulingObjectTableName . ' WHERE principaluri = ?');
+        $stmt->execute([$principalUri]);
+
+        $result = [];
+        foreach ($stmt->fetchAll(\PDO::FETCH_ASSOC) as $row) {
+            $result[] = [
+                'calendardata' => $row['calendardata'],
+                'uri'          => $row['uri'],
+                'lastmodified' => $row['lastmodified'],
+                'etag'         => '"' . $row['etag'] . '"',
+                'size'         => (int)$row['size'],
+            ];
+        }
+
+        return $result;
+
+    }
+
+    /**
+     * Deletes a scheduling object
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @return void
+     */
+    function deleteSchedulingObject($principalUri, $objectUri) {
+
+        $stmt = $this->pdo->prepare('DELETE FROM ' . $this->schedulingObjectTableName . ' WHERE principaluri = ? AND uri = ?');
+        $stmt->execute([$principalUri, $objectUri]);
+
+    }
+
+    /**
+     * Creates a new scheduling object. This should land in a users' inbox.
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @param string $objectData
+     * @return void
+     */
+    function createSchedulingObject($principalUri, $objectUri, $objectData) {
+
+        $stmt = $this->pdo->prepare('INSERT INTO ' . $this->schedulingObjectTableName . ' (principaluri, calendardata, uri, lastmodified, etag, size) VALUES (?, ?, ?, ?, ?, ?)');
+        $stmt->execute([$principalUri, $objectData, $objectUri, time(), md5($objectData), strlen($objectData) ]);
+
+    }
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/SchedulingSupport.php b/vendor/sabre/dav/lib/CalDAV/Backend/SchedulingSupport.php
new file mode 100644
index 000000000..6ec0bf06b
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/SchedulingSupport.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+/**
+ * Implementing this interface adds CalDAV Scheduling support to your caldav
+ * server, as defined in rfc6638.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface SchedulingSupport extends BackendInterface {
+
+    /**
+     * Returns a single scheduling object for the inbox collection.
+     *
+     * The returned array should contain the following elements:
+     *   * uri - A unique basename for the object. This will be used to
+     *           construct a full uri.
+     *   * calendardata - The iCalendar object
+     *   * lastmodified - The last modification date. Can be an int for a unix
+     *                    timestamp, or a PHP DateTime object.
+     *   * etag - A unique token that must change if the object changed.
+     *   * size - The size of the object, in bytes.
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @return array
+     */
+    function getSchedulingObject($principalUri, $objectUri);
+
+    /**
+     * Returns all scheduling objects for the inbox collection.
+     *
+     * These objects should be returned as an array. Every item in the array
+     * should follow the same structure as returned from getSchedulingObject.
+     *
+     * The main difference is that 'calendardata' is optional.
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getSchedulingObjects($principalUri);
+
+    /**
+     * Deletes a scheduling object from the inbox collection.
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @return void
+     */
+    function deleteSchedulingObject($principalUri, $objectUri);
+
+    /**
+     * Creates a new scheduling object. This should land in a users' inbox.
+     *
+     * @param string $principalUri
+     * @param string $objectUri
+     * @param string $objectData
+     * @return void
+     */
+    function createSchedulingObject($principalUri, $objectUri, $objectData);
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/SharingSupport.php b/vendor/sabre/dav/lib/CalDAV/Backend/SharingSupport.php
new file mode 100644
index 000000000..6a11b0ab1
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/SharingSupport.php
@@ -0,0 +1,243 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+/**
+ * Adds support for sharing features to a CalDAV server.
+ *
+ * Note: This feature is experimental, and may change in between different
+ * SabreDAV versions.
+ *
+ * Early warning: Currently SabreDAV provides no implementation for this. This
+ * is, because in it's current state there is no elegant way to do this.
+ * The problem lies in the fact that a real CalDAV server with sharing support
+ * would first need email support (with invite notifications), and really also
+ * a browser-frontend that allows people to accept or reject these shares.
+ *
+ * In addition, the CalDAV backends are currently kept as independent as
+ * possible, and should not be aware of principals, email addresses or
+ * accounts.
+ *
+ * Adding an implementation for Sharing to standard-sabredav would contradict
+ * these goals, so for this reason this is currently not implemented, although
+ * it may very well in the future; but probably not before SabreDAV 2.0.
+ *
+ * The interface works however, so if you implement all this, and do it
+ * correctly sharing _will_ work. It's not particularly easy, and I _urge you_
+ * to make yourself acquainted with the following document first:
+ *
+ * https://trac.calendarserver.org/browser/CalendarServer/trunk/doc/Extensions/caldav-sharing.txt
+ *
+ * An overview
+ * ===========
+ *
+ * Implementing this interface will allow a user to share his or her calendars
+ * to other users. Effectively, when a calendar is shared the calendar will
+ * show up in both the Sharer's and Sharee's calendar-home root.
+ * This interface adds a few methods that ensure that this happens, and there
+ * are also a number of new requirements in the base-class you must now follow.
+ *
+ *
+ * How it works
+ * ============
+ *
+ * When a user shares a calendar, the updateShares() method will be called with
+ * a list of sharees that are now added, and a list of sharees that have been
+ * removed.
+ * Removal is instant, but when a sharee is added the sharee first gets a
+ * chance to accept or reject the invitation for a share.
+ *
+ * After a share is accepted, the calendar will be returned from
+ * getUserCalendars for both the sharer, and the sharee.
+ *
+ * If the sharee deletes the calendar, only their share gets deleted. When the
+ * owner deletes a calendar, it will be removed for everybody.
+ *
+ *
+ * Notifications
+ * =============
+ *
+ * During all these sharing operations, a lot of notifications are sent back
+ * and forward.
+ *
+ * Whenever the list of sharees for a calendar has been changed (they have been
+ * added, removed or modified) all sharees should get a notification for this
+ * change.
+ * This notification is always represented by:
+ *
+ * Sabre\CalDAV\Notifications\Notification\Invite
+ *
+ * In the case of an invite, the sharee may reply with an 'accept' or
+ * 'decline'. These are always represented by:
+ *
+ * Sabre\CalDAV\Notifications\Notification\InviteReply
+ *
+ *
+ * Calendar access by sharees
+ * ==========================
+ *
+ * As mentioned earlier, shared calendars must now also be returned for
+ * getCalendarsForUser for sharees. A few things change though.
+ *
+ * The following properties must be specified:
+ *
+ * 1. {http://calendarserver.org/ns/}shared-url
+ *
+ * This property MUST contain the url to the original calendar, that is.. the
+ * path to the calendar from the owner.
+ *
+ * 2. {http://sabredav.org/ns}owner-principal
+ *
+ * This is a url to to the principal who is sharing the calendar.
+ *
+ * 3. {http://sabredav.org/ns}read-only
+ *
+ * This should be either 0 or 1, depending on if the user has read-only or
+ * read-write access to the calendar.
+ *
+ * Only when this is done, the calendar will correctly be marked as a calendar
+ * that's shared to him, thus allowing clients to display the correct interface
+ * and ACL enforcement.
+ *
+ * If a sharee deletes their calendar, only their instance of the calendar
+ * should be deleted, the original should still exists.
+ * Pretty much any 'dead' WebDAV properties on these shared calendars should be
+ * specific to a user. This means that if the displayname is changed by a
+ * sharee, the original is not affected. This is also true for:
+ *   * The description
+ *   * The color
+ *   * The order
+ *   * And any other dead properties.
+ *
+ * Properties like a ctag should not be different for multiple instances of the
+ * calendar.
+ *
+ * Lastly, objects *within* calendars should also have user-specific data. The
+ * two things that are user-specific are:
+ *   * VALARM objects
+ *   * The TRANSP property
+ *
+ * This _also_ implies that if a VALARM is deleted by a sharee for some event,
+ * this has no effect on the original VALARM.
+ *
+ * Understandably, the this last requirement is one of the hardest.
+ * Realisticly, I can see people ignoring this part of the spec, but that could
+ * cause a different set of issues.
+ *
+ *
+ * Publishing
+ * ==========
+ *
+ * When a user publishes a url, the server should generate a 'publish url'.
+ * This is a read-only url, anybody can use to consume the calendar feed.
+ *
+ * Calendars are in one of two states:
+ *   * published
+ *   * unpublished
+ *
+ * If a calendar is published, the following property should be returned
+ * for each calendar in getCalendarsForUser.
+ *
+ * {http://calendarserver.org/ns/}publish-url
+ *
+ * This element should contain a {DAV:}href element, which points to the
+ * public url that does not require authentication. Unlike every other href,
+ * this url must be absolute.
+ *
+ * Ideally, the following property is always returned
+ *
+ * {http://calendarserver.org/ns/}pre-publish-url
+ *
+ * This property should contain the url that the calendar _would_ have, if it
+ * were to be published. iCal uses this to display the url, before the user
+ * will actually publish it.
+ *
+ *
+ * Selectively disabling publish or share feature
+ * ==============================================
+ *
+ * If Sabre\CalDAV\Property\AllowedSharingModes is returned from
+ * getCalendarsForUser, this allows the server to specify whether either sharing,
+ * or publishing is supported.
+ *
+ * This allows a client to determine in advance which features are available,
+ * and update the interface appropriately. If this property is not returned by
+ * the backend, the SharingPlugin automatically injects it and assumes both
+ * features are available.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface SharingSupport extends NotificationSupport {
+
+    /**
+     * Updates the list of shares.
+     *
+     * The first array is a list of people that are to be added to the
+     * calendar.
+     *
+     * Every element in the add array has the following properties:
+     *   * href - A url. Usually a mailto: address
+     *   * commonName - Usually a first and last name, or false
+     *   * summary - A description of the share, can also be false
+     *   * readOnly - A boolean value
+     *
+     * Every element in the remove array is just the address string.
+     *
+     * Note that if the calendar is currently marked as 'not shared' by and
+     * this method is called, the calendar should be 'upgraded' to a shared
+     * calendar.
+     *
+     * @param mixed $calendarId
+     * @param array $add
+     * @param array $remove
+     * @return void
+     */
+    function updateShares($calendarId, array $add, array $remove);
+
+    /**
+     * Returns the list of people whom this calendar is shared with.
+     *
+     * Every element in this array should have the following properties:
+     *   * href - Often a mailto: address
+     *   * commonName - Optional, for example a first + last name
+     *   * status - See the Sabre\CalDAV\SharingPlugin::STATUS_ constants.
+     *   * readOnly - boolean
+     *   * summary - Optional, a description for the share
+     *
+     * This method may be called by either the original instance of the
+     * calendar, as well as the shared instances. In the case of the shared
+     * instances, it is perfectly acceptable to return an empty array in case
+     * there are privacy concerns.
+     *
+     * @param mixed $calendarId
+     * @return array
+     */
+    function getShares($calendarId);
+
+    /**
+     * This method is called when a user replied to a request to share.
+     *
+     * If the user chose to accept the share, this method should return the
+     * newly created calendar url.
+     *
+     * @param string href The sharee who is replying (often a mailto: address)
+     * @param int status One of the SharingPlugin::STATUS_* constants
+     * @param string $calendarUri The url to the calendar thats being shared
+     * @param string $inReplyTo The unique id this message is a response to
+     * @param string $summary A description of the reply
+     * @return null|string
+     */
+    function shareReply($href, $status, $calendarUri, $inReplyTo, $summary = null);
+
+    /**
+     * Publishes a calendar
+     *
+     * @param mixed $calendarId
+     * @param bool $value
+     * @return void
+     */
+    function setPublishStatus($calendarId, $value);
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/SubscriptionSupport.php b/vendor/sabre/dav/lib/CalDAV/Backend/SubscriptionSupport.php
new file mode 100644
index 000000000..a39289f5e
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/SubscriptionSupport.php
@@ -0,0 +1,89 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+use Sabre\DAV;
+
+/**
+ * Every CalDAV backend must at least implement this interface.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface SubscriptionSupport extends BackendInterface {
+
+    /**
+     * Returns a list of subscriptions for a principal.
+     *
+     * Every subscription is an array with the following keys:
+     *  * id, a unique id that will be used by other functions to modify the
+     *    subscription. This can be the same as the uri or a database key.
+     *  * uri. This is just the 'base uri' or 'filename' of the subscription.
+     *  * principaluri. The owner of the subscription. Almost always the same as
+     *    principalUri passed to this method.
+     *
+     * Furthermore, all the subscription info must be returned too:
+     *
+     * 1. {DAV:}displayname
+     * 2. {http://apple.com/ns/ical/}refreshrate
+     * 3. {http://calendarserver.org/ns/}subscribed-strip-todos (omit if todos
+     *    should not be stripped).
+     * 4. {http://calendarserver.org/ns/}subscribed-strip-alarms (omit if alarms
+     *    should not be stripped).
+     * 5. {http://calendarserver.org/ns/}subscribed-strip-attachments (omit if
+     *    attachments should not be stripped).
+     * 6. {http://calendarserver.org/ns/}source (Must be a
+     *     Sabre\DAV\Property\Href).
+     * 7. {http://apple.com/ns/ical/}calendar-color
+     * 8. {http://apple.com/ns/ical/}calendar-order
+     * 9. {urn:ietf:params:xml:ns:caldav}supported-calendar-component-set
+     *    (should just be an instance of
+     *    Sabre\CalDAV\Property\SupportedCalendarComponentSet, with a bunch of
+     *    default components).
+     *
+     * @param string $principalUri
+     * @return array
+     */
+    function getSubscriptionsForUser($principalUri);
+
+    /**
+     * Creates a new subscription for a principal.
+     *
+     * If the creation was a success, an id must be returned that can be used to reference
+     * this subscription in other methods, such as updateSubscription.
+     *
+     * @param string $principalUri
+     * @param string $uri
+     * @param array $properties
+     * @return mixed
+     */
+    function createSubscription($principalUri, $uri, array $properties);
+
+    /**
+     * Updates a subscription
+     *
+     * The list of mutations is stored in a Sabre\DAV\PropPatch object.
+     * To do the actual updates, you must tell this object which properties
+     * you're going to process with the handle() method.
+     *
+     * Calling the handle method is like telling the PropPatch object "I
+     * promise I can handle updating this property".
+     *
+     * Read the PropPatch documenation for more info and examples.
+     *
+     * @param mixed $subscriptionId
+     * @param \Sabre\DAV\PropPatch $propPatch
+     * @return void
+     */
+    function updateSubscription($subscriptionId, DAV\PropPatch $propPatch);
+
+    /**
+     * Deletes a subscription.
+     *
+     * @param mixed $subscriptionId
+     * @return void
+     */
+    function deleteSubscription($subscriptionId);
+
+}
diff --git a/vendor/sabre/dav/lib/CalDAV/Backend/SyncSupport.php b/vendor/sabre/dav/lib/CalDAV/Backend/SyncSupport.php
new file mode 100644
index 000000000..a934505f9
--- /dev/null
+++ b/vendor/sabre/dav/lib/CalDAV/Backend/SyncSupport.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace Sabre\CalDAV\Backend;
+
+/**
+ * WebDAV-sync support for CalDAV backends.
+ *
+ * In order for backends to advertise support for WebDAV-sync, this interface
+ * must be implemented.
+ *
+ * Implementing this can result in a significant reduction of bandwidth and CPU
+ * time.
+ *
+ * For this to work, you _must_ return a {http://sabredav.org/ns}sync-token
+ * property from getCalendarsFromUser.
+ *
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://sabre.io/license/ Modified BSD License
+ */
+interface SyncSupport extends BackendInterface {
+
+    /**
+     * The getChanges method returns all the changes that have happened, since
+     * the specified syncToken in the specified calendar.
+     *
+     * This function should return an array, such as the following:
+     *
+     * [
+     *   'syncToken' => 'The current synctoken',
+     *   'added'   => [
+     *      'new.txt',
+     *   ],
+     *   'modified'   => [
+     *      'modified.txt',
+     *   ],
+     *   'deleted' => [
+     *      'foo.php.bak',
+     *      'old.txt'
+     *   ]
+     * );
+     *
+     * The returned syncToken property should reflect the *current* syncToken
+     * of the calendar, as reported in the {http://sabredav.org/ns}sync-token
+     * property This is * needed here too, to ensure the operation is atomic.
+     *
+     * If the $syncToken argument is specified as null, this is an initial
+     * sync, and all members should be reported.
+     *
+     * The modified property is an array of nodenames that have changed since
+     * the last token.
+     *
+     * The deleted property is an array with nodenames, that have been deleted
+     * from collection.
+     *
+     * The $syncLevel argument is basically the 'depth' of the report. If it's
+     * 1, you only have to report changes that happened only directly in
+     * immediate descendants. If it's 2, it should also include changes from
+     * the nodes below the child collections. (grandchildren)
+     *
+     * The $limit argument allows a client to specify how many results should
+     * be returned at most. If the limit is not specified, it should be treated
+     * as infinite.
+     *
+     * If the limit (infinite or not) is higher than you're willing to return,
+     * you should throw a Sabre\DAV\Exception\TooMuchMatches() exception.
+     *
+     * If the syncToken is expired (due to data cleanup) or unknown, you must
+     * return null.
+     *
+     * The limit is 'suggestive'. You are free to ignore it.
+     *
+     * @param string $calendarId
+     * @param string $syncToken
+     * @param int $syncLevel
+     * @param int $limit
+     * @return array
+     */
+    function getChangesForCalendar($calendarId, $syncToken, $syncLevel, $limit = null);
+
+}