正在同步日历会议更改

用户可以自由更新或删除其 Google 日历活动。如果用户在为会议创建事件后更新了该事件，您的插件可能需要通过更新会议数据来响应更改。如果您的第三方会议系统依赖于跟踪活动数据，那么在活动发生变化时未更新会议可能会导致会议无法使用，并造成糟糕的用户体验。

随着 Google 日历活动的更改而更新会议数据的过程称为同步。您可以通过创建一个 Apps Script 可安装的触发器来同步活动更改，该触发器会在给定日历中的活动发生更改时触发。很抱歉，该触发器不会报告哪些事件发生了更改，并且您无法将其限制为仅针对包含您创建的会议的事件。而是必须请求获取自上次同步以来对日历所做的所有更改的列表，过滤事件列表，然后相应地进行更新。

一般同步流程如下：

  1. 用户首次创建会议时，系统会初始化同步流程。
  2. 每当用户创建、更新或删除其日历活动时，触发器都会在您的插件项目中执行触发器函数。
  3. 触发器函数会检查上次同步以来的一组事件更改，并确定是否需要更新关联的第三方会议。
  4. 系统会通过发出第三方 API 请求来对会议进行任何必要的更新。
  5. 系统会存储新的同步令牌，以便下次触发器执行时只需检查日历的最新更改。

初始化同步

该插件在第三方系统上成功创建会议后，应创建一个可安装的触发器（如果该触发器尚不存在），以响应此日历中的事件更改。

创建触发器后，初始化应通过创建初始同步令牌完成。为此，您可以直接执行触发器函数。

创建日历触发器

如需同步，您的插件需要检测附加了会议的日历活动何时发生更改。这可通过创建 EventUpdated 可安装的触发器来实现。您的插件只需为每个日历创建一个触发器，并且可以通过编程方式创建这些触发器。

创建触发器的好时机是用户创建其首次会议时，因为此时用户刚开始使用该插件。创建会议并验证没有错误后，您的插件应检查此用户是否存在触发器，如果没有，则创建触发器。

实现同步触发器函数

当 Apps Script 检测到导致触发器触发的条件时，就会执行触发器函数。当用户在指定日历中创建、修改或删除任何活动时，EventUpdated 日历触发器会触发。

您必须实现您的插件使用的触发器函数。此触发器函数应执行以下操作：

  1. 使用 syncToken 调用日历高级服务 Calendar.Events.list()，以检索自上次同步后发生更改的活动列表。通过使用同步令牌，您可以减少您的插件必须检查的事件数量。

    如果触发器函数在执行时没有有效的同步令牌，则会回退到完整同步。完整同步只是尝试检索规定时间范围内的所有事件，以生成新的有效同步令牌。

  2. 系统会检查每个经过修改的事件，以确定其是否有关联的第三方会议。
  3. 如果活动有会议，系统会对其进行检查，了解发生了哪些变化。根据具体更改，您可能需要修改关联的会议。例如，如果删除了某个活动，该插件可能也会一并删除会议。
  4. 如需对会议进行任何必要的更改，只需向第三方系统发出 API 调用即可。
  5. 进行所有必要的更改后，存储 Calendar.Events.list() 方法返回的 nextSyncToken。此同步令牌位于 Calendar.Events.list() 调用返回的最后一页结果中。

更新 Google 日历活动

在某些情况下，您可能希望在同步时更新 Google 日历活动。如果您选择这样做，请使用适当的 Google 日历高级服务请求进行活动更新。请务必将条件更新与 If-Match 标头搭配使用。这样可以防止您的更改无意中覆盖用户在其他客户端中进行的并发更改。

示例

以下示例展示了如何为日历活动及其关联的会议设置同步。

/**
 *  Initializes syncing of conference data by creating a sync trigger and
 *  sync token if either does not exist yet.
 *
 *  @param {String} calendarId The ID of the Google Calendar.
 */
function initializeSyncing(calendarId) {
  // Create a syncing trigger if it doesn't exist yet.
  createSyncTrigger(calendarId);

  // Perform an event sync to create the initial sync token.
  syncEvents({'calendarId': calendarId});
}

/**
 *  Creates a sync trigger if it does not exist yet.
 *
 *  @param {String} calendarId The ID of the Google Calendar.
 */
function createSyncTrigger(calendarId) {
  // Check to see if the trigger already exists; if does, return.
  var allTriggers = ScriptApp.getProjectTriggers();
  for (var i = 0; i < allTriggers.length; i++) {
    var trigger = allTriggers[i];
    if (trigger.getTriggerSourceId() == calendarId) {
      return;
    }
  }

  // Trigger does not exist, so create it. The trigger calls the
  // 'syncEvents()' trigger function when it fires.
  var trigger = ScriptApp.newTrigger('syncEvents')
      .forUserCalendar(calendarId)
      .onEventUpdated()
      .create();
}

/**
 *  Sync events for the given calendar; this is the syncing trigger
 *  function. If a sync token already exists, this retrieves all events
 *  that have been modified since the last sync, then checks each to see
 *  if an associated conference needs to be updated and makes any required
 *  changes. If the sync token does not exist or is invalid, this
 *  retrieves future events modified in the last 24 hours instead. In
 *  either case, a new sync token is created and stored.
 *
 *  @param {Object} e If called by a event updated trigger, this object
 *      contains the Google Calendar ID, authorization mode, and
 *      calling trigger ID. Only the calendar ID is actually used here,
 *      however.
 */
function syncEvents(e) {
  var calendarId = e.calendarId;
  var properties = PropertiesService.getUserProperties();
  var syncToken = properties.getProperty('syncToken');

  var options;
  if (syncToken) {
    // There's an existing sync token, so configure the following event
    // retrieval request to only get events that have been modified
    // since the last sync.
    options = {
      syncToken: syncToken
    };
  } else {
    // No sync token, so configure to do a 'full' sync instead. In this
    // example only recently updated events are retrieved in a full sync.
    // A larger time window can be examined during a full sync, but this
    // slows down the script execution. Consider the trade-offs while
    // designing your add-on.
    var now = new Date();
    var yesterday = new Date();
    yesterday.setDate(now.getDate() - 1);
    options = {
      timeMin: now.toISOString(),          // Events that start after now...
      updatedMin: yesterday.toISOString(), // ...and were modified recently
      maxResults: 50,   // Max. number of results per page of responses
      orderBy: 'updated'
    }
  }

  // Examine the list of updated events since last sync (or all events
  // modified after yesterday if the sync token is missing or invalid), and
  // update any associated conferences as required.
  var events;
  var pageToken;
  do {
    try {
      options.pageToken = pageToken;
      events = Calendar.Events.list(calendarId, options);
    } catch (err) {
      // Check to see if the sync token was invalidated by the server;
      // if so, perform a full sync instead.
      if (err.message ===
            "Sync token is no longer valid, a full sync is required.") {
        properties.deleteProperty('syncToken');
        syncEvents(e);
        return;
      } else {
        throw new Error(err.message);
      }
    }

    // Read through the list of returned events looking for conferences
    // to update.
    if (events.items && events.items.length > 0) {
      for (var i = 0; i < events.items.length; i++) {
         var calEvent = events.items[i];
         // Check to see if there is a record of this event has a
         // conference that needs updating.
         if (eventHasConference(calEvent)) {
           updateConference(calEvent, calEvent.conferenceData.conferenceId);
         }
      }
    }

    pageToken = events.nextPageToken;
  } while (pageToken);

  // Record the new sync token.
  if (events.nextSyncToken) {
    properties.setProperty('syncToken', events.nextSyncToken);
  }
}

/**
 *  Returns true if the specified event has an associated conference
 *  of the type managed by this add-on; retuns false otherwise.
 *
 *  @param {Object} calEvent The Google Calendar event object, as defined by
 *      the Calendar API.
 *  @return {boolean}
 */
function eventHasConference(calEvent) {
  var name = calEvent.conferenceData.conferenceSolution.name || null;

  // This version checks if the conference data solution name matches the
  // one of the solution names used by the add-on. Alternatively you could
  // check the solution's entry point URIs or other solution-specific
  // information.
  if (name) {
    if (name === "My Web Conference" ||
        name === "My Recorded Web Conference") {
      return true;
    }
  }
  return false;
}

/**
 *  Update a conference based on new Google Calendar event information.
 *  The exact implementation of this function is highly dependant on the
 *  details of the third-party conferencing system, so only a rough outline
 *  is shown here.
 *
 *  @param {Object} calEvent The Google Calendar event object, as defined by
 *      the Calendar API.
 *  @param {String} conferenceId The ID used to identify the conference on
 *      the third-party conferencing system.
 */
function updateConference(calEvent, conferenceId) {
  // Check edge case: the event was cancelled
  if (calEvent.status === 'cancelled' || eventHasConference(calEvent)) {
    // Use the third-party API to delete the conference too.


  } else {
    // Extract any necessary information from the event object, then
    // make the appropriate third-party API requests to update the
    // conference with that information.

  }
}