使用Firebase云函数有条件地发送通知？

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.sendNotification = functions.firestore
  .document('users/{userId}')
  .onUpdate((change, context) => {
    const newData = change.after.data();
    const previousData = change.before.data();

    // 检查特定条件是否满足
    if (newData.condition && newData.condition !== previousData.condition) {
      // 构建通知消息
      const message = {
        notification: {
          title: '条件满足',
          body: '您的条件已经满足！',
        },
        topic: 'notifications', // 接收通知的主题
      };

      // 发送通知
      return admin.messaging().send(message)
        .then(() => {
          console.log('通知发送成功');
        })
        .catch((error) => {
          console.error('发送通知时出错：', error);
        });
    }

    return null;
  });