ngOnInit() {
  collection(`cats`)
      .where('chat_room.id', '==', '2a4b86fc')
      .where('created_at_timestamp', '>', 101)
      .on()
      .subscribe(
        data => console.log('message received:', data),
        error => console.log(error)
      );
}


sendMessages() {
    //
    // Validate, only a few messages
    if (this.timestamp > 120) return;

    //
    // Inc
    this.timestamp++;

    setInterval(async () => {
      console.log('sending another message:', this.timestamp);
      const id = Guid.make(2);

      //
      // Create message
      await collection(`cats`)
        .doc(id)
        .set({
          id: id,
          chat_room: {
            id: '2a4b86fc'
          },
          to: {
            uid: 'GlGkOGSYbCNqBK6uaXf7USALw2c2',
            display_name: 'Matheus Receiver'
          },
          from: {
            uid: 'GlGkOGSYbCNqBK6uaXf7USALw2c2',
            display_name: 'Matheus Sender'
          },
          isFile: false,
          file: {},
          message: `message: ${this.timestamp}`,
          created_at: new Date().toISOString(),
          created_at_timestamp: this.timestamp
        })
        .toPromise().then(()=>this.timestamp+=1);
    }, 1000);
  }