/**
  * Ping the registered devices of the recipients of the notification.
  *
  * @param gameMessage contains the information needed for sending and processing the invite
  * @param gems the number of gems picked up in this game
  * @param mobsKilled the number of mobiles killed in this game
  * @param deaths the number of deaths of player in this game
  * @return {@code true} if delivery to all users were successful; {@code false} otherwise
  * @throws IOException
  */
 public static boolean pingGamePlayerSendEndScore(
     GameMessage gameMessage, long gems, long mobsKilled, long deaths) throws IOException {
   boolean success = false;
   for (String toHandle : gameMessage.getTo()) {
     Message msg = new Message.Builder()
         .collapseKey(gameMessage.getFrom())
         .addData(GCM_PAYLOAD_PING_REASON, PING_REASON_PLAYER_END_SCORE)
         .addData(GCM_PAYLOAD_FROM_USER_HANDLE, gameMessage.getFrom())
         .addData(GCM_PAYLOAD_TO_USER_HANDLE, toHandle)
         .addData(GCM_PAYLOAD_GAME_ID, gameMessage.getGameId())
         .addData(GCM_PAYLOAD_MESSAGE, "Here are the endgame scores for this player.")
         .addData("gems", Long.toString(gems))
         .addData("mobs_killed", Long.toString(mobsKilled))
         .addData("deaths", Long.toString(deaths))
         .build();
     if (verifyFields(msg)) {
       DeviceInfo deviceInfo = endpoint.getDeviceInfo(toHandle);
       if (deviceInfo != null) {
         LOG.info("Building game message to send to user: "******" from user: "******"The device was not found in registry for user handle " + toHandle);
       }
     } else {
       LOG.warning("Empty fields in the GCM Message. No invites sent.");
     }
   }
   return success;
 }
 /**
  * Ping a message using the {@link GameMessage}.
  */
 public static boolean pingGameMessage(
     String message, GameMessage gameMessage, String gcmPayloadPingReason) throws IOException {
   boolean success = false;
   for (String toHandle : gameMessage.getTo()) {
     Message msg = new Message.Builder()
         .collapseKey(gameMessage.getFrom())
         .addData(GCM_PAYLOAD_PING_REASON, gcmPayloadPingReason)
         .addData(GCM_PAYLOAD_FROM_USER_HANDLE, gameMessage.getFrom())
         .addData(GCM_PAYLOAD_TO_USER_HANDLE, toHandle)
         .addData(GCM_PAYLOAD_GAME_ID, gameMessage.getGameId())
         .addData(GCM_PAYLOAD_MESSAGE, message)
         .build();
     if (verifyFields(msg)) {
       DeviceInfo deviceInfo = endpoint.getDeviceInfo(toHandle);
       if (deviceInfo != null) {
         LOG.info("Building game message to send to user: "******" from user: "******"The device was not found in registry for user handle " + toHandle);
       }
     } else {
       LOG.warning("Empty fields in the GCM Message. No invites sent.");
     }
   }
   return success;
 }
 /**
  * Ping a message using the {@link FriendMessage}.
  */
 private static boolean pingFriendMessage(
     String message, FriendMessage friendMessage, String gcmPayloadPingReason) throws IOException {
   String toHandle = friendMessage.getTo();
   Message msg = new Message.Builder()
       .collapseKey(friendMessage.getFrom())
       .addData(GCM_PAYLOAD_PING_REASON, gcmPayloadPingReason)
       .addData(GCM_PAYLOAD_FROM_USER_HANDLE, friendMessage.getFrom())
       .addData(GCM_PAYLOAD_TO_USER_HANDLE, toHandle)
       .addData(GCM_PAYLOAD_MESSAGE, message)
       .build();
   if (verifyFields(msg)) {
     DeviceInfo deviceInfo = endpoint.getDeviceInfo(toHandle);
     if (deviceInfo != null) {
       LOG.info("Building friend invite message to send to user: "******" from user: "******"The device was not found in registry for user handle " + toHandle);
     }
   } else {
     LOG.warning("Empty fields in the GCM Message. No message sent.");
   }
   return false;
 }