a workaround to detect and recover when event subscriptions are lost

main.ino

unsigned int last_heartbeat = 0;
#define HEARTBEAT_PERIOD_SECONDS 60
#define MAX_MISSED_HEARTBEATS 3

void setup() {
    Serial.begin(115200);
    Spark.subscribe("heartbeat", heartbeat_handler);
    //Spark.subscribe("heartbeat", heartbeat_handler, MY_DEVICES);
    last_heartbeat = millis();
}

void loop() {
    //it might take a few seconds for the real time clock to get synced, lets assume we weren't turned on in the 1970s, and sync the clock...
    //lets essentially keep this on pause until the clock syncs up
    if (last_heartbeat < 60000) {
        last_heartbeat = millis();
    }

    
    double elapsedSeconds = (millis() - last_heartbeat) / 1000.0;
    if (elapsedSeconds > (MAX_MISSED_HEARTBEATS * HEARTBEAT_PERIOD_SECONDS)) {
        Serial.println("Subscribe is dead, long live subscribe!");
        delay(500);
        System.reset();
    }
    else {
        Serial.println("things are okay... but it's been " + String(elapsedSeconds) + " since last heartbeat");
        delay(1000);
    }
    
}


void heartbeat_handler(const char *topic, const char *data) {
    last_heartbeat = millis();
    Serial.println("Heartbeat... at " + Time.timeStr());
}