const uint BUZZER_PIN = 0;

const uint BUTTON_LED_PIN = 5;
const uint BUTTON_PIN = 6;

const int BREAK_LENGTH = 300000;
const int BREAK_STEP = 2000;

volatile int countdown = 0;
int step;

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  // Order of ISRs matter: RISING should be invoked first
  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRtime, CHANGE);
  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRstate, RISING);
}

void loop() {
  if (countdown > 0) {
    step = min(BREAK_STEP, countdown);
    countdown -= step;
    
    digitalWrite(BUTTON_LED_PIN, HIGH);
    delay(min(BREAK_STEP/2, step));
    digitalWrite(BUTTON_LED_PIN, LOW);
    delay(max(step-BREAK_STEP/2, 0));
  } else {
    tone(BUZZER_PIN, 1000, 100);
    delay(1000);
  }
}