#define DEBOUNCE 10
#define COOLOFF 10

#define PRESS_LONG 1000

#define BUTTON_LEFT 2
#define BUTTON_RIGHT 3
#define LED_OUTPUT 4

volatile unsigned long buttonLeftPressed = 0;
volatile unsigned long buttonLeftReleased = 0;

int output = 0;

void buttonLeftPress() {
  unsigned long t = millis();

  if(buttonLeftPressed > 0
  && t - buttonLeftPressed <= DEBOUNCE) {
    return;
  }

  if(buttonLeftReleased > 0
  && t - buttonLeftReleased <= COOLOFF) {
    return;
  }

  buttonLeftPressed = t;
}

void buttonLeftRelease() {
  unsigned long t = millis();

  if(buttonLeftReleased > 0
  && t - buttonLeftReleased <= DEBOUNCE) {
    return;
  }

  if(buttonLeftPressed > 0
  && t - buttonLeftPressed <= COOLOFF) {
    return;
  }

  buttonLeftReleased = t;
}

void checkButtons() {
  if(buttonLeftReleased > 0) {
    unsigned long duration = buttonLeftReleased - buttonLeftPressed;

    if(duration >= PRESS_LONG) {
      output += 20;
    }
    else {
      output = 2;
    }

    buttonLeftPressed = 0;
    buttonLeftReleased = 0;
  }
}

void setup() {
  Serial.begin(9600);

  pinMode(BUTTON_LEFT, INPUT);

  attachInterrupt(digitalPinToInterrupt(BUTTON_LEFT), buttonLeftPress, FALLING);
  attachInterrupt(digitalPinToInterrupt(BUTTON_LEFT), buttonLeftRelease, RISING);
}

void loop() {
  checkButtons();

  while(output > 0) {
    Serial.println(output, DEC);
    delay(100);
    output--;
  }
}