typedef enum {
  LED_DISPLAY = 500,
  PUSH_BUTTON_DEBOUNCING = 50
} Delays;

typedef enum {
  LED0 = 2,
  LED1 = 3,
  LED2 = 4,
  LED3 = 5
} Leds;

const int LEDS_SIZE = 4;
const int LEDs[LEDS_SIZE] = { LED0, LED1, LED2, LED3 };

typedef enum {
  COUNT_PB = 8,
  FLASH_PB = 9
} Push_Buttons;

unsigned char counter = 0;

void initLeds() {
  for (int i = 0; i < LEDS_SIZE; i++) {
     pinMode(LEDs[i], OUTPUT);
  }
}

void initPushButtons() {
  pinMode(COUNT_PB, INPUT_PULLUP);
  pinMode(FLASH_PB, INPUT_PULLUP);
}

void countLedsUp() {
  /**
    Use for-loop instead of:
    digitalWrite(LED0, counter & 0b00000001);
    digitalWrite(LED1, counter & 0b00000010);
    digitalWrite(LED2, counter & 0b00000100);
    digitalWrite(LED3, counter & 0b00001000);
  */
  for (int i = 0; i < LEDS_SIZE; i++) {
    digitalWrite(LEDs[i], counter & (1 << i));
  }
  delay(LED_DISPLAY);
  counter++;
  if (counter == 16)
    counter = 0;
}

void flashLeds() {
  int ledCurrentState;
  for (int i = 0; i < LEDS_SIZE; i++) {
    ledCurrentState = digitalRead(LEDs[i]);
    digitalWrite(LEDs[i], !ledCurrentState);
  }
  delay(LED_DISPLAY);

  for (int i = 0; i < LEDS_SIZE; i++) {
    ledCurrentState = digitalRead(LEDs[i]);
    digitalWrite(LEDs[i], !ledCurrentState);
  }
  delay(LED_DISPLAY);
}

void setup() {
  initLeds();
  initPushButtons();
  Serial.begin(9600);
}

void loop() {
  int countUpPushButtonStatus = digitalRead(COUNT_PB);
  int flashPushButtonStatus = digitalRead(FLASH_PB);

  if (countUpPushButtonStatus == LOW) {
    Serial.println("Count push-button is pressed ...!");
    countLedsUp();

  } else if (flashPushButtonStatus == LOW) {
    Serial.println("Flash push-button is pressed ...!");
    flashLeds();
    
  }

  delay(PUSH_BUTTON_DEBOUNCING); // debouncing
}