#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>

constexpr auto LED1 = 7;
constexpr auto LED2 = 6;
constexpr auto LED3 = 5;
constexpr auto BTN = 2;

int leds[] = {LED1, LED2, LED3};
int ledCount = sizeof(leds) / sizeof(leds[0]);
bool sequenceActive = true;
unsigned long lastUpdate = 0;
int currentLed = 1;
int lastLed = 0;
const unsigned long interval = 400;
volatile bool stopFlag = false;

unsigned long lastDebounceTime = 0;  // debounce time
const unsigned long debounceDelay = 10; // debounce delay (ms)

volatile unsigned long systemMillis = 0; // custom millis counter

void setup() {
    Serial.println("setup");
  // Configure LEDs as output
  DDRD |= (1 << LED1) | (1 << LED2) | (1 << LED3);
  // Configure button pin as input with pull-up resistor
  DDRD &= ~(1 << BTN);
  PORTD |= (1 << BTN);

  // Configure Timer1 to simulate millis
  TCCR1A = 0;
  TCCR1B = (1 << WGM12) | (1 << CS11) | (1 << CS10); // CTC mode, prescaler 64
  OCR1A = 249; // 1 ms with 16MHz clock
  TIMSK1 = (1 << OCIE1A); // Enable Timer1 compare interrupt

  // Enable external interrupt on BTN (assuming it corresponds to INT0)
  EICRA |= (1 << ISC11); // Trigger on falling edge
  EIMSK |= (1 << INT0);  // Enable INT0 interrupt
  sei();                 // Enable global interrupts

  // Enable watchdog timer with a 1-second timeout
  wdt_enable(WDTO_1S);   
}

// Custom millis function to simulate Arduino's millis()
unsigned long customMillis() {
  unsigned long millisCopy;
  // cli();
  millisCopy = systemMillis;
  // sei();
  return millisCopy;
}

void loop() {
  if (stopFlag)
    return;

  wdt_reset();
  unsigned long currentMillis = customMillis();

  if (currentMillis - lastUpdate >= interval) {
    PORTD &= ~(1 << leds[lastLed]); // Turn off the previous LED
    currentLed++;

    if (currentLed >= ledCount)
      currentLed = 0;

    PORTD |= (1 << leds[currentLed]); // Turn on the current LED
    lastUpdate = customMillis();
    lastLed = currentLed;
  }
}

// ISR for Timer1 compare match to update millis counter
ISR(TIMER1_COMPA_vect) {
  systemMillis++;
}

// External interrupt ISR for button press
ISR(INT0_vect) {
  unsigned long debounceMillis = customMillis();
  if (debounceMillis - lastDebounceTime > debounceDelay) {
    stopFlag = true;
    lastDebounceTime = debounceMillis;
  }
}