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

volatile uint8_t ledPattern = 0b00000001;  // Initial pattern for LEDs

void setup() {
  // Set the LED pins as outputs (pins 0 to 7)
  for (int pin = 0; pin <= 7; pin++) {
    pinMode(pin, OUTPUT);
  }

  // Initialize Timer1
  noInterrupts();           // Disable all interrupts
  TCCR1A = 0;               // Set entire TCCR1A register to 0
  TCCR1B = 0;               // Same for TCCR1B
  TCNT1 = 0;                // Initialize counter value to 0
  OCR1A = 39062;            // Set compare match register for 0.25s intervals (16 MHz clock / 256 prescaler / 0.25s - 1)
  TCCR1B |= (1 << WGM12);   // Turn on CTC mode
  TCCR1B |= (1 << CS12);    // Set CS12 bit for 256 prescaler
  TIMSK1 |= (1 << OCIE1A);  // Enable timer compare interrupt
  interrupts();             // Enable all interrupts
}

ISR(TIMER1_COMPA_vect) {
  // Rotate the LED pattern to the right
  if (ledPattern & 0b00000001) {
    ledPattern = (ledPattern >> 1) | 0b10000000;
  } else {
    ledPattern >>= 1;
  }

  // Output the LED pattern to the pins
  for (int i = 0; i < 8; i++) {
    digitalWrite(i, (ledPattern >> i) & 0x01);
  }
}

void loop() {
}