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

volatile uint8_t currentLED = 0;  // Index of the current LED
const uint8_t ledPins[5] = {3, 4, 5, 6, 7};  // LED pin numbers

void setup() {
  // Set the LED pins as outputs
  for (int i = 0; i < 5; i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], LOW); // Ensure LEDs are off initially
  }

  // Set the external interrupt pin as input
  pinMode(2, INPUT_PULLUP);  // Use internal pull-up resistor

  // Configure external interrupt on pin 2 (INT0)
  noInterrupts();              // Disable all interrupts
  EICRA |= (1 << ISC01);       // Trigger on falling edge of INT0
  EIMSK |= (1 << INT0);        // Enable external interrupt INT0
  interrupts();                // Enable all interrupts
}

ISR(INT0_vect) {
  // Toggle the current LED
  digitalWrite(ledPins[currentLED], !digitalRead(ledPins[currentLED]));

  // Move to the next LED in the pattern
  currentLED++;
  if (currentLED >= 7) {
    currentLED = 0;
  }
}

void loop() {
  // The loop is intentionally left empty
}