// https://wokwi.com/projects/420103535976304641
// https://forum.arduino.cc/t/toggling-between-two-pairs-of-leds/1341607

auto PRESSED = LOW;

const int greenLED = 12;
const int redLED = 10;
const int button = 2;

bool greenNow;
bool lastButtonState;

void setup() {
  pinMode(greenLED, OUTPUT);
  pinMode(redLED, OUTPUT);
  pinMode(button, INPUT_PULLUP);

  digitalWrite(greenLED, HIGH);
  digitalWrite(redLED, LOW);

  greenNow = true;

  lastButtonState = digitalRead(button) == PRESSED;
}

void loop() {
  bool buttonState = digitalRead(button) == PRESSED;

  if (buttonState != lastButtonState) {
    if (buttonState) {
      greenNow = !greenNow;

      digitalWrite(greenLED, greenNow ? HIGH : LOW);
      digitalWrite(redLED, greenNow ? LOW : HIGH);
    }

    lastButtonState = buttonState;
    delay(25);
  }
}