#define PIN_RED         2
#define PIN_YELLOW      3
#define PIN_GREEN       4
#define PIN_BTN         7

#define TIME_GREEN       4000
#define TIME_YELLOW      4000  
#define TIME_RED         8000   

#define STATE_GREEN     0
#define STATE_YELLOW    1
#define STATE_RED       2

int state = STATE_GREEN;
unsigned long startTime = 0;

void setup() {
  pinMode(PIN_RED,    OUTPUT);
  pinMode(PIN_YELLOW, OUTPUT);
  pinMode(PIN_GREEN,  OUTPUT);
  pinMode(PIN_BTN,    INPUT_PULLUP);
  
  startTime = millis();
  updateLights();
}

void loop() {
  unsigned long now     = millis();
  unsigned long elapsed = now - startTime;

  if (digitalRead(PIN_BTN) == LOW && state != STATE_GREEN) {
    transitionTo(STATE_GREEN);
    return;  // 
  }

  switch (state) {
    case STATE_GREEN:
      if (elapsed >= TIME_GREEN) {
        transitionTo(STATE_YELLOW);
      }
      break;

    case STATE_YELLOW:
      if (elapsed >= TIME_YELLOW) {
        transitionTo(STATE_RED);
      }
      break;

    case STATE_RED:
      if (elapsed >= TIME_RED) {
        transitionTo(STATE_GREEN);
      }
      break;
  }
}

void transitionTo(int nextState) {
  state     = nextState;
  startTime = millis();
  updateLights();
}

void updateLights() {
  digitalWrite(PIN_RED,    (state == STATE_RED)    ? HIGH : LOW);
  digitalWrite(PIN_YELLOW, (state == STATE_YELLOW) ? HIGH : LOW);
  digitalWrite(PIN_GREEN,  (state == STATE_GREEN)  ? HIGH : LOW);
}