// Traffic Light FSM - XIAO ESP32-S3
// Red → Yellow → Green → Yellow → repeat

enum State {
  RED,
  RED_YELLOW,
  GREEN,
  YELLOW
};

const int RED_PIN = D2;
const int YELLOW_PIN = D3;
const int GREEN_PIN = D4;

State currentState = RED;
unsigned long lastChange = 0;

void setLights(bool r, bool y, bool g) {
  digitalWrite(RED_PIN, r);
  digitalWrite(YELLOW_PIN, y);
  digitalWrite(GREEN_PIN, g);
}

void setup() {
  pinMode(RED_PIN, OUTPUT);
  pinMode(YELLOW_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
}

void loop() {
  unsigned long now = millis();

  switch (currentState) {
    case RED:
      setLights(true, false, false);
      if (now - lastChange > 2000) {
        currentState = RED_YELLOW;
        lastChange = now;
      }
      break;

    case RED_YELLOW:
      setLights(true, true, false);
      if (now - lastChange > 1000) {
        currentState = GREEN;
        lastChange = now;
      }
      break;

    case GREEN:
      setLights(false, false, true);
      if (now - lastChange > 3000) {
        currentState = YELLOW;
        lastChange = now;
      }
      break;

    case YELLOW:
      setLights(false, true, false);
      if (now - lastChange > 1000) {
        currentState = RED;
        lastChange = now;
      }
      break;
  }
}