constexpr unsigned long overallBlinkTime = 10000;
constexpr unsigned long blinkDelay       =  500;
constexpr unsigned long lightDelay       =  500;

constexpr byte buttonPin = 5;

constexpr int noOfLeds = 3;
byte ledPin[noOfLeds] = {2, 3, 4};

int currentLed = 1;
int lastLed = 0;
unsigned long nextStateTime;
byte button;

enum States {CHOOSELED, ON500, BLINK};
States state = CHOOSELED;

void setup() {
  Serial.begin(115200);
  Serial.println("Start");
  for (int i = 0; i < noOfLeds; i++) {
    pinMode(ledPin[i], OUTPUT);
  }
  pinMode(buttonPin, INPUT_PULLUP);
  randomSeed(analogRead(0));
}

void loop() {
  button = buttonState();
  stateMachine();
}

void stateMachine() {
  switch (state) {
    case CHOOSELED:
      chooseLed();
      break;
    case ON500:
      on500();
      break;
    case BLINK:
      blink();
      break;
  }
}

void blink() {
  static unsigned long lastBlinkTime = 0;
  if (millis() - lastBlinkTime >= blinkDelay) {
    lastBlinkTime = millis();
    byte actState = digitalRead(ledPin[currentLed]);
    digitalWrite(ledPin[currentLed], !actState);
  }
  if (millis() - nextStateTime >= overallBlinkTime) {
    digitalWrite(ledPin[currentLed], LOW);
    changeStateTo(CHOOSELED);
    Serial.println("BLINK -> CHOOSELED " + String(currentLed));
  }
}

void on500() {
  if (millis() - nextStateTime >= lightDelay) {
    if (button == LOW) {
      changeStateTo(BLINK);
      Serial.println("ON500 -> BLINK " + String(currentLed));

    } else {
      digitalWrite(ledPin[currentLed], LOW);
      changeStateTo(CHOOSELED);
      Serial.println("ON500 -> CHOOSELED " + String(currentLed));
    }
  }
}

void chooseLed() {
  if (button == LOW) {
    for (int i = 0; i < noOfLeds; i++) {
      digitalWrite(ledPin[i], LOW);
    }
    while (currentLed == lastLed) {
      currentLed = random(0, noOfLeds);
    }
    lastLed = currentLed;
    digitalWrite(ledPin[currentLed], HIGH);
    changeStateTo(ON500);
    Serial.println("ON500 " + String(currentLed));
  }
}

void changeStateTo(States newState) {
  state = newState;
  nextStateTime = millis();
}

byte buttonState() {
  static unsigned long lastChangeTime = 0;
  static byte lastState = HIGH;
  static byte state = HIGH;
  byte actState = digitalRead(buttonPin);
  if (actState != lastState) {
    lastState = actState;
    lastChangeTime = millis();
  }
  if (state != lastState && millis() - lastChangeTime > 30) {
    state = lastState;
  }
  return state;
}