Arduino Reaction-Time Game

#include <Arduino.h>

enum GameState {
  WAIT_FOR_RELEASE,
  WAIT_RANDOM_DELAY,
  WAIT_FOR_REACTION,
  SHOW_RESULT
};

bool buttonPressedEvent();
bool buttonIsReleased();
void blinkResultLed();
void startWaitingRound();

const uint8_t LED_PIN = 13;
const uint8_t BUTTON_PIN = 2;
const unsigned long DEBOUNCE_MS = 30;
const unsigned long BLINK_MS = 180;

GameState state = WAIT_FOR_RELEASE;
unsigned long stateStartedAt = 0;
unsigned long cueStartedAt = 0;
unsigned long randomDelayMs = 0;

bool rawLastReading = HIGH;
bool stableButtonState = HIGH;
unsigned long lastRawChangeAt = 0;

bool buttonPressedEvent() {
  const bool reading = digitalRead(BUTTON_PIN);
  const unsigned long now = millis();

  if (reading != rawLastReading) {
    rawLastReading = reading;
    lastRawChangeAt = now;
  }

  if ((now - lastRawChangeAt) >= DEBOUNCE_MS && reading != stableButtonState) {
    stableButtonState = reading;
    return stableButtonState == LOW;
  }

  return false;
}

bool buttonIsReleased() {
  return stableButtonState == HIGH;
}

void blinkResultLed() {
  for (uint8_t blink = 0; blink < 3; ++blink) {
    digitalWrite(LED_PIN, HIGH);
    delay(BLINK_MS);
    digitalWrite(LED_PIN, LOW);
    delay(BLINK_MS);
  }
}

void startWaitingRound() {
  digitalWrite(LED_PIN, LOW);
  randomDelayMs = random(1500, 5001);
  stateStartedAt = millis();
  state = WAIT_RANDOM_DELAY;
  Serial.println(F("Get ready..."));
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  digitalWrite(LED_PIN, LOW);

  Serial.begin(115200);
  randomSeed(analogRead(A0) ^ micros());
  Serial.println(F("Reaction-time game ready. Release the button to begin."));
}

void loop() {
  const unsigned long now = millis();
  const bool pressed = buttonPressedEvent();

  switch (state) {
    case WAIT_FOR_RELEASE:
      digitalWrite(LED_PIN, LOW);
      if (buttonIsReleased()) {
        startWaitingRound();
      }
      break;

    case WAIT_RANDOM_DELAY:
      if (pressed) {
        Serial.println(F("False start! Wait for the LED."));
        state = WAIT_FOR_RELEASE;
      } else if (now - stateStartedAt >= randomDelayMs) {
        digitalWrite(LED_PIN, HIGH);
        cueStartedAt = now;
        state = WAIT_FOR_REACTION;
        Serial.println(F("GO!"));
      }
      break;

    case WAIT_FOR_REACTION:
      if (pressed) {
        const unsigned long reactionMs = now - cueStartedAt;
        digitalWrite(LED_PIN, LOW);
        Serial.print(F("Reaction time: "));
        Serial.print(reactionMs);
        Serial.println(F(" ms"));
        state = SHOW_RESULT;
      }
      break;

    case SHOW_RESULT:
      blinkResultLed();
      Serial.println(F("Release the button for the next round."));
      state = WAIT_FOR_RELEASE;
      break;
  }
}