// ================= PIN =================
#define PIN_FAIL     1   // PB1 (LOW = FAIL)
#define PIN_RESTORE  4   // PB4 (LOW = RESTORE)
#define PIN_BUZZ     0   // PB0
#define PIN_MUTE     3   // PB3

// ============== PARAMETER ==============
#define BUZ_FREQ_FAST 3000   // Hz
#define BUZ_ON_SLOW   200    // ms
#define BUZ_OFF_SLOW  1000   // ms

#define DEBOUNCE_MS 50
#define SCAN_MS     10

// ================= STATE =================
enum AlarmState {
  ALARM_IDLE,
  ALARM_FAIL,
  ALARM_RESTORE
};

AlarmState alarmState = ALARM_IDLE;

bool mute = false;
bool lastMute = HIGH;

// debounce
unsigned long tFail = 0;
unsigned long tRestore = 0;
bool failStable = false;
bool restoreStable = false;

// buzzer
unsigned long tToggle = 0;
bool buzState = false;
unsigned long tSlow = 0;

// ================= UTIL =================
bool debounce(bool raw, bool &state, unsigned long &timer, unsigned long now) {
  if (raw != state) {
    if (now - timer > DEBOUNCE_MS) {
      state = raw;
      timer = now;
    }
  } else {
    timer = now;
  }
  return state;
}

// ================= SETUP =================
void setup() {
  pinMode(PIN_FAIL, INPUT_PULLUP);
  pinMode(PIN_RESTORE, INPUT_PULLUP);
  pinMode(PIN_MUTE, INPUT_PULLUP);

  pinMode(PIN_BUZZ, OUTPUT);
  digitalWrite(PIN_BUZZ, LOW);
}

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

  // ---------- INPUT ----------
  bool rawFail    = (digitalRead(PIN_FAIL) == LOW);
  bool rawRestore = (digitalRead(PIN_RESTORE) == LOW);
  bool muteBtn    = digitalRead(PIN_MUTE);

  // ---------- DEBOUNCE ----------
  bool fail    = debounce(rawFail, failStable, tFail, now);
  bool restore = debounce(rawRestore, restoreStable, tRestore, now);

  // ---------- STATE MACHINE ----------
  switch (alarmState) {

    case ALARM_IDLE:
      if (fail) alarmState = ALARM_FAIL;
      else if (restore) alarmState = ALARM_RESTORE;
      break;

    case ALARM_FAIL:
      if (!fail && restore) alarmState = ALARM_RESTORE;
      else if (!fail && !restore) alarmState = ALARM_IDLE;
      break;

    case ALARM_RESTORE:
      if (fail) alarmState = ALARM_FAIL;
      else if (!restore) alarmState = ALARM_IDLE;
      break;
  }

  // ---------- MUTE ----------
  if (lastMute == HIGH && muteBtn == LOW) {
    mute = !mute;
  }
  lastMute = muteBtn;

  // ---------- BUZZER ----------
  if (!mute) {

    // ===== FAIL (TRRRR CONTINUOUS) =====
    if (alarmState == ALARM_FAIL) {

      unsigned long period_us = 1000000UL / BUZ_FREQ_FAST / 2;

      if (micros() - tToggle >= period_us) {
        tToggle = micros();
        buzState = !buzState;
        digitalWrite(PIN_BUZZ, buzState);
      }
    }

    // ===== RESTORE (SLOW BEEP) =====
    else if (alarmState == ALARM_RESTORE) {

      if (now - tSlow > (BUZ_ON_SLOW + BUZ_OFF_SLOW)) {
        tSlow = now;
      }

      if (now - tSlow < BUZ_ON_SLOW) {
        digitalWrite(PIN_BUZZ, HIGH);
      } else {
        digitalWrite(PIN_BUZZ, LOW);
      }
    }

    // ===== IDLE =====
    else {
      digitalWrite(PIN_BUZZ, LOW);
    }

  } else {
    digitalWrite(PIN_BUZZ, LOW);
  }

  // ---------- SCAN TIME ----------
  static unsigned long lastScan = 0;
  while (millis() - lastScan < SCAN_MS);
  lastScan = millis();
}