// Morse SOS on LED when button is pressed
// SAMD21: LED on pin 0, button on pin 1

const int LED_PIN    = 0;
const int BUTTON_PIN = 1;

// Length of one Morse "unit" in milliseconds
const unsigned int UNIT = 200;  // Adjust faster/slower as you like

// For edge-detection and simple debouncing
bool lastButtonState = HIGH;  // with INPUT_PULLUP, HIGH = not pressed
unsigned long lastDebounceTime = 0;
const unsigned long DEBOUNCE_DELAY = 30; // ms

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);  // internal pull-up; button to GND

  digitalWrite(LED_PIN, LOW);
}

// --- Morse helpers ---

void dot() {
  digitalWrite(LED_PIN, HIGH);
  delay(UNIT);              // light on for 1 unit
  digitalWrite(LED_PIN, LOW);
  delay(UNIT);              // gap between elements (1 unit)
}

void dash() {
  digitalWrite(LED_PIN, HIGH);
  delay(3 * UNIT);          // light on for 3 units
  digitalWrite(LED_PIN, LOW);
  delay(UNIT);              // gap between elements (1 unit)
}

// After finishing a letter, we already had a 1-unit gap
// from dot()/dash(), so we only add 2 more units to reach 3 total.
void letterGap() {
  delay(2 * UNIT);
}

void wordGap() {
  // After last element: 1 unit already passed
  // For full 7-unit word gap, add 6 units more.
  delay(6 * UNIT);
}

void sendS() {
  dot();
  dot();
  dot();
  letterGap();
}

void sendO() {
  dash();
  dash();
  dash();
  letterGap();
}

void sendSOS() {
  sendS();
  sendO();
  sendS();
  // optional: word gap after SOS
  wordGap();
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);

  // Debounce: check if state changed
  if (reading != lastButtonState) {
    lastDebounceTime = millis();
    lastButtonState = reading;
  }

  // If state has been stable for a bit, treat it as real
  if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) {
    // Button is active LOW: pressed when reading == LOW
    if (reading == LOW) {
      // Simple: wait until button released, then send SOS once
      // to avoid repeated triggers while held
      while (digitalRead(BUTTON_PIN) == LOW) {
        // do nothing, wait for release
      }

      sendSOS();
    }
  }
}