// Pin config
const int button = 2;
const int led =  4;

// values for morse code, https://morsecode.world/international/timing.html
const int unit = 100;   // base time unit for morse code, smaller is faster
const int dot = unit; // same as dit (.)
const int dash = unit * 3;  // same as dah (-)
const int intra_char_space = unit;  // the gap between dits and dahs within a character
const int inter_char_space = unit * 3;  // the gap between the characters of a word
const int word_space = unit * 7;  // the gap between two words

// status values of button
int pressed = 0;

void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
  pinMode(button, INPUT);
}

// functions of breathing light

void breathing() {
  for (int i = 0; i < 255; i++) {
    analogWrite(led, i);
    delay(1);
  }
  for (int i = 255; i > 0; i--) {
    analogWrite(led, i);
    delay(1);
  }
}

// functions of morse code

// "_" is used for spaces in between words. Every char already ends with a inter_char_space of 3 time units.
void _() {
  delay(word_space - inter_char_space);
}

void s() {
  // ...
  analogWrite(led, 255);
  delay(dot);
  analogWrite(led, 0);
  delay(intra_char_space);
  analogWrite(led, 255);
  delay(dot);
  analogWrite(led, 0);
  delay(intra_char_space);
  analogWrite(led, 255);
  delay(dot);
  analogWrite(led, 0);
  delay(inter_char_space);
}

void o() {
  // ---
  analogWrite(led, 255);
  delay(dash);
  analogWrite(led, 0);
  delay(intra_char_space);
  analogWrite(led, 255);
  delay(dash);
  analogWrite(led, 0);
  delay(intra_char_space);
  analogWrite(led, 255);
  delay(dash);
  analogWrite(led, 0);
  delay(inter_char_space);
}

void loop() {
  pressed = digitalRead(button);
  if (pressed == LOW) {
    // if pressed = true
    // SOS ···---···
    s();
    o();
    s();
    _();
  } else {
    // if pressed = false
    breathing();
    }
  }