// https://forum.arduino.cc/t/button-timing-and-loops/1223168
// https://wokwi.com/projects/390016797849980929  
unsigned long my3SecondTimer  = 0;  // Timer-variables MUST be of type unsigned long
unsigned long my350mSecsTimer = 0;  // Timer-variables MUST be of type unsigned long

const byte buttonPin = 17;
const byte heaterPin = 39;

byte buttonState;

boolean heatingStarted = false;

const byte released = HIGH;
const byte pressed  = LOW;


void setup() {
  Serial.begin(115200);
  Serial.println("Setup-Start");
  pinMode(buttonPin, INPUT_PULLUP);
  digitalWrite (heaterPin, LOW);
  pinMode(heaterPin, OUTPUT);  
  Serial.println("press button to start heater-cycle");
}

void loop() {

  // if heating has not yet started read in the button
  if (heatingStarted == false) {     
    buttonState = digitalRead(buttonPin);
    if ( buttonState == pressed ) {
      Serial.println("Start-Button pressed start heater cycle heater-pulsing");
      heatingStarted = true;      // indicate heating HAS started
      my3SecondTimer  = millis(); // store actual time
      my350mSecsTimer = millis(); // store actual time
      digitalWrite(heaterPin,HIGH);
    }
  }
  else { // heating HAS started and is running

    // check if 350 milliseconds have pased by since heating started
    if (  TimePeriodIsOver(my350mSecsTimer,  350)  ) {
      // when 350 milliseconds REALLY HAVE passed by
      // update timervariable with name "my350mSecsTimer" automatically
      // for next interval
      invertHeaterStateOnOff(); // say what it does
    }
    

    // check if 3000 milliseconds have passed by since heating started
    if (  TimePeriodIsOver(my3SecondTimer, 3000)  ) {
      // when 3000 milliseconds REALLY HAVE passed by
      // not reevant here: update timervariable with name "my3SecondTimer" automatically
      Serial.println("3 seconds over heater switched OFF");
      digitalWrite(heaterPin, LOW);   
      Serial.println("heating cycle finished press button for new heater-cycle");
      Serial.println();
      heatingStarted = false;
    }
  }
}


void invertHeaterStateOnOff() {
  if ( digitalRead(heaterPin) == HIGH) {
    digitalWrite(heaterPin, LOW); 
    Serial.println("Heater  switched OFF");
  }
  else {
    digitalWrite(heaterPin, HIGH);     
    Serial.println("Heater  switched ON");
  }
}

// easy to use helper-function for non-blocking timing
boolean TimePeriodIsOver (unsigned long &startOfPeriod, unsigned long TimePeriod) {
  unsigned long currentMillis  = millis();
  if ( currentMillis - startOfPeriod >= TimePeriod ) {
    // more time than TimePeriod has elapsed since last time if-condition was true
    startOfPeriod = currentMillis; // a new period starts right here so set new starttime
    return true;
  }
  else return false;            // actual TimePeriod is NOT yet over
}