// see state diagram on https://arduino.stackexchange.com/questions/95023/i-need-help-for-applying-a-logic-to-this-code
// scroll through the answers.


int softStart = A0;
int enable = A1;
int powerBTN = A2;

enum State { OFF = 0, ON = 1, WAIT_ON = 2 , WAIT_OFF = 3, IN_SOFT_START = 4, SOFT_START_CONFIRM = 5 } ;
State state  ;
State oldState ;
bool stateChange = true ;

uint32_t inCurrentStateAtMs = 0 ;

void setState ( State newState ) {
  // forces change to new state
  inCurrentStateAtMs = millis() ;
  oldState = state ;
  state = newState ;
  stateChange = true ;
}

void setup() {
  Serial.begin(115200);
  pinMode(softStart, OUTPUT);
  pinMode(enable, OUTPUT);
  pinMode(powerBTN, INPUT_PULLUP) ;
  digitalWrite(enable, LOW);
  digitalWrite(softStart, LOW);

  setState( State::OFF ) ;

}

void loop() {

  if ( stateChange ) {
    //debug
    stateChange = false ;
    Serial.print("state changes to: ");
    Serial.println( state ) ;
  }


  switch ( state ) {

    case State::OFF : {
        if ( ! digitalRead( powerBTN ) && millis() - inCurrentStateAtMs > 100 ) {
          setState( State::WAIT_ON ) ;
        }
        break ;
      }

    case State::WAIT_ON : {
         
          if ( digitalRead( powerBTN ) && millis() - inCurrentStateAtMs < 500 ) {
            digitalWrite( enable, HIGH ) ;
            setState( State::ON );
          }
          else if ( digitalRead( powerBTN ) && millis() - inCurrentStateAtMs >= 500 ) {
            digitalWrite( enable, LOW ) ;
            digitalWrite( softStart, HIGH ) ;
            setState( State::IN_SOFT_START );
          }
         
        break ;
      }

    case State::ON : {
        if ( ! digitalRead( powerBTN ) && millis() - inCurrentStateAtMs > 100 ) {
          setState( State::WAIT_OFF );
        }
        break ;
      }


    case State::WAIT_OFF : {
        if ( digitalRead( powerBTN ) && millis() - inCurrentStateAtMs > 100 ) {
          digitalWrite( enable, LOW ) ;
          setState( State::OFF ) ;
        }
        break;
      }


    case State::IN_SOFT_START : {
        if ( ! digitalRead( powerBTN )  ) {
          digitalWrite( enable, HIGH ) ;
          state = State::SOFT_START_CONFIRM ;
        }
        else if ( millis() - inCurrentStateAtMs > 3000 ) {
          // timeout
          digitalWrite( softStart, LOW ) ;
          setState( State::OFF );
        }
        break ;
      }

    case State::SOFT_START_CONFIRM  : {
        if ( digitalRead( powerBTN ) && millis() - inCurrentStateAtMs > 2000  ) {
          digitalWrite( softStart, LOW ) ;
          setState( State::ON ) ;
        }
        break ;
      }

  } // switch

}  // loop