const byte red_pin    = 10;
const byte yellow_pin =  8;
const byte green_pin  = 12;

const byte sm_Red         = 0; // name "sm_Red" represents         value 0
const byte sm_Green       = 1; // name "sm_Green" represents       value 1
const byte sm_YellowGreen = 2; // name "sm_YellowGreen" represents value 2

byte myStateVar = sm_Red; // variable used for the switch-case-break-stateMachine

// indexed variable (= array of chars) used for printing letters 
const char myStateNames[][16] = {
  "Red",
  "Green",
  "YellowGreen"
};

unsigned long myTimerVar; // variable used for non-blocking timing

void setup () {
  Serial.begin(115200); // open serial interface with "speed" 115200 baud
  Serial.println( F("Setup-Start") );
  pinMode (red_pin, OUTPUT);
  pinMode (yellow_pin, OUTPUT);
  pinMode (green_pin, OUTPUT);
  Serial.println( F("exiting Setup infinite looping begins") );
}


void loop () {
  myTrafficLight_StateMachine(); // call lines of code defined inside void myTrafficLight_StateMachine()
}

// definition of user-defined function with name "myTrafficLight_StateMachine"
void myTrafficLight_StateMachine() {

  printStateWhenChanged(myStateVar); // call lines of code defined inside void printStateWhenChanged (byte p_actualState) 

  
  // depending on which value 0,1 or 2 variable myStateVar has
  // mutually exclusive execute only the code below/inside 
  //    case sm_Red
  // or case sm_Green:
  // or sm_YellowGreen:  
  switch (myStateVar) {

    case sm_Red:
      digitalWrite (red_pin,    HIGH);
      digitalWrite (yellow_pin, LOW);
      digitalWrite (green_pin,  LOW);
      // check if more than 5000 milliseconds of time have passed by
      if ( TimePeriodIsOver(myTimerVar,5000) ) {
        // when REALLY 5000 milliseconds of time HAVE passed by
        myStateVar = sm_Green; // change to state sm_Green
      }
      break; // IMMIDIATELY jump down to END-OF-SWITCH

    case sm_Green:
      digitalWrite (red_pin,    LOW);
      digitalWrite (yellow_pin, LOW);
      digitalWrite (green_pin,  HIGH);
      // check if more than 5000 milliseconds of time have passed by
      if ( TimePeriodIsOver(myTimerVar,5000) ) {
        // when REALLY 5000 milliseconds of time HAVE passed by
        myStateVar = sm_YellowGreen; // change to state sm_YellowGreen
      }
      break; // IMMIDIATELY jump down to END-OF-SWITCH
    
    case sm_YellowGreen:
      digitalWrite (red_pin,    LOW);
      digitalWrite (yellow_pin, HIGH);
      digitalWrite (green_pin,  HIGH);
      // check if more than 2000 milliseconds of time have passed by
      if ( TimePeriodIsOver(myTimerVar,2000) ) {
        // when REALLY 2000 milliseconds of time HAVE passed by
        myStateVar = sm_Red; // change to state sm_Red
      }
      break; // IMMIDIATELY jump down to END-OF-SWITCH

  } // END-OF-SWITCH
}


// 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
}


void printStateWhenChanged (byte p_actualState) {
  static byte lastState; // "static makes value of variable lastState persistant 

  // check if state has CHANGED since last time this function was called
  if (p_actualState != lastState ) {
    // when state HAS changed
    printTimeStampMilliSeconds(); // call lines of code defined under printTimeStampMilliSeconds()
    Serial.print( F("state changed from ") );
    Serial.print(myStateNames[lastState]);
    Serial.print( F(" to ") );
    Serial.print(myStateNames[p_actualState]);
    Serial.println();    
    lastState = p_actualState; // update variable lastState
  }
}

void printTimeStampMilliSeconds() {
  Serial.print("ms:");
  Serial.print(millis() );
  Serial.print(" ");
}