// https://wokwi.com/projects/355045239740731393
// https://forum.arduino.cc/t/is-it-possible-to-mimic-a-rotary-encoder-with-an-arduino/1075058

const byte led_R = 4;  //channel A
const byte led_Y = 3;  //channel B

const byte upButton = A0;
const byte downButton = A1;

unsigned long now;    // always current millis()

char lineBuffer[32];    // for sprintf. TinkerCod?

void setup()
{
  mySetup(115200);
  xprintf("\nhello world.\n"); 

  pinMode(upButton, INPUT_PULLUP);
  pinMode(downButton, INPUT_PULLUP);

  pinMode(led_R, OUTPUT);
  pinMode(led_Y, OUTPUT);
}

# define IDLE 0
# define IN   1

void loop()
{ 
  now = millis();

  if (oneClickFSM() == IDLE) {    // give the quadrature synthesis a chance

    checkCommands();              // not busy, check stimuli and react
  }
}

// just get buttons or serial "commands"
// these just cause one step up or down
// serial character 'z' for up, 'x' for down

void checkCommands()
{
  static unsigned long lastButtonsTime;
  static unsigned char lastUP, lastDOWN;

  if (now - lastButtonsTime > 20) {

    unsigned char thisUP = digitalRead(upButton);
    if (thisUP != lastUP) {

      if (!thisUP)
        kickOneClick(1);

      lastUP = thisUP;
      lastButtonsTime = now;
    } 

    unsigned char thisDOWN = digitalRead(downButton);
    if (thisDOWN != lastDOWN) {

      if (!thisDOWN)
        kickOneClick(-1);

      lastDOWN = thisDOWN;
      lastButtonsTime = now;
    }
  }

  if (Serial.available()) {
    char theChar = Serial.read();

    if (theChar == 'z') kickOneClick(1);
    if (theChar == 'x') kickOneClick(-1);
  }
}


// the synthesizer
// call kickOneClick with -1 or 1 to make start click
// call oneClickFSM() frequently, like every pass through the loop

const int phaseTime = 100;  //duration of each phase of quadrature cycle in milliseconds - can be lower
const unsigned char nPhases = 4;
const byte restPhase = 0;   // where in the quad signal do we stay between clicks?

byte xCount;
byte xDirection;

void kickOneClick(int direction)
{
  sprintf(lineBuffer, "kick it %s\n", direction > 0 ? "UP" : "DOWN");
  Serial.print(lineBuffer);

  xDirection = direction;
  xCount = nPhases;
}

bool oneClickFSM()
{
  static unsigned long lastPhase;

  if (!xCount) return IDLE;

  if (now - lastPhase < phaseTime)
    return IN;

  lastPhase = now;
  --xCount;
  quadFSM(xDirection);

  return xCount ? IN : IDLE;
}

const byte xCLKPin = led_Y;
const byte xDTPin = led_R;

byte quadFSM(byte direction)
{
  static byte state = restPhase;

  state += direction;
  state &= 0x3;

//  xprintf("QFSM %d %d (%d)\n", state, direction, xCount);

  switch (state) {
  case 0 :
    digitalWrite(xDTPin, LOW);
    digitalWrite(xCLKPin, LOW);

    break;

  case 1 :
    digitalWrite(xDTPin, HIGH);
    digitalWrite(xCLKPin, LOW);

    break;
      
  case 2 :
    digitalWrite(xDTPin, HIGH);
    digitalWrite(xCLKPin, HIGH);

    break;

  case 3 :
    digitalWrite(xDTPin, LOW);
    digitalWrite(xCLKPin, HIGH);

    break;
  }
}



//

//
// programmer misses printf...

void xprintf(const char *format, ...)
{
  char buffer[256];
  va_list args;
  va_start(args, format);
  vsprintf(buffer, format, args);
  va_end(args);
  Serial.print(buffer);
}

// programmer forgets day of week, version

void mySetup(unsigned long bandRate)
{
  Serial.begin(bandRate);
  
  char s[] = __FILE__;
  byte b = sizeof(s);
  while ( (b > 0) && (s[b] != 47)) b--;
  char *u = s + b + 1;
 
  xprintf("\nHEllo WOrld!\n");
  xprintf("%s  %s\n\n", __DATE__, u);

  xprintf("!\n");
}