// BUTTONS : 1 to 16 
// reliable debounce
// buttons info : state, fronts down & up, toggle
// multiple buttons can be pressed at a time

#define DELAY_TIMER_BTN    B00000001                  // Button on A0
#define PROG_SEL_BTN       B00000010                  // Button on A1 
#define START_BTN          B00000100                  // Button on A2

unsigned long  prevmillis;                            // for debounce period
unsigned char  prevData;                              // previous reading of buttons
unsigned char  prevSta;                               // Button previous state 
unsigned char  actSta;                                // Button state (pressed, no pressed)
unsigned char  actTog;                                // Toggle
unsigned char  actOn;                                 // down front
unsigned char  actOff;                                // up front


void setup() {                                        // pullups on pins A0,A1,A2  
  PORTC |= B00000111;                                 // A3, A4, A5 as output
  DDRC  |= B00111000;
  Serial.begin(115200);                               //
  Serial.println(F("go ! press a button"));           //
}                                                     //

void isButtonPressed() {

  static unsigned int counter;
//  Serial.print(counter); Serial.print(" ");
  counter++;

  unsigned long now = millis();                       // or use global "now"

  if (now - prevmillis < 25) return;                  // too soon to even look again

  prevmillis = now;                                   // 25 ms debounce delay reached
  unsigned char newData = ~PINC & B00000111;          // 0 when pressed, internal pullup on pins A0, A1, A2

// this section reacts immediatley to a new different reading

  actOn   =  newData & ~prevData;                     // calculate PRESSED  transitioning bits
  actOff  = ~newData & prevData;

  actTog ^= actOn;                                    // apply TOGGLE 

  if (actOn & DELAY_TIMER_BTN) {Serial.print(counter); Serial.println(F(" DELAY pressed ")); }
  if (actOn & PROG_SEL_BTN)    {Serial.print(counter); Serial.println(F(" PROG pressed ")); }
  if (actOn & START_BTN)       {Serial.print(counter); Serial.println(F(" START pressed ")); }
  
  if (actOff & DELAY_TIMER_BTN){Serial.print(counter); Serial.println(F(" released DELAY")); }
  if (actOff & PROG_SEL_BTN)   {Serial.print(counter); Serial.println(F(" released PROG")); }
  if (actOff & START_BTN)      {Serial.print(counter); Serial.println(F(" released START")); }

  digitalWrite(A5, actTog & START_BTN);                // display red led toggle START/STOP 

// this section below develops the idea of a stable press (same for 2 readings)

  unsigned char staBits = ~(newData ^ prevData);

  actSta &= ~staBits;                                  // knock out the old stable bit readings
  actSta |= newData & staBits;                         // and jam the stable readings in there

  digitalWrite(A4, actSta & (PROG_SEL_BTN | DELAY_TIMER_BTN));  // one or both, green led ON 

// and could be used with for a fussier actOn / actOff / actTog by basing them on stable state readings

  unsigned char fussyActOn  = actSta & ~prevSta;
  unsigned char fussyActOff = ~actSta & prevSta;

  if (fussyActOn & DELAY_TIMER_BTN)      {Serial.print(counter); Serial.println(F(" verified fussy DELAY"));}
  if (fussyActOff & DELAY_TIMER_BTN)      {Serial.print(counter); Serial.println(F(" released fussy DELAY"));}

// always...
  prevData = newData;                                 // bump along the history
  prevSta = actSta;                                   // bump along the history
}

void loop() {                                         //
  isButtonPressed();                                  // 
  // delay(250); 
}                                                     //