#define NBUTTONS (int) 1
#define T_BOUNCE 50L

const int DS = 11;
const int ST = 8;
const int SC = 12;
const int BT[] = { A0, A1, A2, A3, A4, A5, 3, 2 };
const char BUFFER[256];

typedef enum btn_type {
  PRESS,
  SWITCH
} btn_type_t;

typedef void (*btn_callback_t) (void *data);

typedef struct btn_callback_range {
  long minimum;
  long interval;
  long maximum;
  btn_callback_t btn_callback;
} btn_callback_range_t;

typedef struct button {
  int pin;
  btn_type_t type;
  long fp; // first high signal
  long ds; // first debounced signal
  long lcb; // last signal
  int ncb;
  btn_callback_range_t *hi_callbacks;
  btn_callback_t lo_callback;
} button_t;

int16_t value = 0;
int8_t units[] = {0,0,0};
unsigned long bl;

int8_t digits[] = {
  0b00111111,
  0b00000110,
  0b01011011,
  0b01001111,
  0b01100110,
  0b01101101,
  0b01111101,
  0b00000111,
  0b01111111,
  0b01101111
};

button_t *buttons;

void setup() {
  initializeButtons();
}

static void initializeButtons() {
  buttons = (button_t *)malloc(NBUTTONS * sizeof(button_t));
  memset(buttons, 0, NBUTTONS * sizeof(button_t));
  for(int i = 0; i < NBUTTONS; ++i) {
    buttons[i].pin = BT[i];
    buttons[i].type = PRESS;
    buttons[i].fp = -1L;
    buttons[i].ds = -1L;
    buttons[i].lcb = -1L;
    buttons[i].ncb = 0;
    pinMode(buttons[i].pin, INPUT);
  }
  buttons[NBUTTONS - 1].type = SWITCH;
}

void loop() {
  checkButtons();
  delay(10);
}

static void checkButtons() {
  long milli = (long) millis();
  for(int i = 0; i < NBUTTONS; ++i) {
    if(digitalRead(buttons[i].pin) == HIGH) {
      if(buttons[i].fp == -1L) {
        buttons[i].fp = milli;
      } else if(buttons[i].ds == -1L) {
        if(milli - buttons[i].fp > T_BOUNCE) {
          buttons[i].ds = milli;
          checkButtonInterval(milli, buttons + i);
        }
      } else {
        checkButtonInterval(milli, buttons + i);
      }
    }
    else {
      if((buttons[i].fp >= 0 && (milli - buttons[i].fp > T_BOUNCE)) || buttons[i].ds >= 0) {
        buttons[i].fp = buttons[i].ds = buttons[i].lcb = -1L;
      }
    }      
  }
}

static void checkButtonInterval(const long milli, const button_t *button) {

}