#include <Joystick.h>

Joystick_ j(0x13, 0x05, 32, 2, false, false, false, false, false, false, false, false, false, false, false); // 32 buttons 2 hats no axes

uint8_t b = 0b00000000; //digital pins 0 to 7; x ^= (1 << n); - toggles nth bit of x.  all other bits left alone.
uint8_t b1 = 0b00000000; //digital pins 8 to 15
uint8_t b2 = 0b00000000; //digital pins 15 to 23
byte pins = 16; // we have 16 buttons

bool g_lastButtonState[16];

//#define DEBUG

void setup() {
  #if defined(DEBUG)
    Serial.begin(9600);           // start serial for output
  #endif
  
  j.begin(); // init joystick
  
  for (int i = 2; i <= pins; i++) {
    pinMode(i, INPUT_PULLUP); // here we enable built-in pull up resistors for each pin, the default state of each pin is now 1
  }
}

void loop() {

// we will read 16 buttons into 3 bytes

  for (int i = 0; i <= pins; i++) {
    bool pin = !digitalRead(i); // note the ! before digitalRead - we invert our value
    if (pin == 1) {
     if (i < 8) {
        b |= (1 << i);       // forces ith bit of b to be 1.  all other bits left alone.
     } else if ( (i >= 8) && (i < 16)) {
        b1 |= (1 <<  (i - 8));
     } else if (i >= 15) {
        b2 |= (1 <<  (i - 16));
     }
   } else {
    if ( i < 8) {
      b &= ~(1 << i);      // forces ith bit of b to be 0.  all other bits left alone.
    } else if ( (i >= 8) && (i < 16)) {
        b1 &= ~(1 << (i - 8));
      } else if (i >= 16) {
        b2 &= ~(1 <<  (i - 16));
      }
    }  
  }

    // we now have 3 bytes with button values, we can then send them to i2c or parse them locally:

    parse_button_array(b,0,0,0);
    parse_button_array(b1,9,0,0);
    parse_button_array(b2,17,0,0);

    #if defined(DEBUG)
      printBits(b);
      Serial.print(" ");
      printBits(b1);
      Serial.print(" ");
      printBits(b2);
      Serial.println();
    #endif
  
}

 void parse_button_array(uint8_t b, uint8_t start_btn, uint8_t end_btn, uint8_t byte_offset) {
    if (end_btn == 0) {
      end_btn = 8;
    }
    for (byte i = byte_offset; i < end_btn; i++) {
      bool v = (b >> i) & 1;
      
      if (v != g_lastButtonState[i + start_btn]) {
            j.setButton(i + start_btn, v);     // here we send a joy button press if the button state has changed, 1st parameter is the button number, 2nd one is the value
      } 
      g_lastButtonState[i + start_btn] = v; // here we save the value to our global array of last known button states
    }
  }