#include "Adafruit_TinyUSB.h"

Adafruit_USBD_HID usb_hid;

#define KEY_NUMLOCK 0x53    // Keyboard Num Lock and Clear
#define KEY_KPSLASH 0x54    // Keypad /
#define KEY_KPASTERISK 0x55 // Keypad *
#define KEY_KPMINUS 0x56    // Keypad -
#define KEY_KPPLUS 0x57     // Keypad +
#define KEY_KPENTER 0x58    // Keypad ENTER
#define KEY_KP1 0x59        // Keypad 1 and End
#define KEY_KP2 0x5a        // Keypad 2 and Down Arrow
#define KEY_KP3 0x5b        // Keypad 3 and PageDn
#define KEY_KP4 0x5c        // Keypad 4 and Left Arrow
#define KEY_KP5 0x5d        // Keypad 5
#define KEY_KP6 0x5e        // Keypad 6 and Right Arrow
#define KEY_KP7 0x5f        // Keypad 7 and Home
#define KEY_KP8 0x60        // Keypad 8 and Up Arrow
#define KEY_KP9 0x61        // Keypad 9 and Page Up
#define KEY_KP0 0x62        // Keypad 0 and Insert
#define KEY_KPDOT 0x63      // Keypad . and Delete

//uint8_t pressedKeys[16];

const uint8_t keyMatrix[17] = {
  KEY_KPMINUS, KEY_KPASTERISK, KEY_KPSLASH, KEY_NUMLOCK,
  KEY_KPPLUS, KEY_KP9, KEY_KP8, KEY_KP7,
  KEY_KPENTER, KEY_KP6, KEY_KP5, KEY_KP4,
  KEY_KP0, KEY_KP3, KEY_KP2, KEY_KP1,
  KEY_KPDOT
};

const uint8_t columnPins[4] = {0, 1, 2, 3};
const uint8_t rowOutPuts[5][5] = {
  { LOW, HIGH, HIGH, HIGH, HIGH},
  {HIGH,  LOW, HIGH, HIGH, HIGH},
  {HIGH, HIGH,  LOW, HIGH, HIGH},
  {HIGH, HIGH, HIGH,  LOW, HIGH},
  {HIGH, HIGH, HIGH, HIGH,  LOW}
};

const int row0 = 4;
const int row1 = 5;
const int row2 = 6;
const int row3 = 7;
const int row4 = 8;

uint8_t const desc_hid_report[] =
{
  TUD_HID_REPORT_DESC_KEYBOARD(),
};

void setup() {
  pinMode(columnPins[0], INPUT);
  pinMode(columnPins[1], INPUT);
  pinMode(columnPins[2], INPUT);
  pinMode(columnPins[3], INPUT);
  
  digitalWrite(columnPins[0], HIGH);
  digitalWrite(columnPins[1], HIGH);
  digitalWrite(columnPins[2], HIGH);
  digitalWrite(columnPins[3], HIGH);

  pinMode(row0, OUTPUT);
  pinMode(row1, OUTPUT);
  pinMode(row2, OUTPUT);
  pinMode(row3, OUTPUT);
  pinMode(row4, OUTPUT);

  usb_hid.setPollInterval(2);
  usb_hid.setReportDescriptor(desc_hid_report, sizeof(desc_hid_report));
  usb_hid.begin();

  while( !USBDevice.mounted() ) delay(1);
}

void loop() {

  delay(2);

  if ( !usb_hid.ready() ) return;

  static bool keyPressedPreviously = false;
  bool anyKeyPressed = false;
  uint8_t count = 0;
  uint8_t keycode[6] = { 0 };

  for (uint8_t row=0; row<5; row++) 
  {
    digitalWrite(row0, rowOutPuts[row][0]);
    digitalWrite(row1, rowOutPuts[row][1]);
    digitalWrite(row2, rowOutPuts[row][2]);
    digitalWrite(row3, rowOutPuts[row][3]);
    digitalWrite(row4, rowOutPuts[row][4]);

    for (uint8_t column=0; column<4; column++) 
    {
      if (digitalRead(columnPins[column]) == 0)
      {
        keycode[count++] = keyMatrix[ row * 4 + column ];
        
        if (count == 6)
        {
          usb_hid.keyboardReport(0, 0, keycode);
          delay(2);

          count = 0;
          memset(keycode, 0, 6);
        }
        
        anyKeyPressed = true;
        keyPressedPreviously = true;
      }
    }
  }

  if ( count )
  {
    usb_hid.keyboardReport(0, 0, keycode);
  }


  
  if ( !anyKeyPressed && keyPressedPreviously )
  {
    keyPressedPreviously = false;
    usb_hid.keyboardRelease(0);
  }
}