#include <LiquidCrystal_I2C.h>

#define I2C_ADDR    0x27
#define LCD_COLUMNS 16
#define LCD_LINES   2

LiquidCrystal_I2C lcd(I2C_ADDR, LCD_COLUMNS, LCD_LINES);

#define NO_KEY_PRESSED 15
#define KEYPAD_DDR DDRD
#define KEYPAD_PORT PORTD
#define KEYPAD_PIN PIND
volatile uint8_t pressed_key = NO_KEY_PRESSED;
volatile bool new_key_flag = false;
volatile uint8_t timer_milliseconds = 0;

void setup() {
  //Serial.begin(115200);
  // put your setup code here, to run once:
  lcd.init();
  lcd.backlight();
  
  pinMode(10, OUTPUT);
  KEYPAD_DDR = 0x78;
  KEYPAD_PORT = 0xFF;


  TCCR0A = (1 << WGM01);
  TCCR0B = (1 << CS01) | (1 << CS00);
  OCR0A = 250;
  TIMSK0 = (1 << OCIE0A);
}

void loop() {
  lcd.setCursor(0,0);
  lcd.print("Pressed: ");
  if(new_key_flag){ 
    lcd.setCursor(9,0);
    lcd.print(pressed_key);
    new_key_flag = false;
  }
  //lcd.print(new_key_flag);
  if(pressed_key == 15){
    digitalWrite(10, HIGH);
  }else{
    digitalWrite(10, LOW);
    new_key_flag = false;
  }
  //delay(30000);
  //Serial.println(pressed_key);
  
}

uint8_t keypad_read(){
  uint8_t shift_array[4]={0x77, 0x6F, 0x5F, 0x3F};
  uint8_t key_code = NO_KEY_PRESSED;
  for (uint8_t i = 0; i < 4 ; ++i){
    KEYPAD_PORT = shift_array[i];
    for (uint8_t j = 0 ; j < 4 ; ++j){
      if ((KEYPAD_PIN & (1 << j)) == 0){
         key_code = (i*4 + j);
         /* Serial.print(key_code);
          Serial.print(" ");*/
         /*lcd.setCursor(9,0);
         lcd.print(key_code);*/
      }
    }
  }

  KEYPAD_DDR = 0x78;
  KEYPAD_PORT = 0xFF;
  
  return key_code;
}

ISR(TIMER0_COMPA_vect){
    TCNT0 = 250;
    timer_milliseconds += 1;

    if (timer_milliseconds >= 250){
      if (new_key_flag == false){
        pressed_key = keypad_read();
        if ( pressed_key != NO_KEY_PRESSED) new_key_flag = true;
      }
      timer_milliseconds = 0;
    }
}