#include <Keypad.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2); // Inisialisasi LCD 16x2
long first = 0;
long second = 0;
double total = 0;
char customKey;
int cursor = 0;
const byte ROWS = 4;
const byte COLS = 4;

char keys[ROWS][COLS] = {
    {'1', '2', '3', '+'},
    {'4', '5', '6', '-'},
    {'7', '8', '9', '*'},
    {'C', '0', '=', '/'}
};

byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};

Keypad customKeypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
    lcd.init(); // Inisialisasi LCD
    lcd.backlight(); // Nyalakan lampu latar LCD
}

void loop() {
    customKey = customKeypad.getKey();
    switch (customKey) {
        case '0' ... '9':
            lcd.setCursor(0, 0);
            first = first * 10 + (customKey - '0');
            lcd.print(first);
            break;
        case '+':
            first = (total != 0 ? total : first);
            cursor = String(first).length();
            lcd.setCursor(cursor, 0);
            lcd.print("+");
            cursor = String(first).length() + 1;
            second = SecondNumber(cursor); 
            total = first + second;
            lcd.setCursor(0, 1);
            lcd.print(total);
            first = 0;
            second = 0;
            break;
        case '-':
            first = (total != 0 ? total : first);
            cursor = String(first).length();
            lcd.setCursor(cursor, 0);
            lcd.print("-");
            cursor = String(first).length() + 1;
            second = SecondNumber(cursor); 
            total = first - second;
            lcd.setCursor(0, 1);
            lcd.print(total);
            first = 0;
            second = 0;
            break;
        case '*':
            first = (total != 0 ? total : first);
            cursor = String(first).length();
            lcd.setCursor(cursor, 0);
            lcd.print("*");
            cursor = String(first).length() + 1;
            second = SecondNumber(cursor); 
            total = first * second;
            lcd.setCursor(0, 1);
            lcd.print(total);
            first = 0;
            second = 0;
            break;
        case '/':
            first = (total != 0 ? total : first);
            cursor = String(first).length();
            lcd.setCursor(cursor, 0);
            lcd.print("/");
            cursor = String(first).length() + 1;
            second = SecondNumber(cursor);
            lcd.setCursor(0, 1);
            if (second == 0) {
                lcd.print("Invalid");
            } else {
                total = (float)first / (float)second;
                lcd.print(total);
            }
            first = 0;
            second = 0;
            break;
        case 'C':
            total = 0;
            lcd.clear();
            break;
    }
}

long SecondNumber(int cursor) {
    second = 0; // Reset nilai kedua
    while (true) {
        customKey = customKeypad.getKey();
        if (customKey >= '0' && customKey <= '9') {
            second = second * 10 + (customKey - '0');
            lcd.setCursor(cursor, 0);
            lcd.print(second);
        }
        if (customKey == '=') {
            break; // Kembali setelah menekan '='
        }
    }
    return second; // Kembalikan nilai kedua
}