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

LiquidCrystal_I2C lcd(0x27, 16, 2); // กำหนดที่อยู่ I2C และขนาดของ LCD

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] = {13, 12, 14, 27}; // ขา GPIO สำหรับ Row
byte colPins[COLS] = {16, 17, 18, 19}; // ขา GPIO สำหรับ Column

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

String input1 = "";
String input2 = "";
char operation = '\0';
bool isSecondInput = false;

void setup() {
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Calculator");
  delay(2000);
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();
  
  if (key) {
    if (key >= '0' && key <= '9') {
      if (isSecondInput) {
        input2 += key;
      } else {
        input1 += key;
      }
      lcd.setCursor(0, 0);
      lcd.print(input1 + " " + operation + " " + input2);
    } else if (key == '+' || key == '-' || key == '*' || key == '/') {
      if (!isSecondInput && input1 != "") {
        operation = key;
        isSecondInput = true;
      }
      lcd.setCursor(0, 0);
      lcd.print(input1 + " " + operation);
    } else if (key == '=') {
      if (input1 != "" && input2 != "" && operation != '\0') {
        float num1 = input1.toFloat();
        float num2 = input2.toFloat();
        float result = 0.0;

        switch (operation) {
          case '+': result = num1 + num2; break;
          case '-': result = num1 - num2; break;
          case '*': result = num1 * num2; break;
          case '/': 
            if (num2 != 0) result = num1 / num2;
            else lcd.print("Err: Div by 0");
            break;
        }

        lcd.clear();
        lcd.setCursor(0, 0);
        lcd.print("Result: ");
        lcd.setCursor(0, 1);
        lcd.print(result);
        
        // เคลียร์ค่าทั้งหมด
        input1 = "";
        input2 = "";
        operation = '\0';
        isSecondInput = false;
        delay(3000); // แสดงผลลัพธ์ 3 วินาที
        lcd.clear();
      }
    } else if (key == 'C') { // เคลียร์ค่าทั้งหมดเมื่อกดปุ่ม C
      input1 = "";
      input2 = "";
      operation = '\0';
      isSecondInput = false;
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("Cleared");
      delay(1000);
      lcd.clear();
    }
  }
}