#include <LiquidCrystal.h>
#include <Keypad.h>

LiquidCrystal lcd(12, 11, 10, 9, 8, 7);

const byte KEYPAD_ROWS = 4;
const byte KEYPAD_COLS = 4;
byte rowPins[KEYPAD_ROWS] = {5, 4, 3, 2};
byte colPins[KEYPAD_COLS] = {A3, A2, A1, A0};
char keys[KEYPAD_ROWS][KEYPAD_COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'.', '0', '=', '/'}
};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, KEYPAD_ROWS, KEYPAD_COLS);

double operand1 = 0;
double operand2 = 0;
char operation = '\0';
bool resultDisplayed = false;

void setup() {
  Serial.begin(115200);
  lcd.begin(16, 2);
  showSplashScreen();
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();
  if (key != NO_KEY) {
    if (isdigit(key) || key == '.') {
      handleDigitInput(key);
    } else if (key == '+' || key == '-' || key == '*' || key == '/') {
      handleOperationInput(key);
    } else if (key == '=') {
      calculateResult();
    }
  }
}

void showSplashScreen() {
  lcd.print("Arduino Calculator");
  delay(2000);
  lcd.clear();
}

void handleDigitInput(char key) {
  if (resultDisplayed) {
    lcd.clear();
    resultDisplayed = false;
  }
  lcd.print(key);
  if (operation == '\0') {
    operand1 = (operand1 * 10) + (key - '0');
  } else {
    operand2 = (operand2 * 10) + (key - '0');
  }
}

void handleOperationInput(char key) {
  if (operation != '\0') {
    calculateResult();
  }
  operation = key;
  lcd.print(key);
}

void calculateResult() {
  double result = 0;
  switch (operation) {
    case '+':
      result = operand1 + operand2;
      break;
    case '-':
      result = operand1 - operand2;
      break;
    case '*':
      result = operand1 * operand2;
      break;
    case '/':
      if (operand2 != 0) {
        result = operand1 / operand2;
      } else {
        lcd.clear();
        lcd.print("Error: Division by 0");
        delay(2000);
        lcd.clear();
        resetCalculator();
        return;
      }
      break;
  }
  lcd.setCursor(0, 1);
  lcd.print("=");
  lcd.print(result);
  operand1 = result;
  operand2 = 0;
  operation = '\0';
  resultDisplayed = true;
}

void resetCalculator() {
  operand1 = 0;
  operand2 = 0;
  operation = '\0';
  resultDisplayed = false;
}