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

const byte ROW_NUM    = 4; //four rows
const byte COLUMN_NUM = 4; //four columns

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

byte pin_rows[ROW_NUM] = {9, 8, 7, 6}; // connect to the row pinouts of the keypad
byte pin_column[COLUMN_NUM] = {5, 4, 3, 2}; // connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM);
LiquidCrystal_I2C lcd(0x27, 16, 2); // Set the I2C address to 0x27 and 16x2 characters

float num1 = 0;
float num2 = 0;
char operation = '\0';
bool newInput = false;

void setup() {
  lcd.begin(16, 2);
  lcd.print("Arduino Calc");
  delay(1000);
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    processKey(key);
    delay(200); // Debounce delay
  }
}

void processKey(char key) {
  if (isdigit(key) || key == '.') {
    handleDigit(key);
  } else if (key == '+' || key == '-' || key == '*' || key == '/') {
    handleOperation(key);
  } else if (key == '=') {
    handleEquals();
  } else if (key == 'C') {
    clearCalculator();
  }
  updateLCD();
}

void handleDigit(char digit) {
  if (newInput) {
    newInput = false;
    lcd.clear();
  }

  lcd.print(digit);

  if (operation == '\0') {
    num1 = num1 * 10 + (digit - '0');
  } else {
    num2 = num2 * 10 + (digit - '0');
  }
}

void handleOperation(char op) {
  if (operation != '\0') {
    handleEquals(); // Perform the previous operation if any
  }

  operation = op;
  newInput = true;
}

void handleEquals() {
  float result = 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.clear();
        lcd.print("Error: Div by 0");
        delay(2000);
        clearCalculator();
        return;
      }
      break;
  }

  lcd.clear();
  lcd.print(result);
  clearCalculator();
}

void clearCalculator() {
  num1 = 0;
  num2 = 0;
  operation = '\0';
  newInput = false;
}

void updateLCD() {
  lcd.setCursor(0, 1);
  lcd.print("                "); // Clear the second line
  lcd.setCursor(0, 1);
  lcd.print(num1);

  if (operation != '\0') {
    lcd.print(" ");
    lcd.print(operation);
    lcd.print(" ");
    lcd.print(num2);
  }
}