#include <Keypad.h>
#include <LiquidCrystal_I2C.h> // If using I2C LCD

// Initialize the LCD (I2C address 0x27 might vary, check your display address)
LiquidCrystal_I2C lcd(0x27, 16, 2); // 16x2 LCD display

// Define the keypad layout
const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},  // Use '*' for multiplication
  {'C', '0', '=', 'X'}   // 'C' for decimal point, 'X' for division
};
byte rowPins[ROWS] = {9, 8, 7, 6};   // Connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3, 2};   // Connect to the column pinouts of the keypad

// Create the keypad object
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

// Variables for calculator
String input = "";
float num1 = 0, num2 = 0;
char operation;
bool resultDisplayed = false;  // Track if a result is displayed

// Push button pin for erase
const int eraseButtonPin = 10;  // Pin for the erase button

void setup() {
  lcd.init();  // Initialize the LCD
  lcd.backlight();  // Turn on the backlight for the LCD
  lcd.clear();      // Clear the LCD screen
  lcd.setCursor(0, 0); // Set the cursor to the first row, first column
  lcd.print("Calculator");  // Display initial text
  delay(2000);  // Wait for 2 seconds
  lcd.clear();  // Clear the screen

  // Setup the button as input
  pinMode(eraseButtonPin, INPUT_PULLUP);  // Use internal pull-up resistor
}

void loop() {
  char key = keypad.getKey();  // Get the key pressed on the keypad

  // Check if the erase button is pressed
  if (digitalRead(eraseButtonPin) == LOW) {
    input = "";  // Clear the input string
    resultDisplayed = false;  // Reset the result flag
    lcd.clear();  // Clear the screen
    lcd.setCursor(0, 0);
    lcd.print("Cleared");  // Indicate cleared
    delay(300);  // Debounce delay for the button
  }

  if (key) {
    // If result was displayed and a number is pressed, start a new calculation
    if (resultDisplayed && (key >= '0' && key <= '9')) {
      input = "";  // Reset input for a new calculation
      resultDisplayed = false;
      lcd.clear();  // Clear the screen for new input
    }

    // Handling number input
    if (key >= '0' && key <= '9') {
      input += key;  // Append the pressed key to the input string
      lcd.setCursor(0, 1);  // Move to the second row
      lcd.print(input);     // Display the input on the LCD
    } 
    // Handling decimal point input
    else if (key == 'C') {
      if (input.indexOf('.') == -1) {  // Prevent multiple decimal points
        input += '.';  // Append the decimal point
        lcd.setCursor(0, 1);
        lcd.print(input);
      }
    } 
    // Handling operator input (+, -, *, X)
    else if (key == 'X' || key == '+' || key == '-' || key == '*') {
      if (!resultDisplayed) {
        num1 = input.toFloat();  // Convert the input string to a float
      }
      operation = key;           // Store the operation
      input = "";                // Clear the input for the next number
      lcd.clear();               // Clear the screen
      lcd.print(num1);           // Display the first number
      lcd.print(operation);      // Display the operation
    } 
    // Handling equal sign and calculation
    else if (key == '=') {
      num2 = input.toFloat();  // Convert the second number
      lcd.clear();
      lcd.print(num1);
      lcd.print(operation);
      lcd.print(num2);

      // Perform the calculation
      float result;
      if (operation == '+') {
        result = num1 + num2;
      } else if (operation == '-') {
        result = num1 - num2;
      } else if (operation == '*') {
        result = num1 * num2;
      } else if (operation == 'X') {
        if (num2 != 0) {
          result = num1 / num2;
        } else {
          lcd.clear();
          lcd.print("Error: Div/0");
          return;
        }
      }

      // Display the result with full precision
      lcd.setCursor(0, 1);  // Move to the second row
      lcd.print("= ");
      lcd.print(result, 6);    // Print the result with up to 6 decimal places (maximum precision for float)
      num1 = result;        // Store result as num1 for further calculations
      resultDisplayed = true;  // Set the flag to indicate the result is displayed
    }
  }
}