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

LiquidCrystal_I2C lcd(0x27, 20, 4); // I2C address and LCD size (20x4)

// Define button pins
const int buttonPin0 = 2;
const int buttonPin1 = 15;
const int buttonPin2 = 4;
const int buttonPin3 = 5;
const int buttonPin4 = 14;
const int buttonPin5 = 27;
const int buttonPin6 = 26;
const int buttonPin7 = 25;
const int buttonPin8 = 33;
const int buttonPin9 = 32;
const int buttonPlus = 12;
const int buttonMinus = 13;
const int buttonMul = 18;
const int buttonDiv = 19;
const int buttonPercentage = 23;
const int buttonEnter = 35;  // GPIO pin for the enter button
const int buttonreset = 34; // GPIO pin for the reset button

String inputString = "";
String expression = "";
bool inputReady = false;

bool isOperator(char c)
{
    return (c == '+' || c == '-' || c == '*' || c == '/' || c == '%');
}

double calculate(double num1, double num2, char operation)
{
    switch (operation)
    {
    case '+':
        return num1 + num2;
    case '-':
        return num1 - num2;
    case '*':
        return num1 * num2;
    case '%':
        return num2 * (num1 / 100);
    case '/':
        if (num2 != 0)
            return num1 / num2;
        else
        {
            // Handle division by zero
            lcd.setCursor(0, 3);
            lcd.print("Error: Division by zero.");
            delay(200);
            return 0;
        }
    default:
        // Handle invalid operation
        lcd.setCursor(0, 3);
        lcd.print("Error: Invalid operation.");
        delay(200);
        return 0;
    }
}

void setup()
{
    lcd.init();
    lcd.backlight();
    lcd.setCursor(0, 0);
    lcd.print("Calculator:");

    // Set button pins as INPUT_PULLUP
    pinMode(buttonPin0, INPUT_PULLUP);
    pinMode(buttonPin1, INPUT_PULLUP);
    pinMode(buttonPin2, INPUT_PULLUP);
    pinMode(buttonPin3, INPUT_PULLUP);
    pinMode(buttonPin4, INPUT_PULLUP);
    pinMode(buttonPin5, INPUT_PULLUP);
    pinMode(buttonPin6, INPUT_PULLUP);
    pinMode(buttonPin7, INPUT_PULLUP);
    pinMode(buttonPin8, INPUT_PULLUP);
    pinMode(buttonPin9, INPUT_PULLUP);
    pinMode(buttonPlus, INPUT_PULLUP);
    pinMode(buttonMinus, INPUT_PULLUP);
    pinMode(buttonMul, INPUT_PULLUP);
    pinMode(buttonDiv, INPUT_PULLUP);
    pinMode(buttonPercentage, INPUT_PULLUP);
    pinMode(buttonEnter, INPUT_PULLUP);
    pinMode(buttonreset, INPUT_PULLUP);
}

void loop()
{
    checkButtons();

    if (inputReady)
    {
        // Evaluate the expression and display the result
        double result = evaluateExpression(expression);
        lcd.setCursor(0, 2);
        lcd.print("Result: " + String(result));

        // Clear the input and expression for the next calculation
        inputString = "";
        expression = "";
        inputReady = false;
    }
}

void checkButtons()
{
    while (digitalRead(buttonEnter) == HIGH)
    {
        // Wait for the "Enter" button to be pressed
    }
    if (digitalRead(buttonreset) == LOW)
    {
        // Reset button is pressed, clear input and expression
        inputString = "";
        expression = "";
        lcd.setCursor(0, 1);
        lcd.print("Input:        "); // Clear input display
        lcd.setCursor(0, 2);
        lcd.print("Result:       "); // Clear result display
        lcd.setCursor(0, 3);
        lcd.print("Expression:   "); // Clear expression display
        delay(200);
    }
    // Capture the entire expression
    inputString = "";
    while (digitalRead(buttonEnter) == LOW)
    {

        if (digitalRead(buttonPin0) == LOW)
        {
            inputString += "0";
        }
        if (digitalRead(buttonPin1) == LOW)
        {
            inputString += "1";
        }
        if (digitalRead(buttonPin2) == LOW)
        {
            inputString += "2";
        }
        if (digitalRead(buttonPin3) == LOW)
        {
            inputString += "3";
        }
        if (digitalRead(buttonPin4) == LOW)
        {
            inputString += "4";
        }
        if (digitalRead(buttonPin5) == LOW)
        {
            inputString += "5";
        }
        if (digitalRead(buttonPin6) == LOW)
        {
            inputString += "6";
        }
        if (digitalRead(buttonPin7) == LOW)
        {
            inputString += "7";
        }
        if (digitalRead(buttonPin8) == LOW)
        {
            inputString += "8";
        }
        if (digitalRead(buttonPin9) == LOW)
        {
            inputString += "9";
        }
        if (digitalRead(buttonPlus) == LOW)
        {
            inputString += "+";
        }
        if (digitalRead(buttonMinus) == LOW)
        {
            inputString += "-";
        }
        if (digitalRead(buttonMul) == LOW)
        {
            inputString += "*";
        }
        if (digitalRead(buttonDiv) == LOW)
        {
            inputString += "/";
        }
        if (digitalRead(buttonPercentage) == LOW)
        {
            inputString += "%";
        }

        // Update the LCD while capturing the expression
        lcd.setCursor(0, 1);
        lcd.print("Input: " + inputString);
        delay(200);
    }

    // Store and display the captured expression
    expression = inputString;
    lcd.setCursor(0, 3);
    lcd.print("Expression: " + expression);
    inputReady = true;
}

double evaluateExpression(String expression)
{
    double result = 0.0;
    char operation = '+';
    String currentNumber = "";

    for (char c : expression)
    {
        if (isOperator(c))
        {
            // An operator is encountered, calculate the result with the current number and operator
            double num = atof(currentNumber.c_str());
            result = calculate(result, num, operation);

            // Reset the current number and update the current operation
            currentNumber = "";
            operation = c;
        }
        else
        {
            // Append the character to the current number
            currentNumber += c;
        }
    }

    // Calculate the result with the last number in the expression
    double num = atof(currentNumber.c_str());
    result = calculate(result, num, operation);

    return result;
}