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

LiquidCrystal_I2C lcd(0x27, 16, 2);

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '0', '*', '+'},
  {' ', ' ', '/', '-'},
  {' ', ' ', '<', '('},
  {' ', 'C', '=', ')'}
};

byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

String equation = "";
String currentBinary = ""; 
bool error = false;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    Serial.println(key);

    if (key == '0' || key == '1') { 
      currentBinary += key;
      equation += key;
      updateLCD();
    } else if (key == '+' || key == '-' || key == '*' || key == '/' || key == '(' || key == ')') {
      if (currentBinary.length()) {
        equation = replaceLastBinaryWithDecimal(equation, currentBinary);
        currentBinary = ""; 
      }
      equation += key;
      updateLCD();
    } else if (key == '=') {
      if (currentBinary.length()) {
        equation = replaceLastBinaryWithDecimal(equation, currentBinary);
        currentBinary = ""; 
        updateLCD();
      }
      delay(1000);
      calculateEquation();
    } else if (key == '<') { 
      if (currentBinary.length()) {
        currentBinary.remove(currentBinary.length() - 1);
        equation.remove(equation.length() - 1);
      } else if (equation.length()) {
        equation.remove(equation.length() - 1);
      }
      updateLCD();
    } else if (key == 'C') { 
      resetCalculator();
    }
  }
}

void updateLCD() {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(equation);
}

String replaceLastBinaryWithDecimal(String eq, String binary) {
  int decimal = binaryToDecimal(binary);
  eq.remove(eq.length() - binary.length()); 
  eq += String(decimal); 
  return eq;
}

void calculateEquation() {
  lcd.clear();

  if (hasInvalidInput(equation)) {
    lcd.setCursor(0, 0);
    lcd.print("Invalid Input!");
    delay(2000);
    resetCalculator();
    return;
  }

  int result = evaluateExpression(equation);

  lcd.setCursor(0, 0);
  lcd.print("Result:");
  lcd.setCursor(0, 1);
  lcd.print(result);
}

bool hasInvalidInput(String eq) {
  if (eq.length() == 0) return true;

  if (eq.indexOf("++") != -1 || eq.indexOf("--") != -1 || eq.indexOf("**") != -1 || eq.indexOf("//") != -1) return true;

  if (eq[0] == '+' || eq[0] == '-' || eq[0] == '*' || eq[0] == '/') return true;
  if (eq[eq.length() - 1] == '+' || eq[eq.length() - 1] == '-' || eq[eq.length() - 1] == '*' || eq[eq.length() - 1] == '/') return true;

  int openParentheses = 0;
  for (int i = 0; i < eq.length(); i++) {
    if (eq[i] == '(') {
      openParentheses++;
    } else if (eq[i] == ')') {
      openParentheses--;
      if (openParentheses < 0) return true; 
    }
  }

  if (openParentheses != 0) return true; 

  return false;
}


int evaluateExpression(String eq) {
  int index = 0;
  return parseExpression(eq, index);
}

int parseExpression(String &eq, int &index) {
  int result = parseTerm(eq, index);

  while (index < eq.length() && (eq[index] == '+' || eq[index] == '-')) {
    char op = eq[index++];
    int term = parseTerm(eq, index);
    if (op == '+') {
      result += term;
    } else if (op == '-') {
      result -= term;
    }
  }

  return result;
}

int parseTerm(String &eq, int &index) {
  int result = parseFactor(eq, index);

  while (index < eq.length() && (eq[index] == '*' || eq[index] == '/')) {
    char op = eq[index++];
    int factor = parseFactor(eq, index);
    if (op == '*') {
      result *= factor;
    } else if (op == '/') {
      result /= factor;
    }
  }

  return result;
}

int parseFactor(String &eq, int &index) {
  if (eq[index] == '(') {
    index++;
    int result = parseExpression(eq, index);
    index++;
    return result;
  }

  int start = index;
  while (index < eq.length() && isDigit(eq[index])) {
    index++;
  }

  return eq.substring(start, index).toInt(); 
}

int binaryToDecimal(String binary) {
  int decimal = 0;
  for (int i = 0; i < binary.length(); i++) {
    decimal = (decimal << 1) | (binary[i] - '0');
  }
  return decimal;
}

bool isDigit(char c) {
  return c >= '0' && c <= '9';
}

void resetCalculator() {
  equation = "";
  currentBinary = "";
  error = false;
  lcd.clear();
}