#include <stack>
#include <string>
#include <Arduino.h>
#include <Keypad.h>
#include <LiquidCrystal_I2C.h>

using namespace std;

const double divide_by_zero_Error = 1.129345696325;
const double syntax_Error = 2.129345696325;

const uint8_t ROWS = 4;
const uint8_t COLS = 4;
char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};
uint8_t colPins[COLS] = {13, 12, 14, 27}; 
uint8_t rowPins[ROWS] = {26, 25, 33, 32}; 

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

LiquidCrystal_I2C lcd(0x27, 16, 2);

string user_input = "";

void printErrorSyntax() {
    lcd.clear();
    lcd.setCursor(5, 0);
    lcd.print("Error");
    lcd.setCursor(5, 1);
    lcd.print("Syntax");
    boolean button_pressed = false;
    while (!button_pressed) {
        if (keypad.getKey()) {
            lcd.clear();
            lcd.cursor();
            lcd.setCursor(1, 0);
            button_pressed = true;
        }
    }
}

void printResult(double result) {
    lcd.setCursor(15, 1);
    byte cursor = 15;
    string result_string = "0" + to_string(round(result * 1000000.0) / 1000000.0);
    for (byte i = result_string.size(); i > 0; i--, cursor--) {
        if (cursor < 0) {
            cursor = 0;
        }
        if (isdigit(result_string[i]) || result_string[i] == '-' || result_string[i] == '.') {
            lcd.setCursor(cursor, 1);
            lcd.print(result_string[i]);
            Serial.print(result_string[i]);
        }
    }
    boolean button_pressed = false;
    while (!button_pressed) {
        if (keypad.getKey()) {
            lcd.clear();
            lcd.cursor();
            lcd.setCursor(1, 0);
            button_pressed = true;
        }
    }
}

void printErrorDivisionByZero() {
    lcd.clear();
    lcd.setCursor(5, 0);
    lcd.print("Error");
    lcd.setCursor(0, 1);
    lcd.print("Division by Zero");
    boolean button_pressed = false;
    while (!button_pressed) {
        if (keypad.getKey()) {
            lcd.clear();
            lcd.cursor();
            lcd.setCursor(1, 0);
            button_pressed = true;
        }
    }
}

bool hasSyntaxErrors(const string& expr) {
    int num_operators = 0;
    int num_digits = 0;
    char last_char = '\0';
    bool last_was_operator = true;

    for (char c : expr) {
        if (isdigit(c) || c == '.') {
            num_digits++;
            last_was_operator = false;
        }
        else if (c == '+' || c == '-') {
            num_operators++;
            if (num_digits == 0 || last_was_operator) {
                return true;
            }
            num_digits = 0;
            last_was_operator = true;
        }
        else if (c == '*' || c == '/') {
            num_operators++;
            if (num_digits == 0 || last_char == '+' || last_char == '-' || last_char == '*' || last_char == '/') {
                return true;
            }
            num_digits = 0;
            last_was_operator = true;
        }
        else {
            return true;
        }
        last_char = c;
    }

    if (num_digits == 0 || num_operators == 0) {
        return true;
    }

    return false;
}

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

bool isOperand(char c) {
    return isdigit(c) || c == '.';
}

int getPriority(char op) {
    if (op == '+' || op == '-') {
        return 1;
    } else if (op == '*' || op == '/') {
        return 2;
    } else {
        return 0;
    }
}

double calculate(string expr) {
    if (hasSyntaxErrors(expr)) {
        printErrorSyntax();
        return syntax_Error;
    }

    stack<double> operands;
    stack<char> operators;

    for (int i = 0; i < expr.length(); i++) {
        char c = expr[i];
        if (c == ' ') {
            continue;
        }
        if (isOperand(c)) {
            string numStr = "";
            while (i < expr.length() && isOperand(expr[i])) {
                numStr += expr[i];
                i++;
            }
            i--;
            double num = stod(numStr);
            operands.push(num);
        }
        else if (isOperator(c)) {
            while (!operators.empty() && getPriority(operators.top()) >= getPriority(c)) {
                char op = operators.top();
                operators.pop();
                double op2 = operands.top();
                operands.pop();
                double op1 = operands.top();
                operands.pop();
                double result;
                switch (op) {
                    case '+':
                        result = op1 + op2;
                        break;
                    case '-':
                        result = op1 - op2;
                        break;
                    case '*':
                        result = op1 * op2;
                        break;
                    case '/':
                        if (op2 == 0) {
                            printErrorDivisionByZero();
                            return divide_by_zero_Error;
                        }
                        result = op1 / op2;
                        break;
                }
                operands.push(result);
            }
            operators.push(c);
        }
    }

    while (!operators.empty()) {
        char op = operators.top();
        operators.pop();
        double op2 = operands.top();
        operands.pop();
        double op1 = operands.top();
        operands.pop();
        double result;
        switch (op) {
            case '+':
                result = op1 + op2;
                break;
            case '-':
                result = op1 - op2;
                break;
            case '*':
                result = op1 * op2;
                break;
            case '/':
                if (op2 == 0) {
                    printErrorDivisionByZero();
                    return divide_by_zero_Error;
                }
                result = op1 / op2;
                break;
        }
        operands.push(result);
    }

    return operands.top();
}

void input(char key_input) {
    int cursor_pos = 0;
    if (key_input == '=') {
        double result = calculate(user_input);
        if (result != divide_by_zero_Error && result != syntax_Error) {
            printResult(result);
        }
        user_input = "";
        return;
    }
    user_input += key_input;
    lcd.print(key_input);
    cursor_pos++;
}

void updateCursor() {
    if (millis() / 250 % 2 == 0) {
        lcd.cursor();
    } else {
        lcd.noCursor();
    }
}

void showSplashScreen() {
    lcd.setCursor(2, 0);
    lcd.print("Emil & Nathan");
    lcd.setCursor(0, 1);
    String message = "Click To Continue";
    for (byte i = 0; i < message.length(); i++) {
        lcd.print(message[i]);
        delay(150);
    }
    delay(500);
}

void setup() {
    Serial.begin(115200);
    lcd.init();
    lcd.clear();
    lcd.backlight();
    showSplashScreen();

    boolean button_pressed = false;
    while (!button_pressed) {
        if (keypad.getKey()) {
            lcd.clear();
            lcd.cursor();
            lcd.setCursor(1, 0);
            button_pressed = true;
        }
    }
}

void loop() {
    updateCursor();
    char key = keypad.getKey();
    if (key) {
        Serial.println(key);
        input(key);
    }
}