#include <avr/io.h>
#include <util/delay.h>
#include <string.h>
#include <stdlib.h>

// Function prototypes
void LCD_Init();
void LCD_Command(uint8_t cmd);
void LCD_Char(uint8_t data);
void LCD_String(const char *str);
void LCD_Clear();
void LCD_SetCursor(uint8_t row, uint8_t col);

uint8_t Keypad_Scan();
void delay_ms(uint16_t ms);

// Main function
int main() {
    uint8_t key;
    char num1[10] = {0};
    char num2[10] = {0};
    char operator = 0;
    uint8_t index = 0;
    int result = 0;

    // Configure LCD and initialize
    LCD_Init();
    LCD_Clear();
    LCD_String("Calculator Ready");

    // Infinite loop
    while (1) {
        key = Keypad_Scan(); // Scan keypad
        if (key) { // If a key was pressed
            if (key >= '0' && key <= '9') { // Number keys
                if (operator == 0) {
                    // Input number 1
                    if (index < sizeof(num1) - 1) {
                        num1[index++] = key;
                        LCD_SetCursor(1, 0);
                        LCD_String(num1);
                    }
                } else {
                    // Input number 2
                    if (index < sizeof(num2) - 1) {
                        num2[index++] = key;
                        LCD_SetCursor(1, 0);
                        LCD_String(num2);
                    }
                }
            } else if (key == '+' || key == '-' || key == '*' || key == '/') {
                operator = key;
                index = 0; // Reset index to accept the second number
                LCD_SetCursor(0, 0);
                LCD_Char(key);
            } else if (key == '=') {
                // Perform the calculation
                int val1 = atoi(num1);
                int val2 = atoi(num2);

                switch (operator) {
                    case '+':
                        result = val1 + val2;
                        break;
                    case '-':
                        result = val1 - val2;
                        break;
                    case '*':
                        result = val1 * val2;
                        break;
                    case '/':
                        if (val2 != 0) result = val1 / val2;
                        else result = 0; // Handle divide by zero
                        break;
                    default:
                        result = 0;
                }

                // Display result
                char resultStr[17];
                snprintf(resultStr, 17, "Result: %d", result);
                LCD_Clear();
                LCD_String(resultStr);
                _delay_ms(1000);
                LCD_Clear();
                LCD_String("Calculator Ready");
                operator = 0;
                index = 0;
                memset(num1, 0, sizeof(num1));
                memset(num2, 0, sizeof(num2));
            }
        }
    }
}

/* LCD Functions */
void LCD_Init() {
    // Set RS, EN, and data lines as outputs
    DDRB |= (1 << PB4) | (1 << PB5);
    DDRD |= 0xF0; // PD4 to PD7 as outputs
    _delay_ms(20);

    // Initialize LCD
    LCD_Command(0x33);
    _delay_ms(5);
    LCD_Command(0x32);
    _delay_ms(5);
    LCD_Command(0x28); // 4-bit mode, 2 lines, 5x8 font
    _delay_ms(5);
    LCD_Command(0x0C); // Display ON, Cursor OFF
    _delay_ms(5);
    LCD_Command(0x06); // Entry mode
    _delay_ms(5);
    LCD_Clear();
}

void LCD_Command(uint8_t cmd) {
    PORTD = (cmd & 0xF0); // Send high nibble
    PORTB |= (1 << PB4);  // RS = 0
    PORTB |= (1 << PB5);  // Enable
    _delay_ms(1);
    PORTB &= ~(1 << PB5);
    _delay_ms(1);
}

void LCD_Char(uint8_t data) {
    PORTD = (data & 0xF0); // Send high nibble
    PORTB |= (1 << PB4); // RS = 1
    PORTB |= (1 << PB5);
    _delay_ms(1);
    PORTB &= ~(1 << PB5);
    _delay_ms(1);
}

void LCD_String(const char *str) {
    while (*str) {
        LCD_Char(*str++);
    }
}

void LCD_Clear() {
    LCD_Command(0x01);
    _delay_ms(2);
}

void LCD_SetCursor(uint8_t row, uint8_t col) {
    if (row == 0) {
        LCD_Command(0x80 + col);
    } else if (row == 1) {
        LCD_Command(0xC0 + col);
    }
}

uint8_t Keypad_Scan() {
    // Set columns as outputs
    DDRB |= 0x0F;
    PORTB = 0x00;

    // Scan rows
    for (uint8_t i = 0; i < 4; i++) {
        PORTB = (1 << i);
        _delay_ms(10);
        for (uint8_t j = 0; j < 4; j++) {
            if (PIND & (1 << j)) {
                return '0' + j + i * 4;
            }
        }
    }
    return 0;
}