#define F_CPU 16000000UL
#include <avr/io.h>
#include <util/delay.h>

// I2C Address of PCF8574 (change to 0x3F if needed)
#define I2C_ADDR 0x27

// LCD Control bits via PCF8574
#define LCD_BACKLIGHT 0x08
#define ENABLE        0x04
#define RW            0x02
#define RS            0x01

// Initialize I2C
void I2C_init() 
{
  TWSR = 0x00;                      // No prescaler
  TWBR = ((F_CPU / 100000UL) - 16) / 2;  // SCL freq = 100kHz
}

// Start condition
void I2C_start() 
{
  TWCR = (1<<TWSTA)|(1<<TWEN)|(1<<TWINT);
  while (!(TWCR & (1<<TWINT)));
}

// Stop condition
void I2C_stop() 
{
  TWCR = (1<<TWSTO)|(1<<TWEN)|(1<<TWINT);
  while (TWCR & (1<<TWSTO));
}

// Send byte
void I2C_write(uint8_t data) 
{
  TWDR = data;
  TWCR = (1<<TWEN)|(1<<TWINT);
  while (!(TWCR & (1<<TWINT)));
}

// Send address
void I2C_send_address(uint8_t addr) 
{
  I2C_start();
  I2C_write(addr << 1);  // Write mode
}

// Write nibble to LCD
void LCD_write_nibble(uint8_t nibble, uint8_t mode) 
{
  uint8_t data = (nibble & 0xF0) | LCD_BACKLIGHT;

  if (mode) data |= RS;      // RS=1 for data
  else data &= ~RS;          // RS=0 for command

  // Pulse Enable
  I2C_send_address(I2C_ADDR);
  I2C_write(data | ENABLE);
  _delay_us(1);
  I2C_write(data & ~ENABLE);
  I2C_stop();
}

// Send byte to LCD
void LCD_send_byte(uint8_t byte, uint8_t mode) 
{
  LCD_write_nibble(byte & 0xF0, mode);          // Send high nibble
  LCD_write_nibble((byte << 4) & 0xF0, mode);   // Send low nibble
  _delay_us(50);
}

// LCD Commands
void LCD_command(uint8_t cmd) 
{
  LCD_send_byte(cmd, 0);
}

void LCD_data(uint8_t data) 
{
  LCD_send_byte(data, 1);
}

void LCD_init() 
{
  _delay_ms(50);
  LCD_write_nibble(0x30, 0);  // Wake up
  _delay_ms(5);
  LCD_write_nibble(0x30, 0);  // Wake up
  _delay_us(150);
  LCD_write_nibble(0x30, 0);  // Wake up
  LCD_write_nibble(0x20, 0);  // 4-bit mode

  LCD_command(0x28);  // 4-bit, 2-line
  LCD_command(0x0C);  // Display ON, Cursor OFF
  LCD_command(0x06);  // Entry mode
  LCD_command(0x01);  // Clear display
  _delay_ms(2);
}

void LCD_setCursor(uint8_t row, uint8_t col) {
  uint8_t row_offsets[] = {0x00, 0x40, 0x14, 0x54};
  LCD_command(0x80 | (col + row_offsets[row]));
}

void LCD_print(const char* str) {
  while (*str) {
    LCD_data(*str++);
  }
}

void setup() {
  I2C_init();
  LCD_init();

  LCD_setCursor(0, 0);
  LCD_print("Hello I2C LCD!");
}

void loop() {
  // Do nothing
}