__asm__(".code16gcc\n");

void vga_graphics_write_at_offset(char, short);
void vga_graphics_write(char);
void vga_graphics_write_with_attr(char, char);
void vga_graphics_write_str(char*);

void vga_graphics_byte_hex(char);
//void vga_graphics_short_hex(short);
//void vga_graphics_int_hex(int);
//void vga_graphics_long_hex(long);

void clear();

static short CURSOR_LOC = 0;
static char* HEX_CHARS = "0123456789abcdef";
char foo[] = "hello how are you";

void _start() {
  clear();
  vga_graphics_write_with_attr('a', 1);
  vga_graphics_write_with_attr('/', 2);
  vga_graphics_write_with_attr('b', 3);
  vga_graphics_write_str(foo);
  vga_graphics_write(':');
  vga_graphics_write(' ');
  vga_graphics_byte_hex(0x40);
  while(1) { }
}

void clear() {
  int TERM_WIDTH = 80;
  int TERM_HEIGHT = 25;

  int i = 0;
  while(i < TERM_WIDTH * TERM_HEIGHT) {
    vga_graphics_write_with_attr(' ', 7);
    i++;
  }
  CURSOR_LOC = 0;
}

void vga_graphics_write_str(char* str) {
  while(*str) {
    vga_graphics_write_with_attr(*str++, 7);
  }
}

void vga_graphics_write_with_attr(char value, char attr) {
  vga_graphics_write_at_offset(value, CURSOR_LOC++);
  vga_graphics_write_at_offset(attr, CURSOR_LOC++);
}

void vga_graphics_write(char value) {
  vga_graphics_write_at_offset(value, CURSOR_LOC);
  CURSOR_LOC += 2;
}

void vga_graphics_byte_hex(char value) {
  char low = value & 0x0f;
  char high = (value & 0xf0) >> 4;
  vga_graphics_write(HEX_CHARS[high]);
  vga_graphics_write(HEX_CHARS[low]);
}

void vga_graphics_write_at_offset(char value, short offset) {
  __asm__(
    "mov %0, %%al          \n"
    "mov %1, %%di          \n"
    "mov %%al, %%gs:(%%di) \n"
    : :"r"(value), "r"(offset) : "%ax", "%di");
}