#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
 
/* Check if the compiler thinks you are targeting the wrong operating system. */
#if defined(__linux__)
#error "You are not using a cross-compiler, you will most certainly run into trouble"
#endif
 
/* This tutorial will only work for the 32-bit ix86 targets. */
#if !defined(__i386__)
#error "This tutorial needs to be compiled with a ix86-elf compiler"
#endif
 
/* Hardware text mode color constants. */
enum vga_color {
    VGA_COLOR_BLACK = 0,
    VGA_COLOR_BLUE = 1,
    VGA_COLOR_GREEN = 2,
    VGA_COLOR_CYAN = 3,
    VGA_COLOR_RED = 4,
    VGA_COLOR_MAGENTA = 5,
    VGA_COLOR_BROWN = 6,
    VGA_COLOR_LIGHT_GREY = 7,
    VGA_COLOR_DARK_GREY = 8,
    VGA_COLOR_LIGHT_BLUE = 9,
    VGA_COLOR_LIGHT_GREEN = 10,
    VGA_COLOR_LIGHT_CYAN = 11,
    VGA_COLOR_LIGHT_RED = 12,
    VGA_COLOR_LIGHT_MAGENTA = 13,
    VGA_COLOR_LIGHT_BROWN = 14,
    VGA_COLOR_WHITE = 15,
};
 
static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) 
{
    return fg | bg << 4;
}
 
static inline uint16_t vga_entry(unsigned char uc, uint8_t color) 
{
    return (uint16_t) uc | (uint16_t) color << 8;
}
 
size_t strlen(const char* str) 
{
    size_t len = 0;
    while (str[len]) len++;
    return len;
}
 
static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;
 
size_t terminal_row;
size_t terminal_column;
uint8_t terminal_color;
uint16_t* terminal_buffer;
 
void terminal_initialize(void) 
{
    terminal_row = 0;
    terminal_column = 0;
    terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
    terminal_buffer = (uint16_t*) 0xB8000;
    for (size_t y = 0; y < VGA_HEIGHT; y++) {
	for (size_t x = 0; x < VGA_WIDTH; x++) {
	    const size_t index = y * VGA_WIDTH + x;
	    terminal_buffer[index] = vga_entry(' ', terminal_color);
	}
    }
}
 
void terminal_setcoor(uint8_t color) 
{
    terminal_color = color;
}
 
void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
{
    const size_t index = y * VGA_WIDTH + x;
    terminal_buffer[index] = vga_entry(c, color);
}

void movescreen()
{
    if (terminal_row == VGA_HEIGHT)
    {
	terminal_row--;
	for(size_t i=0;i<VGA_HEIGHT;i++) for(size_t j=0;j<VGA_WIDTH;j++) terminal_buffer[i*VGA_WIDTH+j]=terminal_buffer[(i+1)*VGA_WIDTH+j];
    }
}
 
void terminal_putchar(char c) 
{
    if(c=='\n') terminal_column = 0,terminal_row++;
    else
    {
	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
	if (++terminal_column == VGA_WIDTH) terminal_column = 0,terminal_row++;
    }
    if (terminal_row == VGA_HEIGHT) movescreen();
}
 
void terminal_write(const char* data, size_t size) 
{
    for (size_t i = 0; i < size; i++) terminal_putchar(data[i]);
}
 
void terminal_writestring(const char* data) 
{
    terminal_write(data, strlen(data));
}

char *rec;
__attribute__ ((constructor)) void foo(void)
{
    rec="aleksa";
}
 
void kernel_main(void) 
{
    terminal_initialize();

    for(size_t i=0;i<50;i++)
    {
	for(size_t j=0;j<i;j++) terminal_writestring("#");
	terminal_writestring("Hello, kernel World!\n");
    }
    terminal_writestring(rec);
}