#include<stdbool.h>
#include<stddef.h>
#include<stdint.h>
#include"vga.h"

static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;

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 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_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()
{
    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_writestring(const char* data) 
{
    for(int i=0;data[i]!='\0';i++) terminal_putchar(data[i]);
}

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");
   }
}