#include "vga.h"
#include <stdint.h>
#include <sys/io.h>

struct __attribute__((packed)) VGAEntry {
  unsigned char text;
  uint8_t foreground : 4;
  uint8_t background : 4;
};
_Static_assert(sizeof(struct VGAEntry) == 2, "sizeof VGAEntry");

const int width = 80;
const int height = 25;

struct VGAEntry *buffer;
int col = 0;
int row = 0;

void
vga_init()
{
  buffer = (struct VGAEntry *)0xc03ff000;
  vga_enable_cursor(0, 15);
  vga_clear(VGA_COLOR_LIGHT_BLUE, VGA_COLOR_LIGHT_GREY);
}

void
vga_clear(enum vga_color foreground, enum vga_color background)
{
  for (int y = 0; y < height; ++y)
    for (int x = 0; x < width; ++x) {
      const int index = y * width + x;
      buffer[index].text = ' ';
      buffer[index].foreground = foreground;
      buffer[index].background = background;
    }
  col = row = 0;
  vga_update_cursor();
}

void
vga_putc(char a)
{
  switch (a) {
  case '\n':
    col = 0;
    ++row;
    break;
  case '\r':
    col = 0;
    break;
  case '\b':
    --col;
    if (col < 0) col = 0;
    break;
  default:
    buffer[row * width + col].text = a;
    ++col;
  }

  if (col == width) {
    col = 0;
    ++row;
  }

  if (row == height) {
    // scroll up
    for (int y = 1; y < height; ++y)
      for (int x = 0; x < width; ++x) {
        const int prev = (y - 1) * width + x;
        const int curr = y * width + x;
        buffer[prev] = buffer[curr];
      }
    // blank out last row
    for (int i = (height - 1) * width; i < height * width; ++i) buffer[i].text = ' ';
    --row;
  }
}

void
vga_puts(const char *string, int len)
{

  if (len == -1)
    while (*string != '\0') {
      vga_putc(*string);
      ++string;
    }

  else
    for (int i = 0; i < len; ++i) { vga_putc(string[i]); }
}

// Cursor
const uint16_t cga_idx_port = 0x3d4;
const uint16_t cga_dat_port = 0x3d5;

const uint8_t cursor_start = 0xa;
const uint8_t cursor_end = 0xb;
const uint8_t cursor_addr_h = 0xe;
const uint8_t cursor_addr_l = 0xf;
const uint8_t cursor_hide = 0x20;

void
vga_enable_cursor(unsigned char start, unsigned char end)
{
  outb(cga_idx_port, cursor_start);
  outb(cga_dat_port, (inb(cga_dat_port) & 0xc0) | start);

  outb(cga_idx_port, cursor_end);
  outb(cga_dat_port, (inb(cga_dat_port) & 0xe0) | end);
}

void
vga_disable_cursor()
{
  outb(cga_idx_port, cursor_start);
  outb(cga_dat_port, cursor_hide);
}

void
vga_update_cursor()
{
  const uint16_t pos = row * width + col;

  outb(cga_idx_port, cursor_addr_l);
  outb(cga_dat_port, pos & 0xff);

  outb(cga_idx_port, cursor_addr_h);
  outb(cga_dat_port, (pos >> 8) & 0xff);
}