#include <nrvn.h>
#include <vga.h>

static size_t vga_x, vga_y;
static uint8_t vga_color;
static uint16_t *vga_buffer;

void vga_init(void) {
	vga_x = vga_y = 0;
	vga_set_color(VGA_LIGHT_MAGENTA, VGA_BLACK);
	vga_buffer = (uint16_t *)0xB8000;
	for (size_t y = 0; y < VGA_HEIGHT; y++)
		for (size_t x = 0; x < VGA_WIDTH; x++)
			vga_buffer[y * VGA_WIDTH + x] = ' ' | (vga_color << 8);
}

void vga_scroll() {
	if (vga_y < VGA_HEIGHT)
		return;

	for (size_t y = 0; y < VGA_HEIGHT - 1; y++) {
		for (size_t x = 0; x < VGA_WIDTH; x++) {
			const size_t from = (y + 1) * VGA_WIDTH + x;
			const size_t to = y * VGA_WIDTH + x;
			vga_buffer[to] = vga_buffer[from];
		}
	}
	vga_y = VGA_HEIGHT - 1;
	for (size_t x = 0; x < VGA_HEIGHT; x++) {
		vga_buffer[vga_y * VGA_WIDTH + x] = ' ' | (vga_color << 8);
	}
}

void vga_update_cursor(void) {
	size_t index = vga_y * VGA_WIDTH + vga_x;

	outb(0x3D4, 14);
	outb(0x3D5, index >> 8);
	outb(0x3D4, 15);
	outb(0x3D5, index);
}

void vga_putn(const size_t number) {
	char digits[32] = { 0 };
	size_t num = number, count = 0;
	do {
		digits[count] = (num % 10) + '0';
		count++;
	} while ((num /= 10) > 0);

	do {
		vga_putc(digits[count]);
	} while (count-- > 0);
}

void vga_putx(const size_t hex) {
	char digits[32] = { 0 };
	size_t num = hex, count = 0;
	do {
		digits[count] = "0123456789abcdef"[num % 16];
		count++;
	} while ((num /= 16) > 0);

	vga_puts("0x");
	do {
		vga_putc(digits[count]);
	} while (count-- > 0);
}

void vga_putc(const char c) {
	switch (c) {
		case '\n':
			vga_x = 0;
			vga_y++;
			break;
		case '\b':
			if (vga_x > 0)
				vga_x--;
			break;
		case '\r':
			vga_x = 0;
			break;
		case '\t':
			break;
		default:
			// Any character greater than and including a space, is a printable character
			if (c >= ' ')
				vga_buffer[vga_y * VGA_WIDTH + vga_x++] = (uint16_t) c | ((uint16_t) vga_color << 8);
	}

	if (vga_x >= VGA_WIDTH) {
		vga_x = 0;
		vga_y++;
	}

	vga_scroll();
	vga_update_cursor();
}

void vga_puts(const char *s) {
	while (*s)
		vga_putc(*s++);
}

void vga_putsn(const char *s, const size_t len) {
	for (size_t i = 0; i < len; i++)
		vga_putc(s[i]);
}

void vga_set_color(const uint8_t fg, const uint8_t bg) {
	vga_color = fg | bg << 4;
}