#include "vga.h"

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

static size_t terminal_row;
static size_t terminal_column;
static uint8_t terminal_color;

/* Note the use of the volatile keyword to prevent the compiler from eliminating dead stores. */
static volatile uint16_t *terminal_buffer;

uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg);
uint16_t vga_entry(unsigned char uc, uint8_t color);

static size_t
strlen(const char *str)
{
	size_t len = 0;
	while (str[len++])
		;
	return len;
}

void
terminal_initialize(size_t startrow)
{
	terminal_row = startrow;
	terminal_column = 0;
	terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
	terminal_buffer = (uint16_t *)0xB8000;
}

void
terminal_setcolor(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
terminal_putchar(char c)
{
	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
	if (++terminal_column == VGA_WIDTH) {
		terminal_column = 0;
		if (++terminal_row == VGA_HEIGHT) terminal_row = 0;
	}
}

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));
}