#include "tty.h"

/* Hardware text mode color constants. */
enum vga_color {
    COLOR_BLACK         = 0,
    COLOR_BLUE          = 1,
    COLOR_GREEN         = 2,
    COLOR_CYAN          = 3,
    COLOR_RED           = 4,
    COLOR_MAGENTA       = 5,
    COLOR_BROWN         = 6,
    COLOR_LIGHT_GREY    = 7,
    COLOR_DARK_GREY     = 8,
    COLOR_LIGHT_BLUE    = 9,
    COLOR_LIGHT_GREEN   = 10,
    COLOR_LIGHT_CYAN    = 11,
    COLOR_LIGHT_RED     = 12,
    COLOR_LIGHT_MAGENTA = 13,
    COLOR_LIGHT_BROWN   = 14,
    COLOR_WHITE         = 15,
};

#define VGA_WIDTH   80
#define VGA_HEIGHT  25
#define VGA_TEXT_BUFFER 0xB8000
#define VGA_COLOR_SHIFT 8

static size_t tty_row;
static size_t tty_col;
static uint8_t tty_color;
static uint16_t* tty_buffer;

static inline uint8_t make_color(enum vga_color fg, enum vga_color bg)
{
    return fg | bg << 4;
}

static inline uint16_t make_vgaentry(char c, uint8_t color)
{
    return ((uint16_t) c) | (((uint16_t) color) << VGA_COLOR_SHIFT);
}

static inline void tty_putentryat(char c, uint8_t color, size_t x, size_t y)
{
    const size_t i = y * VGA_WIDTH + x;
    tty_buffer[i] = make_vgaentry(c, color);
}

void tty_setcolor(uint8_t color)
{
    tty_color = color;
}

void tty_putchar(char c)
{
    tty_putentryat(c, tty_color, tty_col, tty_row);
    if (++tty_col == VGA_WIDTH) {
        tty_col = 0;
        if (++tty_row == VGA_HEIGHT) {
            tty_row = 0;
        }
    }
}

void tty_writestring(const char* data)
{
    for (const char* p = data; *p != 0; p++)
        tty_putchar(*p);
}

void tty_init()
{
    tty_row = 0;
    tty_col = 0;
    tty_buffer = (uint16_t*) VGA_TEXT_BUFFER;
    tty_setcolor(make_color(COLOR_LIGHT_GREY, COLOR_BLACK));
    for (size_t y = 0; y < VGA_HEIGHT; y++) {
        for (size_t x = 0; x < VGA_WIDTH; x++) {
            const size_t i = y * VGA_WIDTH + x;
            tty_buffer[i] = make_vgaentry(' ', tty_color);
        }
    }
}