#include "vga.h"
#include "stddef.h"

#define ROWS 25
#define COLUMNS 80

typedef struct
{
    uint8_t character;
    uint8_t color;
} vga_char_t;

static vga_char_t* vga_buffer = (vga_char_t*)0xb8000;
static uint8_t cursor_row = 0;
static uint8_t cursor_col = 0;

void vga_put_char(char character, uint8_t color)
{
    switch (character)
    {
    case '\n':
    {
        cursor_row += 1;
        cursor_col = 0;
        break;
    }
    case '\r':
    {
        cursor_col = 0;
        break;
    }
    case '\t':
    {
        uint8_t remainder = 4 - (cursor_col % 4);
        cursor_col += remainder;
        break;
    }
    case '\b':
    {
        if (cursor_col > 0)
        {
            cursor_col -= 1;
        }
        else if (cursor_row > 0)
        {
            cursor_row -= 1;

            cursor_col = 0;
            for (int col = COLUMNS - 1; col >= 0; col--)
            {
                vga_char_t cell = vga_buffer[cursor_row * COLUMNS + col];
                if (cell.character != ' ')
                {
                    cursor_col = col;
                    break;
                }
            }
        }

        vga_buffer[cursor_row * COLUMNS + cursor_col] = (vga_char_t){
            .character = ' ',
            .color = VGA_DEFAULT_COLOR,
        };
        break;
    }
    default:
    {
        vga_buffer[COLUMNS * cursor_row + cursor_col] = (vga_char_t){
            .character = character,
            .color = color,
        };
        cursor_col += 1;
        break;
    }
    }

    if (cursor_col >= COLUMNS)
    {
        cursor_col = 0;
        cursor_row += 1;
    }

    if (cursor_row >= ROWS)
    {
        for (size_t row = 1; row < ROWS; row++)
        {
            for (size_t col = 0; col < COLUMNS; col++)
            {
                vga_buffer[COLUMNS * (row - 1) + col] = vga_buffer[COLUMNS * row + col];
            }
        }

        for (size_t col = 0; col < COLUMNS; col++)
        {
            vga_buffer[COLUMNS * (ROWS - 1) + col] = (vga_char_t){
                .character = ' ',
                .color = VGA_DEFAULT_COLOR,
            };
        };

        cursor_row = ROWS - 1;
    }
}

void vga_clear()
{
    for (size_t row = 0; row < ROWS; row++)
    {
        for (size_t col = 0; col < COLUMNS; col++)
        {
            vga_buffer[COLUMNS * row + col] = (vga_char_t){
                .character = ' ',
                .color = VGA_DEFAULT_COLOR,
            };
        }
    }

    cursor_row = 0;
    cursor_col = 0;
}