#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

#include <kernel/tty.h>
#include <kernel/x86/io.h>

#include "vga.h"

/* I/O ports */
#define VGA_COMMAND_PORT 0x3D4
#define VGA_DATA_PORT 0x3D5

/* I/O port commands */
#define VGA_HIGH_BYTE_COMMAND 14
#define VGA_LOW_BYTE_COMMAND 15

static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;
static uint16_t* const VGA_MEMORY = (uint16_t*) 0xB8000;

static size_t terminal_row;
static size_t terminal_column;
static uint8_t terminal_colour;
static struct vga_entry* terminal_buffer;

struct vga_entry {
	char c;
	unsigned char colour;
} __attribute__((packed));

void terminal_set_colour(uint8_t colour)
{
	terminal_colour = colour;
}

void terminal_clear(void)
{
	for (size_t y = 0; y < VGA_HEIGHT; y++)
		for (size_t x = 0; x < VGA_WIDTH; x++)
			terminal_write_cell((y * VGA_WIDTH) + x, ' ');
	terminal_move_cursor(0);
}

void terminal_initialize(void)
{
	terminal_row = 0;
	terminal_column = 0;

	terminal_buffer = (struct vga_entry*) VGA_MEMORY;
	terminal_set_colour(vga_entry_colour(VGA_COLOUR_LIGHT_GREY, VGA_COLOUR_BLACK));

	terminal_clear();
}

void terminal_move_cursor(unsigned short pos)
{
	if (terminal_row >= VGA_HEIGHT)
		terminal_scroll_screen();

	outb(VGA_COMMAND_PORT, VGA_HIGH_BYTE_COMMAND);
	outb(VGA_DATA_PORT, ((pos >> 8) & 0x00FF));
	outb(VGA_COMMAND_PORT, VGA_LOW_BYTE_COMMAND);
	outb(VGA_DATA_PORT, pos & 0x00FF);
}

inline size_t terminal_get_pos(void)
	{return (terminal_row * VGA_WIDTH) + terminal_column;}

void terminal_write_cell(unsigned int i, char c)
{
	struct vga_entry entry;

	entry.c = c;
	entry.colour = terminal_colour;

	terminal_buffer[i] = entry;
}

void terminal_write_character(unsigned int i, char c)
{
	switch(c) {
		case '\n':
			terminal_row += 1;
			__attribute__((fallthrough));
		case '\r':
			terminal_column = 0;
			terminal_move_cursor(terminal_get_pos());
			break;
		default:
			terminal_write_cell(i, c);

			terminal_column += 1;
			if (terminal_column >= VGA_WIDTH) {
				terminal_column = 0;
				terminal_row += 1;
			}

			terminal_move_cursor(terminal_get_pos());
	}
}

void terminal_write(const char* buf, size_t len)
{
	for (size_t i = 0; i < len; i++)
		terminal_write_character(terminal_get_pos(), buf[i]);
}

void terminal_writestring(const char* buf)
{
	terminal_write(buf, strlen(buf));
}

void terminal_scroll_screen(void)
{
	size_t y, x;
	for (y = 0; y < VGA_HEIGHT -1; y++) {
		for (x = 0; x < VGA_WIDTH; x++) {
			terminal_buffer[(y * VGA_WIDTH) + x] =
				terminal_buffer[((y + 1) * VGA_WIDTH) + x];
		}
	}
	for (x = 0; x < VGA_WIDTH; x++)
		terminal_write_cell(((VGA_HEIGHT - 1) * VGA_WIDTH) + x, ' ');

	terminal_row -= 1;
	terminal_column = 0;
	terminal_move_cursor(terminal_get_pos());
}