// screen.c
#include "../include/screen.h"
#include "../include/string.h"
#include "../include/utils.h"

static size_t terminal_row;
static size_t terminal_column;
static uint8_t terminal_color;
static uint16_t* terminal_buffer;

static enum {
	STATE_NORMAL,
	STATE_ESCAPE,
	STATE_BRACKET,
} terminal_state = STATE_NORMAL;

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

inline uint16_t vga_entry(unsigned char uc, uint8_t color) 
{
        return (uint16_t) uc | (uint16_t) color << 8;
}

void terminal_initialize(void) 
{
        terminal_row = 0;
        terminal_column = 0;
        terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
        terminal_buffer = (uint16_t*) 0xB8000;
        for (size_t y = 0; y < VGA_HEIGHT; y++) {
                for (size_t x = 0; x < VGA_WIDTH; x++) {
                        const size_t index = y * VGA_WIDTH + x;
                        terminal_buffer[index] = vga_entry(' ', terminal_color);
                }
        }
}

void terminal_setcolor(uint8_t color) 
{
        terminal_color = color;
}

uint8_t terminal_getcolor()
{
        return terminal_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_scroll(void)
{
        for (size_t y = 0; y < VGA_HEIGHT - 1; y++) {
                for (size_t x = 0; x < VGA_WIDTH; x++) {
                        const size_t index_from = (y + 1) * VGA_WIDTH + x;
                        const size_t index_to = y * VGA_WIDTH + x;
                        terminal_buffer[index_to] = terminal_buffer[index_from];
                }
        }
        for (size_t x = 0; x < VGA_WIDTH; x++) {
                const size_t index = (VGA_HEIGHT - 1) * VGA_WIDTH + x;
                terminal_buffer[index] = vga_entry(' ', terminal_color);
        }
        terminal_row = VGA_HEIGHT - 1;
        terminal_column = 0;
}

void terminal_putchar(char c)
{
	if (terminal_state == STATE_ESCAPE) {
		if (c == '[') {
			terminal_state = STATE_BRACKET;
		} else {
			terminal_state = STATE_NORMAL;
		}
		return;
	} else if (terminal_state == STATE_BRACKET) {
		if (c == 'H') {
			terminal_row = 0;
			terminal_column = 0;
			update_cursor(0, 0);
		}
		terminal_state = STATE_NORMAL;
		return;
	}

	if (c == '\033') {//ESC
		terminal_state = STATE_ESCAPE;
		return;
	}

	if (c == '\b') {
        if (terminal_column > 0) {
            terminal_column--;
        } else if (terminal_row > 0) {
            terminal_row--;
            terminal_column = VGA_WIDTH - 1;
        }
    }
	else if (c == '\n') {
		terminal_column = 0;
		terminal_row++;
	} else {
		terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
		terminal_column++;
	}

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

	if (terminal_row >= VGA_HEIGHT) {
		terminal_scroll();
	}
	update_cursor(terminal_column, terminal_row);
}

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));
}

void update_cursor(int x, int y)
{
	uint16_t pos = y * VGA_WIDTH + x;

	outb(0x3D4, 0x0F);
	outb(0x3D5, (uint8_t) (pos & 0xFF));
	outb(0x3D4, 0x0E);
	outb(0x3D5, (uint8_t) ((pos >> 8) & 0xFF));
}