use core::ptr::Unique;
use spin::Mutex;

const BUFFER_HEIGHT: usize = 25;
const BUFFER_WIDTH: usize = 80;

pub static WRITER: Mutex<Writer> = Mutex::new(Writer {
    column_position: 0,
    color_code: ColorCode::new(Color::LightGreen, Color::Black),
    buffer: unsafe{Unique::new(0xb8000 as *mut _)},
});

#[repr(u8)]
pub enum Color {
    Black      = 0,
    Blue       = 1,
    Green      = 2,
    Cyan       = 3,
    Red        = 4,
    Magenta    = 5,
    Brown      = 6,
    LightGray  = 7,
    DarkGray   = 8,
    LightBlue  = 9,
    LightGreen = 10,
    LightCyan  = 11,
    LightRed   = 12,
    Pink       = 13,
    Yellow     = 14,
    White      = 15,
}

pub struct Writer {
    column_position: usize,
    color_code: ColorCode,
    buffer: Unique<Buffer>,
}

impl Writer {
    pub fn write_byte(&mut self, byte: u8) {
        match byte {
            b'\n' => self.new_line(),
            byte => {
                if self.column_position >= BUFFER_WIDTH {
                    self.new_line();
                }
                let row = BUFFER_HEIGHT - 1;
                let col = self.column_position;

                self.buffer().chars[row][col] = ScreenChar {
                    ascii_character: byte,
                    color_code: self.color_code,
                };
                self.column_position += 1;
            }
        }
    }

    fn buffer(&mut self) -> &mut Buffer {
        unsafe{self.buffer.get_mut()}
    }

    fn new_line(&mut self) {
        for row in 0..(BUFFER_HEIGHT-1) {
            let buffer = self.buffer();
            buffer.chars[row] = buffer.chars[row + 1]
        }
        self.clear_row(BUFFER_HEIGHT-1);
        self.column_position = 0;
    }

    fn clear_row(&mut self, row: usize) {
        let blank = ScreenChar {
            ascii_character: ' ' as u8,
            color_code: self.color_code,
        };
        self.buffer().chars[row] = [blank; BUFFER_WIDTH];
    }
}

#[derive(Clone, Copy)]
struct ColorCode(u8);

impl ColorCode {
    const fn new(foreground: Color, background: Color) -> ColorCode {
        ColorCode((background as u8) << 4 | (foreground as u8))
    }
}

#[derive(Clone, Copy)]
struct ScreenChar {
    ascii_character: u8,
    color_code: ColorCode,
}

struct Buffer {
    chars: [[ScreenChar; BUFFER_WIDTH]; BUFFER_HEIGHT],
}