#include "kernel/kernel_prelude.hats"

staload "./writer.sats"

#define ATS_DYNLOADFLAG 0

%{^
  #define get_buffer() ((void *) 0xB8000)
%}

extern fun get_buffer():<> buffer = "mac#"
extern prfun eat_buffer (pf: buffer): void
extern fun getref (): [l:addr] vtakeoutptr (writer)

fun color_value(c : color): uint8 = 
  case+ c of 
    | Black() => i2u8 0
    | Blue() => i2u8 1
    | Green() => i2u8 2
    | Cyan() => i2u8 3
    | Red() => i2u8 4
    | Magenta() => i2u8 5
    | Brown() => i2u8 6
    | LightGray() => i2u8 7
    | DarkGray() => i2u8 8
    | LightBlue() => i2u8 9
    | LightGreen() => i2u8 10
    | LightCyan() => i2u8 11
    | LightRed() => i2u8 12
    | Pink() => i2u8 13
    | Yellow() => i2u8 14
    | White() => i2u8 15

fun code_value(foreground: color, background:color): uint8 = 
  (color_value(background) << 4) lor color_value(foreground)

local
var _val: writer 

in
implement getref () = let
  extern praxi __assert{l:addr} (ptr: ptr (l)): vtakeout0 (writer@l)
  prval (pf, fpf) = __assert (addr@(_val))
in
  (pf, fpf | addr@(_val))
end
end

fun put_char (c : char, writer: &writer) : void = let
  val buf = get_buffer()
  val pos = writer.position
in
  if (c = '\n') then
    let 
      val new_pos = (pos /  BUFFER_WIDTH + 1) * BUFFER_WIDTH
    in
      if (new_pos < N) then
        writer.position := new_pos
      else
        clear_screen()
    end
  else (
    buf.1->[writer.position] := @{ ascii_character = c, color_code = writer.color_code};

    if (pos < N - 1) then
      writer.position := succ(pos)
    else
      clear_screen());

  let prval() = eat_buffer buf in () end
end


implement put_string (str : string) : void = let
  val (pf, fpf | p_val) = getref()
  implement string_foreach$fwork<writer> (c,env) = put_char(c,env)
  val _ =  string_foreach_env<writer> (g1ofg0(str),!p_val)
  prval() = fpf(pf)
in  
end

implement clear_screen() : void = let
  val (pf, fpf | p_val) = getref()
  fun loop {n : nat | n < N - 1} .<N-n>. (i : int n, wr : &writer) : void = 
    (put_char('\0', wr); if (i < N - 2) then loop(i+1,wr))
  val () = !p_val := @{position = 0, color_code = code_value(White,Black)}
in
  loop(0,!p_val);
  !p_val.position := 0;
  let prval() = fpf(pf) in () end
end