(**
 * Copyright (c) 2015, Fabien Freling
 * All rights reserved.
 *
 * This source code is licensed under the BSD 2-clause license found in the
 * LICENSE file at the top level directory of this source tree.
 *)

let width = 160
let height = 144

type pixel = {
  r : int;
  g : int;
  b : int;
  a : int;
}

type t = {
  data   : pixel array array;
}

type control = {
  lcd_display_enable    : bool;
  tile_map_select       : int;
  window_display_enable : bool;
  tile_data_select      : int;
  bg_tile_map_select    : int;
  sprite_size           : int;
  sprite_enable         : bool;
  bg_display            : bool;
}

let get_lcd_control mem =
  let b = Memory.get mem 0xFF40 |> int_of_char in

  let lcd_display_enable = Bit.is_set b 7 in
  let tile_map_select = if not (Bit.is_set b 6) then 0x9800 else 0x9c00 in
  let window_display_enable = Bit.is_set b 5 in
  let tile_data_select = if not (Bit.is_set b 4) then 0x8800 else 0x8000 in
  let bg_tile_map_select = if not (Bit.is_set b 3) then 0x9800 else 0x9c00 in
  let sprite_size = if not (Bit.is_set b 2) then 8 else 16 in
  let sprite_enable = Bit.is_set b 1 in
  let bg_display = Bit.is_set b 0 in

  {
    lcd_display_enable;
    tile_map_select;
    window_display_enable;
    tile_data_select;
    bg_tile_map_select;
    sprite_size;
    sprite_enable;
    bg_display;
  }

let init =
  {
    data = Array.make_matrix width height { r = 255; g = 255; b = 255; a = 255 }
  }


let render_map mem map_addr =
  let tile_size = 16 in
  let map = Bytes.create (32 * 32 * tile_size) in
  for y = 0 to (32 - 1) do
    for x = 0 to (32 - 1) do
      let tile_number = Memory.get mem (map_addr + (y * 32 + x)) |> int_of_char in
      let src_offset = map_addr + tile_number * tile_size in
      let tile_line_size = 2 in
      let tile_height = 8 in

      for line_index = 0 to (tile_height - 1) do
        let line_offset = src_offset + (line_index * tile_line_size) in
        let dst_y = y * tile_height + line_index in
        let dst_offset = (dst_y * 32 + x) * tile_line_size in
        Bytes.blit mem.vram line_offset map dst_offset tile_line_size
      done
    done
  done


let render mem =
  let
  {
    lcd_display_enable;
    tile_map_select;
    window_display_enable;
    tile_data_select;
    bg_tile_map_select;
    sprite_size;
    sprite_enable;
    bg_display;
  } = get_lcd_control mem in
  let scy = Memory.get mem 0xFF42 |> int_of_char in
  let scx = Memory.get mem 0xFF43 |> int_of_char in
  scx + scy