function _init()
   init_constants()
   init_sound()
   init_mapgen()
   init_player(32, 32)
   generate_map(0, 0)
   debug = false
end


function _update()
   handle_input()
   handle_map_update()
   debug_input()
end

function _draw()
   rectfill(0, 0, 127, 127, 0)
   -- the screen is 128x128 pixels, so it fits 16x16 sprites
   map(camera_pos_x, camera_pos_y, 0, 0, 16, 16)
   draw_player()
   if debug then
      render_debug_info()
   end
end

-- decide whether we need to regenerate the map.
-- if so, call generate_map appropriately and reset coordinates.
function handle_map_update()
   if out_of_bounds(camera_pos_x, camera_pos_y) then
      -- out_of_bounds() checks all screen bounds
      -- we need to regenerate the map, so we generate a map chunk that
      -- places the player in the middle of it.
      generate_map(player_pos_x-32, player_pos_y-32)
      camera_pos_x, camera_pos_y = 24, 24
   end
end

function out_of_bounds(pos_x, pos_y)
   return pos_x < 0 or pos_x > 48 or
      pos_y < 0 or pos_y > 48
end

function debug_input()
   if btn"5" and btn"4" then
      if (btnp"0") debug = "res"
      if (btnp"1") debug = "sfx"
      if (btnp"2") debug = "map"
      if (btnp"3") debug = nil
   end

end

function render_debug_info()
   if debug == "res" then
      clip(0, 0, 32, 24)
      rectfill(0, 0, 32, 24, 0)

      print(stat(0), 0, 0, 15)
      print(stat(1), 0, 8, 15)
      print(stat(9), 0, 16, 15)
      print("/", 12, 16, 15)
      print(stat(8), 20, 16, 15)
   elseif debug == "sfx" then
      clip(0, 0, 16, 8)
      rectfill(0, 0, 16, 8, 0)

      print(stat(24), 0, 0, 15)
   elseif debug == "map" then
      clip(0, 0, 32, 24)
      rectfill(0, 0, 32, 24, 0)

      print(camera_pos_x, 0, 0, 15)
      print(camera_pos_y, 16, 0, 15)
      print(player_pos_x, 0, 8, 15)
      print(player_pos_y, 16, 8, 15)
      print(get_biome_name(player_pos_x, player_pos_y), 0, 16, 15)
   end

   clip()
end