type dir =
  | Left
  | Right
  | Down
  | Up

type background =
  | Grass
  | Water
  | Black

type t =
  { tiles : background array array
  ; mutable player_pos : int * int
  ; mutable player_dir : dir
  ; width : int
  ; height : int
  }

let init () =
  let width = 1000 in
  let height = 1000 in
  let tiles =
    Array.init width (fun _x ->
        Array.init height (fun _y ->
            if Random.int 1000 <= 42 then Water else Grass ) )
  in
  { tiles; player_pos = (20, 3); player_dir = Down; width; height }

let get_tile_kind ~x ~y map =
  try map.tiles.(x).(y) with Invalid_argument _ -> Black

let move map dir =
  if map.player_dir = dir then begin
    let x, y = map.player_pos in
    let x, y =
      match dir with
      | Left -> (x - 1, y)
      | Right -> (x + 1, y)
      | Down -> (x, y + 1)
      | Up -> (x, y - 1)
    in
    match get_tile_kind ~x ~y map with
    | Black | Water -> ()
    | Grass -> map.player_pos <- (x, y)
  end
  else map.player_dir <- dir