(********************************************************************)
(*  OCaml code from the book ``Learn Programming with OCaml''       *)
(*  See https://usr.lmf.cnrs.fr/lpo/                                *)
(*                                                                  *)
(*  Sylvain Conchon and Jean-Christophe Filliâtre                   *)
(*  Copyright 2025 Université Paris-Saclay and CNRS                 *)
(*                                                                  *)
(*  Openly licensed via CC BY SA 4.0                                *)
(*  See https://creativecommons.org/licenses/by-sa/4.0/deed.en      *)
(********************************************************************)

(* Program 11 on page 90
   Breakout without Bricks (2/2) *)

let bounce (x, y) (vx, vy) xp =
  let vx =
    if x <= Draw.left || x >= Draw.right then -. vx else vx in
  let vy =
    if y <= float Draw.thick && x >= xp &&
       x <= xp +. float Draw.paddle || y >= Draw.up
    then -. vy else vy
  in
  (vx, vy)

let new_position (x, y) (vx, vy) = x +. vx, y +. vy

let rec play (x, y) (vx, vy) =
  if y <= Draw.down then begin Printf.eprintf "Game over!\n"; exit 0 end;
  let xp = Draw.game x y in
  let vx, vy = bounce (x, y) (vx, vy) (float xp) in
  let x', y' = new_position (x, y) (vx, vy) in
  play (x', y') (vx, vy)

let () =
  Draw.init();
  let speed = 0.1 in
  let vx = speed *. Random.float 1. in
  let vy = speed *. Random.float 1. in
  play (Draw.right /. 2., float Draw.thick) (vx, vy)

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