(*
copyright (c) 2013, simon cruanes
all rights reserved.

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modification, are permitted provided that the following conditions are met:

redistributions of source code must retain the above copyright notice, this
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*)

(** {6 Quickcheck inspired property-based testing} *)

module Arbitrary = struct
  type 'a t = Random.State.t -> 'a

  let int n st = Random.State.int st n

  let int_range ~start ~stop st =
    let n = stop - start in
    if n <= 0
      then 0
      else start + Random.State.int st n

  let small_int = int 100

  let bool = Random.State.bool

  let float f st = Random.State.float st f

  let char st = Char.chr (Random.State.int st 128)

  let alpha st =
    Char.chr (Char.code 'a' + Random.State.int st (Char.code 'z' - Char.code 'a'))

  let string_len len st =
    let n = len st in
    assert (n>=0);
    let s = String.create n in
    for i = 0 to n-1 do
      s.[i] <- alpha st
    done;
    s

  let string st = string_len (int 10) st

  let map ar f st = f (ar st)

  let rec _make_list ar st acc n =
    if n = 0 then acc else
      let x = ar st in
      _make_list ar st (x::acc) (n-1)

  let list ?(len=int 10) ar st =
    let n = len st in
    _make_list ar st [] n

  let opt ar st =
    if Random.State.bool st
      then Some (ar st)
      else None

  let list_repeat len ar st =
    _make_list ar st [] len

  let array ?(len=int 10) ar st =
    let n = len st in
    Array.init n (fun _ -> ar st)

  let array_repeat n ar st =
    Array.init n (fun _ -> ar st)

  let among_array a st =
    let i = Random.State.int st (Array.length a) in
    a.(i)

  let among l = among_array (Array.of_list l)

  let among_tbl k =
    failwith "among_tbl: not implemented yet"

  let choose l =
    assert (l <> []);
    let a = Array.of_list l in
    fun st ->
      let i = Random.State.int st (Array.length a) in
      a.(i) st

  let _fix ~max ~depth recursive f =
    let rec ar = lazy (fun st -> (Lazy.force ar_rec) st)
    and ar_rec = lazy (f ar) in
    Lazy.force ar

  let fix ?(max=max_int) ~base f =
    let rec ar = lazy
      (fun depth st ->
        if depth >= max || Random.State.bool st
          then base st (* base case *)
        else  (* recurse *)
          let x = (Lazy.force ar) (depth+1) st in
          f x st)
    in
    Lazy.force ar 0

  let fix_depth ~depth ~base f st =
    let max = depth st in
    fix ~max ~base f st
end

(** {2 Pretty printing} *)

module PP = struct
  type 'a t = 'a -> string

  let int = string_of_int
  let bool = string_of_bool
  let float = string_of_float
  let string s = s
  let char c =
    let s = "_" in
    s.[0] <- c;
    s

  let list pp l =
    let b = Buffer.create 25 in
    Buffer.add_char b '(';
    List.iteri (fun i x ->
      if i > 0 then Buffer.add_string b ", ";
      Buffer.add_string b (pp x))
      l;
    Buffer.add_char b ')';
    Buffer.contents b

  let array pp a = 
    let b = Buffer.create 25 in
    Buffer.add_char b '[';
    Array.iteri (fun i x ->
      if i > 0 then Buffer.add_string b ", ";
      Buffer.add_string b (pp x))
      a;
    Buffer.add_char b ']';
    Buffer.contents b
end

(** {2 Testing} *)

module Prop = struct
  type 'a t = 'a -> bool

  exception PrecondFail
  
  let (==>) a b =
    fun x ->
      if not (a x) then raise PrecondFail else b x

  let (&&&) a b x = a x && b x

  let (|||) a b x = a x || b x

  let (!!!) a x = not (a x)
end

type 'a result =
  | Ok of int * int  (* total number / precond failed *)
  | Failed of 'a list
  | Error of exn

let check ?(rand=Random.State.make_self_init ()) ?(n=100) gen prop =
  let precond_failed = ref 0 in
  let failures = ref [] in
  try
    for i = 0 to n - 1 do
      let x = gen rand in
      try
        if not (prop x)
          then failures := x :: !failures
      with Prop.PrecondFail ->
        incr precond_failed
    done;
    match !failures with
    | [] -> Ok (n, !precond_failed)
    | _ -> Failed (!failures)
  with e ->
    Error e

(** {2 Main} *)

let run ?pp ?n ?(rand=Random.State.make_self_init()) ?(name="<no name>") gen prop =
  Printf.printf "testing property %s...\n" name;
  match check ~rand ?n gen prop with
  | Ok (n, prefail) ->
    Printf.printf "passed %d tests (%d preconditions failed)\n" n prefail;
    true
  | Failed l ->
    begin match pp with
    | None -> Printf.printf "%d failures\n" (List.length l)
    | Some pp ->
      Printf.printf "%d failures:\n" (List.length l);
      List.iter
        (fun x -> Printf.printf "  %s\n" (pp x))
        l
    end;
    false
  | Error e ->
    Printf.printf "error: %s\n" (Printexc.to_string e);
    false

let run_tests l =
  let rand = Random.State.make_self_init () in
  let res = ref true in
  List.iter (fun test -> if not (test ~rand) then res := false) l;
  if !res
    then Printf.printf "Success!\n"
    else Printf.printf "Failure.\n";
  !res