(*
copyright (c) 2013-2014, simon cruanes
all rights reserved.

redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.  redistributions in binary
form must reproduce the above copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other materials provided with
the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*)

(** {1 Hash Table with Heterogeneous Keys} *)

type 'b injection = {
  get : (unit -> unit) -> 'b option;
  set : 'b -> (unit -> unit);
}

let create_inj () =
  let r = ref None in
  let get f =
    r := None;
    f ();
    !r
  and set v =
    (fun () -> r := Some v)
  in
  {get;set}

module type S = sig
  type key

  type t
  (** A map containing values of different types, indexed by {!key}. *)

  val empty : t
  (** Empty map *)

  val get : inj:'a injection -> t  -> key -> 'a option
  (** Get the value corresponding to this key, if it exists and
      belongs to the same key *)

  val add : inj:'a injection -> t -> key -> 'a -> t
  (** Bind the key to the value, using [inj] *)

  val find : inj:'a injection -> t -> key -> 'a
  (** Find the value for the given key, which must be of the right type.
      @raise Not_found if either the key is not found, or if its value
        doesn't belong to the right type *)

  val cardinal : t -> int
  (** Number of bindings *)

  val remove : t -> key -> t
  (** Remove the binding for this key *)

  val mem : inj:_ injection-> t -> key -> bool
  (** Is the given key in the map, with the right type? *)

  val iter_keys : f:(key -> unit) -> t -> unit
  (** Iterate on the keys of this map *)

  val fold_keys : f:('a -> key -> 'a) -> x:'a -> t -> 'a
  (** Fold over the keys *)

  (** {2 Iterators} *)

  type 'a sequence = ('a -> unit) -> unit

  val keys_seq : t -> key sequence
  (** All the keys *)

  val bindings_of : inj:'a injection -> t -> (key * 'a) sequence
  (** All the bindings that come from the corresponding injection *)

  type value =
    | Value : ('a injection -> 'a option) -> value

  val bindings : t -> (key * value) sequence
  (** Iterate on all bindings *)
end

module type ORD = sig
  type t
  val compare : t -> t -> int
end

module Make(X : ORD) : S with type key = X.t = struct
  module M = Map.Make(X)

  type key = X.t
  type t = (unit -> unit) M.t

  let empty = M.empty

  let find ~inj map x =
    match inj.get (M.find x map) with
      | None -> raise Not_found
      | Some v -> v

  let get ~inj map x =
    try inj.get (M.find x map)
    with Not_found -> None

  let add ~inj map x y =
    M.add x (inj.set y) map

  let cardinal = M.cardinal

  let remove map x = M.remove x map

  let mem ~inj map x =
    try
      inj.get (M.find x map) <> None
    with Not_found -> false

  let iter_keys ~f map =
    M.iter (fun x _ -> f x) map

  let fold_keys ~f ~x map =
    M.fold (fun x _ acc -> f acc x) map x

  (** {2 Iterators} *)

  type 'a sequence = ('a -> unit) -> unit

  let keys_seq map yield =
    M.iter
      (fun x _ -> yield x)
      map

  let bindings_of ~inj map yield =
    M.iter
      (fun k value ->
        match inj.get value with
        | None -> ()
        | Some v -> yield (k, v)
      ) map

  type value =
    | Value : ('b injection -> 'b option) -> value

  let bindings map yield =
    M.iter
      (fun x y -> yield (x, Value (fun inj -> inj.get y)))
      map
end