(*
copyright (c) 2013, simon cruanes
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*)

(** {1 B-Trees}

Shallow, cache-friendly associative data structure.
See {{: https://en.wikipedia.org/wiki/B-tree} wikipedia}.

Not thread-safe.  *)

type 'a sequence = ('a -> unit) -> unit
type 'a ktree = unit -> [`Nil | `Node of 'a * 'a ktree list]

(** {2 signature} *)

module type S = sig
  type key
  type 'a t

  val create : unit -> 'a t
  (** Empty map *)

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

  val add : key -> 'a -> 'a t -> unit
  (** Add a binding to the tree. Erases the old binding, if any *)

  val remove : key -> 'a t -> unit
  (** Remove the given key, or does nothing if the key isn't present *)

  val get : key -> 'a t -> 'a option
  (** Key lookup *)

  val get_exn : key -> 'a t -> 'a
  (** Unsafe version of {!get}.
      @raise Not_found if the key is not present *)

  val fold : ('b -> key -> 'a -> 'b) -> 'b -> 'a t -> 'b
  (** Fold on bindings *)

  val of_list : (key * 'a) list -> 'a t
  val to_list : 'a t -> (key * 'a) list
  val to_tree : 'a t -> (key * 'a) list ktree
end

(** {2 Functor that builds trees for comparable keys} *)

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

module Make(X : ORDERED) : S with type key = X.t

(* note: to print a B-tree in dot:
{[
let t = some_btree in
let t' = CCKTree.map
  (fun t ->
    [`Shape "square";
     `Label (CCPrint.to_string (CCList.pp (CCPair.pp CCInt.pp CCString.pp)) t)]
  ) (T.to_tree t);;
CCPrint.to_file "/tmp/some_file.dot" "%a\n" (CCKTree.Dot.pp_single "btree") t';
]}
*)