(* Basic counting module.
 * (C) Copyright 2003-2006 Merjis Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA
 *)

type 'a t = ('a, int ref) Hashtbl.t

let create () =
  Hashtbl.create 13

let get_ref counter thing =
  try
    Hashtbl.find counter thing
  with
    Not_found ->
      let r = ref 0 in
      Hashtbl.add counter thing r;
      r

let incr counter thing =
  let r = get_ref counter thing in
  incr r

let decr counter thing =
  let r = get_ref counter thing in
  decr r

let add counter thing n =
  let r = get_ref counter thing in
  r := !r + n

let sub counter thing n =
  let r = get_ref counter thing in
  r := !r - n

let set counter thing n =
  let r = get_ref counter thing in
  r := n

(* Don't use get_ref, to avoid unnecessarily creating 'ref 0's. *)
let get counter thing =
  try
    !(Hashtbl.find counter thing)
  with
    Not_found -> 0

(* This is a common pair of operations, worth optimising. *)
let incr_get counter thing =
  let r = get_ref counter thing in
  Pervasives.incr r;
  !r

let zero = Hashtbl.remove

let read counter =
  let counts =
    Hashtbl.fold (
      fun thing r xs ->
	let r = !r in
	if r <> 0 then (r, thing) :: xs
	else xs
    ) counter [] in
  List.sort (fun (a, _) (b, _) -> compare (b : int) (a : int)) counts

let length = Hashtbl.length

let total counter =
  let total = ref 0 in
  Hashtbl.iter (fun _ r -> total := !total + !r) counter;
  !total

let clear = Hashtbl.clear