(* Encapsulate the attribute/value list type used by Debian.read_packages,
   Debian.parse_control_text, Psql.avl_of_tuple, etc. *)

(*
type t = (string * string) list


let create _ = []
let find = List.assoc
let remove = List.remove_assoc
let add avl key value = (key, value) :: avl
let replace avl key value = (key, value) :: (remove key avl)
*)

(* Reference based version *) 

(*
type t = (string * string) list ref

let create _ = ref []
let find key avl = List.assoc key !avl
let remove key avl = avl := List.remove_assoc key !avl
let add avl key value = avl := (key, value) :: !avl
let replace avl key value =
  avl := (key, value) :: List.remove_assoc key !avl
*)

(* Hash table base version *)

type t = (string, string) Hashtbl.t
let create n = Hashtbl.create n
let find key avl = Hashtbl.find avl key
let remove key avl = Hashtbl.remove avl key
let add avl key value = Hashtbl.add avl key value
let unset key avl = Hashtbl.remove avl key
let replace avl key value = Hashtbl.replace avl key value
let addret avl key value = Hashtbl.add avl key value; avl
let replret avl key value = Hashtbl.replace avl key value; avl
let iter = Hashtbl.iter
let to_list avl =
  let lst = ref [] in
  Hashtbl.iter (fun attr value -> lst := (attr, value) :: !lst) avl;
  !lst
let of_list pairs =
  let avl = create (List.length pairs) in
  List.iter (fun (a, v) -> add avl a v) pairs;
  avl
let filter pred avl =
  let nu = create 50 in
  Hashtbl.iter (fun attr value ->
		  if pred (attr, value) then
		    add nu attr value) avl;
  nu

let merge a b =
  let c = Hashtbl.create 50 in
  Hashtbl.iter (fun attr value -> add c attr value) a;
  Hashtbl.iter (fun attr value -> replace c attr value) b;
  c

(* Derived *)

let search attr avls =
  let rec loop avls =
    match avls with
      [] -> raise Not_found
    | avl :: etc -> try find attr avl with Not_found -> loop etc in
  loop avls