(******************************************************************************)
(*  SXSI : XPath evaluator                                                    *)
(*  Kim Nguyen (Kim.Nguyen@nicta.com.au)                                      *)
(*  Copyright NICTA 2008                                                      *)
(*  Distributed under the terms of the LGPL (see LICENCE)                     *)
(******************************************************************************)

exception InfiniteSet
module type S = 
sig
  type elt
  type t
  type set
  val empty : t
  val any : t
  val is_empty : t -> bool
  val is_any : t -> bool
  val is_finite : t -> bool
  val kind : t -> [ `Finite | `Cofinite ]
  val singleton : elt -> t
  val mem : elt -> t -> bool
  val add : elt -> t -> t
  val remove : elt -> t -> t
  val cup : t -> t -> t
  val cap : t -> t -> t
  val diff : t -> t -> t
  val neg : t -> t
  val compare : t -> t -> int
  val subset : t -> t -> bool
  val kind_split : t list -> t * t
  val fold : (elt -> 'a -> 'a) -> t -> 'a -> 'a
  val for_all : (elt -> bool) -> t -> bool
  val exists : (elt -> bool) -> t -> bool
  val filter : (elt -> bool) -> t -> t
  val partition : (elt -> bool) -> t -> t * t
  val cardinal : t -> int
  val elements : t -> elt list
  val from_list : elt list -> t
  val choose : t -> elt
  val hash : t -> int
  val equal : t -> t -> bool
  val positive : t -> set
  val negative : t -> set
end

module Make (E : Sigs.Set) : S with type elt = E.elt and type set = E.t =
struct

  type elt = E.elt
  type t = Finite of E.t | CoFinite of E.t
  type set = E.t

  let empty = Finite E.empty
  let any = CoFinite E.empty

  let is_empty =  function
      Finite s when E.is_empty s -> true
    | _ -> false

  let is_any = function
      CoFinite s when E.is_empty s -> true
    | _ -> false

  let is_finite = function
    | Finite _ -> true | _ -> false

  let kind = function
      Finite _ -> `Finite 
    | _ -> `Cofinite 

  let mem x = function Finite s -> E.mem x s
    | CoFinite s -> not (E.mem x s)

  let singleton x = Finite (E.singleton x)
  let add e = function 
    | Finite s -> Finite (E.add e s)
    | CoFinite s -> CoFinite (E.remove e s)
  let remove e = function
    | Finite s -> Finite (E.remove e s)
    | CoFinite s -> CoFinite (E.add e s)
	
  let cup s t = match (s,t) with
    | Finite s, Finite t -> Finite (E.union s t)
    | CoFinite s, CoFinite t -> CoFinite ( E.inter s t)
    | Finite s, CoFinite t -> CoFinite (E.diff t s)
    | CoFinite s, Finite t-> CoFinite (E.diff s t)

  let cap s t = match (s,t) with
    | Finite s, Finite t -> Finite (E.inter s t)
    | CoFinite s, CoFinite t -> CoFinite (E.union s t)
    | Finite s, CoFinite t -> Finite (E.diff s t)
    | CoFinite s, Finite t-> Finite (E.diff t s)
	
  let diff s t = match (s,t) with
    | Finite s, Finite t -> Finite (E.diff s t)
    | Finite s, CoFinite t -> Finite(E.inter s t)
    | CoFinite s, Finite t -> CoFinite(E.union t s)
    | CoFinite s, CoFinite t -> Finite (E.diff t s)

  let neg = function 
    | Finite s -> CoFinite s
    | CoFinite s -> Finite s
	
  let compare s t = match (s,t) with
    | Finite s , Finite t -> E.compare s t
    | CoFinite s , CoFinite t -> E.compare t s
    | Finite _, CoFinite _ -> -1
    | CoFinite _, Finite _ -> 1
	
  let subset s t = match (s,t) with
    | Finite s , Finite t -> E.subset s t
    | CoFinite s , CoFinite t -> E.subset t s
    | Finite s, CoFinite t -> E.is_empty (E.inter s t)
    | CoFinite _, Finite _ -> false

	(* given a  list l of type t list, 
	   returns two sets (f,c) where :
	   - f is the union of all the finite sets of l
	   - c is the union of all the cofinite sets of l
	   - f and c are disjoint
	   Invariant : cup f c = List.fold_left cup empty l

	   We treat the CoFinite part explicitely :
	*)

  let kind_split l =
    
    let rec next_finite_cofinite facc cacc = function 
      | [] -> Finite facc, CoFinite (E.diff cacc facc)
      | Finite s ::r -> next_finite_cofinite (E.union s facc) cacc r
      | CoFinite _ ::r when E.is_empty cacc -> next_finite_cofinite facc cacc r
      | CoFinite s ::r -> next_finite_cofinite facc (E.inter cacc s) r
    in
    let rec first_cofinite facc = function
      | [] -> empty,empty
      | Finite s :: r-> first_cofinite (E.union s facc) r
      | CoFinite s :: r -> next_finite_cofinite facc s r  
    in
      first_cofinite E.empty l
	
  let fold f t a = match t with
    | Finite s -> E.fold f s a
    | CoFinite _ -> raise InfiniteSet

  let for_all f = function
    | Finite s -> E.for_all f s
    | CoFinite _ -> raise InfiniteSet

  let exists f = function
    | Finite s -> E.exists f s
    | CoFinite _ -> raise InfiniteSet

  let filter f = function
    | Finite s -> Finite (E.filter f s)
    | CoFinite _ -> raise InfiniteSet

  let partition f = function
    | Finite s -> let a,b = E.partition f s in Finite a,Finite b
    | CoFinite _ -> raise InfiniteSet

  let cardinal = function
    | Finite s -> E.cardinal s
    | CoFinite _ -> raise InfiniteSet

  let elements = function
    | Finite s -> E.elements s
    | CoFinite _ -> raise InfiniteSet
	
  let from_list l = 
    Finite(List.fold_left (fun x a -> E.add a x ) E.empty l)

  let choose = function
      Finite s -> E.choose s
    | _ -> raise InfiniteSet

  let equal a b = 
    match a,b with
      | Finite x, Finite y | CoFinite x, CoFinite y -> E.equal x y
      | _ -> false

  let hash = 
    function Finite x -> (E.hash x)
      | CoFinite x -> ( ~-(E.hash x) land max_int)

  let positive = 
    function
      | Finite x -> x
      | _ -> E.empty

  let negative = 
    function
      | CoFinite x -> x
      | _ -> E.empty

end