(*
Copyright (c) 2013, Simon Cruanes
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*)

(** {2 Hypergraph Representation}

CCGeneralized Hypergraphs. Objects are either constants, or hyperedges that
connect [n] other objets together (a [n]-tuple).

Hashconsing is used to ensure that structural equality implies physical
equality. This makes this module non thread safe.
*)

module type S = sig
  type const
    (** Constants. Those are what can annotate hyperedges or make single,
        leaf, nodes. *)

  type t
    (** An hypergraph. It stores a set of edges, and possibly inherits from
        another graph. *)

  type edge
    (** A single edge of the hypergraph. *)

  val self : t -> edge
    (** The edge that represents (reifies) the hypergraph itself *)

  val eq : edge -> edge -> bool
    (** Equality of the two edges. *)

  val arity : edge -> int
    (** Number of sub-elements of the edge (how many other edges it connects
        together) *)

  val nth : edge -> int -> edge
    (** [nth x i] accesses the [i]-th sub-node of [x].
        @raise Invalid_argument if [i >= arity x]. *)

  val make_graph : ?parent:t -> unit -> t
    (** New graph, possibly inheriting from another graph. *)

  val make_edge : t -> edge array -> edge
    (** Create a new hyperedge from an ordered tuple of sub-edges.
        The edge belongs to the given graph.
        The array must not be used afterwards and must not be empty.
        @raise Invalid_argument if the array is empty *)

  val make_const : t -> const -> edge
    (** Constant edge, without sub-edges *)

  val fresh : t -> edge
    (** Fresh edge, without constant. It is equal to no other edge. *)

  module EdgeTbl : Hashtbl.S with type key = edge

  val pp : ?printed:unit EdgeTbl.t ->
           Buffer.t -> edge -> unit
    (** Print the edge on the buffer. @param printed: sub-edges already
        printed. *)

  val fmt : Format.formatter -> edge -> unit
  val to_string : edge -> string
end

module type PARAM = sig
  type const

  val eq : const -> const -> bool
  val hash : const -> int
  val to_string : const -> string  (* for printing *)
end

module Make(P : PARAM) : S with type const = P.const

(** {2 Useful default} *)

module DefaultParam : sig
  type const =
    | S of string
    | I of int

  include PARAM with type const := const

  val i : int -> const
  val s : string -> const
end

module Default : sig
  include S with type const = DefaultParam.const

  module Lexbuf : sig
    type t

    val of_string : string -> t

    val of_fun : (unit -> string option) -> t

    val of_chan : in_channel -> t
  end

  val parse_edge : t -> Lexbuf.t -> [ `Ok of edge | `Error of string ]

  val edge_of_string : t -> string -> [ `Ok of edge | `Error of string ]
end