(*
Copyright (c) 2013, Simon Cruanes
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.  Redistributions in binary
form must reproduce the above copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other materials provided with
the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*)

(** {1 Hash combinators} *)

type t = int

type 'a sequence = ('a -> unit) -> unit
type 'a gen = unit -> 'a option
type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]

let _r = 47
let _m = 0xc6a4a7935bd1e995L

let init = _m

(* combine key [k] with the current state [s] *)
let combine_murmur_ s k =
  let k = Int64.mul _m k in
  let k = Int64.logxor k (Int64.shift_right k _r) in
  let k = Int64.mul _m k in
  let s = Int64.logxor s k in
  let s = Int64.mul _m s in
  s

let finish s =
  let s = Int64.logxor s (Int64.shift_right s _r) in
  let s = Int64.mul s _m in
  let s = Int64.logxor s (Int64.shift_right s _r) in
  (Int64.to_int s) land max_int

let apply f x = finish (f x init)

(** {2 Combinators} *)

(** {2 Generic Hashing} *)

module type HASH = sig
  type state

  val int : int -> state -> state
  val bool : bool -> state -> state
  val char : char -> state -> state
  val int32 : int32 -> state -> state
  val int64 : int64 -> state -> state
  val nativeint : nativeint -> state -> state
  val slice : string -> int -> int -> state -> state
  (** [slice s i len state] hashes the slice [[i, ... i+len)] of [s]
      into [state] *)
end

module type S = sig
  include HASH

  type 'a hash_fun = 'a -> state -> state

  val string : string hash_fun

  val list : 'a hash_fun -> 'a list hash_fun

  val array : 'a hash_fun -> 'a array hash_fun

  val opt : 'a hash_fun -> 'a option hash_fun
  val pair : 'a hash_fun -> 'b hash_fun -> ('a * 'b) hash_fun
  val triple : 'a hash_fun -> 'b hash_fun -> 'c hash_fun -> ('a * 'b * 'c) hash_fun

  val if_ : bool -> 'a hash_fun -> 'a hash_fun -> 'a hash_fun
  (** Decide which hash function to use depending on the boolean *)

  (** {2 Iterators} *)

  val seq : 'a hash_fun -> 'a sequence hash_fun
  val gen : 'a hash_fun -> 'a gen hash_fun
  val klist : 'a hash_fun -> 'a klist hash_fun
end

module Base = struct
  type state = int64
  let int i s = combine_murmur_ s (Int64.of_int i)
  let bool x s = combine_murmur_ s (if x then 1L else 2L)
  let char x s = combine_murmur_ s (Int64.of_int (Char.code x))
  let int32 x s = combine_murmur_ s (Int64.of_int32 x)
  let int64 x s = combine_murmur_ s x
  let nativeint x s = combine_murmur_ s (Int64.of_nativeint x)

  let slice x i len s =
    let j=i+len in
    let rec aux i s =
      if i=j then s else aux (i+1) (char x.[i] s)
    in
    aux i s
end

module Make(H : HASH) : S with type state = H.state = struct
  include H

  type 'a hash_fun = 'a -> state -> state

  let rec list f l s = match l with
    | [] -> s
    | x::l' -> list f l' (f x s)

  let array f a s = Array.fold_right f a s

  let opt f o h = match o with
    | None -> h
    | Some x -> f x h
  let pair h1 h2 (x,y) s = h2 y (h1 x s)
  let triple h1 h2 h3 (x,y,z) s = h3 z (h2 y (h1 x s))

  let string x s = slice x 0 (String.length x) s

  let if_ b then_ else_ h =
    if b then then_ h else else_ h

  let seq f seq s =
    let s = ref s in
    seq (fun x -> s := f x !s);
    !s

  let rec gen f g s = match g () with
    | None -> s
    | Some x -> gen f g (f x s)

  let rec klist f l s = match l () with
    | `Nil -> s
    | `Cons (x,l') -> klist f l' (f x s)
end

include Make(Base)

(* deprecated aliases *)

let int_ = int
let bool_ = bool
let char_ = char
let int32_ = int32
let int64_ = int64
let nativeint_ = nativeint
let string_ = string

let list_ = list
let array_ = array