(**************************************************************************)
(*                                                                        *)
(*    Copyright (c) 2014 - 2016.                                          *)
(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
(*                                                                        *)
(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
(*                                                                        *)
(**************************************************************************)

(* Tezos Protocol Implementation - Random number generation *)

open Tezos_hash

type seed = B of State_hash.t
type t = T of State_hash.t
type sequence = S of State_hash.t
type nonce = MBytes.t

let nonce_encoding = Data_encoding.bytes

let init = "1234567890123456789012"
let zero_bytes = MBytes.of_string (String.make Nonce_hash.size '\000')

let state_hash_encoding =
  let open Data_encoding in
  conv
    State_hash.to_bytes
    State_hash.of_bytes
    (Fixed.bytes Nonce_hash.size)

let seed_encoding =
  let open Data_encoding in
  conv
    (fun (B b) -> b)
    (fun b -> B b)
    state_hash_encoding

let empty = B (State_hash.hash_bytes [MBytes.of_string init])

let nonce (B state) nonce =
  B (State_hash.hash_bytes ( [State_hash.to_bytes state; nonce] ))

let initialize_new (B state) append =
  T (State_hash.hash_bytes
       (State_hash.to_bytes state :: zero_bytes :: append ))

let xor_higher_bits i b =
  let higher = MBytes.get_int32 b 0 in
  let r = Int32.logxor higher i in
  let res = MBytes.copy b in
  MBytes.set_int32 res 0 r;
  res

let sequence (T state) n =
  State_hash.to_bytes state
  |> xor_higher_bits n
  |> (fun b -> S (State_hash.hash_bytes [b]))

let take (S state) =
  let b = State_hash.to_bytes state in
  let h = State_hash.hash_bytes [b] in
  (State_hash.to_bytes h, S h)

let take_int32 s bound =
  if Compare.Int32.(bound <= 0l)
  then invalid_arg "Seed_repr.take_int32" (* FIXME *)
  else
    let rec loop s =
      let bytes, s = take s in
      let r = Int32.abs (MBytes.get_int32 bytes 0) in
      let drop_if_over =
        Int32.sub Int32.max_int (Int32.rem Int32.max_int bound) in
      if Compare.Int32.(r >= drop_if_over)
      then loop s
      else
        let v = Int32.rem r bound in
        v, s
    in
    loop s

type error += Unexpected_nonce_length

let make_nonce nonce =
  if Compare.Int.(MBytes.length nonce <> Constants_repr.nonce_length)
  then error Unexpected_nonce_length
  else ok nonce

let hash nonce = Nonce_hash.hash_bytes [nonce]

let check_hash nonce hash =
  Compare.Int.(MBytes.length nonce = Constants_repr.nonce_length)
  && Nonce_hash.equal (Nonce_hash.hash_bytes [nonce]) hash

let nonce_hash_key_part = Nonce_hash.to_path

let initial_nonce_0 =
  hash
    (MBytes.of_string (String.make Constants_repr.nonce_length '\000'))

let initial_seed_0 = B (State_hash.hash_bytes [])
let initial_seed_1 =
  nonce initial_seed_0
    (MBytes.of_string (String.make Constants_repr.nonce_length '\000'))
let initial_seed_2 =
  nonce initial_seed_1
    (MBytes.of_string (String.make Constants_repr.nonce_length '\000'))