(library (sph scrypt)
  (export
    scrypt
    scrypt->string
    scrypt-check
    scrypt-defaults
    sph-scrypt-description)
  (import
    (rnrs base)
    (rnrs bytevectors)
    (sph)
    (system foreign)
    (only (guile)
      dynamic-link
      dynamic-func
      inexact->exact))

  (define sph-scrypt-description
    "use the scrypt key derivation function. depends on https://github.com/jkalbhenn/scrypt")

  (define libscrypt (dynamic-link "libscrypt"))

  (define foreign-scrypt->string
    (pointer->procedure int (dynamic-func "scrypt_to_string_base91" libscrypt)
      (list (q *) size_t (q *) size_t uint64 uint32 uint32 size_t (q *) (q *))))

  (define foreign-scrypt
    (pointer->procedure int (dynamic-func "scrypt" libscrypt)
      (list (q *) size_t (q *) size_t uint64 uint32 uint32 (q *) size_t)))

  (define foreign-scrypt-set-defaults
    (pointer->procedure int (dynamic-func "scrypt_set_defaults" libscrypt) (q (* * * * * *))))

  (define pointer-size (sizeof (q *)))

  (define* (scrypt->string password #:optional salt (size 0) (N 0) (r 0) (p 0))
    "bytevector bytevector integer integer integer integer -> string:base91-encoded-hash"
    (let
      ( (r (bytevector->pointer (make-bytevector pointer-size 0)))
        (r-len (make-bytevector pointer-size 0)))
      (foreign-scrypt->string (bytevector->pointer password) (bytevector-length password)
        (if salt (bytevector->pointer salt) %null-pointer) (if salt (bytevector-length salt) 0)
        N r p size r (bytevector->pointer r-len))
      (pointer->string (dereference-pointer r)
        (bytevector-uint-ref r-len 0 (endianness little) pointer-size))))

  (define (scrypt-defaults)
    "-> (salt salt-length size N r p)
    get scrypt-library defaults for the values"
    (let
      ( (salt (bytevector->pointer (make-bytevector pointer-size)))
        (salt-length (make-bytevector pointer-size)) (size (make-bytevector (sizeof size_t)))
        (N (make-bytevector (sizeof uint64))) (r (make-bytevector (sizeof uint32)))
        (p (make-bytevector (sizeof uint32))))
      (apply foreign-scrypt-set-defaults salt
        (map bytevector->pointer (list salt-length size N r p)))
      (list
        (pointer->bytevector (dereference-pointer salt)
          (bytevector-uint-ref salt-length 0 (endianness little) (sizeof size_t)))
        (bytevector-uint-ref size 0 (endianness little) (sizeof size_t))
        (inexact->exact (/ (log (bytevector-u64-ref N 0 (endianness little))) (log 2)))
        (bytevector-u32-ref r 0 (endianness little)) (bytevector-u32-ref p 0 (endianness little)))))

  (define (scrypt password salt size logN r p)
    "bytevector bytevector integer integer integer integer -> bytevector:hash"
    (let (result (make-bytevector size 0))
      (foreign-scrypt (bytevector->pointer password) (bytevector-length password)
        (bytevector->pointer salt) (bytevector-length salt)
        (expt 2 logN) r p (bytevector->pointer result) size)
      result))

  (define (scrypt-check key . args) (bytevector=? key (apply scrypt args))))