;; This file is part of eris-cl.
;; Copyright (C) 2022 Piotr Szarmański

;; eris-cl is free software: you can redistribute it and/or modify it under the
;; terms of the GNU Lesser General Public License as published by the Free
;; Software Foundation, either version 3 of the License, or (at your option) any
;; later version.

;; eris-cl is distributed in the hope that it will be useful, but WITHOUT ANY
;; WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
;; A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

;; You should have received a copy of the GNU Lesser General Public License along with
;; eris-cl. If not, see <https://www.gnu.org/licenses/>.

;; This file contains the backend protocol.
(in-package :eris)

(defclass encoding-backend ()
  ((output-function :type function)))

(defclass decoding-backend ()
  ((fetch-function :type function)))

(defclass p/encoding-backend ()
  ())

(defgeneric fetch-data (read-capability backend &key &allow-other-keys)
  (:documentation
   "Using the BACKEND, return a stream that decodes the provided READ-CAPABILITY
object."))

(defgeneric store-data (input backend &key secret block-size &allow-other-keys)
  (:documentation
   "Using the BACKEND, store the INPUT, which is either a stream or an octet
vector. An additional 32-byte octet-vector SECRET can be provided in order to
protect the data from attacks against convergent encryption.

BLOCK-SIZE is by default 32kib, except if the input is a file or vector with a
size less than 16kib. It should be set either to 1024b or 32kib."))


;; Default methods

(defmethod fetch-data (read-capability (backend decoding-backend) &key &allow-other-keys)
  (declare (type read-capability read-capability))
  (with-slots (fetch-function) backend
    (eris-decode read-capability fetch-function)))

(defmethod store-data (input (backend encoding-backend) &key (secret null-secret) (block-size 32kib) &allow-other-keys)
  (declare (type octet-vector secret))
  (with-slots (output-function) backend
    (eris-encode input ;; According to ERIS spec recommendation.
                 (if (> (etypecase input
                          (pathname (file-size input))
                          (file-stream (file-length input))
                          (vector (length input))
                          (t block-size))
                        16384)
                     32kib
                     1kib)
                 output-function
                 :secret secret)))

(defgeneric p/store-data (input backend &key secret block-size threads)
  (:documentation "Like store-data but parallel. lparallel:*kernel* has to be bound before
calling."))

(defmethod p/store-data (input (backend p/encoding-backend)
                         &key (secret null-secret) (block-size 32kib) &allow-other-keys)
  (with-slots (output-function) backend
    (p/eris-encode input
                   (if (> (etypecase input
                          (pathname (file-size input))
                          (file-stream (file-length input))
                          (vector (length input))
                          (t block-size))
                        16384)
                     32kib
                     1kib)
                   output-function :secret secret)))