(define-module (sph base64))
(use-modules (rnrs io ports) (rnrs arithmetic fixnums) (rnrs base) (rnrs bytevectors) (rnrs conditions))
(export sph-base64-description base64-decode base64-decode-port base64-encode base64-encode-port)

(define copyright
  "modified by sph.
   Copyright (c) 2009 Takeshi Abe. All rights reserved.
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:
   1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
   2. 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.
   3. Neither the name of the authors nor the names of its contributors
   may be used to endorse or promote products derived from this
   software without specific prior written permission.
   ;;
   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
   OWNER 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.")

(define sph-base64-description "encoder/decoder")

(define *table*
  (quote
    #(#\A #\B #\C
      #\D #\E
      #\F #\G
      #\H #\I
      #\J #\K
      #\L #\M
      #\N #\O
      #\P #\Q
      #\R #\S
      #\T #\U
      #\V #\W
      #\X #\Y
      #\Z #\a
      #\b #\c
      #\d #\e
      #\f #\g
      #\h #\i
      #\j #\k
      #\l #\m
      #\n #\o
      #\p #\q #\r #\s #\t #\u #\v #\w #\x #\y #\z #\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9 #\+ #\/)))

(define (base64-encode-port iport oport)
  (define (put-alphabet i) (put-char oport (vector-ref *table* i))) (assert (binary-port? iport))
  (assert (textual-port? oport))
  (let loop ((b0 (get-u8 iport)) (n 0))
    (cond
      ((eof-object? b0) n)
      (else (put-alphabet (fxarithmetic-shift-right b0 2))
        (let ((p0 (fxarithmetic-shift-left (fxbit-field b0 0 2) 4)) (b1 (get-u8 iport)))
          (cond
            ((eof-object? b1) (put-alphabet p0) (put-string oport "==") (+ n 4))
            (else (put-alphabet (fxior p0 (fxarithmetic-shift-right b1 4)))
              (let ((p1 (fxarithmetic-shift-left (fxbit-field b1 0 4) 2)) (b2 (get-u8 iport)))
                (cond
                  ((eof-object? b2) (put-alphabet p1) (put-char oport #\=) (+ n 4))
                  (else (put-alphabet (fxior p1 (fxarithmetic-shift-right b2 6)))
                    (put-alphabet (fxbit-field b2 0 6)) (loop (get-u8 iport) (+ n 4))))))))))))

(define (base64-encode bv) (assert (bytevector? bv))
  (call-with-port (open-bytevector-input-port bv)
    (lambda (iport)
      (call-with-string-output-port (lambda (oport) (base64-encode-port iport oport))))))

(define-condition-type &invalid-encoding &condition
  make-invalid-encoding invalid-encoding? (position invalid-encoding-position))

(define-condition-type &unknown-alphabet &condition
  make-unknown-alphabet unknown-alphabet? (char unknown-alphabet-char))

(define (base64-decode-port iport oport)
  (define (c->i c)
    (let ((n (char->integer c)))
      (cond
        ((<= 65 n 90) (- n 65))
        ((<= 97 n 122) (- n 71))
        ((<= 48 n 57) (+ n 4))
        ((char=? #\+ c) 62)
        ((char=? #\/ c) 63)
        (else (raise (make-unknown-alphabet c))))))
  (define-syntax put-bytes
    (syntax-rules ()
      ( (_ c0 c1)
        (let*
          ( (i0 (c->i c0)) (i1 (c->i c1))
            (b0 (fxior (fxarithmetic-shift-left i0 2) (fxbit-field i1 4 6))))
          (put-u8 oport b0) i1))
      ( (_ c0 c1 c2)
        (let*
          ( (i1 (put-bytes c0 c1)) (i2 (c->i c2))
            (b1 (fxior (fxarithmetic-shift-left (fxbit-field i1 0 4) 4) (fxbit-field i2 2 6))))
          (put-u8 oport b1) i2))
      ( (_ c0 c1 c2 c3)
        (let*
          ( (i2 (put-bytes c0 c1 c2))
            (b2 (fxior (fxarithmetic-shift-left (fxbit-field i2 0 2) 6) (c->i c3))))
          (put-u8 oport b2)))))
  (assert (textual-port? iport)) (assert (binary-port? oport))
  (let loop ((c0 (get-char iport)) (n 0))
    (if (eof-object? c0) n
      (let ((c1 (get-char iport))) (if (eof-object? c1) (raise (make-invalid-encoding (+ n 1))))
        (let ((c2 (get-char iport))) (if (eof-object? c2) (raise (make-invalid-encoding (+ n 2))))
          (let ((c3 (get-char iport)))
            (cond
              ((eof-object? c3) (raise (make-invalid-encoding (+ n 3))))
              ( (char=? #\= c2)
                (cond
                  ((char=? #\= c3) (put-bytes c0 c1) (+ n 1))
                  (else (raise (make-invalid-encoding (+ n 3))))))
              ((char=? #\= c3) (put-bytes c0 c1 c2) (+ n 2))
              (else (put-bytes c0 c1 c2 c3) (loop (get-char iport) (+ n 3))))))))))

(define (base64-decode str) (assert (string? str))
  (call-with-port (open-string-input-port str)
    (lambda (iport)
      (call-with-bytevector-output-port (lambda (oport) (base64-decode-port iport oport))))))