;; -*- mode: scheme; coding: utf-8 -*-
;;
;; This module was renamed from (weinholt text base64 (1 0 20100612)) to
;; (guix base64) by Nikita Karetnikov <nikita@karetnikov.org> on
;; February 12, 2014.
;;
;; Copyright © 2009, 2010 Göran Weinholt <goran@weinholt.se>
;;
;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;;
;; This program 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 General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
#!r6rs

;; RFC 4648 Base-N Encodings

(library (guix base64)
  (export base64-encode
          base64-decode
          base64-alphabet
          base64url-alphabet
          get-delimited-base64
          put-delimited-base64)
  (import (rnrs)
          (only (srfi :13 strings)
                string-index
                string-prefix? string-suffix?
                string-concatenate string-trim-both))

  (define base64-alphabet
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")

  (define base64url-alphabet
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_")

  (define base64-encode
    (case-lambda
      ;; Simple interface. Returns a string containing the canonical
      ;; base64 representation of the given bytevector.
      ((bv)
       (base64-encode bv 0 (bytevector-length bv) #f #f base64-alphabet #f))
      ((bv start)
       (base64-encode bv start (bytevector-length bv) #f #f base64-alphabet #f))
      ((bv start end)
       (base64-encode bv start end #f #f base64-alphabet #f))
      ((bv start end line-length)
       (base64-encode bv start end line-length #f base64-alphabet #f))
      ((bv start end line-length no-padding)
       (base64-encode bv start end line-length no-padding base64-alphabet #f))
      ((bv start end line-length no-padding alphabet)
       (base64-encode bv start end line-length no-padding alphabet #f))
      ;; Base64 encodes the bytes [start,end[ in the given bytevector.
      ;; Lines are limited to line-length characters (unless #f),
      ;; which must be a multiple of four. To omit the padding
      ;; characters (#\=) set no-padding to a true value. If port is
      ;; #f, returns a string.
      ((bv start end line-length no-padding alphabet port)
       (assert (or (not line-length) (zero? (mod line-length 4))))
       (let-values (((p extract) (if port
                                     (values port (lambda () (values)))
                                     (open-string-output-port))))
         (letrec ((put (if line-length
                           (let ((chars 0))
                             (lambda (p c)
                               (when (fx=? chars line-length)
                                 (set! chars 0)
                                 (put-char p #\linefeed))
                               (set! chars (fx+ chars 1))
                               (put-char p c)))
                           put-char)))
           (let lp ((i start))
             (cond ((= i end))
                   ((<= (+ i 3) end)
                    (let ((x (bytevector-uint-ref bv i (endianness big) 3)))
                      (put p (string-ref alphabet (fxbit-field x 18 24)))
                      (put p (string-ref alphabet (fxbit-field x 12 18)))
                      (put p (string-ref alphabet (fxbit-field x 6 12)))
                      (put p (string-ref alphabet (fxbit-field x 0 6)))
                      (lp (+ i 3))))
                   ((<= (+ i 2) end)
                    (let ((x (fxarithmetic-shift-left (bytevector-u16-ref bv i (endianness big)) 8)))
                      (put p (string-ref alphabet (fxbit-field x 18 24)))
                      (put p (string-ref alphabet (fxbit-field x 12 18)))
                      (put p (string-ref alphabet (fxbit-field x 6 12)))
                      (unless no-padding
                        (put p #\=))))
                   (else
                    (let ((x (fxarithmetic-shift-left (bytevector-u8-ref bv i) 16)))
                      (put p (string-ref alphabet (fxbit-field x 18 24)))
                      (put p (string-ref alphabet (fxbit-field x 12 18)))
                      (unless no-padding
                        (put p #\=)
                        (put p #\=)))))))
         (extract)))))

  ;; Decodes a base64 string. The string must contain only pure
  ;; unpadded base64 data.
  (define base64-decode
    (case-lambda
      ((str)
       (base64-decode str base64-alphabet #f))
      ((str alphabet)
       (base64-decode str alphabet #f))
      ((str alphabet port)
       (unless (zero? (mod (string-length str) 4))
         (error 'base64-decode
                "input string must be a multiple of four characters"))
       (let-values (((p extract) (if port
                                     (values port (lambda () (values)))
                                     (open-bytevector-output-port))))
         (do ((i 0 (+ i 4)))
             ((= i (string-length str))
              (extract))
           (let ((c1 (string-ref str i))
                 (c2 (string-ref str (+ i 1)))
                 (c3 (string-ref str (+ i 2)))
                 (c4 (string-ref str (+ i 3))))
             ;; TODO: be more clever than string-index
             (let ((i1 (string-index alphabet c1))
                   (i2 (string-index alphabet c2))
                   (i3 (string-index alphabet c3))
                   (i4 (string-index alphabet c4)))
               (cond ((and i1 i2 i3 i4)
                      (let ((x (fxior (fxarithmetic-shift-left i1 18)
                                      (fxarithmetic-shift-left i2 12)
                                      (fxarithmetic-shift-left i3 6)
                                      i4)))
                        (put-u8 p (fxbit-field x 16 24))
                        (put-u8 p (fxbit-field x 8 16))
                        (put-u8 p (fxbit-field x 0 8))))
                     ((and i1 i2 i3 (char=? c4 #\=)
                           (= i (- (string-length str) 4)))
                      (let ((x (fxior (fxarithmetic-shift-left i1 18)
                                      (fxarithmetic-shift-left i2 12)
                                      (fxarithmetic-shift-left i3 6))))
                        (put-u8 p (fxbit-field x 16 24))
                        (put-u8 p (fxbit-field x 8 16))))
                     ((and i1 i2 (char=? c3 #\=) (char=? c4 #\=)
                           (= i (- (string-length str) 4)))
                      (let ((x (fxior (fxarithmetic-shift-left i1 18)
                                      (fxarithmetic-shift-left i2 12))))
                        (put-u8 p (fxbit-field x 16 24))))
                     (else
                      (error 'base64-decode "invalid input"
                             (list c1 c2 c3 c4)))))))))))

  (define (get-line-comp f port)
    (if (port-eof? port)
        (eof-object)
        (f (get-line port))))

  ;; Reads the common -----BEGIN/END type----- delimited format from
  ;; the given port. Returns two values: a string with the type and a
  ;; bytevector containing the base64 decoded data. The second value
  ;; is the eof object if there is an eof before the BEGIN delimiter.
  (define (get-delimited-base64 port)
    (define (get-first-data-line port)
      ;; Some MIME data has header fields in the same format as mail
      ;; or http. These are ignored.
      (let ((line (get-line-comp string-trim-both port)))
        (cond ((eof-object? line) line)
              ((string-index line #\:)
               (let lp ()               ;read until empty line
                 (let ((line (get-line-comp string-trim-both port)))
                   (if (string=? line "")
                       (get-line-comp string-trim-both port)
                       (lp)))))
              (else line))))
    (let ((line (get-line-comp string-trim-both port)))
      (cond ((eof-object? line)
             (values "" (eof-object)))
            ((string=? line "")
             (get-delimited-base64 port))
            ((and (string-prefix? "-----BEGIN " line)
                  (string-suffix? "-----" line))
             (let* ((type (substring line 11 (- (string-length line) 5)))
                    (endline (string-append "-----END " type "-----")))
               (let-values (((outp extract) (open-bytevector-output-port)))
                 (let lp ((line (get-first-data-line port)))
                   (cond ((eof-object? line)
                          (error 'get-delimited-base64
                                 "unexpected end of file"))
                         ((string-prefix? "-" line)
                          (unless (string=? line endline)
                            (error 'get-delimited-base64
                                   "bad end delimiter" type line))
                          (values type (extract)))
                         (else
                          (unless (and (= (string-length line) 5)
                                       (string-prefix? "=" line)) ;Skip Radix-64 checksum
                            (base64-decode line base64-alphabet outp))
                          (lp (get-line-comp string-trim-both port))))))))
            (else ;skip garbage (like in openssl x509 -in foo -text output).
             (get-delimited-base64 port)))))

  (define put-delimited-base64
    (case-lambda
      ((port type bv line-length)
       (display (string-append "-----BEGIN " type "-----\n") port)
       (base64-encode bv 0 (bytevector-length bv)
                      line-length #f base64-alphabet port)
       (display (string-append "\n-----END " type "-----\n") port))
      ((port type bv)
       (put-delimited-base64 port type bv 76)))))