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;;; guile-email --- Guile email parser
;;; Copyright © 2018 Arun Isaac <arunisaac@systemreboot.net>
;;;
;;; This file is part of guile-email.
;;;
;;; guile-email is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU Affero General Public License as
;;; published by the Free Software Foundation; either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; guile-email 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
;;; Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public
;;; License along with guile-email.  If not, see
;;; <http://www.gnu.org/licenses/>.

(define-module (email quoted-printable)
  #:use-module (rnrs)
  #:use-module (ice-9 format)
  #:use-module (ice-9 match)
  #:use-module (srfi srfi-26)
  #:export (quoted-printable-decode
            quoted-printable-encode
            q-encoding-decode
            q-encoding-encode))

;; TODO: Error out on invalid quoted-printable input
(define quoted-printable-decode
  (match-lambda*
    (((? string? str))
     (call-with-input-string str quoted-printable-decode))
    (((? port? in))
     (let-values (((out get-bytevector)
                   (open-bytevector-output-port)))
       (call-with-port
        out (lambda (out)
              (quoted-printable-decode in out)
              (get-bytevector)))))
    (((? port? in) (? port? out))
     (let ((c (read-char in)))
       (cond
        ((eof-object? c) out)
        ((char=? c #\=)
         ;; TODO: Support "\r\n" line ending
         (let ((c1 (read-char in)))
           (unless (char=? c1 #\Newline)
             (let ((c2 (read-char in)))
               (put-u8 out (string->number (string c1 c2) 16)))))
         (quoted-printable-decode in out))
        (else (put-u8 out (char->integer c))
              (quoted-printable-decode in out)))))))

(define quoted-printable-encode
  (match-lambda*
    (((? bytevector? bv))
     (call-with-port (open-bytevector-input-port bv)
                     quoted-printable-encode))
    (((? port? in))
     (call-with-output-string
       (cut quoted-printable-encode in <>)))
    (((? port? in) (? port? out))
     (quoted-printable-encode in out 76))
    (((? port? in) (? port? out) (? integer? number-of-chars-left-on-this-line))
     (let ((x (get-u8 in))
           (put-into-output
            (lambda (str)
              (let* ((len (string-length str))
                     (break-line? (<= number-of-chars-left-on-this-line len)))
                (put-string
                 out (string-append (if break-line? "=\n" "") str))
                (if break-line?
                    (- 76 len)
                    (- number-of-chars-left-on-this-line len))))))
       (unless (eof-object? x)
         (let ((c (integer->char x)))
           (quoted-printable-encode
            in out
            (put-into-output
             (if (char-set-contains?
                  (char-set-delete
                   (ucs-range->char-set (char->integer #\space)
                                        (char->integer #\delete))
                   #\=)
                  c)
                 (string c)
                 (format #f "=~:@(~2,'0x~)" x))))))))))

(define (q-encoding-decode str)
  (quoted-printable-decode
   (string-map
    (lambda (c)
      (if (char=? c #\_) #\Space c))
    str)))

(define (q-encoding-encode bv)
  (string-map
   (lambda (c)
     (if (char=? c #\Space) #\_ c))
   (quoted-printable-encode bv)))