;;; guile-email --- Guile email parser
;;; Copyright © 2018, 2020 Arun Isaac <arunisaac@systemreboot.net>
;;; Copyright © 2023 Andrew Whatson <whatson@tailcall.au>
;;;
;;; 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 bytevectors)
  #:use-module (rnrs io ports)
  #: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))
     (call-with-bytevector-output-port
      (cut quoted-printable-decode in <>)))
    (((? port? in) (? port? out))
     (let ((c (read-char in)))
       (cond
        ((eof-object? c) out)
        ((char=? c #\=)
         (let ((c1 (read-char in)))
           ;; Skip if \n was read.
           (unless (char=? c1 #\Newline)
             (let ((c2 (read-char in)))
               ;; Skip if \r\n was read.
               (unless (and (char=? c1 #\Return)
                            (char=? c2 #\Newline))
                 (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-style-encode
          in out literal-char-set
          #:optional (number-of-chars-left-on-this-line 76))
  (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-style-encode
         in out literal-char-set
         (put-into-output
          (if (char-set-contains? literal-char-set c)
              (string c)
              (format #f "=~:@(~2,'0x~)" x))))))))

;; Character set of characters to be represented by themselves in
;; quoted-printable encoding
(define %quoted-printable-literal-char-set
  (char-set-delete
   (ucs-range->char-set (char->integer #\space)
                        (char->integer #\delete))
   #\=))

;; Character set of characters to be represented by themselves in Q
;; encoding
(define %q-encoding-literal-char-set
  (char-set-delete
   %quoted-printable-literal-char-set
   #\? #\_))

(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-style-encode
      in out %quoted-printable-literal-char-set))))

(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))
   (call-with-port (open-bytevector-input-port bv)
     (lambda (in)
       (call-with-output-string
         (cut quoted-printable-style-encode in <>
              %q-encoding-literal-char-set))))))