;;; undigest.el --- digest-cracking support for the RMAIL mail reader  -*- lexical-binding:t -*-

;; Copyright (C) 1985-1986, 1994, 1996, 2001-2025 Free Software
;; Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; Keywords: mail

;; This file is part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; See Internet RFC 934 and RFC 1153.
;; Also limited support for MIME digest encapsulation.

;;; Code:

(eval-when-compile (require 'cl-lib))
(require 'rmail)

(defcustom rmail-forward-separator-regex
  "^----.*\\([Ff]orwarded\\|[Oo]riginal\\).*[Mm]essage"
  "Regexp to match the string that introduces forwarded messages.
This is not a header, but a string contained in the body of the message.
You may need to customize it for local needs."
  :type 'regexp
  :group 'rmail-headers)


(defconst rmail-digest-methods
  '(rmail-digest-parse-mixed-mime
    rmail-digest-parse-mime
    rmail-digest-parse-rfc1153strict
    rmail-digest-parse-rfc1153sloppy
    rmail-digest-parse-rfc934)
  "List of digest parsing functions, first tried first.

These functions operate on the current narrowing, and take no argument.
A function returns nil if it cannot parse the digest.  If it can, it
returns a list of cons pairs containing the start and end positions of
each undigestified message as markers.")

(defun rmail-content-type-boundary (type)
  "If Content-type is of type TYPE, return its boundary; otherwise, return nil."
  (goto-char (point-min))
  (let ((head-end (save-excursion (search-forward "\n\n" nil t) (point))))
    (when (re-search-forward
           (concat "^Content-type: " type ";"
                   "\\s-* boundary=\"?\\([^\";\n]+\\)[\";\n]")
           head-end t)
      (match-string 1))))

(defun rmail-digest-parse-mixed-mime ()
  "Like `rmail-digest-parse-mime', but for multipart/mixed messages."
  (when-let ((boundary (rmail-content-type-boundary "multipart/mixed")))
    (let ((global-sep (concat "\n--" boundary))
          (digest (concat "^Content-type: multipart/digest;"
                          "\\s-* boundary=\"?\\([^\";\n]+\\)[\";\n]"))
          result)
      (search-forward global-sep nil t)
      (while (not (or result (eobp)))
        ;; For each part, see if it is a multipart/digest.
        (let* ((limit (save-excursion (search-forward global-sep nil 'move)
                                      (point)))
               (beg (and (re-search-forward digest limit t)
                         (match-beginning 0)))
               digest-sep)
          (when (and beg
                     (setq digest-sep (concat "\n--" (match-string 1)))
                     ;; Search for 1st sep.
                     (search-forward digest-sep nil t))
            ;; Skip body part headers.
            (search-forward "\n\n" nil t)
            ;; Push the 1st message.
            (push (cons (copy-marker beg) (copy-marker (point-marker) t))
                  result)
            ;; Push the rest of the messages.
            (let ((start (make-marker))
                  done)
              (while (and (search-forward digest-sep limit 'move) (not done))
                (move-marker start (match-beginning 0))
                (and (looking-at "--$") (setq done t))
                (search-forward "\n\n")
                (push (cons (copy-marker start)
                            (copy-marker (point-marker) t))
                      result))))
          (goto-char limit)))
      (nreverse result))))

(defun rmail-digest-parse-mime ()
  (goto-char (point-min))
  (when (let ((head-end (progn (search-forward "\n\n" nil t) (point))))
	  (goto-char (point-min))
	  (and head-end			; FIXME always true
	       (re-search-forward
		(concat
		 "^Content-type: multipart/digest;"
		 "\\s-* boundary=\"?\\([^\";\n]+\\)[\";\n]")
                head-end t)
	       (search-forward (match-string 1) nil t)))
    ;; Ok, prolog separator found
    (let ((start (make-marker))
	  (end (make-marker))
	  (separator (concat "\n--" (match-string 0) "\n\n"))
	  result)
      (while (search-forward separator nil t)
	(move-marker start (match-beginning 0))
	(move-marker end (match-end 0))
	(cl-pushnew (cons (copy-marker start) (copy-marker end t))
                    result :test #'equal))
      ;; Return the list of marker pairs
      (nreverse result))))

(defun rmail-digest-parse-rfc1153strict ()
  "Parse following strictly the method defined in RFC 1153.
See rmail-digest-methods."
 (rmail-digest-rfc1153
  "^-\\{70\\}\n\n"
  "^\n-\\{30\\}\n\n"
  "^\n-\\{30\\}\n\nEnd of .* Digest.*\n\\*\\{15,\\}\n+\\'"))

(defun rmail-digest-parse-rfc1153sloppy ()
  "Parse using the method defined in RFC 1153, allowing for some sloppiness.
See rmail-digest-methods."
 (rmail-digest-rfc1153
  "^-\\{55,\\}\n\n"
  "^\n-\\{27,\\}\n\n"
  ;; GNU Mailman knowingly (see comment at line 353 of ToDigest.py in
  ;; Mailman source) produces non-conformant rfc 1153 digests, in that
  ;; the trailer contains a "digest footer" like this:
  ;; _______________________________________________
  ;; <one or more lines of list blurb>
  ;;
  ;; End of Foo Digest...
  ;; **************************************
  "^\nEnd of"))

(defun rmail-digest-rfc1153 (prolog-sep message-sep trailer-sep)
  (goto-char (point-min))
  (when (re-search-forward prolog-sep nil t)
    ;; Ok, prolog separator found
    (let ((start (make-marker))
	  (end (make-marker))
	  separator result)
      (move-marker start (match-beginning 0))
      (move-marker end (match-end 0))
      (setq result (list (cons (copy-marker start) (copy-marker end t))))
      (when (re-search-forward message-sep nil t)
	;; Ok, at least one message separator found
	(setq separator (match-string 0))
	(when (re-search-forward trailer-sep nil t)
	  ;; Wonderful, we found a trailer, too.  Now, go on splitting
	  ;; the digest into separate rmail messages
	  (goto-char (cdar result))
	  (while (search-forward separator nil t)
	    (move-marker start (match-beginning 0))
	    (move-marker end (match-end 0))
	    (cl-pushnew (cons (copy-marker start) (copy-marker end t))
                        result :test #'equal))
	  ;; Undo masking of separators inside digestified messages
	  (goto-char (point-min))
	  (while (search-forward
		  (string-replace "\n-" "\n " separator) nil t)
	    (replace-match separator))
	  ;; Return the list of marker pairs
	  (nreverse result))))))

(defun rmail-digest-parse-rfc934 ()
  (goto-char (point-min))
  (when (re-search-forward "^\n?-[^ ].*\n\n?" nil t)
    ;; Message separator found
    (let ((start (make-marker))
	  (end (make-marker))
	  (separator (match-string 0))
	  result)
      (goto-char (point-min))
      (while (search-forward separator nil t)
	(move-marker start (match-beginning 0))
	(move-marker end (match-end 0))
	(cl-pushnew (cons (copy-marker start) (copy-marker end t))
                    result :test #'equal))
      ;; Undo masking of separators inside digestified messages
      (goto-char (point-min))
      (while (search-forward "\n- -" nil t)
	(replace-match "\n-"))
      ;; Return the list of marker pairs
      (nreverse result))))

(declare-function rmail-update-summary "rmailsum" (&rest ignore))

;;;###autoload
(defun undigestify-rmail-message ()
  "Break up a digest message into its constituent messages.
Leaves original message, deleted, before the undigestified messages."
  (interactive)
  (set-buffer rmail-buffer)
  (let ((buff (current-buffer))
        (current rmail-current-message)
	(msgbeg (rmail-msgbeg rmail-current-message))
	(msgend (rmail-msgend rmail-current-message)))
    (if (rmail-buffers-swapped-p) (set-buffer rmail-view-buffer))
    (widen)
    (let ((error t)
	  (buffer-read-only nil))
      (goto-char msgend)
      (let ((msg-copy (buffer-substring-no-properties msgbeg msgend)))
	(narrow-to-region (point) (point))
	(insert "\n" msg-copy))
      (goto-char (point-min))
      (unwind-protect
	  (progn
	    (let ((fill-prefix "")
		  (case-fold-search t)
		  digest-name fun-list sep-list start end)
	      (setq digest-name (mail-strip-quoted-names
				 (save-restriction
				   (search-forward "\n\n" nil 'move)
				   (narrow-to-region (point-min) (point))
				   (or (mail-fetch-field "Reply-To")
				       (mail-fetch-field "To")
				       (mail-fetch-field "Apparently-To")
				       (mail-fetch-field "From")))))
	      (unless digest-name
		(error "Message is not a digest--bad header"))
	      (setq fun-list rmail-digest-methods)
	      (while (and fun-list
			  (null (setq sep-list (funcall (car fun-list)))))
		(setq fun-list (cdr fun-list)))
	      (unless sep-list
		(error "Message is not a digest--no messages found"))
	      ;; Split the digest into separate rmail messages.
	      (while sep-list
		(setq start (caar sep-list)
		      end (cdar sep-list))
		(delete-region start end)
		(goto-char start)
		(search-forward "\n\n" (caar (cdr sep-list)) 'move)
		(save-restriction
		  (narrow-to-region end (point))
		  (goto-char (point-min))
		  (insert "\nFrom rmail@localhost  " (current-time-string) "\n")
		  (save-excursion
		    (forward-line -1)
		    (rmail-add-mbox-headers))
		  (unless (mail-fetch-field "To")
		    (insert "To: " digest-name "\n")))
		(set-marker start nil)
		(set-marker end nil)
		(setq sep-list (cdr sep-list))))
	    (setq error nil)
	    (message "Message successfully undigestified")
	    (set-buffer buff)
	    (rmail-swap-buffers-maybe)
	    (goto-char (point-max))
	    ;; FIXME use rmail-count-new-messages.
	    (rmail-set-message-counters)
	    (set-buffer-modified-p t)
	    (rmail-show-message current)
	    (rmail-delete-forward)
	    (if (rmail-summary-exists)
		(rmail-select-summary (rmail-update-summary))))
	(when error
	  (delete-region (point-min) (point-max))
	  (set-buffer buff)
	  (rmail-show-message current))))))

;;;###autoload
(defun unforward-rmail-message ()
  "Extract a forwarded message from the containing message.
This puts the forwarded message into a separate rmail message following
the containing message.  This command is only useful when messages are
forwarded with `rmail-enable-mime-composing' set to nil."
  (interactive)
  (set-buffer rmail-buffer)
  (let ((buff (current-buffer))
        (current rmail-current-message)
        (beg (rmail-msgbeg rmail-current-message))
        (msgend (rmail-msgend rmail-current-message))
	(error t))
    (unwind-protect
	(progn
	  (if (rmail-buffers-swapped-p) (set-buffer rmail-view-buffer))
	  (widen)
	  (goto-char beg)
	  (search-forward "\n\n" msgend)
	  (narrow-to-region beg (point))
	  (let ((old-fwd-from (mail-fetch-field "Forwarded-From" nil nil t))
		(old-fwd-date (mail-fetch-field "Forwarded-Date" nil nil t))
		(fwd-from (mail-fetch-field "From"))
		(fwd-date (mail-fetch-field "Date"))
		(buffer-read-only nil)
		prefix forward-msg end)
	    (widen)
	    (narrow-to-region beg msgend)
	    (cond ((re-search-forward rmail-forward-separator-regex nil t)
		   (forward-line 1)
		   (skip-chars-forward "\n")
		   (setq beg (point))
		   (setq end (if (re-search-forward "^----.*[^- \t\n]" nil t)
				 (match-beginning 0) (point-max)))
		   (setq forward-msg
			 (replace-regexp-in-string
			  "^- -" "-" (buffer-substring beg end))))
		  ((and (re-search-forward "^\\(> ?\\)[a-zA-Z-]+: .*\n" nil t)
			(setq beg (match-beginning 0))
			(setq prefix (match-string-no-properties 1))
			(goto-char beg)
			(looking-at (concat "\\(" prefix ".+\n\\)*"
					    prefix "Date: ."))
			(looking-at (concat "\\(" prefix ".+\n\\)*"
					    prefix "From: .+\n"
					    "\\(" prefix ".+\n\\)*"
					    "\\(> ?\\)?\n" prefix)))
		   (re-search-forward "^[^>\n]" nil 'move)
		   (backward-char)
		   (skip-chars-backward " \t\n")
		   (forward-line 1)
		   (setq end (point))
		   (setq forward-msg
			 (replace-regexp-in-string
			  (if (string= prefix ">") "^>" "> ?")
			  "" (buffer-substring beg end))))
		  (t
		   (error "No forwarded message found")))
	    (widen)
	    (goto-char msgend)
	    ;; Insert a fake From line.
	    ;; FIXME we could construct one using the From and Date headers
	    ;; of the forwarded message - is it worth it?
	    (insert "\n\nFrom rmail@localhost  " (current-time-string) "\n")
	    (setq beg (point))		; start of header
	    (while old-fwd-from
	      (insert "Forwarded-From: " (car old-fwd-from) "\n")
	      (insert "Forwarded-Date: " (car old-fwd-date) "\n")
	      (setq old-fwd-from (cdr old-fwd-from))
	      (setq old-fwd-date (cdr old-fwd-date)))
	    (insert "Forwarded-From: " fwd-from "\n")
	    (insert "Forwarded-Date: " fwd-date "\n")
	    (insert forward-msg "\n")
	    (goto-char beg)
	    (re-search-forward "\n$" nil 'move) ; end of header
	    (narrow-to-region beg (point))
	    (goto-char (point-min))
	    (while (not (eobp))
	      (unless (looking-at "^[a-zA-Z-]+: ")
		(insert "\t"))
	      (forward-line))
	    (widen)
	    (goto-char beg)
	    (forward-line -1)
	    (rmail-add-mbox-headers))		; marks as unseen
	  (setq error nil)
	  (set-buffer buff)
	  (rmail-swap-buffers-maybe)
	  (goto-char (point-max))
	  ;; FIXME use rmail-count-new-messages.
	  (rmail-set-message-counters)
	  (set-buffer-modified-p t)
	  (rmail-show-message current)
	  (if (rmail-summary-exists)
	      (rmail-select-summary (rmail-update-summary))))
      (when error
	(set-buffer buff)
	(rmail-show-message current)))))

(provide 'undigest)

;;; undigest.el ends here
