;;; unrmail.el --- convert Rmail Babyl files to mbox files  -*- lexical-binding: t; -*-

;; Copyright (C) 1992, 2001-2021 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:

;;; Code:

;;;###autoload
(defun batch-unrmail ()
  "Convert old-style Rmail Babyl files to mbox format.
Specify the input Rmail Babyl file names as command line arguments.
For each Rmail file, the corresponding output file name
is made by adding `.mail' at the end.
For example, invoke `emacs -batch -f batch-unrmail RMAIL'."
  (if (not noninteractive)
      (error "`batch-unrmail' is to be used only with -batch"))
  (let ((error nil))
    (while command-line-args-left
      (or (unrmail (car command-line-args-left)
		   (concat (car command-line-args-left) ".mail"))
	  (setq error t))
      (setq command-line-args-left (cdr command-line-args-left)))
    (message "Done")
    (kill-emacs (if error 1 0))))

(declare-function mail-mbox-from "mail-utils" ())
(defvar rmime-magic-string)		; in rmime.el, if you have it

(defcustom unrmail-mbox-format 'mboxrd
  "The mbox format that `unrmail' should produce.
These formats separate messages using lines that start with \"From \".
Therefore any lines in the message bodies that start with \"From \"
must be quoted.  The `mboxo' format just prepends a \">\" to such lines.
This is not reversible, because given a line starting with \">From \" in
an mboxo file, it is not possible to know whether the original had a \">\"
or not.  The `mboxrd' format avoids this by also quoting \">From \" as
\">>From \", and so on.  For this reason, mboxrd is recommended.

See also `rmail-mbox-format'."
  :type '(choice (const mboxrd)
		 (const mboxo))
  :version "24.4"
  :group 'rmail-files)

;;;###autoload
(defun unrmail (file to-file)
  "Convert old-style Rmail Babyl file FILE to mbox format file TO-FILE.
The variable `unrmail-mbox-format' controls which mbox format to use."
  (interactive "fUnrmail (babyl file): \nFUnrmail into (new mailbox file): ")
  (with-temp-buffer
    ;; Read in the old Rmail file with no decoding.
    (let ((coding-system-for-read 'raw-text))
      (insert-file-contents file))
    ;; But make it multibyte.
    (set-buffer-multibyte t)
    (setq buffer-file-coding-system 'raw-text-unix)

    (if (not (looking-at "BABYL OPTIONS"))
	(error "This file is not in Babyl format"))

    ;; Decode the file contents just as Rmail did.
    (let ((coding-system rmail-file-coding-system)
	  from to)
      (goto-char (point-min))
      (search-forward "\n\^_" nil t)	; Skip BABYL header.
      (setq from (point))
      (goto-char (point-max))
      (search-backward "\n\^_" from 'mv)
      (if (= from (setq to (point)))
	  (error "The input file contains no messages"))
      (unless (and coding-system
		   (coding-system-p coding-system))
	(setq coding-system
	      ;; Emacs 21.1 and later writes RMAIL files in emacs-mule, but
	      ;; earlier versions did that with the current buffer's encoding.
	      ;; So we want to favor detection of emacs-mule (whose normal
	      ;; priority is quite low), but still allow detection of other
	      ;; encodings if emacs-mule won't fit.
	      (car (with-coding-priority '(emacs-mule)
		     (detect-coding-region from to)))))
      (unless (memq coding-system
		    '(undecided undecided-unix))
	(set-buffer-modified-p t)	; avoid locking when decoding
	(let ((buffer-undo-list t))
	  (decode-coding-region from to coding-system))
	(setq coding-system last-coding-system-used))

      (setq buffer-file-coding-system nil)

      ;; We currently don't use this value, but maybe we should.
      (setq save-buffer-coding-system
	    (or coding-system 'undecided)))

    ;; Default the directory of TO-FILE based on where FILE is.
    (setq to-file (expand-file-name to-file default-directory))
    (condition-case ()
	(delete-file to-file)
      (file-error nil))
    (message "Writing messages to %s..." to-file)
    (goto-char (point-min))

    (let ((temp-buffer (get-buffer-create " unrmail"))
	  (from-buffer (current-buffer)))

      ;; Process the messages one by one.
      (while (re-search-forward "^\^_\^l" nil t)
	(let ((beg (point))
	      (end (save-excursion
		     (if (re-search-forward "^\^_\\(\^l\\|\\'\\)" nil t)
			 (match-beginning 0)
		       (point-max))))
	      (coding 'raw-text)
	      label-line attrs keywords
	      mail-from reformatted)
	  (with-current-buffer temp-buffer
	    (setq buffer-undo-list t)
	    (erase-buffer)
	    (setq buffer-file-coding-system coding)
	    (insert-buffer-substring from-buffer beg end)
	    (goto-char (point-min))
	    (forward-line 1)
	    ;; Record whether the header is reformatted.
	    (setq reformatted (= (following-char) ?1))

	    ;; Collect the label line, then get the attributes
	    ;; and the keywords from it.
	    (setq label-line
		  (buffer-substring (point)
				    (save-excursion (forward-line 1)
						    (point))))
	    (re-search-forward ",, ?")
	    (unless (eolp)
	      (setq keywords
		    (buffer-substring (point)
				      (progn (end-of-line)
					     (1- (point)))))
	      ;; Mbox rmail needs the spaces.  Bug#2303.
	      ;;; (setq keywords
	      ;;; 	    (replace-regexp-in-string ", " "," keywords))
	      )

	    (setq attrs
		  (list
		   (if (string-match ", answered," label-line) ?A ?-)
		   (if (string-match ", deleted," label-line) ?D ?-)
		   (if (string-match ", edited," label-line) ?E ?-)
		   (if (string-match ", filed," label-line) ?F ?-)
		   (if (string-match ", retried," label-line) ?R ?-)
		   (if (string-match ", forwarded," label-line) ?S ?-)
		   (if (string-match ", unseen," label-line) ?U ?-)
		   (if (string-match ", resent," label-line) ?r ?-)))

	    ;; Delete the special Babyl lines at the start,
	    ;; and the ***EOOH*** line, and the reformatted header if any.
	    (goto-char (point-min))
	    (if reformatted
		(progn
		  (forward-line 2)
		  ;; Delete Summary-Line headers.
		  (let ((case-fold-search t))
		    (while (looking-at "Summary-Line:")
		      (forward-line 1)))
		  (delete-region (point-min) (point))
		  ;; Delete the old reformatted header.
		  (re-search-forward "^[*][*][*] EOOH [*][*][*]\n")
		  (forward-line -1)
		  (let ((start (point)))
		    (search-forward "\n\n")
		    (delete-region start (point))))
	      ;; Not reformatted.  Delete the special
	      ;; lines before the real header.
	      (re-search-forward "^[*][*][*] EOOH [*][*][*]\n")
	      (delete-region (point-min) (point)))

	    ;; Handle rmime formatting.
	    (when (require 'rmime nil t)
	      (let ((start (point)))
		(while (search-forward rmime-magic-string nil t))
		(delete-region start (point))))

	    ;; Some operations on the message header itself.
	    (goto-char (point-min))
	    (save-restriction
	      (narrow-to-region
	       (point-min)
	       (save-excursion (search-forward "\n\n" nil 'move) (point)))

	      ;; Fetch or construct what we should use in the `From ' line.
	      (setq mail-from (or (let ((from (mail-fetch-field "Mail-From")))
				    ;; mail-mbox-from (below) returns a
				    ;; string that ends in a newline, but
				    ;; but mail-fetch-field does not, so
				    ;; we append a newline here.
				    (if from
					(format "%s\n" from)))
				  (mail-mbox-from)))

	      ;; If the message specifies a coding system, use it.
	      (let ((maybe-coding (mail-fetch-field "X-Coding-System")))
		(if maybe-coding
		    (setq coding
			  ;; Force Unix EOLs.
			  (coding-system-change-eol-conversion
			   (intern maybe-coding) 0))
		  ;; If there's no X-Coding-System header, assume the
		  ;; message was never decoded.
		  (setq coding 'raw-text-unix)))

	      ;; Delete the Mail-From: header field if any.
	      (when (re-search-forward "^Mail-from:" nil t)
		(beginning-of-line)
		(delete-region (point)
			       (progn (forward-line 1) (point)))))

	    (goto-char (point-min))
	    ;; Insert the `From ' line.
	    (insert mail-from)
	    ;; Record the keywords and attributes in our special way.
	    (insert "X-RMAIL-ATTRIBUTES: " (apply #'string attrs) "\n")
	    (when keywords
	      (insert "X-RMAIL-KEYWORDS: " keywords "\n"))
	    ;; Convert From to >From, etc.
	    (let ((case-fold-search nil)
		  (fromline (if (eq 'mboxrd unrmail-mbox-format)
			    "^>*From "
			  "^From ")))
	      (while (re-search-forward fromline nil t)
		(beginning-of-line)
		(insert ?>)
		(forward-line 1)))
	    (goto-char (point-max))
	    ;; Add terminator blank line to message.
	    (insert "\n")
	    ;; Write it to the output file, suitably encoded.
	    (let ((coding-system-for-write coding))
	      (write-region (point-min) (point-max) to-file t
			    'nomsg)))))
      (kill-buffer temp-buffer))
    (message "Writing messages to %s...done" to-file)))

(provide 'unrmail)

;;; unrmail.el ends here