;;; flow-fill.el --- interpret RFC2646 "flowed" text

;; Copyright (C) 2000, 2001, 2002, 2003 Free Software Foundation, Inc.

;; Author: Simon Josefsson <jas@pdc.kth.se>
;; 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 2, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; This implement decoding of RFC2646 formatted text, including the
;; quoted-depth wins rules.

;; Theory of operation: search for lines ending with SPC, save quote
;; length of line, remove SPC and concatenate line with the following
;; line if quote length of following line matches current line.

;; When no further concatenations are possible, we've found a
;; paragraph and we let `fill-region' fill the long line into several
;; lines with the quote prefix as `fill-prefix'.

;; Todo: implement basic `fill-region' (Emacs and XEmacs
;;       implementations differ..)

;;; History:

;; 2000-02-17  posted on ding mailing list
;; 2000-02-19  use `point-at-{b,e}ol' in XEmacs
;; 2000-03-11  no compile warnings for point-at-bol stuff
;; 2000-03-26  committed to gnus cvs
;; 2000-10-23  don't flow "-- " lines, make "quote-depth wins" rule
;;             work when first line is at level 0.
;; 2002-01-12  probably incomplete encoding support
;; 2003-12-08  started working on test harness.

;;; Code:

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

(defcustom fill-flowed-display-column 'fill-column
  "Column beyond which format=flowed lines are wrapped, when displayed.
This can be a Lisp expression or an integer."
  :type '(choice (const :tag "Standard `fill-column'" fill-column)
		 (const :tag "Fit Window" (- (window-width) 5))
		 (sexp)
		 (integer)))

(defcustom fill-flowed-encode-column 66
  "Column beyond which format=flowed lines are wrapped, in outgoing messages.
This can be a Lisp expression or an integer.
RFC 2646 suggests 66 characters for readability."
  :type '(choice (const :tag "Standard fill-column" fill-column)
		 (const :tag "RFC 2646 default (66)" 66)
		 (sexp)
		 (integer)))

;;;###autoload
(defun fill-flowed-encode (&optional buffer)
  (with-current-buffer (or buffer (current-buffer))
    ;; No point in doing this unless hard newlines is used.
    (when use-hard-newlines
      (let ((start (point-min)) end)
	;; Go through each paragraph, filling it and adding SPC
	;; as the last character on each line.
	(while (setq end (text-property-any start (point-max) 'hard 't))
	  (let ((fill-column (eval fill-flowed-encode-column)))
	    (fill-region start end t 'nosqueeze 'to-eop))
	  (goto-char start)
	  ;; `fill-region' probably distorted end.
	  (setq end (text-property-any start (point-max) 'hard 't))
	  (while (and (< (point) end)
		      (re-search-forward "$" (1- end) t))
	    (insert " ")
	    (setq end (1+ end))
	    (forward-char))
	  (goto-char (setq start (1+ end)))))
      t)))

;;;###autoload
(defun fill-flowed (&optional buffer)
  (save-excursion
    (set-buffer (or (current-buffer) buffer))
    (goto-char (point-min))
    (while (re-search-forward " $" nil t)
      (when (save-excursion
	      (beginning-of-line)
	      (looking-at "^\\(>*\\)\\( ?\\)"))
	(let ((quote (match-string 1))
	      sig)
	  (if (string= quote "")
	      (setq quote nil))
	  (when (and quote (string= (match-string 2) ""))
	    (save-excursion
	      ;; insert SP after quote for pleasant reading of quoted lines
	      (beginning-of-line)
	      (when (> (skip-chars-forward ">") 0)
		(insert " "))))
	  ;; XXX slightly buggy handling of "-- "
	  (while (and (save-excursion
			(ignore-errors (backward-char 3))
			(setq sig (looking-at "-- "))
			(looking-at "[^-][^-] "))
		      (save-excursion
			(unless (eobp)
			  (forward-char 1)
			  (looking-at (format "^\\(%s\\)\\([^>\n\r]\\)"
					      (or quote " ?"))))))
	    (save-excursion
	      (replace-match (if (string= (match-string 2) " ")
				 "" "\\2")))
	    (backward-delete-char -1)
	    (end-of-line))
	  (unless sig
	    (condition-case nil
		(let ((fill-prefix (when quote (concat quote " ")))
		      (fill-column (eval fill-flowed-display-column))
		      filladapt-mode)
		  (fill-region (point-at-bol)
			       (min (1+ (point-at-eol))
				    (point-max))
			       'left 'nosqueeze))
	      (error
	       (forward-line 1)
	       nil))))))))

;; Test vectors.

(eval-when-compile
  (defvar show-trailing-whitespace))

(defvar fill-flowed-encode-tests
  '(
    ;; The syntax of each list element is:
    ;; (INPUT . EXPECTED-OUTPUT)
    ("> Thou villainous ill-breeding spongy dizzy-eyed 
> reeky elf-skinned pigeon-egg! 
>> Thou artless swag-bellied milk-livered 
>> dismal-dreaming idle-headed scut!
>>> Thou errant folly-fallen spleeny reeling-ripe 
>>> unmuzzled ratsbane!
>>>> Henceforth, the coding style is to be strictly 
>>>> enforced, including the use of only upper case.
>>>>> I've noticed a lack of adherence to the coding 
>>>>> styles, of late.
>>>>>> Any complaints?
" . "> Thou villainous ill-breeding spongy dizzy-eyed reeky elf-skinned
> pigeon-egg! 
>> Thou artless swag-bellied milk-livered dismal-dreaming idle-headed
>> scut!
>>> Thou errant folly-fallen spleeny reeling-ripe unmuzzled ratsbane!
>>>> Henceforth, the coding style is to be strictly enforced,
>>>> including the use of only upper case.
>>>>> I've noticed a lack of adherence to the coding styles, of late.
>>>>>> Any complaints?
")
;    ("
;> foo
;> 
;> 
;> bar
;" . "
;> foo bar
;")
    ))

(defun fill-flowed-test ()
  (interactive "")
  (switch-to-buffer (get-buffer-create "*Format=Flowed test output*"))
  (erase-buffer)
  (setq show-trailing-whitespace t)
  (dolist (test fill-flowed-encode-tests)
    (let (start output)
      (insert "***** BEGIN TEST INPUT *****\n")
      (insert (car test))
      (insert "***** END TEST INPUT *****\n\n")
      (insert "***** BEGIN TEST OUTPUT *****\n")
      (setq start (point))
      (insert (car test))
      (save-restriction
	(narrow-to-region start (point))
	(fill-flowed))
      (setq output (buffer-substring start (point-max)))
      (insert "***** END TEST OUTPUT *****\n")
      (unless (string= output (cdr test))
	(insert "\n***** BEGIN TEST EXPECTED OUTPUT *****\n")
	(insert (cdr test))
	(insert "***** END TEST EXPECTED OUTPUT *****\n"))
      (insert "\n\n")))
  (goto-char (point-max)))

(provide 'flow-fill)

;;; arch-tag: addc0040-bc53-4f17-b4bc-1eb44eed6f0b
;;; flow-fill.el ends here