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+;;; longlines.el --- automatically wrap long lines
+
+;; Copyright (C) 2000, 2001, 2004, 2005 by Free Software Foundation, Inc.
+
+;; Authors:    Kai Grossjohann <Kai.Grossjohann@CS.Uni-Dortmund.DE>
+;;             Alex Schroeder <alex@gnu.org>
+;;             Chong Yidong <cyd@stupidchicken.com>
+;; Maintainer: Chong Yidong <cyd@stupidchicken.com>
+;; Keywords: convenience
+
+;; 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:
+
+;; Some text editors save text files with long lines, and they
+;; automatically break these lines at whitespace, without actually
+;; inserting any newline characters.  When doing `M-q' in Emacs, you
+;; are inserting newline characters.  Longlines mode provides a file
+;; format which wraps the long lines when reading a file and unwraps
+;; the lines when saving the file.  It can also wrap and unwrap
+;; automatically as editing takes place.
+
+;; Special thanks to Rod Smith for many useful bug reports.
+
+;;; Code:
+
+(require 'easy-mmode)
+
+(defgroup longlines nil
+  "Automatic wrapping of long lines when loading files."
+  :group 'fill)
+
+(defcustom longlines-auto-wrap t
+  "*Non-nil means long lines are automatically wrapped after each command.
+Otherwise, you can perform filling using `fill-paragraph' or
+`auto-fill-mode'.  In any case, the soft newlines will be removed
+when the file is saved to disk."
+  :group 'longlines
+  :type 'boolean)
+
+(defcustom longlines-wrap-follows-window-size nil
+  "*Non-nil means wrapping and filling happen at the edge of the window.
+Otherwise, `fill-column' is used, regardless of the window size.  This
+does not work well when the buffer is displayed in multiple windows
+with differing widths."
+  :group 'longlines
+  :type 'boolean)
+
+(defcustom longlines-show-hard-newlines nil
+  "*Non-nil means each hard newline is marked with a symbol.
+You can also enable the display temporarily, using the command
+`longlines-show-hard-newlines'"
+  :group 'longlines
+  :type 'boolean)
+
+(defcustom longlines-show-effect (propertize "|\n" 'face 'escape-glyph)
+  "*A string to display when showing hard newlines.
+This is used when `longlines-show-hard-newlines' is on."
+  :group 'longlines
+  :type 'string)
+
+;; Internal variables
+
+(defvar longlines-wrap-beg nil)
+(defvar longlines-wrap-end nil)
+(defvar longlines-wrap-point nil)
+(defvar longlines-showing nil)
+
+(make-variable-buffer-local 'longlines-wrap-beg)
+(make-variable-buffer-local 'longlines-wrap-end)
+(make-variable-buffer-local 'longlines-wrap-point)
+(make-variable-buffer-local 'longlines-showing)
+
+;; Mode
+
+;;;###autoload
+(define-minor-mode longlines-mode
+  "Toggle Long Lines mode.
+In Long Lines mode, long lines are wrapped if they extend beyond
+`fill-column'.  The soft newlines used for line wrapping will not
+show up when the text is yanked or saved to disk.
+
+If `longlines-auto-wrap' is non-nil, lines are automatically
+wrapped whenever the buffer is changed.  You can always call
+`fill-paragraph' to fill individual paragraphs.
+
+If `longlines-show-hard-newlines' is non-nil, hard newlines will
+be marked by a symbol."
+  nil " ll" nil
+  (if longlines-mode
+      ;; Turn on longlines mode
+      (progn
+        (use-hard-newlines 1 'never)
+        (set (make-local-variable 'require-final-newline) nil)
+        (add-to-list 'buffer-file-format 'longlines)
+        (add-hook 'change-major-mode-hook 'longlines-mode-off nil t)
+        (make-local-variable 'buffer-substring-filters)
+        (add-to-list 'buffer-substring-filters 'longlines-encode-string)
+        (when longlines-wrap-follows-window-size
+          (set (make-local-variable 'fill-column)
+               (- (window-width) window-min-width))
+          (add-hook 'window-configuration-change-hook
+                    'longlines-window-change-function nil t))
+        (let ((buffer-undo-list t)
+              (mod (buffer-modified-p)))
+          ;; Turning off undo is OK since (spaces + newlines) is
+          ;; conserved, except for a corner case in
+          ;; longlines-wrap-lines that we'll never encounter from here
+          (longlines-decode-region (point-min) (point-max))
+          (longlines-wrap-region (point-min) (point-max))
+          (set-buffer-modified-p mod))
+        (when (and longlines-show-hard-newlines
+                   (not longlines-showing))
+          (longlines-show-hard-newlines))
+        (when longlines-auto-wrap
+          (auto-fill-mode 0)
+          (add-hook 'after-change-functions
+                    'longlines-after-change-function nil t)
+          (add-hook 'post-command-hook
+                    'longlines-post-command-function nil t)))
+    ;; Turn off longlines mode
+    (setq buffer-file-format (delete 'longlines buffer-file-format))
+    (if longlines-showing
+        (longlines-unshow-hard-newlines))
+    (let ((buffer-undo-list t))
+      (longlines-encode-region (point-min) (point-max)))
+    (remove-hook 'change-major-mode-hook 'longlines-mode-off t)
+    (remove-hook 'before-kill-functions 'longlines-encode-region t)
+    (remove-hook 'after-change-functions 'longlines-after-change-function t)
+    (remove-hook 'post-command-hook 'longlines-post-command-function t)
+    (remove-hook 'window-configuration-change-hook
+                 'longlines-window-change-function t)
+    (kill-local-variable 'fill-column)))
+
+(defun longlines-mode-off ()
+  "Turn off longlines mode.
+This function exists to be called by `change-major-mode-hook' when the
+major mode changes."
+  (longlines-mode 0))
+
+;; Showing the effect of hard newlines in the buffer
+
+(defface longlines-visible-face
+  '((t (:background "red")))
+  "Face used to make hard newlines visible in `longlines-mode'.")
+
+(defun longlines-show-hard-newlines (&optional arg)
+  "Make hard newlines visible by adding a face.
+With optional argument ARG, make the hard newlines invisible again."
+  (interactive "P")
+  (let ((buffer-undo-list t)
+        (mod (buffer-modified-p)))
+    (if arg
+        (longlines-unshow-hard-newlines)
+      (setq longlines-showing t)
+      (longlines-show-region (point-min) (point-max)))
+    (set-buffer-modified-p mod)))
+
+(defun longlines-show-region (beg end)
+  "Make hard newlines between BEG and END visible."
+  (let* ((pmin (min beg end))
+         (pmax (max beg end))
+         (pos (text-property-any pmin pmax 'hard t)))
+    (while pos
+      (put-text-property pos (1+ pos) 'display
+                         (copy-sequence longlines-show-effect))
+      (setq pos (text-property-any (1+ pos) pmax 'hard t)))))
+
+(defun longlines-unshow-hard-newlines ()
+  "Make hard newlines invisible again."
+  (interactive)
+  (setq longlines-showing nil)
+  (let ((pos (text-property-any (point-min) (point-max) 'hard t)))
+    (while pos
+      (remove-text-properties pos (1+ pos) '(display))
+      (setq pos (text-property-any (1+ pos) (point-max) 'hard t)))))
+
+;; Wrapping the paragraphs.
+
+(defun longlines-wrap-region (beg end)
+  "Wrap each successive line, starting with the line before BEG.
+Stop when we reach lines after END that don't need wrapping, or the
+end of the buffer."
+  (setq longlines-wrap-point (point))
+  (goto-char beg)
+  (forward-line -1)
+  ;; Two successful longlines-wrap-line's in a row mean successive
+  ;; lines don't need wrapping.
+  (while (null (and (longlines-wrap-line)
+                    (or (eobp)
+                        (and (>= (point) end)
+                             (longlines-wrap-line))))))
+  (goto-char longlines-wrap-point))
+
+(defun longlines-wrap-line ()
+  "If the current line needs to be wrapped, wrap it and return nil.
+If wrapping is performed, point remains on the line.  If the line does
+not need to be wrapped, move point to the next line and return t."
+  (if (longlines-set-breakpoint)
+      (progn (backward-char 1)
+             (delete-char 1)
+             (insert-char ?\n 1)
+             nil)
+    (if (longlines-merge-lines-p)
+        (progn (end-of-line)
+               (delete-char 1)
+     ;; After certain commands (e.g. kill-line), there may be two
+     ;; successive soft newlines in the buffer.  In this case, we
+     ;; replace these two newlines by a single space.  Unfortunately,
+     ;; this breaks the conservation of (spaces + newlines), so we
+     ;; have to fiddle with longlines-wrap-point.
+               (if (or (bolp) (eolp))
+                   (if (> longlines-wrap-point (point))
+                       (setq longlines-wrap-point
+                             (1- longlines-wrap-point)))
+                 (insert-char ?  1))
+               nil)
+      (forward-line 1)
+      t)))
+
+(defun longlines-set-breakpoint ()
+  "Place point where we should break the current line, and return t.
+If the line should not be broken, return nil; point remains on the
+line."
+  (move-to-column fill-column)
+  (if (and (re-search-forward "[^ ]" (line-end-position) 1)
+           (> (current-column) fill-column))
+      ;; This line is too long.  Can we break it?
+      (or (longlines-find-break-backward)
+          (progn (move-to-column fill-column)
+                 (longlines-find-break-forward)))))
+
+(defun longlines-find-break-backward ()
+  "Move point backward to the first available breakpoint and return t.
+If no breakpoint is found, return nil."
+  (and (search-backward " " (line-beginning-position) 1)
+       (save-excursion
+         (skip-chars-backward " " (line-beginning-position))
+         (null (bolp)))
+       (progn (forward-char 1)
+              (if (and fill-nobreak-predicate
+                       (run-hook-with-args-until-success
+                        'fill-nobreak-predicate))
+                  (progn (skip-chars-backward " " (line-beginning-position))
+                         (longlines-find-break-backward))
+                t))))
+
+(defun longlines-find-break-forward ()
+  "Move point forward to the first available breakpoint and return t.
+If no break point is found, return nil."
+  (and (search-forward " " (line-end-position) 1)
+       (progn (skip-chars-forward " " (line-end-position))
+              (null (eolp)))
+       (if (and fill-nobreak-predicate
+                (run-hook-with-args-until-success
+                 'fill-nobreak-predicate))
+           (longlines-find-break-forward)
+         t)))
+
+(defun longlines-merge-lines-p ()
+  "Return t if part of the next line can fit onto the current line.
+Otherwise, return nil.  Text cannot be moved across hard newlines."
+  (save-excursion
+    (end-of-line)
+    (and (null (eobp))
+         (null (get-text-property (point) 'hard))
+         (let ((space (- fill-column (current-column))))
+           (forward-line 1)
+           (if (eq (char-after) ? )
+               t ; We can always merge some spaces
+             (<= (if (search-forward " " (line-end-position) 1)
+                     (current-column)
+                   (1+ (current-column)))
+                 space))))))
+
+(defun longlines-decode-region (beg end)
+  "Turn all newlines between BEG and END into hard newlines."
+  (save-excursion
+    (goto-char (min beg end))
+    (while (search-forward "\n" (max beg end) t)
+      (set-hard-newline-properties
+       (match-beginning 0) (match-end 0)))))
+
+(defun longlines-encode-region (beg end &optional buffer)
+  "Replace each soft newline between BEG and END with exactly one space.
+Hard newlines are left intact.  The optional argument BUFFER exists for
+compatibility with `format-alist', and is ignored."
+  (save-excursion
+    (let ((mod (buffer-modified-p)))
+      (goto-char (min beg end))
+      (while (search-forward "\n" (max (max beg end)) t)
+        (unless (get-text-property (match-beginning 0) 'hard)
+          (replace-match " ")))
+      (set-buffer-modified-p mod)
+      end)))
+
+(defun longlines-encode-string (string)
+  "Return a copy of STRING with each soft newline replaced by a space.
+Hard newlines are left intact."
+  (let* ((str (copy-sequence string))
+         (pos (string-match "\n" str)))
+    (while pos
+      (if (null (get-text-property pos 'hard str))
+          (aset str pos ? ))
+      (setq pos (string-match "\n" str (1+ pos))))
+    str))
+
+;; Auto wrap
+
+(defun longlines-auto-wrap (&optional arg)
+  "Turn on automatic line wrapping, and wrap the entire buffer.
+With optional argument ARG, turn off line wrapping."
+  (interactive "P")
+  (remove-hook 'after-change-functions 'longlines-after-change-function t)
+  (remove-hook 'post-command-hook 'longlines-post-command-function t)
+  (if arg
+      (progn (setq longlines-auto-wrap nil)
+             (message "Auto wrap disabled."))
+    (setq longlines-auto-wrap t)
+    (add-hook 'after-change-functions
+              'longlines-after-change-function nil t)
+    (add-hook 'post-command-hook
+              'longlines-post-command-function nil t)
+    (let ((mod (buffer-modified-p)))
+      (longlines-wrap-region (point-min) (point-max))
+      (set-buffer-modified-p mod))
+    (message "Auto wrap enabled.")))
+
+(defun longlines-after-change-function (beg end len)
+  "Update `longlines-wrap-beg' and `longlines-wrap-end'.
+This is called by `after-change-functions' to keep track of the region
+that has changed."
+  (unless undo-in-progress
+    (setq longlines-wrap-beg
+          (if longlines-wrap-beg (min longlines-wrap-beg beg) beg))
+    (setq longlines-wrap-end
+          (if longlines-wrap-end (max longlines-wrap-end end) end))))
+
+(defun longlines-post-command-function ()
+  "Perform line wrapping on the parts of the buffer that have changed.
+This is called by `post-command-hook' after each command."
+  (when longlines-wrap-beg
+    (cond ((or (eq this-command 'yank)
+               (eq this-command 'yank-pop))
+           (longlines-decode-region (point) (mark t))
+           (if longlines-showing
+               (longlines-show-region (point) (mark t))))
+          ((and (eq this-command 'newline) longlines-showing)
+           (save-excursion
+             (if (search-backward "\n" nil t)
+                 (longlines-show-region
+                  (match-beginning 0) (match-end 0))))))
+    (unless (or (eq this-command 'fill-paragraph)
+                (eq this-command 'fill-region))
+      (longlines-wrap-region longlines-wrap-beg longlines-wrap-end))
+    (setq longlines-wrap-beg nil)
+    (setq longlines-wrap-end nil)))
+
+(defun longlines-window-change-function ()
+  "Re-wrap the buffer if the window width has changed.
+This is called by `window-size-change-functions'."
+  (when (/= fill-column (- (window-width) window-min-width))
+    (setq fill-column (- (window-width) window-min-width))
+    (let ((mod (buffer-modified-p)))
+      (longlines-wrap-region (point-min) (point-max))
+      (set-buffer-modified-p mod))))
+
+;; Loading and saving
+
+(add-to-list
+ 'format-alist
+ (list 'longlines "Automatically wrap long lines." nil
+       'longlines-decode-region 'longlines-encode-region t nil))
+
+(provide 'longlines)
+
+;;; longlines.el ends here