undo-tree.el

;;; undo-tree.el --- Treat undo history as a tree


;; Copyright (C) 2009-2010 Toby Cubitt

;; Author: Toby Cubitt <toby-undo-tree@dr-qubit.org>
;; Version: 0.2.1
;; Keywords: undo, redo, history, tree
;; URL: http://www.dr-qubit.org/emacs.php
;; Git Repository: http://www.dr-qubit.org/git/undo-tree.git

;; This file is NOT part of 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.

;; This program 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 <http://www.gnu.org/licenses/>.


;;; Commentary:
;;
;; Emacs has a powerful undo system. Unlike the standard undo/redo system in
;; most software, it allows you to recover *any* past state of a buffer
;; (whereas the standard undo/redo system can lose past states as soon as you
;; redo). However, this power comes at a price: many people find Emacs' undo
;; system confusing and difficult to use, spawning a number of packages that
;; replace it with the less powerful but more intuitive undo/redo system.
;;
;; Both the loss of data with standard undo/redo, and the confusion of Emacs'
;; undo, stem from trying to treat undo history as a linear sequence of
;; changes. It's not. The `undo-tree-mode' provided by this package replaces
;; Emacs' undo system with a system that treats undo history as what it is: a
;; branching tree of changes. This simple idea allows the more intuitive
;; behaviour of the standard undo/redo system to be combined with the power of
;; never losing any history. An added side bonus is that undo history can in
;; some cases be stored more efficiently, allowing more changes to accumulate
;; before Emacs starts discarding history.
;;
;; The only downside to this more advanced yet simpler undo system is that it
;; was inspired by Vim. But, after all, most successful religions steal the
;; best ideas from their competitors!
;;
;;
;; Installation
;; ============
;;
;; This package has only been tested with Emacs versions 22, 23 and CVS. It
;; will not work without modifications in earlier versions of Emacs.
;;
;; To install `undo-tree-mode', make sure this file is saved in a directory in
;; your `load-path', and add the line:
;;
;;   (require 'undo-tree)
;;
;; to your .emacs file. Byte-compiling undo-tree.el is recommended (e.g. using
;; "M-x byte-compile-file" from within emacs).
;;
;; If you want to replace the standard Emacs' undo system with the
;; `undo-tree-mode' system in all buffers, you can enable it globally by
;; adding:
;;
;;   (global-undo-tree-mode)
;;
;; to your .emacs file.
;;
;;
;; Quick-Start
;; ===========
;;
;; If you're the kind of person who likes jump in the car and drive, without
;; bothering to first figure out whether the button on the left dips the
;; headlights or operates the ejector seat (after all, you'll soon figure it
;; out when you push it), then here's the minimum you need to know:
;;
;; `undo-tree-mode' and `global-undo-tree-mode'
;;   Enable undo-tree mode (either in the current buffer or globally).
;;
;; C-_  C-/  (`undo-tree-undo')
;;   Undo changes.
;;
;; M-_  C-?  (`undo-tree-redo')
;;   Redo changes.
;;
;; `undo-tree-switch-branch'
;;   Switch undo-tree branch.
;;   (What does this mean? Better press the button and see!)
;;
;; C-x u  (`undo-tree-visualize')
;;   Visualize the undo tree.
;;   (Better try pressing this button too!)
;;
;; C-x r u  (`undo-tree-save-state-to-register')
;;   Save current buffer state to register.
;;
;; C-x r U  (`undo-tree-restore-state-from-register')
;;   Restore buffer state from register.
;;
;;
;; In the undo-tree visualizer:
;;
;; <up>  p  C-p  (`undo-tree-visualize-undo')
;;   Undo changes.
;;
;; <down>  n  C-n  (`undo-tree-visualize-redo')
;;   Redo changes.
;;
;; <left>  b  C-b  (`undo-tree-visualize-switch-branch-left')
;;   Switch to previous undo-tree branch.
;;
;; <right>  f  C-f  (`undo-tree-visualize-switch-branch-right')
;;   Switch to next undo-tree branch.
;;
;; t  (`undo-tree-visualizer-toggle-timestamps')
;;   Toggle display of time-stamps.
;;
;; q  C-q  (`undo-tree-visualizer-quit')
;;   Quit undo-tree-visualizer.
;;
;; ,  <
;;   Scroll left.
;;
;; .  >
;;   Scroll right.
;;
;; <pgup>
;;   Scroll up.
;;
;; <pgdown>
;;   Scroll down.
;;
;;
;;
;; Undo Systems
;; ============
;;
;; To understand the different undo systems, it's easiest to consider an
;; example. Imagine you make a few edits in a buffer. As you edit, you
;; accumulate a history of changes, which we might visualize as a string of
;; past buffer states, growing downwards:
;;
;;                                o  (initial buffer state)
;;                                |
;;                                |
;;                                o  (first edit)
;;                                |
;;                                |
;;                                o  (second edit)
;;                                |
;;                                |
;;                                x  (current buffer state)
;;
;;
;; Now imagine that you undo the last two changes. We can visualize this as
;; rewinding the current state back two steps:
;;
;;                                o  (initial buffer state)
;;                                |
;;                                |
;;                                x  (current buffer state)
;;                                |
;;                                |
;;                                o
;;                                |
;;                                |
;;                                o
;;
;;
;; However, this isn't a good representation of what Emacs' undo system
;; does. Instead, it treats the undos as *new* changes to the buffer, and adds
;; them to the history:
;;
;;                                o  (initial buffer state)
;;                                |
;;                                |
;;                                o  (first edit)
;;                                |
;;                                |
;;                                o  (second edit)
;;                                |
;;                                |
;;                                x  (buffer state before undo)
;;                                |
;;                                |
;;                                o  (first undo)
;;                                |
;;                                |
;;                                x  (second undo)
;;
;;
;; Actually, since the buffer returns to a previous state after an undo,
;; perhaps a better way to visualize it is to imagine the string of changes
;; turning back on itself:
;;
;;        (initial buffer state)  o
;;                                |
;;                                |
;;                  (first edit)  o  x  (second undo)
;;                                |  |
;;                                |  |
;;                 (second edit)  o  o  (first undo)
;;                                | /
;;                                |/
;;                                o  (buffer state before undo)
;;
;; Treating undos as new changes might seem a strange thing to do. But the
;; advantage becomes clear as soon as we imagine what happens when you edit
;; the buffer again. Since you've undone a couple of changes, new edits will
;; branch off from the buffer state that you've rewound to. Conceptually, it
;; looks like this:
;;
;;                                o  (initial buffer state)
;;                                |
;;                                |
;;                                o
;;                                |\
;;                                | \
;;                                o  x  (new edit)
;;                                |
;;                                |
;;                                o
;;
;; The standard undo/redo system only lets you go backwards and forwards
;; linearly. So as soon as you make that new edit, it discards the old
;; branch. Emacs' undo just keeps adding changes to the end of the string. So
;; the undo history in the two systems now looks like this:
;;
;;            Undo/Redo:                      Emacs' undo
;;
;;               o                                o
;;               |                                |
;;               |                                |
;;               o                                o  o
;;               .\                               |  |\
;;               . \                              |  | \
;;               .  x  (new edit)                 o  o  |
;;   (discarded  .                                | /   |
;;     branch)   .                                |/    |
;;               .                                o     |
;;                                                      |
;;                                                      |
;;                                                      x  (new edit)
;;
;; Now, what if you change your mind about those undos, and decide you did
;; like those other changes you'd made after all? With the standard undo/redo
;; system, you're lost. There's no way to recover them, because that branch
;; was discarded when you made the new edit.
;;
;; However, in Emacs' undo system, those old buffer states are still there in
;; the undo history. You just have to rewind back through the new edit, and
;; back through the changes made by the undos, until you reach them. Of
;; course, since Emacs treats undos (even undos of undos!) as new changes,
;; you're really weaving backwards and forwards through the history, all the
;; time adding new changes to the end of the string as you go:
;;
;;                       o
;;                       |
;;                       |
;;                       o  o     o  (undo new edit)
;;                       |  |\    |\
;;                       |  | \   | \
;;                       o  o  |  |  o  (undo the undo)
;;                       | /   |  |  |
;;                       |/    |  |  |
;;      (trying to get   o     |  |  x  (undo the undo)
;;       to this state)        | /
;;                             |/
;;                             o
;;
;; So far, this is still reasonably intuitive to use. It doesn't behave so
;; differently to standard undo/redo, except that by going back far enough you
;; can access changes that would be lost in standard undo/redo.
;;
;; However, imagine that after undoing as just described, you decide you
;; actually want to rewind right back to the initial state. If you're lucky,
;; and haven't invoked any command since the last undo, you can just keep on
;; undoing until you get back to the start:
;;
;;      (trying to get   o              x  (got there!)
;;       to this state)  |              |
;;                       |              |
;;                       o  o     o     o  (keep undoing)
;;                       |  |\    |\    |
;;                       |  | \   | \   |
;;                       o  o  |  |  o  o  (keep undoing)
;;                       | /   |  |  | /
;;                       |/    |  |  |/
;;      (already undid   o     |  |  o  (got this far)
;;       to this state)        | /
;;                             |/
;;                             o
;;
;; But if you're unlucky, and you happen to have moved the point (say) after
;; getting to the state labelled "got this far", then you've "broken the undo
;; chain". Hold on to something solid, because things are about to get
;; hairy. If you try to undo now, Emacs thinks you're trying to undo the
;; undos! So to get back to the initial state you now have to rewind through
;; *all* the changes, including the undos you just did:
;;
;;      (trying to get   o                          x  (finally got there!)
;;       to this state)  |                          |
;;                       |                          |
;;                       o  o     o     o     o     o
;;                       |  |\    |\    |\    |\    |
;;                       |  | \   | \   | \   | \   |
;;                       o  o  |  |  o  o  o  |  o  o
;;                       | /   |  |  | /   |  |  | /
;;                       |/    |  |  |/    |  |  |/
;;      (already undid   o     |  |  o<.   |  |  o
;;       to this state)        | /     :   | /
;;                             |/      :   |/
;;                             o       :   o
;;                                     :
;;                             (got this far, but
;;                              broke the undo chain)
;;
;; Confused?
;;
;; In practice you can just hold down the undo key until you reach the buffer
;; state that you want. But whatever you do, don't move around in the buffer
;; to *check* that you've got back to where you want! Because you'll break the
;; undo chain, and then you'll have to traverse the entire string of undos
;; again, just to get back to the point at which you broke the
;; chain. Undo-in-region and commands such as `undo-only' help to make using
;; Emacs' undo a little easier, but nonetheless it remains confusing for many
;; people.
;;
;;
;; So what does `undo-tree-mode' do? Remember the diagram we drew to represent
;; the history we've been discussing (make a few edits, undo a couple of them,
;; and edit again)? The diagram that conceptually represented our undo
;; history, before we started discussing specific undo systems? It looked like
;; this:
;;
;;                                o  (initial buffer state)
;;                                |
;;                                |
;;                                o
;;                                |\
;;                                | \
;;                                o  x  (current state)
;;                                |
;;                                |
;;                                o
;;
;; Well, that's *exactly* what the undo history looks like to
;; `undo-tree-mode'.  It doesn't discard the old branch (as standard undo/redo
;; does), nor does it treat undos as new changes to be added to the end of a
;; linear string of buffer states (as Emacs' undo does). It just keeps track
;; of the tree of branching changes that make up the entire undo history.
;;
;; If you undo from this point, you'll rewind back up the tree to the previous
;; state:
;;
;;                                o
;;                                |
;;                                |
;;                                x  (undo)
;;                                |\
;;                                | \
;;                                o  o
;;                                |
;;                                |
;;                                o
;;
;; If you were to undo again, you'd rewind back to the initial state. If on
;; the other hand you redo the change, you'll end up back at the bottom of the
;; most recent branch:
;;
;;                                o  (undo takes you here)
;;                                |
;;                                |
;;                                o  (start here)
;;                                |\
;;                                | \
;;                                o  x  (redo takes you here)
;;                                |
;;                                |
;;                                o
;;
;; So far, this is just like the standard undo/redo system. But what if you
;; want to return to a buffer state located on a previous branch of the
;; history? Since `undo-tree-mode' keeps the entire history, you simply need
;; to tell it to switch to a different branch, and then redo the changes you
;; want:
;;
;;                                o
;;                                |
;;                                |
;;                                o  (start here, but switch
;;                                |\  to the other branch)
;;                                | \
;;                        (redo)  o  o
;;                                |
;;                                |
;;                        (redo)  x
;;
;; Now you're on the other branch, if you undo and redo changes you'll stay on
;; that branch, moving up and down through the buffer states located on that
;; branch. Until you decide to switch branches again, of course.
;;
;; Real undo trees might have multiple branches and sub-branches:
;;
;;                                o
;;                            ____|______
;;                           /           \
;;                          o             o
;;                      ____|__         __|
;;                     /    |  \       /   \
;;                    o     o   o     o     x
;;                    |               |
;;                   / \             / \
;;                  o   o           o   o
;;
;; Trying to imagine what Emacs' undo would do as you move about such a tree
;; will likely frazzle your brain circuits! But in `undo-tree-mode', you're
;; just moving around this undo history tree. Most of the time, you'll
;; probably only need to stay on the most recent branch, in which case it
;; behaves like standard undo/redo, and is just as simple to understand. But
;; if you ever need to recover a buffer state on a different branch, the
;; possibility of switching between branches and accessing the full undo
;; history is still there.
;;
;;
;;
;; The Undo-Tree Visualizer
;; ========================
;;
;; Actually, it gets better. You don't have to imagine all these tree
;; diagrams, because `undo-tree-mode' includes an undo-tree visualizer which
;; draws them for you! In fact, it draws even better diagrams: it highlights
;; the node representing the current buffer state, it highlights the current
;; branch, and (by hitting "t") you can toggle the display of
;; time-stamps. (There's one other tiny difference: the visualizer puts the
;; most recent branch on the left rather than the right.)
;;
;; In the visualizer, the usual keys for moving up and down a buffer instead
;; move up and down the undo history tree (e.g. the up and down arrow keys, or
;; "C-n" and "C-p"). The state of the "parent" buffer (the buffer whose undo
;; history you are visualizing) is updated as you move around the undo tree in
;; the visualizer. If you reach a branch point in the visualizer, the usual
;; keys for moving forward and backward in a buffer instead switch branch
;; (e.g. the left and right arrow keys, or "C-f" and "C-b"). And clicking with
;; the mouse on any node in the visualizer will take you directly to that
;; node, resetting the state of the parent buffer to the state represented by
;; that node.
;;
;; It can be useful to see how long ago the parent buffer was in the state
;; represented by a particular node in the visualizer. Hitting "t" in the
;; visualizer toggles the display of time-stamps for all the nodes. (Note
;; that, because of the way `undo-tree-mode' works, these time-stamps may be
;; somewhat later than the true times, especially if it's been a long time
;; since you last undid any changes.)
;;
;; Finally, hitting "q" will quit the visualizer, leaving the parent buffer in
;; whatever state you ended at.
;;
;;
;;
;; Drawbacks
;; =========
;;
;; `undo-tree-mode' doesn't support "undo in region", i.e. selectively undoing
;; only the changes that affect the region. Support for this is planned for a
;; future version.



;;; Change Log:
;;
;; Version 0.2.1
;; * modified `undo-tree-node' defstruct and macros to allow arbitrary
;;   meta-data to be stored in a plist associated with a node, and
;;   reimplemented storage of visualizer data on top of this
;; * display registers storing undo-tree state in visualizer
;; * implemented keyboard selection in visualizer
;; * rebuild `buffer-undo-list' from tree when disabling `undo-tree-mode'
;;
;; Version 0.2
;; * added support for marker undo entries
;;
;; Version 0.1.7
;; * pass null argument to `kill-buffer' call in `undo-tree-visualizer-quit',
;;   since the argument's not optional in earlier Emacs versions
;; * added match for "No further redo information" to
;;   `debug-ignored-errors' to prevent debugger being called on this error
;; * made `undo-tree-visualizer-quit' select the window displaying the
;;   visualizer's parent buffer, or switch to the parent buffer if no window
;;   is displaying it
;; * fixed bug in `undo-tree-switch-branch'
;; * general code tidying and reorganisation
;; * fixed bugs in history-discarding logic
;; * fixed bug in `undo-tree-insert' triggered by `undo-tree-visualizer-set'
;;   by ensuring mark is deactivated
;;
;; Version 0.1.6
;; * added `undo-tree-mode-lighter' customization option to allow the
;;   mode-line lighter to be changed
;; * bug-fix in `undo-tree-discard-node'
;; * added `undo-tree-save-state-to-register' and
;;   `undo-tree-restore-state-from-register' commands and keybindings for
;;   saving/restoring undo-tree states using registers
;;
;; Version 0.1.5
;; * modified `undo-tree-visualize' to mark the visualizer window as
;;   soft-dedicated, and changed `undo-tree-visualizer-quit' to use
;;   `kill-buffer', so that the visualizer window is deleted along with its
;;   buffer if the visualizer buffer was displayed in a new window, but not if
;;   it was displayed in an existing window.
;;
;; Version 0.1.4
;; * modified `undo-tree-undo' and `undo-tree-redo' to always replace
;;   redo/undo entries with new ones generated by `primitive-undo', as the new
;;   changesets will restore the point more reliably
;;
;; Version 0.1.3
;; * fixed `undo-tree-visualizer-quit' to remove `after-change-functions'
;;   hook there, rather than in `undo-tree-kill-visualizer'
;;
;; Version 0.1.2
;; * fixed keybindings
;; * renamed `undo-tree-visualizer-switch-previous-branch' and
;;   `undo-tree-visualizer-switch-next-branch' to
;;   `undo-tree-visualizer-switch-branch-left' and
;;   `undo-tree-visualizer-switch-branch-right'
;;
;; Version 0.1.1
;; * prevented `undo-tree-kill-visualizer' from killing visualizer when
;;   undoing/redoing from the visualizer, which completely broke the
;;   visualizer!
;; * changed one redo binding, so that at least one set of undo/redo bindings
;;   works in a terminal
;; * bound vertical scrolling commands in `undo-tree-visualizer-map', in case
;;   they aren't bound globally
;; * added missing :group argument to `defface's
;;
;; Version 0.1
;; * initial release



;;; Code:

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

;; `characterp' isn't defined in Emacs versions <= 22
(unless (fboundp 'characterp)
  (defalias 'characterp 'char-valid-p))


;;; =====================================================================
;;;              Global variables and customization options

(defvar buffer-undo-tree nil
  "Tree of undo entries in current buffer.")
(make-variable-buffer-local 'buffer-undo-tree)


(defgroup undo-tree nil
  "Tree undo/redo."
  :group 'undo)

(defcustom undo-tree-mode-lighter " Undo-Tree"
  "Lighter displayed in mode line
when `undo-tree-mode' is enabled."
  :group 'undo-tree
  :type 'string)

(defcustom undo-tree-visualizer-spacing 3
  "Horizontal spacing in undo-tree visualization.
Must be a postivie odd integer."
  :group 'undo-tree
  :type '(integer
          :match (lambda (w n) (and (integerp n) (> n 0) (= (mod n 2) 1)))))
(make-variable-buffer-local 'undo-tree-visualizer-spacing)

(defvar undo-tree-map nil
  "Keymap used in undo-tree-mode.")


(defface undo-tree-visualizer-default-face
  '((((class color)) :foreground "gray"))
  "*Face used to draw undo-tree in visualizer."
  :group 'undo-tree)

(defface undo-tree-visualizer-current-face
  '((((class color)) :foreground "red"))
  "*Face used to highlight current undo-tree node in visualizer."
  :group 'undo-tree)

(defface undo-tree-visualizer-active-branch-face
  '((((class color) (background dark))
     (:foreground "white" :weight bold))
    (((class color) (background light))
     (:foreground "black" :weight bold)))
  "*Face used to highlight active undo-tree branch
in visualizer."
  :group 'undo-tree)

(defface undo-tree-visualizer-register-face
  '((((class color)) :foreground "yellow"))
  "*Face used to highlight undo-tree nodes saved to a register
in visualizer."
  :group 'undo-tree)

(defvar undo-tree-visualizer-map nil
  "Keymap used in undo-tree visualizer.")

(defvar undo-tree-visualizer-selection-map nil
  "Keymap used in undo-tree visualizer selection mode.")


(defvar undo-tree-visualizer-parent-buffer nil
  "Parent buffer in visualizer.")
(make-variable-buffer-local 'undo-tree-visualizer-parent-buffer)

(defvar undo-tree-visualizer-timestamps nil
  "Non-nil when visualizer is displaying time-stamps.")
(make-variable-buffer-local 'undo-tree-visualizer-timestamps)

(defconst undo-tree-visualizer-buffer-name " *undo-tree*")

;; prevent debugger being called on "No further redo information"
(add-to-list 'debug-ignored-errors "^No further redo information")




;;; =================================================================
;;;                     Setup default keymaps

(unless undo-tree-map
  (setq undo-tree-map (make-sparse-keymap))
  ;; remap `undo' and `undo-only' to `undo-tree-undo'
  (define-key undo-tree-map [remap undo] 'undo-tree-undo)
  (define-key undo-tree-map [remap undo-only] 'undo-tree-undo)
  ;; bind standard undo bindings (since these match redo counterparts)
  (define-key undo-tree-map (kbd "C-/") 'undo-tree-undo)
  (define-key undo-tree-map "\C-_" 'undo-tree-undo)
  ;; redo doesn't exist normally, so define our own keybindings
  (define-key undo-tree-map (kbd "C-?") 'undo-tree-redo)
  (define-key undo-tree-map (kbd "M-_") 'undo-tree-redo)
  ;; just in case something has defined `redo'...
  (define-key undo-tree-map [remap redo] 'undo-tree-redo)
  ;; we use "C-x u" for the undo-tree visualizer
  (define-key undo-tree-map (kbd "\C-x u") 'undo-tree-visualize)
  ;; bind register commands
  (define-key undo-tree-map (kbd "C-x r u")
    'undo-tree-save-state-to-register)
  (define-key undo-tree-map (kbd "C-x r U")
    'undo-tree-restore-state-from-register))


(unless undo-tree-visualizer-map
  (setq undo-tree-visualizer-map (make-keymap))
  ;; vertical motion keys undo/redo
  (define-key undo-tree-visualizer-map [remap previous-line]
    'undo-tree-visualize-undo)
  (define-key undo-tree-visualizer-map [remap next-line]
    'undo-tree-visualize-redo)
  (define-key undo-tree-visualizer-map [up]
    'undo-tree-visualize-undo)
  (define-key undo-tree-visualizer-map "p"
    'undo-tree-visualize-undo)
  (define-key undo-tree-visualizer-map "\C-p"
    'undo-tree-visualize-undo)
  (define-key undo-tree-visualizer-map [down]
    'undo-tree-visualize-redo)
  (define-key undo-tree-visualizer-map "n"
    'undo-tree-visualize-redo)
  (define-key undo-tree-visualizer-map "\C-n"
    'undo-tree-visualize-redo)
  ;; horizontal motion keys switch branch
  (define-key undo-tree-visualizer-map [remap forward-char]
    'undo-tree-visualize-switch-branch-right)
  (define-key undo-tree-visualizer-map [remap backward-char]
    'undo-tree-visualize-switch-branch-left)
  (define-key undo-tree-visualizer-map [right]
    'undo-tree-visualize-switch-branch-right)
  (define-key undo-tree-visualizer-map "f"
    'undo-tree-visualize-switch-branch-right)
  (define-key undo-tree-visualizer-map "\C-f"
    'undo-tree-visualize-switch-branch-right)
  (define-key undo-tree-visualizer-map [left]
    'undo-tree-visualize-switch-branch-left)
  (define-key undo-tree-visualizer-map "b"
    'undo-tree-visualize-switch-branch-left)
  (define-key undo-tree-visualizer-map "\C-b"
    'undo-tree-visualize-switch-branch-left)
  ;; mouse sets buffer state to node at click
  (define-key undo-tree-visualizer-map [mouse-1]
    'undo-tree-visualizer-mouse-set)
  ;; toggle timestamps
  (define-key undo-tree-visualizer-map "t"
    'undo-tree-visualizer-toggle-timestamps)
  ;; selection mode
  (define-key undo-tree-visualizer-map "s"
    'undo-tree-visualizer-selection-mode)
  ;; horizontal scrolling may be needed if the tree is very wide
  (define-key undo-tree-visualizer-map ","
    'undo-tree-visualizer-scroll-left)
  (define-key undo-tree-visualizer-map "."
    'undo-tree-visualizer-scroll-right)
  (define-key undo-tree-visualizer-map "<"
    'undo-tree-visualizer-scroll-left)
  (define-key undo-tree-visualizer-map ">"
    'undo-tree-visualizer-scroll-right)
  ;; vertical scrolling may be needed if the tree is very tall
  (define-key undo-tree-visualizer-map [next] 'scroll-up)
  (define-key undo-tree-visualizer-map [prior] 'scroll-down)
  ;; quit visualizer
  (define-key undo-tree-visualizer-map "q"
    'undo-tree-visualizer-quit)
  (define-key undo-tree-visualizer-map "\C-q"
    'undo-tree-visualizer-quit))


(unless undo-tree-visualizer-selection-map
  (setq undo-tree-visualizer-selection-map (make-keymap))
  ;; vertical motion keys move up and down tree
  (define-key undo-tree-visualizer-selection-map [remap previous-line]
    'undo-tree-visualizer-select-previous)
  (define-key undo-tree-visualizer-selection-map [remap next-line]
    'undo-tree-visualizer-select-next)
  (define-key undo-tree-visualizer-selection-map [up]
    'undo-tree-visualizer-select-previous)
  (define-key undo-tree-visualizer-selection-map "p"
    'undo-tree-visualizer-select-previous)
  (define-key undo-tree-visualizer-selection-map "\C-p"
    'undo-tree-visualizer-select-previous)
  (define-key undo-tree-visualizer-selection-map [down]
    'undo-tree-visualizer-select-next)
  (define-key undo-tree-visualizer-selection-map "n"
    'undo-tree-visualizer-select-next)
  (define-key undo-tree-visualizer-selection-map "\C-n"
    'undo-tree-visualizer-select-next)
  ;; vertical scroll keys move up and down quickly
  (define-key undo-tree-visualizer-selection-map [next]
    (lambda () (interactive) (undo-tree-visualizer-select-next 10)))
  (define-key undo-tree-visualizer-selection-map [prior]
    (lambda () (interactive) (undo-tree-visualizer-select-previous 10)))
  ;; horizontal motion keys move to left and right siblings
  (define-key undo-tree-visualizer-selection-map [remap forward-char]
    'undo-tree-visualizer-select-right)
  (define-key undo-tree-visualizer-selection-map [remap backward-char]
    'undo-tree-visualizer-select-left)
  (define-key undo-tree-visualizer-selection-map [right]
    'undo-tree-visualizer-select-right)
  (define-key undo-tree-visualizer-selection-map "f"
    'undo-tree-visualizer-select-right)
  (define-key undo-tree-visualizer-selection-map "\C-f"
    'undo-tree-visualizer-select-right)
  (define-key undo-tree-visualizer-selection-map [left]
    'undo-tree-visualizer-select-left)
  (define-key undo-tree-visualizer-selection-map "b"
    'undo-tree-visualizer-select-left)
  (define-key undo-tree-visualizer-selection-map "\C-b"
    'undo-tree-visualizer-select-left)
  ;; horizontal scroll keys move left or right quickly
  (define-key undo-tree-visualizer-selection-map ","
    (lambda () (interactive) (undo-tree-visualizer-select-left 10)))
  (define-key undo-tree-visualizer-selection-map "."
    (lambda () (interactive) (undo-tree-visualizer-select-right 10)))
  (define-key undo-tree-visualizer-selection-map "<"
    (lambda () (interactive) (undo-tree-visualizer-select-left 10)))
  (define-key undo-tree-visualizer-selection-map ">"
    (lambda () (interactive) (undo-tree-visualizer-select-right 10)))
  ;; mouse or <enter> sets buffer state to node at point/click
  (define-key undo-tree-visualizer-selection-map "\r"
    'undo-tree-visualizer-set)
  (define-key undo-tree-visualizer-selection-map [mouse-1]
    'undo-tree-visualizer-mouse-set)
  ;; toggle timestamps
  (define-key undo-tree-visualizer-selection-map "t"
    'undo-tree-visualizer-toggle-timestamps)
  ;; quit visualizer selection mode
  (define-key undo-tree-visualizer-selection-map "s"
    'undo-tree-visualizer-mode)
  ;; quit visualizer
  (define-key undo-tree-visualizer-selection-map "q"
    'undo-tree-visualizer-quit)
  (define-key undo-tree-visualizer-selection-map "\C-q"
    'undo-tree-visualizer-quit))




;;; =====================================================================
;;;                     Undo-tree data structure

(defstruct
  (undo-tree
   :named
   (:constructor nil)
   (:constructor make-undo-tree
                 (&aux
                  (root (make-undo-tree-node nil nil))
                  (current root)
                  (size 0)
		  (object-pool (make-hash-table :test 'eq :weakness 'value))))
   (:copier nil))
  root current size object-pool)



(defstruct
  (undo-tree-node
   (:type vector)   ; create unnamed struct
   (:constructor nil)
   (:constructor make-undo-tree-node
                 (previous undo
                  &aux
                  (timestamp (current-time))
                  (branch 0)))
   (:constructor make-undo-tree-node-backwards
                 (next-node undo
                  &aux
                  (next (list next-node))
                  (timestamp (current-time))
                  (branch 0)))
   (:copier nil))
  previous next undo redo timestamp branch meta-data)


(defmacro undo-tree-node-p (n)
  (let ((len (length (make-undo-tree-node nil nil))))
    `(and (vectorp ,n) (= (length ,n) ,len))))



(defstruct
  (undo-tree-visualizer-data
   (:type vector)   ; create unnamed struct
   (:constructor nil)
   (:constructor make-undo-tree-visualizer-data
		 (&optional lwidth cwidth rwidth marker))
   (:copier nil))
  lwidth cwidth rwidth marker)


(defmacro undo-tree-visualizer-data-p (v)
  (let ((len (length (make-undo-tree-visualizer-data))))
    `(and (vectorp ,v) (= (length ,v) ,len))))

(defmacro undo-tree-node-clear-visualizer-data (node)
  `(setf (undo-tree-node-meta-data ,node)
	 (delq nil
	       (delq :visualizer
		     (plist-put (undo-tree-node-meta-data ,node)
				:visualizer nil)))))


(defmacro undo-tree-node-lwidth (node)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (when (undo-tree-visualizer-data-p v)
       (undo-tree-visualizer-data-lwidth v))))

(defmacro undo-tree-node-cwidth (node)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (when (undo-tree-visualizer-data-p v)
       (undo-tree-visualizer-data-cwidth v))))

(defmacro undo-tree-node-rwidth (node)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (when (undo-tree-visualizer-data-p v)
       (undo-tree-visualizer-data-rwidth v))))

(defmacro undo-tree-node-marker (node)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (when (undo-tree-visualizer-data-p v)
       (undo-tree-visualizer-data-marker v))))


(defsetf undo-tree-node-lwidth (node) (val)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (unless (undo-tree-visualizer-data-p v)
       (setf (undo-tree-node-meta-data ,node)
	     (plist-put (undo-tree-node-meta-data ,node) :visualizer
			(setq v (make-undo-tree-visualizer-data)))))
     (setf (undo-tree-visualizer-data-lwidth v) ,val)))

(defsetf undo-tree-node-cwidth (node) (val)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (unless (undo-tree-visualizer-data-p v)
       (setf (undo-tree-node-meta-data ,node)
	     (plist-put (undo-tree-node-meta-data ,node) :visualizer
			(setq v (make-undo-tree-visualizer-data)))))
     (setf (undo-tree-visualizer-data-cwidth v) ,val)))

(defsetf undo-tree-node-rwidth (node) (val)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (unless (undo-tree-visualizer-data-p v)
       (setf (undo-tree-node-meta-data ,node)
	     (plist-put (undo-tree-node-meta-data ,node) :visualizer
			(setq v (make-undo-tree-visualizer-data)))))
     (setf (undo-tree-visualizer-data-rwidth v) ,val)))

(defsetf undo-tree-node-marker (node) (val)
  `(let ((v (plist-get (undo-tree-node-meta-data ,node) :visualizer)))
     (unless (undo-tree-visualizer-data-p v)
       (setf (undo-tree-node-meta-data ,node)
	     (plist-put (undo-tree-node-meta-data ,node) :visualizer
			(setq v (make-undo-tree-visualizer-data)))))
     (setf (undo-tree-visualizer-data-marker v) ,val)))



(defmacro undo-tree-node-register (node)
  `(plist-get (undo-tree-node-meta-data ,node) :register))

(defsetf undo-tree-node-register (node) (val)
  `(setf (undo-tree-node-meta-data ,node)
	 (plist-put (undo-tree-node-meta-data ,node) :register ,val)))




;;; =====================================================================
;;;              Basic undo-tree data structure functions

(defun undo-tree-grow (undo)
  "Add an UNDO node to current branch of `buffer-undo-tree'."
  (let* ((current (undo-tree-current buffer-undo-tree))
         (new (make-undo-tree-node current undo)))
    (push new (undo-tree-node-next current))
    (setf (undo-tree-current buffer-undo-tree) new)))


(defun undo-tree-grow-backwards (node undo)
  "Add an UNDO node *above* undo-tree NODE, and return new node.
Note that this will overwrite NODE's \"previous\" link, so should
only be used on a detached NODE, never on nodes that are already
part of `buffer-undo-tree'."
  (let ((new (make-undo-tree-node-backwards node undo)))
    (setf (undo-tree-node-previous node) new)
    new))


(defun undo-tree-splice-node (node splice)
  "Splice NODE into undo tree, below node SPLICE.
Note that this will overwrite NODE's \"next\" and \"previous\"
links, so should only be used on a detached NODE, never on nodes
that are already part of `buffer-undo-tree'."
  (setf (undo-tree-node-next node) (undo-tree-node-next splice)
	(undo-tree-node-branch node) (undo-tree-node-branch splice)
	(undo-tree-node-previous node) splice
	(undo-tree-node-next splice) (list node)
	(undo-tree-node-branch splice) 0)
  (dolist (n (undo-tree-node-next node))
    (setf (undo-tree-node-previous n) node)))


(defun undo-tree-snip-node (node)
  "Snip NODE out of undo tree."
  (let* ((parent (undo-tree-node-previous node))
	 position p)
    ;; if NODE is only child, replace parent's next links with NODE's
    (if (= (length (undo-tree-node-next parent)) 0)
	(setf (undo-tree-node-next parent) (undo-tree-node-next node)
	      (undo-tree-node-branch parent) (undo-tree-node-branch node))
      ;; otherwise...
      (setq position (undo-tree-position node (undo-tree-node-next parent)))
      (cond
       ;; if active branch used do go via NODE, set parent's branch to active
       ;; branch of NODE
       ((= (undo-tree-node-branch parent) position)
	(setf (undo-tree-node-branch parent)
	      (+ position (undo-tree-node-branch node))))
       ;; if active branch didn't go via NODE, update parent's branch to point
       ;; to same node as before
       ((> (undo-tree-node-branch parent) position)
	(incf (undo-tree-node-branch parent)
	      (1- (length (undo-tree-node-next node))))))
      ;; replace NODE in parent's next list with NODE's entire next list
      (if (= position 0)
	  (setf (undo-tree-node-next parent)
		(nconc (undo-tree-node-next node)
		       (cdr (undo-tree-node-next parent))))
	(setq p (nthcdr (1- position) (undo-tree-node-next parent)))
	(setcdr p (nconc (undo-tree-node-next node) (cddr p)))))
    ;; update previous links of NODE's children
    (dolist (n (undo-tree-node-next node))
      (setf (undo-tree-node-previous n) parent))))


(defun undo-tree-mapc (--undo-tree-mapc-function-- undo-tree)
  ;; Apply FUNCTION to each node in UNDO-TREE.
  (let ((stack (list (undo-tree-root undo-tree)))
        node)
    (while stack
      (setq node (pop stack))
      (funcall --undo-tree-mapc-function-- node)
      (setq stack (append (undo-tree-node-next node) stack)))))


(defmacro undo-tree-num-branches ()
  "Return number of branches at current undo tree node."
  '(length (undo-tree-node-next (undo-tree-current buffer-undo-tree))))


(defun undo-tree-position (node list)
  "Find the first occurrence of NODE in LIST.
Return the index of the matching item, or nil of not found.
Comparison is done with 'eq."
  (let ((i 0))
    (catch 'found
      (while (progn
               (when (eq node (car list)) (throw 'found i))
               (incf i)
               (setq list (cdr list))))
      nil)))


(defvar *undo-tree-id-counter* 0)
(make-variable-buffer-local '*undo-tree-id-counter*)

(defmacro undo-tree-generate-id ()
  ;; Generate a new, unique id (uninterned symbol).
  ;; The name is made by appending a number to "undo-tree-id".
  ;; (Copied from CL package `gensym'.)
  `(let ((num (prog1 *undo-tree-id-counter* (incf *undo-tree-id-counter*))))
     (make-symbol (format "undo-tree-id%d" num))))




;;; =====================================================================
;;;    Utility functions for handling `buffer-undo-list' and changesets

(defmacro undo-list-marker-elt-p (elt)
  `(markerp (car-safe ,elt)))

(defmacro undo-list-GCd-marker-elt-p (elt)
  `(and (symbolp (car-safe ,elt)) (numberp (cdr-safe ,elt))))


(defun undo-tree-move-GC-elts-to-pool (elt)
  ;; Move elements that can be garbage-collected into `buffer-undo-tree'
  ;; object pool, substituting a unique id that can be used to retrieve them
  ;; later. (Only markers require this treatment currently.)
  (when (undo-list-marker-elt-p elt)
    (let ((id (undo-tree-generate-id)))
      (puthash id (car elt) (undo-tree-object-pool buffer-undo-tree))
      (setcar elt id))))


(defun undo-tree-restore-GC-elts-from-pool (elt)
  ;; Replace object id's in ELT with corresponding objects from
  ;; `buffer-undo-tree' object pool and return modified ELT, or return nil if
  ;; any object in ELT has been garbage-collected.
  (if (undo-list-GCd-marker-elt-p elt)
      (when (setcar elt (gethash (car elt)
				 (undo-tree-object-pool buffer-undo-tree)))
	elt)
    elt))


(defun undo-list-clean-GCd-elts (undo-list)
  ;; Remove object id's from UNDO-LIST that refer to elements that have been
  ;; garbage-collected. UNDO-LIST is modified by side-effect.
  (while (undo-list-GCd-marker-elt-p (car undo-list))
    (unless (gethash (caar undo-list)
		     (undo-tree-object-pool buffer-undo-tree))
      (setq undo-list (cdr undo-list))))
  (let ((p undo-list))
    (while (cdr p)
      (when (and (undo-list-GCd-marker-elt-p (cadr p))
		 (null (gethash (car (cadr p))
				(undo-tree-object-pool buffer-undo-tree))))
	(setcdr p (cddr p)))
      (setq p (cdr p))))
  undo-list)


(defun undo-list-pop-changeset ()
  ;; Pop changeset from `buffer-undo-list'.
  ;; discard undo boundaries at head of list
  (while (null (car buffer-undo-list))
    (setq buffer-undo-list (cdr buffer-undo-list)))
  ;; pop elements up to next undo boundary
  (unless (eq (car buffer-undo-list) 'undo-tree-canary)
    (let* ((changeset (list (pop buffer-undo-list)))
           (p changeset))
      (while (progn
	       (undo-tree-move-GC-elts-to-pool (car p))
	       (car buffer-undo-list))
        (setcdr p (list (pop buffer-undo-list)))
	(setq p (cdr p)))
      changeset)))


(defun undo-tree-copy-list (undo-list)
  ;; Return a deep copy of first changeset in `undo-list'. Object id's are
  ;; replaced by corresponding objects from `buffer-undo-tree' object-pool.
  (when undo-list
    (let (copy p)
      ;; if first element contains an object id, replace it with object from
      ;; pool, discarding element entirely if it's been GC'd
      (while (null copy)
	(setq copy
	      (undo-tree-restore-GC-elts-from-pool (pop undo-list))))
      (setq copy (list copy)
	    p copy)
      ;; copy remaining elements, replacing object id's with objects from
      ;; pool, or discarding them entirely if they've been GC'd
      (while undo-list
	(when (setcdr p (undo-tree-restore-GC-elts-from-pool
			 (undo-copy-list-1 (pop undo-list))))
	  (setcdr p (list (cdr p)))
	  (setq p (cdr p))))
      copy)))



(defun undo-list-transfer-to-tree ()
  ;; Transfer entries accumulated in `buffer-undo-list' to `buffer-undo-tree'.

  ;; if `buffer-undo-tree' is empty, create initial undo-tree and make sure
  ;; there's a canary at end of `buffer-undo-list'
  (when (null buffer-undo-tree)
    (setq buffer-undo-tree (make-undo-tree))
    (let ((elt (last buffer-undo-list)))
      (unless (eq (car elt) 'undo-tree-canary)
	(setcdr elt '(nil undo-tree-canary)))))

  ;; if `buffer-undo-list' is empty, add a canary
  (if (null buffer-undo-list)
      (setq buffer-undo-list '(nil undo-tree-canary))
    (unless (eq (cadr buffer-undo-list) 'undo-tree-canary)
      ;; create new node from first changeset in `buffer-undo-list', save old
      ;; `buffer-undo-tree' current node, and make new node the current node
      (let* ((node (make-undo-tree-node nil (undo-list-pop-changeset)))
             (splice (undo-tree-current buffer-undo-tree))
             (size (undo-list-byte-size (undo-tree-node-undo node))))
        (setf (undo-tree-current buffer-undo-tree) node)
        ;; grow tree fragment backwards using `buffer-undo-list' changesets
        (while (and buffer-undo-list
                    (not (eq (cadr buffer-undo-list) 'undo-tree-canary)))
          (setq node
                (undo-tree-grow-backwards node (undo-list-pop-changeset)))
          (incf size (undo-list-byte-size (undo-tree-node-undo node))))
        ;; if no undo history has been discarded from `buffer-undo-list' since
        ;; last transfer, splice new tree fragment onto end of old
        ;; `buffer-undo-tree' current node
        (if (eq (cadr buffer-undo-list) 'undo-tree-canary)
            (progn
              (setf (undo-tree-node-previous node) splice)
              (push node (undo-tree-node-next splice))
              (setf (undo-tree-node-branch splice) 0)
              (incf (undo-tree-size buffer-undo-tree) size))
          ;; if undo history has been discarded, replace entire
          ;; `buffer-undo-tree' with new tree fragment
          (setq node (undo-tree-grow-backwards node nil))
          (setf (undo-tree-root buffer-undo-tree) node)
          (setq buffer-undo-list '(nil undo-tree-canary))
          (setf (undo-tree-size buffer-undo-tree) size)))
      ;; discard undo history if necessary
      (undo-tree-discard-history))))


(defun undo-list-byte-size (undo-list)
  ;; Return size (in bytes) of UNDO-LIST
  (let ((size 0) (p undo-list))
    (while p
      (incf size 8)  ; cons cells use up 8 bytes
      (when (and (consp (car p)) (stringp (caar p)))
        (incf size (string-bytes (caar p))))
      (setq p (cdr p)))
    size))



(defun undo-list-rebuild-from-tree ()
  "Rebuild `buffer-undo-list' from information in `buffer-undo-tree'."
  (setq buffer-undo-list nil)
  (let ((stack (list (list (undo-tree-root buffer-undo-tree)))))
    (push (sort (mapcar 'identity (undo-tree-node-next (caar stack)))
		(lambda (a b)
		  (time-less-p (undo-tree-node-timestamp a)
			       (undo-tree-node-timestamp b))))
	  stack)
    ;; Traverse tree in depth-and-oldest-first order, but add undo records on
    ;; the way down, and redo records on the way up.
    (while (or (car stack)
	       (not (eq (car (nth 1 stack))
			(undo-tree-current buffer-undo-tree))))
      (if (car stack)
	  (progn
	    (setq buffer-undo-list
		  (append (undo-tree-node-undo (caar stack)) buffer-undo-list))
	    (undo-boundary)
	    (push (sort (mapcar 'identity (undo-tree-node-next (caar stack)))
			(lambda (a b)
			  (time-less-p (undo-tree-node-timestamp a)
				       (undo-tree-node-timestamp b))))
		  stack))
	(pop stack)
	(setq buffer-undo-list
	      (append (undo-tree-node-redo (caar stack)) buffer-undo-list))
	(undo-boundary)
	(pop (car stack))))))




;;; =====================================================================
;;;                  History discarding functions

(defun undo-tree-oldest-leaf (node)
  ;; Return oldest leaf node below NODE.
  (while (undo-tree-node-next node)
    (setq node
          (car (sort (mapcar 'identity (undo-tree-node-next node))
                     (lambda (a b)
                       (time-less-p (undo-tree-node-timestamp a)
                                    (undo-tree-node-timestamp b)))))))
  node)


(defun undo-tree-discard-node (node)
  ;; Discard NODE from `buffer-undo-tree', and return next in line for
  ;; discarding.

  ;; don't discard current node
  (unless (eq node (undo-tree-current buffer-undo-tree))

    ;; discarding root node...
    (if (eq node (undo-tree-root buffer-undo-tree))
        (cond
         ;; should always discard branches before root
         ((> (length (undo-tree-node-next node)) 1)
          (error "Trying to discard undo-tree root which still\
 has multiple branches"))
         ;; don't discard root if current node is only child
         ((eq (car (undo-tree-node-next node))
              (undo-tree-current buffer-undo-tree))
	  nil)
	 ;; discard root
         (t
          ;; make child of root into new root
          (setq node (setf (undo-tree-root buffer-undo-tree)
                           (car (undo-tree-node-next node))))
	  ;; update undo-tree size
	  (decf (undo-tree-size buffer-undo-tree)
		(+ (undo-list-byte-size (undo-tree-node-undo node))
		   (undo-list-byte-size (undo-tree-node-redo node))))
	  ;; discard new root's undo data
	  (setf (undo-tree-node-undo node) nil
		(undo-tree-node-redo node) nil)
          ;; if new root has branches, or new root is current node, next node
          ;; to discard is oldest leaf, otherwise it's new root
          (if (or (> (length (undo-tree-node-next node)) 1)
                  (eq (car (undo-tree-node-next node))
                      (undo-tree-current buffer-undo-tree)))
              (undo-tree-oldest-leaf node)
            node)))

      ;; discarding leaf node...
      (let* ((parent (undo-tree-node-previous node))
             (current (nth (undo-tree-node-branch parent)
                           (undo-tree-node-next parent))))
	;; update undo-tree size
	(decf (undo-tree-size buffer-undo-tree)
	      (+ (undo-list-byte-size (undo-tree-node-undo node))
		 (undo-list-byte-size (undo-tree-node-redo node))))
        (setf (undo-tree-node-next parent)
                (delq node (undo-tree-node-next parent))
              (undo-tree-node-branch parent)
                (undo-tree-position current (undo-tree-node-next parent)))
        ;; if parent has branches, or parent is current node, next node to
        ;; discard is oldest leaf, otherwise it's parent
        (if (or (eq parent (undo-tree-current buffer-undo-tree))
                (and (undo-tree-node-next parent)
                     (or (not (eq parent (undo-tree-root buffer-undo-tree)))
                         (> (length (undo-tree-node-next parent)) 1))))
            (undo-tree-oldest-leaf parent)
          parent)))))



(defun undo-tree-discard-history ()
  "Discard undo history until we're within memory usage limits
set by `undo-limit', `undo-strong-limit' and `undo-outer-limit'."

  (when (> (undo-tree-size buffer-undo-tree) undo-limit)
    ;; if there are no branches off root, first node to discard is root;
    ;; otherwise it's leaf node at botom of oldest branch
    (let ((node (if (> (length (undo-tree-node-next
                                (undo-tree-root buffer-undo-tree))) 1)
                    (undo-tree-oldest-leaf (undo-tree-root buffer-undo-tree))
                  (undo-tree-root buffer-undo-tree))))

      ;; discard nodes until memory use is within `undo-strong-limit'
      (while (and node
                  (> (undo-tree-size buffer-undo-tree) undo-strong-limit))
        (setq node (undo-tree-discard-node node)))

      ;; discard nodes until next node to discard would bring memory use
      ;; within `undo-limit'
      (while (and node
		  ;; check first if last discard has brought us within
		  ;; `undo-limit', in case we can avoid more expensive
		  ;; `undo-strong-limit' calculation
		  ;; Note: this assumes undo-strong-limit > undo-limit;
		  ;;       if not, effectively undo-strong-limit = undo-limit
		  (> (undo-tree-size buffer-undo-tree) undo-limit)
                  (> (- (undo-tree-size buffer-undo-tree)
			;; if next node to discard is root, the memory we
			;; free-up comes from discarding changesets from its
			;; only child...
			(if (eq node (undo-tree-root buffer-undo-tree))
			    (+ (undo-list-byte-size
				(undo-tree-node-undo
				 (car (undo-tree-node-next node))))
			       (undo-list-byte-size
				(undo-tree-node-redo
				 (car (undo-tree-node-next node)))))
			  ;; ...otherwise, it comes from discarding changesets
			  ;; from along with the node itself
			  (+ (undo-list-byte-size (undo-tree-node-undo node))
			     (undo-list-byte-size (undo-tree-node-redo node)))
			  ))
                     undo-limit))
        (setq node (undo-tree-discard-node node)))

      ;; if we're still over the `undo-outer-limit', discard entire history
      (when (> (undo-tree-size buffer-undo-tree) undo-outer-limit)
        ;; query first if `undo-ask-before-discard' is set
        (if undo-ask-before-discard
            (when (yes-or-no-p
                   (format
                    "Buffer `%s' undo info is %d bytes long;  discard it? "
                    (buffer-name) (undo-tree-size buffer-undo-tree)))
              (setq buffer-undo-tree nil))
          ;; otherwise, discard and display warning
          (display-warning
           '(undo discard-info)
           (concat
            (format "Buffer `%s' undo info was %d bytes long.\n"
                    (buffer-name) (undo-tree-size buffer-undo-tree))
            "The undo info was discarded because it exceeded\
 `undo-outer-limit'.

This is normal if you executed a command that made a huge change
to the buffer. In that case, to prevent similar problems in the
future, set `undo-outer-limit' to a value that is large enough to
cover the maximum size of normal changes you expect a single
command to make, but not so large that it might exceed the
maximum memory allotted to Emacs.

If you did not execute any such command, the situation is
probably due to a bug and you should report it.

You can disable the popping up of this buffer by adding the entry
\(undo discard-info) to the user option `warning-suppress-types',
which is defined in the `warnings' library.\n")
           :warning)
          (setq buffer-undo-tree nil)))
      )))




;;; =====================================================================
;;;                 Visualizer-related functions

(defun undo-tree-compute-widths (undo-tree)
  "Recursively compute widths for all UNDO-TREE's nodes."
  (let ((stack (list (undo-tree-root undo-tree)))
        res)
    (while stack
      ;; try to compute widths for node at top of stack
      (if (undo-tree-node-p
           (setq res (undo-tree-node-compute-widths (car stack))))
          ;; if computation fails, it returns a node whose widths still need
          ;; computing, which we push onto the stack
          (push res stack)
        ;; otherwise, store widths and remove it from stack
        (setf (undo-tree-node-lwidth (car stack)) (aref res 0)
              (undo-tree-node-cwidth (car stack)) (aref res 1)
              (undo-tree-node-rwidth (car stack)) (aref res 2))
        (pop stack)))))


(defun undo-tree-node-compute-widths (node)
  ;; Compute NODE's left-, centre-, and right-subtree widths. Returns widths
  ;; (in a vector) if successful. Otherwise, returns a node whose widths need
  ;; calculating before NODE's can be calculated.
  (let ((num-children (length (undo-tree-node-next node)))
        (lwidth 0) (cwidth 0) (rwidth 0)
        p w)
    (catch 'need-widths
      (cond
       ;; leaf nodes have 0 width
       ((= 0 num-children)
        (setf cwidth 1
              (undo-tree-node-lwidth node) 0
              (undo-tree-node-cwidth node) 1
              (undo-tree-node-rwidth node) 0))

       ;; odd number of children
       ((= (mod num-children 2) 1)
        (setq p (undo-tree-node-next node))
        ;; compute left-width
        (dotimes (i (/ num-children 2))
          (if (undo-tree-node-lwidth (car p))
              (incf lwidth (+ (undo-tree-node-lwidth (car p))
                              (undo-tree-node-cwidth (car p))
                              (undo-tree-node-rwidth (car p))))
            ;; if child's widths haven't been computed, return that child
            (throw 'need-widths (car p)))
          (setq p (cdr p)))
        (if (undo-tree-node-lwidth (car p))
            (incf lwidth (undo-tree-node-lwidth (car p)))
          (throw 'need-widths (car p)))
        ;; centre-width is inherited from middle child
        (setf cwidth (undo-tree-node-cwidth (car p)))
        ;; compute right-width
        (incf rwidth (undo-tree-node-rwidth (car p)))
        (setq p (cdr p))
        (dotimes (i (/ num-children 2))
          (if (undo-tree-node-lwidth (car p))
              (incf rwidth (+ (undo-tree-node-lwidth (car p))
                              (undo-tree-node-cwidth (car p))
                              (undo-tree-node-rwidth (car p))))
            (throw 'need-widths (car p)))
          (setq p (cdr p))))

       ;; even number of children
       (t
        (setq p (undo-tree-node-next node))
        ;; compute left-width
        (dotimes (i (/ num-children 2))
          (if (undo-tree-node-lwidth (car p))
              (incf lwidth (+ (undo-tree-node-lwidth (car p))
                              (undo-tree-node-cwidth (car p))
                              (undo-tree-node-rwidth (car p))))
            (throw 'need-widths (car p)))
          (setq p (cdr p)))
        ;; centre-width is 0 when number of children is even
        (setq cwidth 0)
        ;; compute right-width
        (dotimes (i (/ num-children 2))
          (if (undo-tree-node-lwidth (car p))
              (incf rwidth (+ (undo-tree-node-lwidth (car p))
                              (undo-tree-node-cwidth (car p))
                              (undo-tree-node-rwidth (car p))))
            (throw 'need-widths (car p)))
          (setq p (cdr p)))))

      ;; return left-, centre- and right-widths
      (vector lwidth cwidth rwidth))))


(defun undo-tree-clear-visualizer-data (undo-tree)
  ;; Clear visualizer data from UNDO-TREE.
  (undo-tree-mapc
   (lambda (node) (undo-tree-node-clear-visualizer-data node))
   undo-tree))




;;; =====================================================================
;;;                        Undo-tree commands

(define-minor-mode undo-tree-mode
  "Toggle undo-tree mode.
With no argument, this command toggles the mode.
A positive prefix argument turns the mode on.
A negative prefix argument turns it off.

Undo-tree-mode replaces Emacs' standard undo feature with a more
powerful yet easier to use version, that treats the undo history
as what it is: a tree.

The following keys are available in `undo-tree-mode':

  \\{undo-tree-map}

Within the undo-tree visualizer, the following keys are available:

  \\{undo-tree-visualizer-map}"

  nil                       ; init value
  undo-tree-mode-lighter    ; lighter
  undo-tree-map             ; keymap
  ;; if disabling `undo-tree-mode', rebuild `buffer-undo-list' from tree so
  ;; Emacs undo can work
  (unless undo-tree-mode
    (undo-list-rebuild-from-tree)
    (setq buffer-undo-tree nil)))


(defun turn-on-undo-tree-mode ()
  "Enable undo-tree-mode."
  (undo-tree-mode 1))


(define-globalized-minor-mode global-undo-tree-mode
  undo-tree-mode turn-on-undo-tree-mode)



(defun undo-tree-undo (&optional arg)
  "Undo changes. A numeric ARG serves as a repeat count."
  (interactive "p")
  ;; throw error if undo is disabled in buffer
  (when (eq buffer-undo-list t) (error "No undo information in this buffer"))

  (let ((undo-in-progress t)
	current)
    ;; if `buffer-undo-tree' is empty, create initial undo-tree
    (when (null buffer-undo-tree)
      (setq buffer-undo-tree (make-undo-tree)))
    ;; transfer entries accumulated in `buffer-undo-list' to
    ;; `buffer-undo-tree'
    (undo-list-transfer-to-tree)

    (dotimes (i (or arg 1))
      (setq current (undo-tree-current buffer-undo-tree))
      ;; check if at top of undo tree
      (if (null (undo-tree-node-previous
                 (undo-tree-current buffer-undo-tree)))
          (error "No further undo information")
	;; remove any GC'd elements from node's undo list
	(setq current (undo-tree-current buffer-undo-tree))
	(decf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-undo current)))
	(setf (undo-tree-node-undo current)
	      (undo-list-clean-GCd-elts (undo-tree-node-undo current)))
	(incf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-undo current)))
        ;; undo one record from undo tree
        (primitive-undo 1 (undo-tree-copy-list (undo-tree-node-undo current)))
        ;; pop redo entries that `primitive-undo' has added to
        ;; `buffer-undo-list' and record them in current node's redo record,
	;; replacing existing entry if one already exists
        (when (undo-tree-node-redo current)
	  (decf (undo-tree-size buffer-undo-tree)
		(undo-list-byte-size (undo-tree-node-redo current))))
	(setf (undo-tree-node-redo current) (undo-list-pop-changeset))
	(incf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-redo current)))
        ;; rewind current node
        (setf (undo-tree-current buffer-undo-tree)
	      (undo-tree-node-previous current))
        ;; update timestamp
        (setf (undo-tree-node-timestamp (undo-tree-current buffer-undo-tree))
              (current-time))))

    ;; inform user if at branch point
    (when (> (undo-tree-num-branches) 1) (message "Undo branch point!"))))



(defun undo-tree-redo (&optional arg)
  "Redo changes. A numeric ARG serves as a repeat count."
  (interactive "p")
  ;; throw error if undo is disabled in buffer
  (when (eq buffer-undo-list t) (error "No undo information in this buffer"))

  (let ((undo-in-progress t)
	current)
    ;; if `buffer-undo-tree' is empty, create initial undo-tree
    (when (null buffer-undo-tree)
      (setq buffer-undo-tree (make-undo-tree)))
    ;; transfer entries accumulated in `buffer-undo-list' to
    ;; `buffer-undo-tree'
    (undo-list-transfer-to-tree)

    (dotimes (i (or arg 1))
      ;; check if at bottom of undo tree
      (if (null (undo-tree-node-next (undo-tree-current buffer-undo-tree)))
	  (error "No further redo information")
	;; advance current node
	(setq current (undo-tree-current buffer-undo-tree)
	      current (setf (undo-tree-current buffer-undo-tree)
			    (nth (undo-tree-node-branch current)
				 (undo-tree-node-next current))))
	;; remove any GC'd elements from node's redo list
	(decf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-redo current)))
	(setf (undo-tree-node-redo current)
	      (undo-list-clean-GCd-elts (undo-tree-node-redo current)))
	(incf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-redo current)))
	;; redo one record from undo tree
	(primitive-undo 1 (undo-tree-copy-list
			   (undo-tree-node-redo current)))
	;; pop undo entries that `primitive-undo' has added to
	;; `buffer-undo-list' and record them in current node's undo record,
	;; replacing existing entry if one already exists
	(when (undo-tree-node-undo current)
	  (decf (undo-tree-size buffer-undo-tree)
		(undo-list-byte-size (undo-tree-node-undo current))))
	(setf (undo-tree-node-undo current) (undo-list-pop-changeset))
	(incf (undo-tree-size buffer-undo-tree)
	      (undo-list-byte-size (undo-tree-node-undo current)))
	;; update timestamp
	(setf (undo-tree-node-timestamp current) (current-time))))

    ;; inform user if at branch point
    (when (> (undo-tree-num-branches) 1) (message "Undo branch point!"))))



(defun undo-tree-switch-branch (branch)
  "Switch to a different BRANCH of the undo tree.
This will affect which branch to descend when *redoing* changes
using `undo-tree-redo'."
  (interactive (list (or (and prefix-arg (prefix-numeric-value prefix-arg))
                         (and (not (eq buffer-undo-list t))
			      (or (undo-list-transfer-to-tree) t)
                              (> (undo-tree-num-branches) 1)
                              (read-number
                               (format "Branch (0-%d): "
                                       (1- (undo-tree-num-branches))))))))
  ;; throw error if undo is disabled in buffer
  (when (eq buffer-undo-list t) (error "No undo information in this buffer"))
  ;; sanity check branch number
  (when (<= (undo-tree-num-branches) 1) (error "Not at undo branch point"))
  (when (or (< branch 0) (> branch (1- (undo-tree-num-branches))))
    (error "Invalid branch number"))
  ;; transfer entries accumulated in `buffer-undo-list' to `buffer-undo-tree'
  (undo-list-transfer-to-tree)
  ;; switch branch
  (setf (undo-tree-node-branch (undo-tree-current buffer-undo-tree))
	branch))


(defun undo-tree-set (node)
  ;; Set buffer to state corresponding to NODE. Returns intersection point
  ;; between path back from current node and path back from selected NODE.
  (let ((path (make-hash-table :test 'eq))
        (n node))
    (puthash (undo-tree-root buffer-undo-tree) t path)
    ;; build list of nodes leading back from selected node to root, updating
    ;; branches as we go to point down to selected node
    (while (progn
             (puthash n t path)
             (when (undo-tree-node-previous n)
               (setf (undo-tree-node-branch (undo-tree-node-previous n))
                     (undo-tree-position
                      n (undo-tree-node-next (undo-tree-node-previous n))))
               (setq n (undo-tree-node-previous n)))))
    ;; work backwards from current node until we intersect path back from
    ;; selected node
    (setq n (undo-tree-current buffer-undo-tree))
    (while (not (gethash n path))
      (setq n (undo-tree-node-previous n)))
    ;; ascend tree until intersection node
    (while (not (eq (undo-tree-current buffer-undo-tree) n))
      (undo-tree-undo))
    ;; descend tree until selected node
    (while (not (eq (undo-tree-current buffer-undo-tree) node))
      (undo-tree-redo))
    n))  ; return intersection node



(defun undo-tree-save-state-to-register (register)
  "Store current undo-tree state to REGISTER.
The saved state can be restored using
`undo-tree-restore-state-from-register'.
Argument is a character, naming the register."
  (interactive "cUndo-tree state to register: ")
  ;; throw error if undo is disabled in buffer
  (when (eq buffer-undo-list t) (error "No undo information in this buffer"))
  ;; transfer entries accumulated in `buffer-undo-list' to `buffer-undo-tree'
  (undo-list-transfer-to-tree)
  ;; save current node to REGISTER
  (set-register register (undo-tree-current buffer-undo-tree))
  ;; record REGISTER in current node, for visualizer
  (setf (undo-tree-node-register (undo-tree-current buffer-undo-tree))
	register))



(defun undo-tree-restore-state-from-register (register)
  "Restore undo-tree state from REGISTER.
The state must be saved using `undo-tree-save-state-to-register'.
Argument is a character, naming the register."
  (interactive "cRestore undo-tree state from register: ")
  ;; throw error if undo is disabled in buffer, or if register doesn't contain
  ;; an undo-tree node
  (let ((node (get-register register)))
    (cond
     ((eq buffer-undo-list t)
      (error "No undo information in this buffer"))
     ((not (undo-tree-node-p node))
      (error "Register doesn't contain undo-tree state")))
    ;; transfer entries accumulated in `buffer-undo-list' to `buffer-undo-tree'
    (undo-list-transfer-to-tree)
    ;; restore buffer state corresponding to saved node
    (undo-tree-set node)))




;;; =====================================================================
;;;                       Undo-tree visualizer

(defun undo-tree-visualize ()
  "Visualize the current buffer's undo tree."
  (interactive)
  (deactivate-mark)
  ;; throw error if undo is disabled in buffer
  (when (eq buffer-undo-list t) (error "No undo information in this buffer"))
  ;; transfer entries accumulated in `buffer-undo-list' to `buffer-undo-tree'
  (undo-list-transfer-to-tree)
  ;; add hook to kill visualizer buffer if original buffer is changed
  (add-hook 'before-change-functions 'undo-tree-kill-visualizer nil t)
  ;; prepare *undo-tree* buffer, then draw tree in it
  (let ((undo-tree buffer-undo-tree)
        (buff (current-buffer))
	(display-buffer-mark-dedicated 'soft))
    (switch-to-buffer-other-window undo-tree-visualizer-buffer-name)
    (undo-tree-visualizer-mode)
    (setq undo-tree-visualizer-parent-buffer buff)
    (setq buffer-undo-tree undo-tree)
    (setq buffer-read-only nil)
    (undo-tree-draw-tree undo-tree)
    (setq buffer-read-only t)))


(defun undo-tree-kill-visualizer (&rest dummy)
  ;; Kill visualizer. Added to `before-change-functions' hook of original
  ;; buffer when visualizer is invoked.
  (unless undo-in-progress
    (unwind-protect
	(with-current-buffer undo-tree-visualizer-buffer-name
	  (undo-tree-visualizer-quit)))))



(defun undo-tree-draw-tree (undo-tree)
  ;; Draw UNDO-TREE in current buffer.
  (erase-buffer)
  (undo-tree-move-down 1)      ; top margin
  (undo-tree-clear-visualizer-data undo-tree)
  (undo-tree-compute-widths undo-tree)
  (undo-tree-move-forward
   (max (/ (window-width) 2)
        (+ (undo-tree-node-char-lwidth (undo-tree-root undo-tree))
           ;; add space for left part of left-most time-stamp
           (if undo-tree-visualizer-timestamps 4 0)
           2)))                ; left margin
  ;; draw undo-tree
  (let ((undo-tree-insert-face 'undo-tree-visualizer-default-face)
        (stack (list (undo-tree-root undo-tree)))
        (n (undo-tree-root undo-tree)))
    ;; link root node to its representation in visualizer
    (unless (markerp (undo-tree-node-marker n))
      (setf (undo-tree-node-marker n) (make-marker))
      (set-marker-insertion-type (undo-tree-node-marker n) nil))
    (move-marker (undo-tree-node-marker n) (point))
    ;; draw nodes from stack until stack is empty
    (while stack
      (setq n (pop stack))
      (goto-char (undo-tree-node-marker n))
      (setq n (undo-tree-draw-subtree n nil))
      (setq stack (append stack n))))
  ;; highlight active branch
  (goto-char (undo-tree-node-marker (undo-tree-root undo-tree)))
  (let ((undo-tree-insert-face 'undo-tree-visualizer-active-branch-face))
    (undo-tree-highlight-active-branch (undo-tree-root undo-tree)))
  ;; highlight current node
  (undo-tree-draw-node (undo-tree-current undo-tree) 'current))


(defun undo-tree-highlight-active-branch (node)
  ;; Draw highlighted active branch below NODE in current buffer.
  (let ((stack (list node)))
    ;; link node to its representation in visualizer
    (unless (markerp (undo-tree-node-marker node))
      (setf (undo-tree-node-marker node) (make-marker))
      (set-marker-insertion-type (undo-tree-node-marker node) nil))
    (move-marker (undo-tree-node-marker node) (point))
    ;; draw active branch
    (while stack
      (setq node (pop stack))
      (goto-char (undo-tree-node-marker node))
      (setq node (undo-tree-draw-subtree node 'active))
      (setq stack (append stack node)))))


(defun undo-tree-draw-node (node &optional current)
  ;; Draw symbol representing NODE in visualizer.
  (goto-char (undo-tree-node-marker node))
  ;; if displaying timestamps, represent node by timestamp
  (if undo-tree-visualizer-timestamps
      (progn
        (backward-char 4)
        (if current (undo-tree-insert ?*) (undo-tree-insert ? ))
        (undo-tree-insert
         (undo-tree-timestamp-to-string (undo-tree-node-timestamp node)))
        (backward-char 5)
        (move-marker (undo-tree-node-marker node) (point))
        (put-text-property (- (point) 3) (+ (point) 5)
                           'undo-tree-node node))
    ;; represent node by differentl symbols, depending on whether it's the
    ;; current node or is saved in a register
    (let ((register (undo-tree-node-register node)))
      (cond
       (current
	(let ((undo-tree-insert-face
	       (cons 'undo-tree-visualizer-current-face
		     (and (boundp 'undo-tree-insert-face)
			  (or (and (consp undo-tree-insert-face)
				   undo-tree-insert-face)
			      (list undo-tree-insert-face))))))
	  (undo-tree-insert ?x)))
       ((and register (eq node (get-register register)))
	(let ((undo-tree-insert-face
	       (cons 'undo-tree-visualizer-register-face
		     (and (boundp 'undo-tree-insert-face)
			  (or (and (consp undo-tree-insert-face)
				   undo-tree-insert-face)
			      (list undo-tree-insert-face))))))
	  (undo-tree-insert register)))
       (t (undo-tree-insert ?o))))
    (backward-char 1)
    (put-text-property (point) (1+ (point)) 'undo-tree-node node)))


(defun undo-tree-draw-subtree (node &optional active-branch)
  ;; Draw subtree rooted at NODE. The subtree will start from point.
  ;; If ACTIVE-BRANCH is non-nil, just draw active branch below NODE.
  ;; If TIMESTAP is non-nil, draw time-stamps instead of "o" at nodes.
  (let ((num-children (length (undo-tree-node-next node)))
        node-list pos trunk-pos n)
    ;; draw node itself
    (undo-tree-draw-node node)

    (cond
     ;; if we're at a leaf node, we're done
     ((= num-children 0))

     ;; if node has only one child, draw it (not strictly necessary to deal
     ;; with this case separately, but as it's by far the most common case
     ;; this makes the code clearer and more efficient)
     ((= num-children 1)
      (undo-tree-move-down 1)
      (undo-tree-insert ?|)
      (backward-char 1)
      (undo-tree-move-down 1)
      (undo-tree-insert ?|)
      (backward-char 1)
      (undo-tree-move-down 1)
      (setq n (car (undo-tree-node-next node)))
      ;; link next node to its representation in visualizer
      (unless (markerp (undo-tree-node-marker n))
        (setf (undo-tree-node-marker n) (make-marker))
        (set-marker-insertion-type (undo-tree-node-marker n) nil))
      (move-marker (undo-tree-node-marker n) (point))
      ;; add next node to list of nodes to draw next
      (push n node-list))

     ;; if node had multiple children, draw branches
     (t
      (undo-tree-move-down 1)
      (undo-tree-insert ?|)
      (backward-char 1)
      (setq trunk-pos (point))
      ;; left subtrees
      (backward-char
       (- (undo-tree-node-char-lwidth node)
          (undo-tree-node-char-lwidth
           (car (undo-tree-node-next node)))))
      (setq pos (point))
      (setq n (cons nil (undo-tree-node-next node)))
      (dotimes (i (/ num-children 2))
        (setq n (cdr n))
        (when (or (null active-branch)
                  (eq (car n)
                      (nth (undo-tree-node-branch node)
                           (undo-tree-node-next node))))
          (undo-tree-move-forward 2)
          (undo-tree-insert ?_ (- trunk-pos pos 2))
          (goto-char pos)
          (undo-tree-move-forward 1)
          (undo-tree-move-down 1)
          (undo-tree-insert ?/)
          (backward-char 2)
          (undo-tree-move-down 1)
          ;; link node to its representation in visualizer
          (unless (markerp (undo-tree-node-marker (car n)))
            (setf (undo-tree-node-marker (car n)) (make-marker))
            (set-marker-insertion-type (undo-tree-node-marker (car n)) nil))
          (move-marker (undo-tree-node-marker (car n)) (point))
          ;; add node to list of nodes to draw next
          (push (car n) node-list))
        (goto-char pos)
        (undo-tree-move-forward
         (+ (undo-tree-node-char-rwidth (car n))
            (undo-tree-node-char-lwidth (cadr n))
            undo-tree-visualizer-spacing 1))
        (setq pos (point)))
      ;; middle subtree (only when number of children is odd)
      (when (= (mod num-children 2) 1)
        (setq n (cdr n))
        (when (or (null active-branch)
                  (eq (car n)
                      (nth (undo-tree-node-branch node)
                           (undo-tree-node-next node))))
          (undo-tree-move-down 1)
          (undo-tree-insert ?|)
          (backward-char 1)
          (undo-tree-move-down 1)
          ;; link node to its representation in visualizer
          (unless (markerp (undo-tree-node-marker (car n)))
            (setf (undo-tree-node-marker (car n)) (make-marker))
            (set-marker-insertion-type (undo-tree-node-marker (car n)) nil))
          (move-marker (undo-tree-node-marker (car n)) (point))
          ;; add node to list of nodes to draw next
          (push (car n) node-list))
        (goto-char pos)
        (undo-tree-move-forward
         (+ (undo-tree-node-char-rwidth (car n))
            (if (cadr n) (undo-tree-node-char-lwidth (cadr n)) 0)
            undo-tree-visualizer-spacing 1))
        (setq pos (point)))
      ;; right subtrees
      (incf trunk-pos)
      (dotimes (i (/ num-children 2))
        (setq n (cdr n))
        (when (or (null active-branch)
                  (eq (car n)
                      (nth (undo-tree-node-branch node)
                           (undo-tree-node-next node))))
          (goto-char trunk-pos)
          (undo-tree-insert ?_ (- pos trunk-pos 1))
          (goto-char pos)
          (backward-char 1)
          (undo-tree-move-down 1)
          (undo-tree-insert ?\\)
          (undo-tree-move-down 1)
          ;; link node to its representation in visualizer
          (unless (markerp (undo-tree-node-marker (car n)))
            (setf (undo-tree-node-marker (car n)) (make-marker))
            (set-marker-insertion-type (undo-tree-node-marker (car n)) nil))
          (move-marker (undo-tree-node-marker (car n)) (point))
          ;; add node to list of nodes to draw next
          (push (car n) node-list))
        (when (cdr n)
          (goto-char pos)
          (undo-tree-move-forward
           (+ (undo-tree-node-char-rwidth (car n))
              (if (cadr n) (undo-tree-node-char-lwidth (cadr n)) 0)
              undo-tree-visualizer-spacing 1))
          (setq pos (point))))
      ))
    ;; return list of nodes to draw next
    (nreverse node-list)))



(defun undo-tree-node-char-lwidth (node)
  ;; Return left-width of NODE measured in characters.
  (if (= (length (undo-tree-node-next node)) 0) 0
    (- (* (+ undo-tree-visualizer-spacing 1) (undo-tree-node-lwidth node))
       (if (= (undo-tree-node-cwidth node) 0)
           (1+ (/ undo-tree-visualizer-spacing 2)) 0))))


(defun undo-tree-node-char-rwidth (node)
  ;; Return right-width of NODE measured in characters.
  (if (= (length (undo-tree-node-next node)) 0) 0
    (- (* (+ undo-tree-visualizer-spacing 1) (undo-tree-node-rwidth node))
       (if (= (undo-tree-node-cwidth node) 0)
           (1+ (/ undo-tree-visualizer-spacing 2)) 0))))


(defun undo-tree-insert (str &optional arg)
  ;; Insert character or string STR ARG times, overwriting, and using
  ;; `undo-tree-insert-face'.
  (unless arg (setq arg 1))
  (when (characterp str)
    (setq str (make-string arg str))
    (setq arg 1))
  (dotimes (i arg) (insert str))
  (setq arg (* arg (length str)))
  (undo-tree-move-forward arg)
  ;; make sure mark isn't active, otherwise `backward-delete-char' might
  ;; delete region instead of single char if transient-mark-mode is enabled
  (setq mark-active nil)
  (backward-delete-char arg)
  (when (boundp 'undo-tree-insert-face)
    (put-text-property (- (point) arg) (point) 'face undo-tree-insert-face)))


(defun undo-tree-move-down (&optional arg)
  ;; Move down, extending buffer if necessary.
  (let ((row (line-number-at-pos))
        (col (current-column))
        line)
    (unless arg (setq arg 1))
    (forward-line arg)
    (setq line (line-number-at-pos))
    ;; if buffer doesn't have enough lines, add some
    (when (/= line (+ row arg))
      (insert (make-string (- arg (- line row)) ?\n)))
    (undo-tree-move-forward col)))


(defun undo-tree-move-forward (&optional arg)
  ;; Move forward, extending buffer if necessary.
  (unless arg (setq arg 1))
  (let ((n (- (line-end-position) (point))))
    (if (> n arg)
        (forward-char arg)
      (end-of-line)
      (insert (make-string (- arg n) ? )))))


(defun undo-tree-timestamp-to-string (timestamp)
  ;; Convert TIMESTAMP to hh:mm:ss string.
  (let ((time (decode-time timestamp)))
    (format "%02d:%02d:%02d" (nth 2 time) (nth 1 time) (nth 0 time))))




;;; =====================================================================
;;;                    Visualizer mode commands

(defun undo-tree-visualizer-mode ()
  "Major mode used in undo-tree visualizer.

The undo-tree visualizer can only be invoked from a buffer in
which `undo-tree-mode' is enabled. The visualizer displays the
undo history tree graphically, and allows you to browse around
the undo history, undoing or redoing the corresponding changes in
the parent buffer.

Within the undo-tree visualizer, the following keys are available:

  \\{undo-tree-visualizer-map}"
  (interactive)
  (setq major-mode 'undo-tree-visualizer-mode)
  (setq mode-name "undo-tree-visualizer-mode")
  (use-local-map undo-tree-visualizer-map)
  (setq truncate-lines t)
  (setq cursor-type nil)
  (setq buffer-read-only t))



(defun undo-tree-visualize-undo (&optional arg)
  "Undo changes. A numeric ARG serves as a repeat count."
  (interactive "p")
  (setq buffer-read-only nil)
  (let ((undo-tree-insert-face 'undo-tree-visualizer-active-branch-face))
    (undo-tree-draw-node (undo-tree-current buffer-undo-tree)))
  (switch-to-buffer-other-window undo-tree-visualizer-parent-buffer)
  (deactivate-mark)
  (unwind-protect
      (undo-tree-undo arg)
    (switch-to-buffer-other-window undo-tree-visualizer-buffer-name)
    (undo-tree-draw-node (undo-tree-current buffer-undo-tree) 'current)
    (setq buffer-read-only t)))


(defun undo-tree-visualize-redo (&optional arg)
  "Redo changes. A numeric ARG serves as a repeat count."
  (interactive "p")
  (setq buffer-read-only nil)
  (let ((undo-tree-insert-face 'undo-tree-visualizer-active-branch-face))
    (undo-tree-draw-node (undo-tree-current buffer-undo-tree)))
  (switch-to-buffer-other-window undo-tree-visualizer-parent-buffer)
  (deactivate-mark)
  (unwind-protect
      (undo-tree-redo arg)
    (switch-to-buffer-other-window undo-tree-visualizer-buffer-name)
    (goto-char (undo-tree-node-marker (undo-tree-current buffer-undo-tree)))
    (undo-tree-draw-node (undo-tree-current buffer-undo-tree) 'current)
    (setq buffer-read-only t)))


(defun undo-tree-visualize-switch-branch-right (arg)
  "Switch to next branch of the undo tree.
This will affect which branch to descend when *redoing* changes
using `undo-tree-redo' or `undo-tree-visualizer-redo'."
  (interactive "p")
  ;; un-highlight old active branch below current node
  (setq buffer-read-only nil)
  (goto-char (undo-tree-node-marker (undo-tree-current buffer-undo-tree)))
  (let ((undo-tree-insert-face 'undo-tree-visualizer-default-face))
    (undo-tree-highlight-active-branch (undo-tree-current buffer-undo-tree)))
  ;; increment branch
  (let ((branch (undo-tree-node-branch (undo-tree-current buffer-undo-tree))))
  (setf (undo-tree-node-branch (undo-tree-current buffer-undo-tree))
        (cond
         ((>= (+ branch arg) (undo-tree-num-branches))
          (1- (undo-tree-num-branches)))
         ((<= (+ branch arg) 0) 0)
         (t (+ branch arg))))
  ;; highlight new active branch below current node
  (goto-char (undo-tree-node-marker (undo-tree-current buffer-undo-tree)))
  (let ((undo-tree-insert-face 'undo-tree-visualizer-active-branch-face))
    (undo-tree-highlight-active-branch (undo-tree-current buffer-undo-tree)))
  ;; re-highlight current node
  (undo-tree-draw-node (undo-tree-current buffer-undo-tree) 'current)
  (setq buffer-read-only t)))


(defun undo-tree-visualize-switch-branch-left (arg)
  "Switch to previous branch of the undo tree.
This will affect which branch to descend when *redoing* changes
using `undo-tree-redo' or `undo-tree-visualizer-redo'."
  (interactive "p")
  (undo-tree-visualize-switch-branch-right (- arg)))


(defun undo-tree-visualizer-quit ()
  "Quit the undo-tree visualizer."
  (interactive)
  (undo-tree-clear-visualizer-data buffer-undo-tree)
  ;; remove kill visualizer hook from parent buffer
  (unwind-protect
      (with-current-buffer undo-tree-visualizer-parent-buffer
	(remove-hook 'before-change-functions 'undo-tree-kill-visualizer t))
    (let ((parent undo-tree-visualizer-parent-buffer)
	  window)
      (kill-buffer nil)
      (if (setq window (get-buffer-window parent))
	  (select-window window)
	(switch-to-buffer parent)))))


(defun undo-tree-visualizer-set (&optional pos)
  "Set buffer to state corresponding to undo tree node
at POS, or point if POS is nil."
  (interactive)
  (unless pos (setq pos (point)))
  (let ((node (get-text-property pos 'undo-tree-node)))
    (when node
      ;; set parent buffer to state corresponding to node at POS
      (set-buffer undo-tree-visualizer-parent-buffer)
      (undo-tree-set node)
      (set-buffer undo-tree-visualizer-buffer-name)
      (setq buffer-read-only nil)
      ;; re-draw undo tree
      (undo-tree-draw-tree buffer-undo-tree)
      (setq buffer-read-only t))))


(defun undo-tree-visualizer-mouse-set (pos)
  "Set buffer to state corresponding to undo tree node
at mouse event POS."
  (interactive "@e")
  (undo-tree-visualizer-set (event-start (nth 1 pos))))


(defun undo-tree-visualizer-toggle-timestamps ()
  "Toggle display of time-stamps."
  (interactive)
  (setq undo-tree-visualizer-spacing
        (if (setq undo-tree-visualizer-timestamps
                  (not undo-tree-visualizer-timestamps))
            ;; need sufficient space if TIMESTAMP is set
            (max 9 (default-value 'undo-tree-visualizer-spacing))
          (default-value 'undo-tree-visualizer-spacing)))
  ;; redraw tree
  (setq buffer-read-only nil)
  (undo-tree-draw-tree buffer-undo-tree)
  (setq buffer-read-only t))


(defun undo-tree-visualizer-scroll-left (&optional arg)
  (interactive "p")
  (scroll-right (or arg 1) t))


(defun undo-tree-visualizer-scroll-right (&optional arg)
  (interactive "p")
  (scroll-left (or arg 1) t))




;;; =====================================================================
;;;                    Visualizer selection mode

(defun undo-tree-visualizer-selection-mode ()
  "Major mode used to select nodes in undo-tree visualizer."
  (interactive)
  (setq major-mode 'undo-tree-visualizer-selection-mode)
  (setq mode-name "undo-tree-visualizer-selection-mode")
  (use-local-map undo-tree-visualizer-selection-map)
  (setq cursor-type 'box))


(defun undo-tree-visualizer-select-previous (&optional arg)
  "Move to previous node."
  (interactive "p")
  (let ((node (get-text-property (point) 'undo-tree-node)))
    (catch 'top
      (dotimes (i arg)
	(unless (undo-tree-node-previous node) (throw 'top t))
	(setq node (undo-tree-node-previous node))))
    (goto-char (undo-tree-node-marker node))))


(defun undo-tree-visualizer-select-next (&optional arg)
  "Move to next node."
  (interactive "p")
  (let ((node (get-text-property (point) 'undo-tree-node)))
    (catch 'bottom
      (dotimes (i arg)
	(unless (nth (undo-tree-node-branch node) (undo-tree-node-next node))
	  (throw 'bottom t))
	(setq node
	      (nth (undo-tree-node-branch node) (undo-tree-node-next node)))))
    (goto-char (undo-tree-node-marker node))))


(defun undo-tree-visualizer-select-right (&optional arg)
  "Move right to a sibling node."
  (interactive "p")
  (let ((pos (point))
	(end (line-end-position))
	node)
    (catch 'end
      (dotimes (i arg)
	(while (not node)
	  (forward-char)
	  (setq node (get-text-property (point) 'undo-tree-node))
	  (when (= (point) end) (throw 'end t)))))
    (goto-char (if node (undo-tree-node-marker node) pos))))


(defun undo-tree-visualizer-select-left (&optional arg)
  "Move left to a sibling node."
  (interactive "p")
  (let ((pos (point))
	(beg (line-beginning-position))
	node)
    (catch 'beg
      (dotimes (i arg)
	(while (not node)
	  (backward-char)
	  (setq node (get-text-property (point) 'undo-tree-node))
	  (when (= (point) beg) (throw 'beg t)))))
    (goto-char (if node (undo-tree-node-marker node) pos))))



(provide 'undo-tree)

;;; undo-tree.el ends here