[feature] add a restore function to org-brain-visualize-mode (#345)

* [feature] add a restore function to org-brain-visualize-mode

Like how user calls "Info" mode, if there is no `org-brain-visualize'
buffer exists, then everything is the same as before. If there
is *org-brain* buffer exists, switch to *org-brain*.

This feature is helpful for users who need constantly switch between
the Org-brain and the working documents.

The `quit' message can be further improved by using a better-quitting
strategy. However, the function right now can achieve this feature. It
is unclear what side effects will bring to the current packages.
Careful review should be taken.

* [mis] indentation

* [clean up]

* [clean up]

* [internal] change function name

* [internal] simplify checking exisence of *org-brain* buffer

* [internal] using `when` instead of `if` since there is no else clause

* [internal] no need for `progn`

* [feature] add `org-brain-visualize-dwim' for easy access

README.org

@@ -234,11 +234,15 @@ among entries.
 
 * Usage
 
-You can create new entries by =M-x org-brain-visualize= and then typing the name
-of a non-existing entry. You could also use =M-x org-brain-add-entry= if you do
-not want to visualize the new entry. Also commands which add children, parents
-and friends, or links to entries, can create new entries in the same way. Se
-/General information/ below.
+You can create new entries by =M-x org-brain-visualize= and then
+typing the name of a non-existing entry. You can go back to the
+=*org-brain*= buffer by =M-x org-brain-visualize-dwim=. It will switch
+to the =*org-brain*= buffer. If there's no such buffer, or if already
+there, run =org-brain-visualize=. You could also use =M-x
+org-brain-add-entry= if you do not want to visualize the new entry.
+Also commands which add children, parents and friends, or links to
+entries, can create new entries in the same way. Se /General
+information/ below.
 
 If you find that =org-brain= is missing entries, or list entries which doesn't
 exist, try using =M-x org-brain-update-id-locations=, which syncs the

org-brain.el

@@ -2432,6 +2432,19 @@ Unless WANDER is t, `org-brain-stop-wandering' will be run."
           (pop-to-buffer "*org-brain*")
         (pop-to-buffer-same-window "*org-brain*")))))
 
+;;;###autoload
+(defun org-brain-visualize-dwim ()
+  "Switch to the *org-brain* buffer.
+If there's no such buffer, or if already there, run `org-brain-visualize'."
+  (interactive)
+  (if (and (not (org-brain-maybe-switch-brain))
+           (not (eq major-mode 'org-brain-visualize-mode))
+           (get-buffer "*org-brain*"))
+      (if org-brain-open-same-window
+          (pop-to-buffer "*org-brain*")
+        (pop-to-buffer-same-window "*org-brain*"))
+    (call-interactively #'org-brain-visualize)))
+
 ;;;###autoload
 (defun org-brain-visualize-entry-at-pt ()
   "Use `org-brain-visualize' on the `org-brain-entry-at-pt'.