Window configurations stack management

The stack size is now customizable. Always remove the oldest window
configurations in excess to respect the stack size.

Avoid stack duplicates and add the current window configuration to
the tail of the stack before reverting to a previous configuration.

Author: mehw

resize-window.el

@@ -82,6 +82,11 @@ This is also valuable to see that you are in resize mode."
   :type 'boolean
   :group 'resize-window)
 
+(defcustom resize-window-stack-size 16
+  "Size of the stack for holding window configurations."
+  :type 'integer
+  :group 'resize-window)
+
 (defcustom resize-window-swap-capital-and-lowercase-behavior nil
   "Reverse default behavior of lower case and uppercase arguments."
   :type 'boolean
@@ -96,7 +101,10 @@ This is also valuable to see that you are in resize mode."
   "List of background overlays.")
 
 (defvar resize-window--window-stack ()
-  "Stack for holding window configurations.")
+  "Stack for holding window configurations.
+
+It is an alist of format ((configuration . time)...), where time
+is the time when the configuration was saved/visited.")
 
 (defface resize-window-background
   '((t (:foreground "gray40")))
@@ -241,6 +249,9 @@ If SCALED, then call action with the `resize-window-uppercase-argument'."
 Press n to resize down, p to resize up, b to resize left and f
 to resize right."
   (interactive)
+  (resize-window--refresh-stack)
+  ;; NOTE: Do not trim the stack here. Let stack requests to handle
+  ;; window configurations in excess.
   (resize-window--add-backgrounds)
   (resize-window--notify "Resize mode: enter character, ? for help")
   (condition-case nil
@@ -391,13 +402,111 @@ Restore the help menu only if it is currently open."
           (resize-window--display-menu 'open)
         (resize-window--add-backgrounds)))))
 
+(defun resize-window--apply-config (config)
+  "Return the window configuration CONFIG after applying it.
+Return nil if CONFIG isn't a proper window configuration.
+Do not change the current window configuration."
+  (when (window-configuration-p config)
+    (save-excursion
+      (save-window-excursion
+        (set-window-configuration config)
+        (resize-window--window-config)))))
+
+(defun resize-window--refresh-stack ()
+  "Refresh the stack and remove adjacent duplicates.
+Each window configuration is restored and saved again.
+
+The configurations saved time is not changed. Always remove the
+older configuration when a duplicate is found.
+
+A refresh reveals duplicate configurations. When a configuration
+is restored that takes account of the current state of the frame.
+Since killed buffers cannot be dug up, applying a state will use
+what it finds, and so two configurations may end up the same."
+  (let (stack)
+    (dotimes (n (length resize-window--window-stack))
+      (let* ((this-member (nth n resize-window--window-stack))
+             (this-config (resize-window--apply-config (car this-member)))
+             (this-svtime (cdr this-member))
+             (prev-config (caar stack))
+             (prev-svtime (cdar stack)))
+        (if (and this-config prev-config
+                 (compare-window-configurations this-config prev-config))
+            (when (time-less-p prev-svtime this-svtime)
+              (setcar stack this-member))
+          (when this-config
+            (push this-member stack)))))
+    (setq resize-window--window-stack (nreverse stack))))
+
+(defun resize-window--window-trim ()
+  "Trim the oldest window configurations in excess from the stack.
+Return the removed configurations."
+  (let* ((size (length resize-window--window-stack))
+         (trim (- size resize-window-stack-size)))
+    (when (> trim 0)
+      (let ((oldest-members
+             (sort (copy-sequence resize-window--window-stack)
+                   (lambda (a b)
+                     (time-less-p (cdr a) (cdr b))))))
+        (nbutlast oldest-members (- size trim))
+        (dotimes (n (length oldest-members))
+          (let ((old-member (nth n oldest-members)))
+            (setq resize-window--window-stack
+                  (delq old-member resize-window--window-stack))))
+        oldest-members))))
+
 (defun resize-window--window-push ()
-  "Save the current state in the stack."
-  (push (resize-window--window-config) resize-window--window-stack))
+  "Save the current window configuration in the stack.
+Return the configuration if saved.
+
+Trim adjacent duplicates and old configurations when necessary.
+
+See also `resize-window-stack-size'."
+  (let* ((curr-config (resize-window--window-config))
+         (curr-member (cons curr-config (current-time)))
+         (prev-config nil))
+    ;; trim duplicates from the tail
+    (while (and (setq prev-config (caar (last resize-window--window-stack)))
+                (setq prev-config (resize-window--apply-config prev-config))
+                (compare-window-configurations curr-config prev-config)
+                (nbutlast resize-window--window-stack)))
+    ;; trim duplicates from the head
+    (while (and (setq prev-config (caar resize-window--window-stack))
+                (setq prev-config (resize-window--apply-config prev-config))
+                (compare-window-configurations curr-config prev-config)
+                (pop resize-window--window-stack)))
+    (push curr-member resize-window--window-stack)
+    (resize-window--window-trim)
+    (when resize-window--window-stack
+      curr-member)))
 
 (defun resize-window--window-pop ()
-  "Return the first element and remove it from the stack."
-  (pop resize-window--window-stack))
+  "Restore a previous window configuration.
+Return the configuration if restored.
+
+Save the current configuration to the tail of the stack.
+
+Trim adjacent duplicates and old configurations when necessary.
+
+See also `resize-window-stack-size'."
+  (resize-window--window-trim)
+  (let* ((curr-config (resize-window--window-config))
+         (curr-member (cons curr-config (current-time)))
+         (prev-config nil))
+    ;; trim duplicates from the tail
+    (while (and (setq prev-config (caar (last resize-window--window-stack)))
+                (setq prev-config (resize-window--apply-config prev-config))
+                (compare-window-configurations curr-config prev-config)
+                (nbutlast resize-window--window-stack)))
+    ;; trim duplicates from the head
+    (while (and (setq prev-config (car (pop resize-window--window-stack)))
+                (setq prev-config (resize-window--apply-config prev-config))
+                (compare-window-configurations curr-config prev-config)))
+    (when prev-config
+      (setq resize-window--window-stack
+            (append resize-window--window-stack (list curr-member)))
+      (resize-window--restore-config prev-config)
+      prev-config)))
 
 (defun resize-window--kill-other-windows ()
   "Delete other windows."