"Return WORKGROUP's working-wconfig.

If WORKGROUP is the current workgroup in `selected-frame', and

NOUPDATE is nil, set its working wconfig in `selected-frame' to

`wg-current-wconfig' and return the updated wconfig.  Otherwise

return WORKGROUP's current undo state."

  (if (and (not noupdate) (wg-current-workgroup-p workgroup))

      (wg-set-workgroup-working-wconfig workgroup (wg-current-wconfig))

    (wg-with-undo workgroup (state undo-pointer undo-list)

      (nth undo-pointer undo-list))))

(defun wg-update-current-workgroup-working-wconfig ()

  "Update `selected-frame's current workgroup's working-wconfig

with `wg-current-wconfig'."

  (wg-awhen (wg-current-workgroup t)

    (wg-set-workgroup-working-wconfig it (wg-current-wconfig))))

(defun wg-restore-wconfig-undoably (wconfig &optional noundo)

  "Restore WCONFIG in `selected-frame', saving undo information."

  (when noundo (wg-unflag-undoify-window-configuration-change))

  (wg-update-current-workgroup-working-wconfig)

  (wg-restore-wconfig wconfig))

(defun wg-workgroup-offset-position-in-undo-list (workgroup increment)

  "Increment WORKGROUP's undo-pointer by INCREMENT.

Also restore the wconfig at the incremented undo-pointer if

WORKGROUP is current."

  (wg-with-undo workgroup (state undo-pointer undo-list)

    (let ((new-pointer (+ undo-pointer increment)))

      (when (wg-within new-pointer 0 (length undo-list))

        (when (wg-current-workgroup-p workgroup)

          (wg-restore-wconfig-undoably (nth new-pointer undo-list) t))

        (setf (wg-workgroup-state-undo-pointer state) new-pointer)))))

(defun wg-undoify-window-configuration-change ()

  "Conditionally `wg-add-wconfig-to-undo-list'.

Added to `post-command-hook'."

  (when (and

         ;; When the window config has changed,

         wg-window-configuration-changed

         ;; and undoification is still on for the current command

         wg-undoify-window-configuration-change

         ;; and the change didn't occur while the minibuffer is active,

         (wg-minibuffer-inactive-p))

    ;; and there's a current workgroup,

    (wg-when-let ((workgroup (wg-current-workgroup t)))

      ;; add the current wconfig to that workgroup's undo list:

      (wg-add-wconfig-to-undo-list workgroup (wg-current-wconfig))))

  ;; Reset all flags no matter what:

  (setq wg-window-configuration-changed nil

        wg-undoify-window-configuration-change t

        wg-already-updated-working-wconfig nil))

(defun wg-update-working-wconfig-hook ()

  "Used in before advice on all functions that trigger

`window-configuration-change-hook' to save up to date undo info

before the change."

  (when (and (not wg-already-updated-working-wconfig)

             (wg-minibuffer-inactive-p))

    (wg-update-current-workgroup-working-wconfig)

    (setq wg-already-updated-working-wconfig t)))

;;; base wconfig updating

(defun wg-update-all-base-wconfigs ()

  "Update every workgroup's base wconfig with

`wg-workgroup-update-base-wconfig'."

  (dolist (workgroup (wg-workgroup-list))

    (wg-awhen (wg-workgroup-selected-frame-wconfig workgroup)

      (setf (wg-workgroup-base-wconfig workgroup) it

            (wg-workgroup-selected-frame-wconfig workgroup) nil))))

(defun wg-update-working-wconfig-on-delete-frame (frame)

  "Update FRAME's current workgroup's working-wconfig before

FRAME is deleted, so we don't lose its state."

  (with-selected-frame frame

    (wg-update-current-workgroup-working-wconfig)))

;;; workgroup saved wconfigs

(defun wg-workgroup-saved-wconfig-names (workgroup)

  "Return a new list of the names of all WORKGROUP's saved wconfigs."

  (mapcar 'wg-wconfig-name (wg-workgroup-saved-wconfigs workgroup)))

(defun wg-workgroup-get-saved-wconfig (workgroup wconfig-or-name)

  "Return the wconfig in WORKGROUP's saved wconfigs named WCONFIG-OR-NAME.

WCONFIG-OR-NAME must be either a string or a wconfig.  If

WCONFIG-OR-NAME is a string and there is no saved wconfig with

that name, return nil.  If WCONFIG-OR-NAME is a wconfig, and it

is a member of WORKGROUP's saved wconfigs, return is as given.

Otherwise return nil."

  (let ((wconfigs (wg-workgroup-saved-wconfigs workgroup)))

    (etypecase wconfig-or-name

      (wg-wconfig (car (memq wconfig-or-name wconfigs)))

      (string (find wconfig-or-name wconfigs

                    :key 'wg-wconfig-name

                    :test 'string=)))))

(defun wg-workgroup-save-wconfig (workgroup wconfig)

  "Add WCONFIG to WORKGROUP's saved wconfigs.  WCONFIG must have

a name.  If there's already a wconfig with the same name in

WORKGROUP's saved wconfigs, replace it."

  (let ((name (wg-wconfig-name wconfig)))

    (unless name (error "Attempt to save a nameless wconfig"))

    (setf (wg-workgroup-modified workgroup) t)

    (wg-asetf (wg-workgroup-saved-wconfigs workgroup)

              (cons wconfig (remove* name it

                                     :key 'wg-wconfig-name

                                     :test 'string=)))))

(defun wg-workgroup-kill-saved-wconfig (workgroup wconfig-or-name)

  "Delete WCONFIG-OR-NAME from WORKGROUP's saved wconfigs.

WCONFIG-OR-NAME is resolved with `wg-workgroup-get-saved-wconfig'."

  (wg-when-let ((wconfig (wg-workgroup-get-saved-wconfig

                          workgroup wconfig-or-name)))

    (wg-asetf (wg-workgroup-saved-wconfigs workgroup) (remq wconfig it)

              (wg-workgroup-modified workgroup) t)))

;;; garbage collection

;; update buf list

(defun wg-update-buffer-in-buf-list (&optional buffer)

  "Update BUFFER's corresponding buf in `wg-buf-list'.

BUFFER nil defaults to `current-buffer'."

  (let ((buffer (or buffer (current-buffer))))

    (wg-when-let ((uid (wg-buffer-uid buffer))

                  (old-buf (wg-find-buf-by-uid uid))

                  (new-buf (wg-buffer-to-buf buffer)))

      (setf (wg-buf-uid new-buf) (wg-buf-uid old-buf))

      (wg-asetf (wg-buf-list) (cons new-buf (remove old-buf it))))))

(defun wg-update-buf-list (&optional buffer-list)

  "Update all bufs in `wg-buf-list' corresponding to buffers in BUFFER-LIST."

  (mapc 'wg-update-buffer-in-buf-list (or buffer-list (buffer-list))))

;; gc buf uids

(defun wg-workgroup-gc-buf-uids (workgroup)

  "Remove buf uids from WORKGROUP that have no referent in `wg-buf-list'."

  (wg-asetf (wg-workgroup-strong-buf-uids workgroup)

            (wg-remove-if-not 'wg-find-buf-by-uid it)

            (wg-workgroup-weak-buf-uids workgroup)

            (wg-remove-if-not 'wg-find-buf-by-uid it)))

(defun wg-gc-buf-uids ()

  "Remove from all workgroups those buf uids that have no referent in `wg-buf-list'."

  (mapc 'wg-workgroup-gc-buf-uids (wg-workgroup-list)))

;; gc bufs

(defun wg-wtree-buf-uids (wtree)

  "Return a new list of the buf uids of all wins in wtree."

  (wg-flatten-wtree wtree 'wg-win-buf-uid))

(defun wg-wtree-unique-buf-uids (wtree)

  "Return a list of the unique buf uids of all wins in wtree."

  (remove-duplicates (wg-wtree-buf-uids wtree) :test 'string=))

(defun wg-wconfig-buf-uids (wconfig)

  "Return WCONFIG's wtree's `wg-wtree-buf-uids'."

  (wg-wtree-unique-buf-uids (wg-wconfig-wtree wconfig)))

(defun wg-workgroup-base-wconfig-buf-uids (workgroup)

  "Return a new list of all unique buf uids in WORKGROUP's working wconfig."

  (wg-wconfig-buf-uids (wg-workgroup-base-wconfig workgroup)))

(defun wg-workgroup-saved-wconfigs-buf-uids (workgroup)

  "Return a new list of all unique buf uids in WORKGROUP's base wconfig."

  (reduce 'wg-string-list-union

          (wg-workgroup-saved-wconfigs workgroup)

          :key 'wg-wconfig-buf-uids))

(defun wg-workgroup-all-wconfig-buf-uids (workgroup)

  "Return a new list of all unique buf uids in WORKGROUP's wconfigs."

  (union (wg-workgroup-base-wconfig-buf-uids workgroup)

         (wg-workgroup-saved-wconfigs-buf-uids workgroup)

         :test 'string=))

(defun wg-workgroup-all-buf-uids (workgroup)

  "Return a new list of all unique buf uids in WORKGROUP."

  (reduce 'wg-string-list-union

          (list (wg-workgroup-base-wconfig-buf-uids workgroup)

                (wg-workgroup-saved-wconfigs-buf-uids workgroup)

(defun wg-session-all-buf-uids (&optional session)

  "Return a new list of all unique buf uids in SESSION.

SESSION nil defaults to `wg-current-session'."

  (reduce 'wg-string-list-union

          (wg-session-workgroup-list (or session (wg-current-session)))

          :key 'wg-workgroup-all-buf-uids))

(defun wg-buffer-list-all-uids (&optional buffer-list)

  "Return a list of the uids of all buffers in BUFFER-LIST in

which `wg-buffer-uid' is locally bound.

BUFFER-LIST nil defaults to `buffer-list'."

  (delq nil (mapcar 'wg-buffer-uid (or buffer-list (buffer-list)))))

(defun wg-all-buf-uids (&optional session buffer-list)

  "Return the union of `wg-session-all-buf-uids' and `wg-buffer-list-all-uids'."

  (union (wg-session-all-buf-uids session)

         (wg-buffer-list-all-uids buffer-list)

         :test 'string=))

(defun wg-gc-bufs ()

  "gc bufs from `wg-buf-list' that are no longer needed."

  (let ((all-buf-uids (wg-all-buf-uids)))

    (wg-asetf (wg-buf-list)

              (wg-remove-if-not (lambda (uid) (member uid all-buf-uids)) it

                             :key 'wg-buf-uid))))

;; FIXME: Duplicate buf names probably shouldn't be allowed.  An unrelated error

;; causes two *scratch* buffers to be present, triggering the "uids don't match"

;; error.  Write something to remove bufs with duplicate names.

(defun wg-perform-session-maintenance ()

  "Perform various maintenance operations on the current Workgroups session."

  (wg-update-current-workgroup-working-wconfig)

  (wg-update-all-base-wconfigs)

  (wg-gc-bufs)

  (wg-gc-buf-uids)

  (wg-update-buf-list))

;; session consistency testing

(defun wg-session-uids-consistent-p ()

  "Return t if there are no duplicate bufs or buf uids in the wrong places,

nil otherwise."

  (and (every (lambda (wg)

                (not (wg-dups-p (wg-workgroup-associated-buf-uids wg)

                                :test 'string=)))

              (wg-workgroup-list))

       (not (wg-dups-p (wg-buf-list) :key 'wg-buf-uid :test 'string=))

       (not (wg-dups-p (wg-workgroup-list) :key 'wg-workgroup-uid :test 'string=))))

;;; workgroup restoration

(defun wg-restore-workgroup-associated-buffers-internal (workgroup)

  "Restore all the buffers associated with WORKGROUP that can be restored."

  (save-window-excursion

    (delete nil (mapcar 'wg-restore-buffer

                        (wg-workgroup-associated-bufs workgroup)))))

(defun wg-restore-workgroup (workgroup)

  "Restore WORKGROUP in `selected-frame'."

  (when wg-restore-associated-buffers

    (wg-restore-workgroup-associated-buffers-internal workgroup))

  (let (wg-flag-modified)

    (wg-restore-wconfig-undoably

     (wg-workgroup-working-wconfig workgroup) t)))

;;; workgroup-list ops

(defun wg-delete-workgroup (workgroup)

  "Remove WORKGROUP from `wg-workgroup-list'.

Also delete all references to it by `wg-workgroup-state-table',

`wg-current-workgroup' and `wg-previous-workgroup'."

  (dolist (frame (frame-list))

    (remhash (wg-workgroup-uid workgroup) (wg-workgroup-state-table frame))

    (when (wg-current-workgroup-p workgroup frame)

      (wg-set-current-workgroup nil frame))

    (when (wg-previous-workgroup-p workgroup frame)

      (wg-set-previous-workgroup nil frame)))

  (setf (wg-workgroup-list) (remove workgroup (wg-workgroup-list-or-error)))

  (setf (wg-session-modified (wg-current-session)) t)

  workgroup)

(defun wg-add-workgroup (workgroup &optional index)

  "Add WORKGROUP to `wg-workgroup-list' at INDEX or the end.

If a workgroup with the same name exists, overwrite it."

  (wg-awhen (wg-find-workgroup-by :name (wg-workgroup-name workgroup) t)

    (unless index (setq index (wg-position it (wg-workgroup-list-or-error))))

    (wg-delete-workgroup it))

  (wg-asetf (wg-workgroup-list)

            (wg-insert-before workgroup it (or index (length it))))

  (setf (wg-session-modified (wg-current-session)) t)

  workgroup)

(defun wg-check-and-add-workgroup (workgroup)

  "Add WORKGROUP to `wg-workgroup-list'.

Ask to overwrite if a workgroup with the same name exists."

  (let ((name (wg-workgroup-name workgroup))

        (uid (wg-workgroup-uid workgroup)))

    (when (wg-find-workgroup-by :uid uid t)

      (error "A workgroup with uid %S already exists" uid))

    (when (wg-find-workgroup-by :name name t)

      (unless (or wg-no-confirm-on-destructive-operation

                  (y-or-n-p (format "%S exists. Overwrite? " name)))

        (error "Cancelled"))))

  (wg-add-workgroup workgroup))

(defun wg-make-and-add-workgroup (name &optional blank)

  "Create a workgroup named NAME and add it with `wg-check-and-add-workgroup'."

  (wg-check-and-add-workgroup

   (wg-make-workgroup

    :name name

    :base-wconfig (if blank (wg-make-blank-wconfig)

                    (wg-current-wconfig)))))

(defun wg-get-workgroup-create (workgroup)

  "Return the workgroup specified by WORKGROUP, creating a new one if needed.

If `wg-get-workgroup' on WORKGROUP returns a workgroup, return it.

Otherwise, if WORKGROUP is a string, create a new workgroup with

that name and return it. Otherwise error."

  (or (wg-get-workgroup workgroup t)

      (if (stringp workgroup)

          (when (or (not wg-confirm-on-get-workgroup-create)

                    (y-or-n-p (format "%S doesn't exist.  Create it? "

                                      workgroup)))

            (wg-make-and-add-workgroup workgroup))

        ;; Call this again for its error message

        (wg-get-workgroup workgroup))))

(defun wg-cyclic-offset-workgroup (workgroup n)

  "Offset WORKGROUP's position in `wg-workgroup-list' by N."

  (let ((workgroup-list (wg-workgroup-list-or-error)))

    (unless (member workgroup workgroup-list)

      (error "Workgroup isn't present in `wg-workgroup-list'."))

    (setf (wg-workgroup-list) (wg-cyclic-offset-elt workgroup workgroup-list n)

          (wg-session-modified (wg-current-session)) t)))

(defun wg-swap-workgroups-in-workgroup-list (workgroup1 workgroup2)

  "Swap the positions of WORKGROUP1 and WORKGROUP2 in `wg-workgroup-list'."

  (let ((workgroup-list (wg-workgroup-list-or-error)))

    (when (eq workgroup1 workgroup2)

      (error "Can't swap a workgroup with itself"))

    (unless (and (memq workgroup1 workgroup-list)

                 (memq workgroup2 workgroup-list))

      (error "Both workgroups aren't present in `wg-workgroup-list'."))

    (setf (wg-workgroup-list) (wg-util-swap workgroup1 workgroup2 workgroup-list)

          (wg-session-modified (wg-current-session)) t)))

(defun wg-cyclic-nth-from-workgroup (workgroup &optional n)

  "Return the workgroup N places from WORKGROUP in `wg-workgroup-list'."

  (wg-cyclic-nth-from-elt workgroup (wg-workgroup-list-or-error) (or n 1)))

;;; buffer association

(defun wg-associate-buffers (workgroup window-or-emacs-window-tree)

  "Associate the buffers visible in window elements of

WINDOW-OR-EMACS-WINDOW-TREE with the given WORKGROUP.

WINDOW-OR-EMACS-WINDOW-TREE must be either a window or a tree of

the form produced by `(car (window-tree))'."

  (wg-aif (windowp window-or-emacs-window-tree)

      (with-current-buffer (window-buffer window-or-emacs-window-tree)

        (setq wg-buffer-workgroup workgroup))

    (dolist (w (cddr window-or-emacs-window-tree))

      (when w (wg-associate-buffers workgroup w)))))

(defun wg-associate-frame-buffers ()

  "Associate the buffers visible in the current frame with the

current workgroup (unless it is currently being deactivated)."

  (wg-awhen (wg-current-workgroup :noerror)

    (unless (member it wg-deactivation-list)

      (wg-associate-buffers it (car (window-tree))))))

(defun wg-associate-all-frame-buffers ()

  "Associate all visible buffers with the current

workgroup (unless it is currently being deactivated)."

  (mapcar 'wg-associate-frame-buffers (frame-list)))

(defun wg-buffer-predicate (buffer)

  "Return t iff the given BUFFER should be considered a candidate

for display by `other-buffer' in the current workgroup."

  (or (not wg-associate-buffers)

      (wg-awhen (wg-current-workgroup :noerror)

        (with-current-buffer buffer