(= (length (wg-workgroup-list)) 0))

    (wg-create-workgroup wg-first-wg-name)

    (wg-mark-everything-unmodified)))

(defun wg-pickel-workgroup-parameters (workgroup)

  "Return a copy of WORKGROUP after pickeling its parameters.

If WORKGROUP's parameters are non-nil, otherwise return

WORKGROUP."

  (if (not (wg-workgroup-parameters workgroup)) workgroup

    (let ((copy (wg-copy-workgroup workgroup)))

      (wg-asetf (wg-workgroup-parameters copy) (wg-pickel it))

      copy)))

(defun wg-unpickel-workgroup-parameters (workgroup)

  "If WORKGROUP's parameters are non-nil, return a copy of

WORKGROUP after unpickeling its parameters. Otherwise return

WORKGROUP."

  (if (not (wg-workgroup-parameters workgroup)) workgroup

    (let ((copy (wg-copy-workgroup workgroup)))

      (wg-asetf (wg-workgroup-parameters copy) (wg-unpickel it))

      copy)))

(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)))

  (wg-flag-session-modified)

  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."

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

    (unless index (setq index (cl-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))))

  (wg-flag-session-modified)

  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 with current `window-tree'.

If BLANK - then just scratch buffer.

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)

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

        (wg-get-workgroup workgroup))))  ; Call this again for its error message

(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-session-uids-consistent-p ()

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

nil otherwise."

  (and (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=))))

(defun wg-find-session-file (filename)

  "Load a session visiting FILENAME, creating one if none already exists."

  (interactive "FFind session file: ")

  (cond ((file-exists-p filename)

         ;; TODO: handle errors when reading object

         (let ((session (read (f-read-text filename))))

           (unless (wg-session-p session)

             (error "%S is not a Workgroups session file." filename))

           (setf (wg-session-file-name session) filename)

           (wg-reset-internal (wg-unpickel-session-parameters session)))

         (if wg-control-frames (wg-restore-frames))

         (awhen (wg-workgroup-list)

           (if (and wg-open-this-wg

                    (member wg-open-this-wg (wg-workgroup-names)))

               (wg-switch-to-workgroup wg-open-this-wg)

             (if (and wg-load-last-workgroup

                      (member (wg-session-parameter 'last-workgroup) (wg-workgroup-names)))

                 (wg-switch-to-workgroup (wg-session-parameter 'last-workgroup))

               (wg-switch-to-workgroup (car it)))

             ))

         (wg-fontified-message (:cmd "Loaded: ") (:file filename))

         (wg-mark-everything-unmodified))

        (t

         (wg-query-and-save-if-modified)

         (wg-reset-internal (wg-make-session :file-name filename))

         (wg-fontified-message (:cmd "(New Workgroups session file)")))))

(defalias 'wg-open-session 'wg-find-session-file)

(defun wg-write-sexp-to-file (sexp file)

  "Write the printable representation of SEXP to FILE."

  (with-temp-buffer

    (let ((print-level nil)  (print-length nil))

      (insert (format "%S" sexp)))

    (write-file file)))

;; 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)

  ;; Update every workgroup's base wconfig with `wg-workgroup-update-base-wconfig'

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

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

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

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

  ;; Garbage collection

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

    (wg-asetf (wg-buf-list)

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

                                :key 'wg-buf-uid)))

  (mapc 'wg-workgroup-gc-buf-uids (wg-workgroup-list))  ; Remove buf uids that have no referent in `wg-buf-list'

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

(defun wg-save-session-as (filename &optional confirm)

  "Write the current session into file FILENAME.

This makes the session visit that file, and marks it as not modified.

If optional second arg CONFIRM is non-nil, this function asks for

confirmation before overwriting an existing file.  Interactively,

confirmation is required unless you supply a prefix argument."

  (interactive (list (read-file-name "Save session as: ")

                     (not current-prefix-arg)))

  (when (and confirm (file-exists-p filename))

    (unless (y-or-n-p (format "File `%s' exists; overwrite? " filename))

      (error "Cancelled")))

  (unless (file-writable-p filename)

    (error "File %s can't be written to" filename))

  (wg-perform-session-maintenance)

  (setf (wg-session-file-name (wg-current-session)) filename)

  (setf (wg-session-version (wg-current-session)) wg-version)

  ;; Save opened frames as a session parameter "frame-list".

  ;; Exclude `selected-frame' and daemon one (if any).

  ;; http://stackoverflow.com/questions/21151992/why-emacs-as-daemon-gives-1-more-frame-than-is-opened

  (if wg-control-frames

      (let ((fl (frame-list)))

        ;; TODO: remove using dash

        (mapc (lambda (frame)

                (if (string-equal "initial_terminal" (terminal-name frame))

                    (delete frame fl))) fl)

        (setq fl (delete (selected-frame) fl))

        (let (wg-flag-modified)

  (wg-write-sexp-to-file (wg-pickel-all-session-parameters) filename)

  (wg-fontified-message (:cmd "Wrote: ") (:file filename))

  (wg-mark-everything-unmodified))

(defalias 'wg-write-session-file 'wg-save-session-as)

(defun wg-get-session-file ()

  "Return the filename in which to save the session."

  (or (aif (wg-current-session t) (wg-session-file-name it))

      wg-session-file))

;;(read-file-name (format "Save session as [%s]: " wg-session-file))

(defun wg-save-session (&optional force)

  "Save the current Workgroups session if it's been modified.

When FORCE - save session regardless of whether it's been modified."

  (interactive "P")

  (if (and (not (wg-modified-p)) (not force))

      (wg-message "(The session is unmodified)")

    (wg-save-session-as (wg-get-session-file))))

(defun wg-reset-internal (&optional session)

  "Reset Workgroups, setting `wg-current-session' to SESSION.

Resets all frame parameters, buffer-local vars, current session

object, etc.  SESSION nil defaults to a new, blank session."

  (mapc 'wg-reset-frame (frame-list))

  (mapc 'wg-reset-buffer (wg-buffer-list-emacs))

  (setq wg-wconfig-kill-ring nil)

  (setq wg-current-session (or session (wg-make-session))))

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

  "Return the union of all SESSION buf-uids and BUFFER-LIST uids."

  (cl-union (cl-reduce 'wg-string-list-union  ; (wg-session-all-buf-uids session)

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

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

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

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

            :test 'string=))

(defun wg-modified-p ()

  "Return t when the current session or any of its workgroups are modified."

  (aif (wg-current-session t)

      (or (wg-session-modified it)

          (cl-some 'wg-workgroup-modified (wg-workgroup-list)))))

(defun wg-mark-everything-unmodified ()

  "Mark the session and all workgroups as unmodified."

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

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

    (setf (wg-workgroup-modified workgroup) nil)))

(defun wg-session-parameter (parameter &optional default session)

  "Return session's value for PARAMETER.

If PARAMETER is not found, return DEFAULT which defaults to nil.

SESSION nil defaults to the current session."

  (wg-aget (wg-session-parameters (or session (wg-current-session)))

           parameter default))

(defun wg-set-session-parameter (parameter value &optional session)

  "Set PARAMETER to VALUE in SESSION.

SESSION nil means use the current session.  Return value."

    (wg-set-parameter (wg-session-parameters session) parameter value)

    (wg-flag-session-modified session)

    value))

(defun wg-remove-session-parameter (parameter &optional session)

  "Remove parameter PARAMETER from SESSION's parameters."

  (let ((session (or session (wg-current-session))))

    (wg-asetf (wg-session-parameters session) (wg-aremove it parameter))

    (wg-flag-session-modified session)))

(defun wg-session-local-value (variable &optional session)

  "Return the value of VARIABLE in SESSION.

SESSION nil defaults to the current session.  If VARIABLE does

not have a session-local binding in SESSION, the value is

resolved by Emacs."

  (let* ((undefined (cl-gensym))

         (value (wg-session-parameter variable undefined session)))

    (if (not (eq value undefined)) value

      (symbol-value variable))))

(defun wg-reset-frame (frame)

  "Reset Workgroups' `frame-parameters' in FRAME to nil."

  (set-frame-parameter frame 'wg-workgroup-state-table nil)

  (set-frame-parameter frame 'wg-current-workgroup-uid nil)

  (set-frame-parameter frame 'wg-previous-workgroup-uid nil))

(defun wg-save-session-on-exit (behavior)

  "Perform session-saving operations based on BEHAVIOR."

  (cl-case behavior

    (ask (wg-query-and-save-if-modified))

    (save (wg-save-session))))

(defun wg-reload-session ()

  "Reload current workgroups session."

  (interactive)

  (let* ((file (wg-get-session-file))

         (exists (file-exists-p file)))

    (condition-case err

        (wg-open-session file)

      (progn

        (wg-create-first-wg)

        (message "Error loading session-file: %s" err))))

        ;; TODO: print what exactly happened

  (wg-create-first-wg))

(defun wg-save-session-on-emacs-exit ()

  "Call `wg-save-session-on-exit' with `wg-emacs-exit-save-behavior'.

Added to `kill-emacs-query-functions'."

  (wg-save-session-on-exit wg-emacs-exit-save-behavior) t)

(defun wg-save-session-on-workgroups-mode-exit ()

  "Call `wg-save-session-on-exit' with `wg-workgroups-mode-exit-save-behavior'.

Called when `workgroups-mode' is turned off."

  (wg-save-session-on-exit wg-workgroups-mode-exit-save-behavior) t)

(defun wg-pickel-all-session-parameters (&optional session)

  "Return a copy of SESSION after pickeling its parameters.

And the parameters of all its workgroups."

  (let ((copy (wg-copy-session (or session (wg-current-session)))))

    (when (wg-session-parameters copy)

      (wg-asetf (wg-session-parameters copy) (wg-pickel it)))

    (wg-asetf (wg-session-workgroup-list copy)

              (cl-mapcar 'wg-pickel-workgroup-parameters it))

    copy))

(defun wg-unpickel-session-parameters (session)

  "Return a copy of SESSION after unpickeling its parameters.

And the parameters of all its workgroups."

  (let ((copy (wg-copy-session session)))

    (when (wg-session-parameters copy)

      (wg-asetf (wg-session-parameters copy) (wg-unpickel it)))

    (wg-asetf (wg-session-workgroup-list copy)

              (cl-mapcar 'wg-unpickel-workgroup-parameters it))

    copy))

(defvar wg-buffer-workgroup nil

  "Associating each buffer with the workgroup.

In which it most recently appeared.")

(make-variable-buffer-local 'wg-buffer-workgroup)

(defun wg-workgroup-associated-buf-uids (&optional workgroup)

  "Return a new list containing all of WORKGROUP's associated buf uids."

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

    (append (wg-workgroup-strong-buf-uids it)

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

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

  "Return a new list containing all of WORKGROUP's associated bufs."

  (delete nil (mapcar 'wg-find-buf-by-uid

                      (wg-workgroup-associated-buf-uids workgroup))))

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

  "Return a new list containing all of WORKGROUP's associated buffer objects."

  (delete nil (mapcar 'wg-restore-buffer

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

(defun wg-workgroup-strongly-associate-bufobj (workgroup bufobj)

  "Strongly associate BUFOBJ with WORKGROUP."

  (let* ((uid (wg-bufobj-uid-or-add bufobj))

         (remp (wg-removef-p uid (wg-workgroup-weak-buf-uids workgroup)

                             :test 'string=))

         (addp (wg-pushnew-p uid (wg-workgroup-strong-buf-uids workgroup)

                             :test 'string=)))

    (when (or remp addp)

      (wg-flag-workgroup-modified workgroup)

      bufobj)))

(defun wg-workgroup-weakly-associate-bufobj (workgroup bufobj)

  "Weakly associate BUFOBJ with WORKGROUP."

  (let* ((uid (wg-bufobj-uid-or-add bufobj))

         (remp (wg-removef-p uid (wg-workgroup-strong-buf-uids workgroup)

                             :test 'string=))

         (addp (wg-pushnew-p uid (wg-workgroup-weak-buf-uids workgroup)

                             :test 'string=)))

    (when (or remp addp)

      (wg-flag-workgroup-modified workgroup)

      bufobj)))

(defun wg-workgroup-associate-bufobj (workgroup bufobj &optional weak)

  "Associate BUFOBJ with WORKGROUP.

WEAK non-nil means weakly associate it.  Otherwise strongly associate it."

  (if weak (wg-workgroup-weakly-associate-bufobj workgroup bufobj)

    (wg-workgroup-strongly-associate-bufobj workgroup bufobj)))

(defun wg-workgroup-dissociate-bufobj (workgroup bufobj)

  "Dissociate BUFOBJ from WORKGROUP."

  (let* ((uid (wg-bufobj-uid-or-add bufobj))

         (rem1p (wg-removef-p uid (wg-workgroup-strong-buf-uids workgroup)

                              :test 'string=))

         (rem2p (wg-removef-p uid (wg-workgroup-weak-buf-uids workgroup)

                              :test 'string=)))

    (when (or rem1p rem2p)

      (wg-flag-workgroup-modified workgroup)

      bufobj)))

(defun wg-workgroup-dissociate-weakly-associated-buffers (workgroup)

  "Dissociate from WORKGROUP all weakly associated buffers."

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

    (wg-flag-workgroup-modified workgroup)

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

(defun wg-workgroup-dissociate-strongly-associated-buffers (workgroup)

  "Dissociate from WORKGROUP all strongly associated buffers."

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

    (wg-flag-workgroup-modified workgroup)

    (setf (wg-workgroup-strong-buf-uids workgroup) nil)))

(defun wg-workgroup-dissociate-all-buffers (workgroup)

  "Dissociate from WORKGROUP all its associated buffers."

  (wg-workgroup-dissociate-weakly-associated-buffers workgroup)

  (wg-workgroup-dissociate-strongly-associated-buffers workgroup))

(defun wg-auto-dissociate-buffer-hook ()

  "`kill-buffer-hook' that automatically dissociates buffers from workgroups."

  (when wg-dissociate-buffer-on-kill-buffer

    (awhen (wg-current-workgroup t)

      (wg-workgroup-dissociate-bufobj it (current-buffer)))))

(defun wg-associate-buffer-with-workgroup (&optional workgroup buffer weak)

  "Associate BUFFER with WORKGROUP.

WEAK non-nil means weakly associate BUFFER."

  (interactive (list nil nil current-prefix-arg))

  (let* ((workgroup (wg-get-workgroup workgroup))

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

         (bname (buffer-name buffer))

         (wgname (wg-workgroup-name workgroup)))

    (if (wg-workgroup-associate-bufobj workgroup buffer weak)

        (wg-message "%s-associated %S with %s"

                    (if weak "Weakly" "Strongly") bname wgname)

      (wg-message "%S is already associated with %s" bname wgname))))

(defun wg-associate-visible-buffers-with-workgroup (&optional workgroup weak)

  "Associate all buffers visible in `selected-frame' with WORKGROUP.

WEAK non-nil means weakly associate them.  Otherwise strongly

associate them."

  (interactive (list nil current-prefix-arg))

  (let ((workgroup (wg-get-workgroup workgroup))

        (buffers (mapcar 'window-buffer (window-list))))

    (dolist (buffer buffers)

      (wg-workgroup-associate-bufobj workgroup buffer weak))

    (wg-fontified-message

      (:cmd (format "%s associated: " (if weak "Weakly" "Strongly")))

      (wg-display-internal 'wg-buffer-display buffers))))

(defun wg-dissociate-buffer-from-workgroup (&optional workgroup buffer)

  "Dissociate BUFFER from WORKGROUP."

  (interactive (list nil nil))

  (let ((workgroup (wg-get-workgroup workgroup))

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

    (wg-message

     (if (wg-workgroup-dissociate-bufobj workgroup buffer)

         "Dissociated %S from %s" "%S isn't associated with %s")