;;; tab-bar.el --- frame-local tabs with named persistent window configurations -*- lexical-binding: t; -*-

;; Copyright (C) 2019 Free Software Foundation, Inc.

;; Author: Juri Linkov <juri@linkov.net>
;; Keywords: frames tabs
;; Maintainer: emacs-devel@gnu.org

;; This file is part of GNU 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.

;; GNU Emacs 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Provides `tab-bar-mode' to control display of the tab bar and
;; bindings for the global tab bar.

;; The normal global binding for [tab-bar] (below) uses the value of
;; `tab-bar-map' as the actual keymap to define the tab bar.  Modes
;; may either bind items under the [tab-bar] prefix key of the local
;; map to add to the global bar or may set `tab-bar-map'
;; buffer-locally to override it.

;;; Code:

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

\f
(defgroup tab-bar nil
  "Frame-local tabs."
  :group 'convenience
  :version "27.1")

(defgroup tab-bar-faces nil
  "Faces used in the tab bar."
  :group 'tab-bar
  :group 'faces
  :version "27.1")

(defface tab-bar
  '((((type x w32 ns) (class color))
     :height 1.1
     :background "grey85"
     :foreground "black")
    (((type x) (class mono))
     :background "grey")
    (t
     :inverse-video t))
  "Tab bar face."
  :version "27.1"
  :group 'tab-bar-faces)

(defface tab-bar-tab
  '((((class color) (min-colors 88))
     :box (:line-width 1 :style released-button))
    (t
     :inverse-video nil))
  "Tab bar face for selected tab."
  :version "27.1"
  :group 'tab-bar-faces)

(defface tab-bar-tab-inactive
  '((default
      :inherit tab-bar-tab)
    (((class color) (min-colors 88))
     :background "grey75")
    (t
     :inverse-video t))
  "Tab bar face for non-selected tab."
  :version "27.1"
  :group 'tab-bar-faces)

\f
(define-minor-mode tab-bar-mode
  "Toggle the tab bar in all graphical frames (Tab Bar mode)."
  :global t
  ;; It's defined in C/cus-start, this stops the d-m-m macro defining it again.
  :variable tab-bar-mode
  (let ((val (if tab-bar-mode 1 0)))
    (dolist (frame (frame-list))
      (set-frame-parameter frame 'tab-bar-lines val))
    ;; If the user has given `default-frame-alist' a `tab-bar-lines'
    ;; parameter, replace it.
    (if (assq 'tab-bar-lines default-frame-alist)
        (setq default-frame-alist
              (cons (cons 'tab-bar-lines val)
                    (assq-delete-all 'tab-bar-lines
                                     default-frame-alist)))))
  (when tab-bar-mode
    (global-set-key [(control shift iso-lefttab)] 'tab-previous)
    (global-set-key [(control shift tab)]         'tab-previous)
    (global-set-key [(control tab)]               'tab-next)))

(defun tab-bar-handle-mouse (event)
  "Text-mode emulation of switching tabs on the tab bar.
This command is used when you click the mouse in the tab bar
on a console which has no window system but does have a mouse."
  (interactive "e")
  (let* ((x-position (car (posn-x-y (event-start event))))
         (keymap (lookup-key (cons 'keymap (nreverse (current-active-maps))) [tab-bar]))
         (column 0))
    (when x-position
      (unless (catch 'done
                (map-keymap
                 (lambda (_key binding)
                   (when (eq (car-safe binding) 'menu-item)
                     (when (> (+ column (length (nth 1 binding))) x-position)
                       ;; TODO: handle close
                       (unless (get-text-property (- x-position column) 'close-tab (nth 1 binding))
                         (call-interactively (nth 2 binding)))
                       (throw 'done t))
                     (setq column (+ column (length (nth 1 binding))))))
                 keymap))
        ;; Clicking anywhere outside existing tabs will add a new tab
        (tab-bar-new-tab)))))

;; Used in the Show/Hide menu, to have the toggle reflect the current frame.
(defun toggle-tab-bar-mode-from-frame (&optional arg)
  "Toggle tab bar on or off, based on the status of the current frame.
See `tab-bar-mode' for more information."
  (interactive (list (or current-prefix-arg 'toggle)))
  (if (eq arg 'toggle)
      (tab-bar-mode (if (> (frame-parameter nil 'tab-bar-lines) 0) 0 1))
    (tab-bar-mode arg)))

(defvar tab-bar-map (make-sparse-keymap)
  "Keymap for the tab bar.
Define this locally to override the global tab bar.")

(global-set-key [tab-bar]
                `(menu-item ,(purecopy "tab bar") ignore
                            :filter tab-bar-make-keymap))

(defconst tab-bar-keymap-cache (make-hash-table :weakness t :test 'equal))

(defun tab-bar-make-keymap (&optional _ignore)
  "Generate an actual keymap from `tab-bar-map'.
Its main job is to show tabs in the tab bar."
  (if (= 1 (length tab-bar-map))
      (tab-bar-make-keymap-1)
    (let ((key (cons (frame-terminal) tab-bar-map)))
      (or (gethash key tab-bar-keymap-cache)
          (puthash key tab-bar-map tab-bar-keymap-cache)))))

\f
(defcustom tab-bar-show t
  "Defines when to show the tab bar.
If t, enable `tab-bar-mode' automatically on using the commands that
create new window configurations (e.g. `tab-new').
If the value is `1', then hide the tab bar when it has only one tab,
and show it again once more tabs are created.
If nil, always keep the tab bar hidden.  In this case it's still
possible to use persistent named window configurations by relying on
keyboard commands `tab-list', `tab-new', `tab-close', `tab-next', etc."
  :type '(choice (const :tag "Always" t)
                 (const :tag "When more than one tab" 1)
                 (const :tag "Never" nil))
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (tab-bar-mode
          (if (or (eq val t)
                  (and (natnump val) (> (length (tab-bar-tabs)) val)))
              1 -1)))
  :group 'tab-bar
  :version "27.1")

(defcustom tab-bar-new-tab-choice t
  "Defines what to show in a new tab.
If t, start a new tab with the current buffer, i.e. the buffer
that was current before calling the command that adds a new tab
(this is the same what `make-frame' does by default).
If the value is a string, use it as a buffer name switch to a buffer
if such buffer exists, or switch to a buffer visiting the file or
directory that the string specifies.  If the value is a function,
call it with no arguments and switch to the buffer that it returns.
If nil, duplicate the contents of the tab that was active
before calling the command that adds a new tab."
  :type '(choice (const     :tag "Current buffer" t)
                 (string    :tag "Buffer" "*scratch*")
                 (directory :tag "Directory" :value "~/")
                 (file      :tag "File" :value "~/.emacs")
                 (function  :tag "Function")
                 (const     :tag "Duplicate tab" nil))
  :group 'tab-bar
  :version "27.1")

(defvar tab-bar-new-button
  (propertize " + "
              'display `(image :type xpm
                               :file ,(expand-file-name
                                       "images/tabs/new.xpm"
                                       data-directory)
                               :margin (2 . 0)
                               :ascent center))
  "Button for creating a new tab.")

(defcustom tab-bar-close-button-show t
  "Defines where to show the close tab button.
If t, show the close tab button on all tabs.
If `selected', show it only on the selected tab.
If `non-selected', show it only on non-selected tab.
If nil, don't show it at all."
  :type '(choice (const :tag "On all tabs" t)
                 (const :tag "On selected tab" selected)
                 (const :tag "On non-selected tabs" non-selected)
                 (const :tag "None" nil))
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-bar
  :version "27.1")

(defvar tab-bar-close-button
  (propertize " x"
              'display `(image :type xpm
                               :file ,(expand-file-name
                                       "images/tabs/close.xpm"
                                       data-directory)
                               :margin (2 . 0)
                               :ascent center)
              'close-tab t
              :help "Click to close tab")
  "Button for closing the clicked tab.")

(defcustom tab-bar-tab-hints nil
  "Show absolute numbers on tabs in the tab bar before the tab name.
This helps to select the tab by its number using `tab-bar-select-tab'."
  :type 'boolean
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-bar
  :version "27.1")

(defvar tab-bar-separator nil)

\f
(defcustom tab-bar-tab-name-function #'tab-bar-tab-name-selected-window
  "Function to get a tab name.
Function gets no arguments.
The choice is between displaying only the name of the current buffer
in the tab name (default), or displaying the names of all buffers
from all windows in the window configuration."
  :type '(choice (const :tag "Selected window buffer" tab-bar-tab-name-selected-window)
                 (const :tag "All window buffers" tab-bar-tab-name-all-windows)
                 (function  :tag "Function"))
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-bar
  :version "27.1")

(defun tab-bar-tab-name-selected-window ()
  "Generate tab name from the buffer of the selected window.
Also add the number of windows in the window configuration."
  (format "%s (%d)" (buffer-name) (length (window-list-1 nil 'nomini))))

(defun tab-bar-tab-name-all-windows ()
  "Generate tab name from buffers of all windows."
  (mapconcat #'buffer-name
             (delete-dups (mapcar #'window-buffer
                                  (window-list-1 (frame-first-window)
                                                 'nomini)))
             ", "))

(defvar tab-bar-tabs-function #'tab-bar-tabs
  "Function to get a list of tabs to display in the tab bar.
This function should return a list of alists with parameters
that include at least the element (name . TAB-NAME).
For example, '((tab (name . \"Tab 1\")) (current-tab (name . \"Tab 2\")))
By default, use function `tab-bar-tabs'.")

(defun tab-bar-tabs ()
  "Return a list of tabs belonging to the selected frame.
Ensure the frame parameter `tabs' is pre-populated.
Return its existing value or a new value."
  (let ((tabs (frame-parameter nil 'tabs)))
    (unless tabs
      ;; Create default tabs
      (setq tabs (list (tab-bar--current-tab)))
      (set-frame-parameter nil 'tabs tabs))
    tabs))

(defun tab-bar-make-keymap-1 ()
  "Generate an actual keymap from `tab-bar-map', without caching."
  (let* ((separator (or tab-bar-separator (if window-system " " "|")))
         (i 0)
         (tabs (funcall tab-bar-tabs-function))
         (current-tab-name (assq 'name (assq 'current-tab tabs))))
    (when current-tab-name
      (setf (cdr current-tab-name) (funcall tab-bar-tab-name-function)))
    (append
     '(keymap (mouse-1 . tab-bar-handle-mouse))
     (mapcan
      (lambda (tab)
        (setq i (1+ i))
        (append
         `((,(intern (format "sep-%i" i)) menu-item ,separator ignore))
         (cond
          ((eq (car tab) 'current-tab)
           `((current-tab
              menu-item
              ,(propertize (concat (if tab-bar-tab-hints (format "%d " i) "")
                                   (cdr (assq 'name tab))
                                   (or (and tab-bar-close-button-show
                                            (not (eq tab-bar-close-button-show
                                                     'non-selected))
                                            tab-bar-close-button) ""))
                           'face 'tab-bar-tab)
              ignore
              :help "Current tab")))
          (t
           `((,(intern (format "tab-%i" i))
              menu-item
              ,(propertize (concat (if tab-bar-tab-hints (format "%d " i) "")
                                   (cdr (assq 'name tab))
                                   (or (and tab-bar-close-button-show
                                            (not (eq tab-bar-close-button-show
                                                     'selected))
                                            tab-bar-close-button) ""))
                           'face 'tab-bar-tab-inactive)
              ,(or
                (cdr (assq 'binding tab))
                `(lambda ()
                   (interactive)
                   (tab-bar-select-tab ,i)))
              :help "Click to visit tab"))))
         `((,(if (eq (car tab) 'current-tab) 'C-current-tab (intern (format "C-tab-%i" i)))
            menu-item ""
            ,(or
              (cdr (assq 'close-binding tab))
              `(lambda ()
                 (interactive)
                 (tab-bar-close-tab ,i)))))))
      tabs)
     (when tab-bar-new-button
       `((sep-add-tab menu-item ,separator ignore)
         (add-tab menu-item ,tab-bar-new-button tab-bar-new-tab
                  :help "New tab"))))))

\f
(defun tab-bar--tab ()
  `(tab
    (name . ,(funcall tab-bar-tab-name-function))
    (time . ,(time-convert nil 'integer))
    (wc . ,(current-window-configuration))
    (ws . ,(window-state-get
            (frame-root-window (selected-frame)) 'writable))))

(defun tab-bar--current-tab ()
  `(current-tab
    (name . ,(funcall tab-bar-tab-name-function))))

(defun tab-bar--current-tab-index (&optional tabs)
  ;; FIXME: could be replaced with 1-liner using seq-position
  (let ((tabs (or tabs (tab-bar-tabs)))
        (i 0))
    (catch 'done
      (while tabs
        (when (eq (car (car tabs)) 'current-tab)
          (throw 'done i))
        (setq i (1+ i) tabs (cdr tabs))))))

(defun tab-bar--tab-index (tab &optional tabs)
  ;; FIXME: could be replaced with 1-liner using seq-position
  (let ((tabs (or tabs (tab-bar-tabs)))
        (i 0))
    (catch 'done
      (while tabs
        (when (eq (car tabs) tab)
          (throw 'done i))
        (setq i (1+ i) tabs (cdr tabs))))
    i))

(defun tab-bar--tab-index-by-name (name &optional tabs)
  ;; FIXME: could be replaced with 1-liner using seq-position
  (let ((tabs (or tabs (tab-bar-tabs)))
        (i 0))
    (catch 'done
      (while tabs
        (when (equal (cdr (assq 'name (car tabs))) name)
          (throw 'done i))
        (setq i (1+ i) tabs (cdr tabs))))
    i))

\f
(defun tab-bar-select-tab (&optional arg)
  "Switch to the tab by its absolute position ARG in the tab bar.
When this command is bound to a numeric key (with a prefix or modifier),
calling it without an argument will translate its bound numeric key
to the numeric argument.  ARG counts from 1."
  (interactive "P")
  (unless (integerp arg)
    (let ((key (event-basic-type last-command-event)))
      (setq arg (if (and (characterp key) (>= key ?1) (<= key ?9))
                    (- key ?0)
                  1))))

  (let* ((tabs (tab-bar-tabs))
         (from-index (tab-bar--current-tab-index tabs))
         (to-index (1- (max 1 (min arg (length tabs))))))
    (unless (eq from-index to-index)
      (let* ((from-tab (tab-bar--tab))
             (to-tab (nth to-index tabs))
             (wc (cdr (assq 'wc to-tab)))
             (ws (cdr (assq 'ws to-tab))))

        ;; During the same session, use window-configuration to switch
        ;; tabs, because window-configurations are more reliable
        ;; (they keep references to live buffers) than window-states.
        ;; But after restoring tabs from a previously saved session,
        ;; its value of window-configuration is unreadable,
        ;; so restore its saved window-state.
        (if (window-configuration-p wc)
            (set-window-configuration wc)
          (if ws (window-state-put ws (frame-root-window (selected-frame))
                                   'safe)))

        (when from-index
          (setf (nth from-index tabs) from-tab))
        (setf (nth to-index tabs) (tab-bar--current-tab)))

      (when tab-bar-mode
        (force-mode-line-update)))))

(defun tab-bar-switch-to-next-tab (&optional arg)
  "Switch to ARGth next tab."
  (interactive "p")
  (unless (integerp arg)
    (setq arg 1))
  (let* ((tabs (tab-bar-tabs))
         (from-index (or (tab-bar--current-tab-index tabs) 0))
         (to-index (mod (+ from-index arg) (length tabs))))
    (tab-bar-select-tab (1+ to-index))))

(defun tab-bar-switch-to-prev-tab (&optional arg)
  "Switch to ARGth previous tab."
  (interactive "p")
  (unless (integerp arg)
    (setq arg 1))
  (tab-bar-switch-to-next-tab (- arg)))

(defun tab-bar-switch-to-tab (name)
  "Switch to the tab by NAME."
  (interactive (list (completing-read "Switch to tab by name: "
                                      (mapcar (lambda (tab)
                                                (cdr (assq 'name tab)))
                                              (tab-bar-tabs)))))
  (tab-bar-select-tab (1+ (tab-bar--tab-index-by-name name))))

\f
(defcustom tab-bar-new-tab-to 'right
  "Defines where to create a new tab.
If `leftmost', create as the first tab.
If `left', create to the left from the current tab.
If `right', create to the right from the current tab.
If `rightmost', create as the last tab."
  :type '(choice (const :tag "First tab" leftmost)
                 (const :tag "To the left" left)
                 (const :tag "To the right" right)
                 (const :tag "Last tab" rightmost))
  :group 'tab-bar
  :version "27.1")

(defun tab-bar-new-tab ()
  "Add a new tab at the position specified by `tab-bar-new-tab-to'."
  (interactive)
  (let* ((tabs (tab-bar-tabs))
         (from-index (tab-bar--current-tab-index tabs))
         (from-tab (tab-bar--tab)))

    (when tab-bar-new-tab-choice
      (delete-other-windows)
      ;; Create a new window to get rid of old window parameters
      ;; (e.g. prev/next buffers) of old window.
      (split-window) (delete-window)
      (let ((buffer
             (if (functionp tab-bar-new-tab-choice)
                 (funcall tab-bar-new-tab-choice)
               (if (stringp tab-bar-new-tab-choice)
                   (or (get-buffer tab-bar-new-tab-choice)
                       (find-file-noselect tab-bar-new-tab-choice))))))
        (when (buffer-live-p buffer)
          (switch-to-buffer buffer))))

    (when from-index
      (setf (nth from-index tabs) from-tab))
    (let ((to-tab (tab-bar--current-tab))
          (to-index (pcase tab-bar-new-tab-to
                      ('leftmost 0)
                      ('rightmost (length tabs))
                      ('left (1- (or from-index 1)))
                      ('right (1+ (or from-index 0))))))
      (setq to-index (max 0 (min (or to-index 0) (length tabs))))
      (cl-pushnew to-tab (nthcdr to-index tabs))
      (when (eq to-index 0)
        ;; pushnew handles the head of tabs but not frame-parameter
        (set-frame-parameter nil 'tabs tabs)))

    (when (and (not tab-bar-mode)
               (or (eq tab-bar-show t)
                   (and (natnump tab-bar-show)
                        (> (length tabs) tab-bar-show))))
      (tab-bar-mode 1))
    (if tab-bar-mode
        (force-mode-line-update)
      (message "Added new tab at %s" tab-bar-new-tab-to))))

\f
(defcustom tab-bar-close-tab-select 'right
  "Defines what tab to select after closing the specified tab.
If `left', select the adjacent left tab.
If `right', select the adjacent right tab."
  :type '(choice (const :tag "Select left tab" left)
                 (const :tag "Select right tab" right))
  :group 'tab-bar
  :version "27.1")

(defun tab-bar-close-tab (&optional arg to-index)
  "Close the tab specified by its absolute position ARG.
If no ARG is specified, then close the current tab and switch
to the tab specified by `tab-bar-close-tab-select'.
ARG counts from 1.
Optional TO-INDEX could be specified to override the value of
`tab-bar-close-tab-select' programmatically with a position
of an existing tab to select after closing the current tab.
TO-INDEX counts from 1."
  (interactive "P")
  (let* ((tabs (tab-bar-tabs))
         (current-index (tab-bar--current-tab-index tabs))
         (close-index (if (integerp arg) (1- arg) current-index)))

    ;; Select another tab before deleting the current tab
    (when (eq current-index close-index)
      (let ((to-index (or (if to-index (1- to-index))
                          (pcase tab-bar-close-tab-select
                            ('left (1- current-index))
                            ('right (if (> (length tabs) (1+ current-index))
                                        (1+ current-index)
                                      (1- current-index)))))))
        (setq to-index (max 0 (min (or to-index 0) (1- (length tabs)))))
        (tab-bar-select-tab (1+ to-index))
        ;; Re-read tabs after selecting another tab
        (setq tabs (tab-bar-tabs))))

    (set-frame-parameter nil 'tabs (delq (nth close-index tabs) tabs))

    (when (and tab-bar-mode
               (and (natnump tab-bar-show)
                    (<= (length tabs) tab-bar-show)))
      (tab-bar-mode -1))
    (if tab-bar-mode
        (force-mode-line-update)
      (message "Deleted tab and switched to %s" tab-bar-close-tab-select))))

(defun tab-bar-close-tab-by-name (name)
  "Close the tab by NAME."
  (interactive (list (completing-read "Close tab by name: "
                                      (mapcar (lambda (tab)
                                                (cdr (assq 'name tab)))
                                              (tab-bar-tabs)))))
  (tab-bar-close-tab (1+ (tab-bar--tab-index-by-name name))))

(defun tab-close-other ()
  "Close all tabs on the selected frame, except the selected one."
  (interactive)
  (let* ((tabs (tab-bar-tabs))
         (current-index (tab-bar--current-tab-index tabs)))
    (when current-index
      (set-frame-parameter nil 'tabs (list (nth current-index tabs)))
      (if tab-bar-mode
          (force-mode-line-update)
        (message "Deleted all other tabs")))))

\f
;;; Short aliases

(defalias 'tab-new      'tab-bar-new-tab)
(defalias 'tab-close    'tab-bar-close-tab)
(defalias 'tab-select   'tab-bar-select-tab)
(defalias 'tab-next     'tab-bar-switch-to-next-tab)
(defalias 'tab-previous 'tab-bar-switch-to-prev-tab)
(defalias 'tab-list     'tab-bar-list)

\f
;;; Non-graphical access to frame-local tabs (named window configurations)

(defun tab-bar-list ()
  "Display a list of named window configurations.
The list is displayed in the buffer `*Tabs*'.
It's placed in the center of the frame to resemble a window list
displayed by a window switcher in some window managers on Alt+Tab.

In this list of window configurations you can delete or select them.
Type ? after invocation to get help on commands available.
Type q to remove the list of window configurations from the display.

The first column shows `D' for for a window configuration you have
marked for deletion."
  (interactive)
  (let ((dir default-directory)
        (minibuf (minibuffer-selected-window)))
    (let ((tab-bar-show nil)) ; don't enable tab-bar-mode if it's disabled
      (tab-bar-new-tab))
    ;; Handle the case when it's called in the active minibuffer.
    (when minibuf (select-window (minibuffer-selected-window)))
    (delete-other-windows)
    ;; Create a new window to replace the existing one, to not break the
    ;; window parameters (e.g. prev/next buffers) of the window just saved
    ;; to the window configuration.  So when a saved window is restored,
    ;; its parameters left intact.
    (split-window) (delete-window)
    (let ((switch-to-buffer-preserve-window-point nil))
      (switch-to-buffer (tab-bar-list-noselect)))
    (setq default-directory dir))
  (message "Commands: d, x; RET; q to quit; ? for help."))

(defun tab-bar-list-noselect ()
  "Create and return a buffer with a list of window configurations.
The list is displayed in a buffer named `*Tabs*'.

For more information, see the function `tab-bar-list'."
  (let* ((tabs (delq nil (mapcar (lambda (tab) ; remove current tab
                                   (unless (eq (car tab) 'current-tab)
                                     tab))
                                 (tab-bar-tabs))))
         ;; Sort by recency
         (tabs (sort tabs (lambda (a b) (< (cdr (assq 'time b))
                                           (cdr (assq 'time a)))))))
    (with-current-buffer (get-buffer-create
                          (format " *Tabs*<%s>" (or (frame-parameter nil 'window-id)
                                                    (frame-parameter nil 'name))))
      (erase-buffer)
      (tab-bar-list-mode)
      (setq buffer-read-only nil)
      ;; Vertical alignment to the center of the frame
      (insert-char ?\n (/ (- (frame-height) (length tabs) 1) 2))
      ;; Horizontal alignment to the center of the frame
      (setq tab-bar-list-column (- (/ (frame-width) 2) 15))
      (dolist (tab tabs)
        (insert (propertize
                 (format "%s %s\n"
                         (make-string tab-bar-list-column ?\040)
                         (propertize
                          (cdr (assq 'name tab))
                          'mouse-face 'highlight
                          'help-echo "mouse-2: select this window configuration"))
                 'tab tab)))
      (goto-char (point-min))
      (goto-char (or (next-single-property-change (point) 'tab) (point-min)))
      (when (> (length tabs) 1)
        (tab-bar-list-next-line))
      (move-to-column tab-bar-list-column)
      (set-buffer-modified-p nil)
      (current-buffer))))

(defvar tab-bar-list-column 3)
(make-variable-buffer-local 'tab-bar-list-column)

(defvar tab-bar-list-mode-map
  (let ((map (make-keymap)))
    (suppress-keymap map t)
    (define-key map "q"    'quit-window)
    (define-key map "\C-m" 'tab-bar-list-select)
    (define-key map "d"    'tab-bar-list-delete)
    (define-key map "k"    'tab-bar-list-delete)
    (define-key map "\C-d" 'tab-bar-list-delete-backwards)
    (define-key map "\C-k" 'tab-bar-list-delete)
    (define-key map "x"    'tab-bar-list-execute)
    (define-key map " "    'tab-bar-list-next-line)
    (define-key map "n"    'tab-bar-list-next-line)
    (define-key map "p"    'tab-bar-list-prev-line)
    (define-key map "\177" 'tab-bar-list-backup-unmark)
    (define-key map "?"    'describe-mode)
    (define-key map "u"    'tab-bar-list-unmark)
    (define-key map [mouse-2] 'tab-bar-list-mouse-select)
    (define-key map [follow-link] 'mouse-face)
    map)
  "Local keymap for `tab-bar-list-mode' buffers.")

(define-derived-mode tab-bar-list-mode nil "Window Configurations"
  "Major mode for selecting a window configuration.
Each line describes one window configuration in Emacs.
Letters do not insert themselves; instead, they are commands.
\\<tab-bar-list-mode-map>
\\[tab-bar-list-mouse-select] -- select window configuration you click on.
\\[tab-bar-list-select] -- select current line's window configuration.
\\[tab-bar-list-delete] -- mark that window configuration to be deleted, and move down.
\\[tab-bar-list-delete-backwards] -- mark that window configuration to be deleted, and move up.
\\[tab-bar-list-execute] -- delete marked window configurations.
\\[tab-bar-list-unmark] -- remove all kinds of marks from current line.
  With prefix argument, also move up one line.
\\[tab-bar-list-backup-unmark] -- back up a line and remove marks."
  (setq truncate-lines t)
  (setq buffer-read-only t))

(defun tab-bar-list-current-tab (error-if-non-existent-p)
  "Return window configuration described by this line of the list."
  (let* ((where (save-excursion
                  (beginning-of-line)
                  (+ 2 (point) tab-bar-list-column)))
         (tab (and (not (eobp)) (get-text-property where 'tab))))
    (or tab
        (if error-if-non-existent-p
            (user-error "No window configuration on this line")
          nil))))

(defun tab-bar-list-next-line (&optional arg)
  (interactive)
  (forward-line arg)
  (beginning-of-line)
  (move-to-column tab-bar-list-column))

(defun tab-bar-list-prev-line (&optional arg)
  (interactive)
  (forward-line (- arg))
  (beginning-of-line)
  (move-to-column tab-bar-list-column))

(defun tab-bar-list-unmark (&optional backup)
  "Cancel all requested operations on window configuration on this line and move down.
Optional prefix arg means move up."
  (interactive "P")
  (beginning-of-line)
  (move-to-column tab-bar-list-column)
  (let* ((buffer-read-only nil))
    (delete-char 1)
    (insert " "))
  (forward-line (if backup -1 1))
  (move-to-column tab-bar-list-column))

(defun tab-bar-list-backup-unmark ()
  "Move up and cancel all requested operations on window configuration on line above."
  (interactive)
  (forward-line -1)
  (tab-bar-list-unmark)
  (forward-line -1)
  (move-to-column tab-bar-list-column))

(defun tab-bar-list-delete (&optional arg)
  "Mark window configuration on this line to be deleted by \\<tab-bar-list-mode-map>\\[tab-bar-list-execute] command.
Prefix arg is how many window configurations to delete.
Negative arg means delete backwards."
  (interactive "p")
  (let ((buffer-read-only nil))
    (if (or (null arg) (= arg 0))
        (setq arg 1))
    (while (> arg 0)
      (delete-char 1)
      (insert ?D)
      (forward-line 1)
      (setq arg (1- arg)))
    (while (< arg 0)
      (delete-char 1)
      (insert ?D)
      (forward-line -1)
      (setq arg (1+ arg)))
    (move-to-column tab-bar-list-column)))

(defun tab-bar-list-delete-backwards (&optional arg)
  "Mark window configuration on this line to be deleted by \\<tab-bar-list-mode-map>\\[tab-bar-list-execute] command.
Then move up one line.  Prefix arg means move that many lines."
  (interactive "p")
  (tab-bar-list-delete (- (or arg 1))))

(defun tab-bar-list-delete-from-list (tab)
  "Delete the window configuration from both lists."
  (set-frame-parameter nil 'tabs (delq tab (tab-bar-tabs))))

(defun tab-bar-list-execute ()
  "Delete window configurations marked with \\<tab-bar-list-mode-map>\\[tab-bar-list-delete] commands."
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (let ((buffer-read-only nil))
      (while (re-search-forward
              (format "^%sD" (make-string tab-bar-list-column ?\040))
              nil t)
        (forward-char -1)
        (let ((tab (tab-bar-list-current-tab nil)))
          (when tab
            (tab-bar-list-delete-from-list tab)
            (beginning-of-line)
            (delete-region (point) (progn (forward-line 1) (point))))))))
  (beginning-of-line)
  (move-to-column tab-bar-list-column)
  (when tab-bar-mode
    (force-mode-line-update)))

(defun tab-bar-list-select ()
  "Select this line's window configuration.
This command deletes and replaces all the previously existing windows
in the selected frame."
  (interactive)
  (let* ((to-tab (tab-bar-list-current-tab t)))
    (kill-buffer (current-buffer))
    ;; Delete the current window configuration
    (tab-bar-close-tab nil (1+ (tab-bar--tab-index to-tab)))))

(defun tab-bar-list-mouse-select (event)
  "Select the window configuration whose line you click on."
  (interactive "e")
  (set-buffer (window-buffer (posn-window (event-end event))))
  (goto-char (posn-point (event-end event)))
  (tab-bar-list-select))

\f
(defun switch-to-buffer-other-tab (buffer-or-name &optional norecord)
  "Switch to buffer BUFFER-OR-NAME in another tab.
Like \\[switch-to-buffer-other-frame] (which see), but creates a new tab."
  (interactive
   (list (read-buffer-to-switch "Switch to buffer in other tab: ")))
  (let ((tab-bar-new-tab-choice t))
    (tab-bar-new-tab))
  (delete-other-windows)
  (switch-to-buffer buffer-or-name norecord))

(defun find-file-other-tab (filename &optional wildcards)
  "Edit file FILENAME, in another tab.
Like \\[find-file-other-frame] (which see), but creates a new tab."
  (interactive
   (find-file-read-args "Find file in other tab: "
                        (confirm-nonexistent-file-or-buffer)))
  (let ((value (find-file-noselect filename nil nil wildcards)))
    (if (listp value)
        (progn
          (setq value (nreverse value))
          (switch-to-buffer-other-tab (car value))
          (mapc 'switch-to-buffer (cdr value))
          value)
      (switch-to-buffer-other-tab value))))

(define-key ctl-x-6-map "2" 'tab-new)
(define-key ctl-x-6-map "1" 'tab-close-other)
(define-key ctl-x-6-map "0" 'tab-close)
(define-key ctl-x-6-map "o" 'tab-next)
(define-key ctl-x-6-map "b" 'switch-to-buffer-other-tab)
(define-key ctl-x-6-map "f" 'find-file-other-tab)
(define-key ctl-x-6-map "\C-f" 'find-file-other-tab)

\f
(provide 'tab-bar)

;;; tab-bar.el ends here