;;; tab-line.el --- window-local tabs with window buffers -*- lexical-binding: t; -*-

;; Copyright (C) 2019-2020 Free Software Foundation, Inc.

;; Author: Juri Linkov <juri@linkov.net>
;; Keywords: windows 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:

;; To enable this mode, run `M-x global-tab-line-mode'.

;;; Code:

(require 'seq) ; tab-line.el is not pre-loaded so it's safe to use it here

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

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

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

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

(defface tab-line-tab-current
  '((default
      :inherit tab-line-tab)
    (((class color) (min-colors 88))
     :background "grey85"))
  "Tab line face for tab with current buffer in selected window."
  :version "27.1"
  :group 'tab-line-faces)

(defface tab-line-highlight
  '((default :inherit tab-line-tab))
  "Tab line face for highlighting."
  :version "27.1"
  :group 'tab-line-faces)

(defface tab-line-close-highlight
  '((t :foreground "red"))
  "Tab line face for highlighting of the close button."
  :version "27.1"
  :group 'tab-line-faces)

\f
(defvar tab-line-tab-map
  (let ((map (make-sparse-keymap)))
    (define-key map [tab-line mouse-1] 'tab-line-select-tab)
    (define-key map [tab-line mouse-2] 'tab-line-close-tab)
    (define-key map "\C-m" 'tab-line-select-tab)
    map)
  "Local keymap for `tab-line-mode' window tabs.")

(defvar tab-line-add-map
  (let ((map (make-sparse-keymap)))
    (define-key map [tab-line mouse-1] 'tab-line-new-tab)
    (define-key map [tab-line mouse-2] 'tab-line-new-tab)
    (define-key map "\C-m" 'tab-line-new-tab)
    map)
  "Local keymap to add `tab-line-mode' window tabs.")

(defvar tab-line-tab-close-map
  (let ((map (make-sparse-keymap)))
    (define-key map [tab-line mouse-1] 'tab-line-close-tab)
    (define-key map [tab-line mouse-2] 'tab-line-close-tab)
    map)
  "Local keymap to close `tab-line-mode' window tabs.")

(defvar tab-line-left-map
  (let ((map (make-sparse-keymap)))
    (define-key map [tab-line mouse-1] 'tab-line-hscroll-left)
    (define-key map [tab-line mouse-2] 'tab-line-hscroll-left)
    (define-key map "\C-m" 'tab-line-new-tab)
    map)
  "Local keymap to scroll `tab-line-mode' window tabs to the left.")

(defvar tab-line-right-map
  (let ((map (make-sparse-keymap)))
    (define-key map [tab-line mouse-1] 'tab-line-hscroll-right)
    (define-key map [tab-line mouse-2] 'tab-line-hscroll-right)
    (define-key map "\C-m" 'tab-line-new-tab)
    map)
  "Local keymap to scroll `tab-line-mode' window tabs to the right.")

\f
(defcustom tab-line-new-tab-choice t
  "Defines what to show in a new tab.
If t, display a selection menu with all available buffers.
If the value is a function, call it with no arguments."
  :type '(choice (const     :tag "Buffer menu" t)
                 (function  :tag "Function"))
  :group 'tab-line
  :version "27.1")

(defcustom tab-line-new-button-show t
  "If non-nil, show the \"New tab\" button in the tab line."
  :type 'boolean
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-line
  :version "27.1")

(defvar tab-line-new-button
  (propertize " + "
              'display `(image :type xpm
                               :file "tabs/new.xpm"
                               :margin (2 . 0)
                               :ascent center)
              'keymap tab-line-add-map
              'mouse-face 'tab-line-highlight
              'help-echo "Click to add tab")
  "Button for creating a new tab.")

(defcustom tab-line-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-line
  :version "27.1")

(defvar tab-line-close-button
  (propertize " x"
              'display `(image :type xpm
                               :file "tabs/close.xpm"
                               :margin (2 . 0)
                               :ascent center)
              'keymap tab-line-tab-close-map
              'mouse-face 'tab-line-close-highlight
              'help-echo "Click to close tab")
  "Button for closing the clicked tab.")

(defvar tab-line-left-button
  (propertize " <"
              'display `(image :type xpm
                               :file "tabs/left-arrow.xpm"
                               :margin (2 . 0)
                               :ascent center)
              'keymap tab-line-left-map
              'mouse-face 'tab-line-highlight
              'help-echo "Click to scroll left")
  "Button for scrolling horizontally to the left.")

(defvar tab-line-right-button
  (propertize "> "
              'display `(image :type xpm
                               :file "tabs/right-arrow.xpm"
                               :margin (2 . 0)
                               :ascent center)
              'keymap tab-line-right-map
              'mouse-face 'tab-line-highlight
              'help-echo "Click to scroll right")
  "Button for scrolling horizontally to the right.")

(defvar tab-line-separator nil
  "String that delimits tabs.")

\f
(defcustom tab-line-tab-name-function #'tab-line-tab-name-buffer
  "Function to get a tab name.
Function gets two arguments: tab to get name for and a list of tabs
to display.  By default, use function `tab-line-tab-name'."
  :type '(choice (const :tag "Buffer name"
                        tab-line-tab-name-buffer)
                 (const :tag "Truncated buffer name"
                        tab-line-tab-name-truncated-buffer)
                 (function  :tag "Function"))
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-line
  :version "27.1")

(defun tab-line-tab-name-buffer (buffer &optional _buffers)
  "Generate tab name from BUFFER.
Reduce tab width proportionally to space taken by other tabs.
This function can be overridden by changing the default value of the
variable `tab-line-tab-name-function'."
  (buffer-name buffer))

(defcustom tab-line-tab-name-truncated-max 20
  "Maximum length of the tab name from the current buffer.
Effective when `tab-line-tab-name-function' is customized
to `tab-line-tab-name-truncated-buffer'."
  :type 'integer
  :group 'tab-line
  :version "27.1")

(defvar tab-line-tab-name-ellipsis
  (if (char-displayable-p ?…) "…" "..."))

(defun tab-line-tab-name-truncated-buffer (buffer &optional _buffers)
  "Generate tab name from BUFFER.
Truncate it to the length specified by `tab-line-tab-name-truncated-max'.
Append ellipsis `tab-line-tab-name-ellipsis' in this case."
  (let ((tab-name (buffer-name buffer)))
    (if (< (length tab-name) tab-line-tab-name-truncated-max)
        tab-name
      (propertize (truncate-string-to-width
                   tab-name tab-line-tab-name-truncated-max nil nil
                   tab-line-tab-name-ellipsis)
                  'help-echo tab-name))))

\f
(defcustom tab-line-tabs-function #'tab-line-tabs-window-buffers
  "Function to get a list of tabs to display in the tab line.
This function should return either a list of buffers whose names will
be displayed, or just a list of strings to display in the tab line.
By default, use function `tab-line-tabs-window-buffers' that
returns a list of buffers associated with the selected window.
When `tab-line-tabs-mode-buffers', return a list of buffers
with the same major mode as the current buffer."
  :type '(choice (const :tag "Window buffers"
                        tab-line-tabs-window-buffers)
                 (const :tag "Same mode buffers"
                        tab-line-tabs-mode-buffers)
                 (const :tag "Grouped buffers"
                        tab-line-tabs-buffer-groups)
                 (function :tag "Function"))
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
         (set-default sym val)
         (force-mode-line-update))
  :group 'tab-line
  :version "27.1")

(defvar tab-line-tabs-buffer-list-function #'tab-line-tabs-buffer-list
  "Function to return a global list of buffers.
Used only for `tab-line-tabs-mode-buffers' and `tab-line-tabs-buffer-groups'.")

(defun tab-line-tabs-buffer-list ()
  (seq-filter (lambda (b) (and (buffer-live-p b)
                               (/= (aref (buffer-name b) 0) ?\s)))
              (seq-uniq (append (list (current-buffer))
                                (mapcar #'car (window-prev-buffers))
                                (buffer-list)))))

(defun tab-line-tabs-mode-buffers ()
  "Return a list of buffers with the same major mode with current buffer."
  (let ((mode major-mode))
    (seq-sort-by #'buffer-name #'string<
                 (seq-filter (lambda (b) (with-current-buffer b
                                           (derived-mode-p mode)))
                             (funcall tab-line-tabs-buffer-list-function)))))

(defvar tab-line-tabs-buffer-group-function nil
  "Function to put a buffer to the group.
Takes a buffer as arg and should return a group name as string.
When the return value is nil, filter out the buffer.")

(defvar tab-line-tabs-buffer-group-sort-function nil
  "Function to sort buffers in group.")

(defvar tab-line-tabs-buffer-groups-sort-function #'string<
  "Function to sort group names.")

(defvar tab-line-tabs-buffer-groups mouse-buffer-menu-mode-groups
  "How to group various major modes together in the tab line.
Each element has the form (REGEXP . GROUPNAME).
If the major mode's name string matches REGEXP, use GROUPNAME instead.")

(defun tab-line-tabs-buffer-group-name (&optional buffer)
  (if (functionp tab-line-tabs-buffer-group-function)
      (funcall tab-line-tabs-buffer-group-function buffer)
    (let ((mode (if buffer (with-current-buffer buffer
                             (format-mode-line mode-name))
                  (format-mode-line mode-name))))
      (or (cdr (seq-find (lambda (group)
                           (string-match-p (car group) mode))
                         tab-line-tabs-buffer-groups))
          mode))))

(defun tab-line-tabs-buffer-groups ()
  (if (window-parameter nil 'tab-line-groups)
      (let* ((buffers (funcall tab-line-tabs-buffer-list-function))
             (groups
              (seq-sort tab-line-tabs-buffer-groups-sort-function
                        (delq nil (mapcar #'car (seq-group-by
                                                 (lambda (buffer)
                                                   (tab-line-tabs-buffer-group-name
                                                    buffer))
                                                 buffers)))))
             (selected-group (window-parameter nil 'tab-line-group))
             (tabs
              (mapcar (lambda (group)
                        `(tab
                          (name . ,group)
                          (selected . ,(equal group selected-group))
                          (select . ,(lambda ()
                                       (set-window-parameter nil 'tab-line-groups nil)
                                       (set-window-parameter nil 'tab-line-group group)
                                       (set-window-parameter nil 'tab-line-hscroll nil)))))
                      groups)))
        tabs)

    (let* ((window-parameter (window-parameter nil 'tab-line-group))
           (group-name (tab-line-tabs-buffer-group-name (current-buffer)))
           (group (prog1 (or window-parameter group-name "All")
                    (when (equal window-parameter group-name)
                      (set-window-parameter nil 'tab-line-group nil))))
           (group-tab `(tab
                        (name . ,group)
                        (select . ,(lambda ()
                                     (set-window-parameter nil 'tab-line-groups t)
                                     (set-window-parameter nil 'tab-line-group group)
                                     (set-window-parameter nil 'tab-line-hscroll nil)))))
           (buffers
            (seq-filter (lambda (b)
                          (equal (tab-line-tabs-buffer-group-name b) group))
                        (funcall tab-line-tabs-buffer-list-function)))
           (sorted-buffers (if (functionp tab-line-tabs-buffer-group-sort-function)
                               (seq-sort tab-line-tabs-buffer-group-sort-function
                                         buffers)
                             buffers))
           (tabs (mapcar (lambda (buffer)
                           `(tab
                             (name . ,(funcall tab-line-tab-name-function buffer))
                             (selected . ,(eq buffer (current-buffer)))
                             (buffer . ,buffer)
                             (close . ,(lambda (&optional b)
                                         ;; kill-buffer because bury-buffer
                                         ;; won't remove the buffer from tab-line
                                         (kill-buffer (or b buffer))))))
                         sorted-buffers)))
      (cons group-tab tabs))))

(defun tab-line-tabs-window-buffers ()
  "Return a list of tabs that should be displayed in the tab line.
By default returns a list of window buffers, i.e. buffers previously
shown in the same window where the tab line is displayed.
This list can be overridden by changing the default value of the
variable `tab-line-tabs-function'."
  (let* ((window (selected-window))
         (buffer (window-buffer window))
         (next-buffers (seq-remove (lambda (b) (eq b buffer))
                                   (window-next-buffers window)))
         (next-buffers (seq-filter #'buffer-live-p next-buffers))
         (prev-buffers (seq-remove (lambda (b) (eq b buffer))
                                   (mapcar #'car (window-prev-buffers window))))
         (prev-buffers (seq-filter #'buffer-live-p prev-buffers))
         ;; Remove next-buffers from prev-buffers
         (prev-buffers (seq-difference prev-buffers next-buffers)))
    (append (reverse prev-buffers)
            (list buffer)
            next-buffers)))

\f
(defun tab-line-format-template (tabs)
  "Template for displaying tab line for selected window."
  (let* ((selected-buffer (window-buffer))
         (separator (or tab-line-separator (if window-system " " "|")))
         (hscroll (window-parameter nil 'tab-line-hscroll))
         (strings
          (mapcar
           (lambda (tab)
             (let* ((buffer-p (bufferp tab))
                    (selected-p (if buffer-p
                                    (eq tab selected-buffer)
                                  (cdr (assq 'selected tab))))
                    (name (if buffer-p
                              (funcall tab-line-tab-name-function tab tabs)
                            (cdr (assq 'name tab)))))
               (concat
                separator
                (apply 'propertize
                       (concat (propertize name 'keymap tab-line-tab-map)
                               (or (and (or buffer-p (assq 'buffer tab) (assq 'close tab))
                                        tab-line-close-button-show
                                        (not (eq tab-line-close-button-show
                                                 (if selected-p 'non-selected 'selected)))
                                        tab-line-close-button) ""))
                       `(
                         tab ,tab
                         ,@(if selected-p '(selected t))
                         face ,(if selected-p
                                   (if (eq (selected-window) (old-selected-window))
                                       'tab-line-tab-current
                                     'tab-line-tab)
                                 'tab-line-tab-inactive)
                         mouse-face tab-line-highlight)))))
           tabs))
         (hscroll-data (tab-line-auto-hscroll strings hscroll)))
    (setq hscroll (nth 1 hscroll-data))
    (append
     (if (null (nth 0 hscroll-data))
         (when hscroll
           (setq hscroll nil)
           (set-window-parameter nil 'tab-line-hscroll hscroll))
       (list separator
             (when (and (numberp hscroll) (not (zerop hscroll)))
               tab-line-left-button)
             (when (if (numberp hscroll)
                       (< (truncate hscroll) (1- (length strings)))
                     (> (length strings) 1))
               tab-line-right-button)))
     (if hscroll (nthcdr (truncate hscroll) strings) strings)
     (list separator)
     (when (and (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
                tab-line-new-button-show
                tab-line-new-button)
       (list tab-line-new-button)))))

(defvar tab-line-auto-hscroll)

(defun tab-line-format ()
  "Template for displaying tab line for selected window."
  (let* ((tabs (funcall tab-line-tabs-function))
         (cache-key (list tabs
                          ;; handle buffer renames
                          (buffer-name (window-buffer))
                          ;; handle tab-line scrolling
                          (window-parameter nil 'tab-line-hscroll)
                          ;; for setting face 'tab-line-tab-current'
                          (eq (selected-window) (old-selected-window))))
         (cache (window-parameter nil 'tab-line-cache)))
    ;; Enable auto-hscroll again after it was disabled on manual scrolling.
    ;; The moment to enable it is when the window-buffer was updated.
    (when (and tab-line-auto-hscroll        ; if auto-hscroll was enabled
               (integerp (nth 2 cache-key)) ; integer on manual scroll
               cache                        ; window-buffer was updated
               (not (equal (nth 1 (car cache)) (nth 1 cache-key))))
      (set-window-parameter nil 'tab-line-hscroll (float (nth 2 cache-key))))
    (or (and cache (equal (car cache) cache-key) (cdr cache))
        (cdr (set-window-parameter
              nil 'tab-line-cache
              (cons cache-key (tab-line-format-template tabs)))))))

\f
(defcustom tab-line-auto-hscroll t
  "Allow or disallow automatic horizontal scrolling of the tab line.
Non-nil means the tab line are automatically scrolled horizontally to make
the selected tab visible."
  :type 'boolean
  :group 'tab-line
  :version "27.1")

(defvar tab-line-auto-hscroll-buffer (generate-new-buffer " *tab-line-hscroll*"))

(defun tab-line-auto-hscroll (strings hscroll)
  (with-current-buffer tab-line-auto-hscroll-buffer
    (let ((truncate-partial-width-windows nil)
          (inhibit-modification-hooks t)
          show-arrows)
      (setq truncate-lines nil)
      (erase-buffer)
      (apply 'insert strings)
      (goto-char (point-min))
      (add-face-text-property (point-min) (point-max) 'tab-line)
      ;; Continuation means tab-line doesn't fit completely,
      ;; thus scroll arrows are needed for scrolling.
      (setq show-arrows (> (vertical-motion 1) 0))
      ;; Try to auto-hscroll only when scrolling is needed,
      ;; but no manual scrolling was performed before.
      (when (and tab-line-auto-hscroll
                 show-arrows
                 ;; Do nothing when scrolled manually
                 (not (integerp hscroll)))
        (let ((selected (seq-position strings 'selected
                                      (lambda (str prop)
                                        (get-pos-property 1 prop str)))))
          (cond
           ((null selected)
            ;; Do nothing if no tab is selected
            )
           ((or (not (numberp hscroll)) (< selected (truncate hscroll)))
            ;; Selected is scrolled to the left, or no scrolling yet
            (erase-buffer)
            (apply 'insert (reverse (seq-subseq strings 0 (1+ selected))))
            (goto-char (point-min))
            (add-face-text-property (point-min) (point-max) 'tab-line)
            (if (> (vertical-motion 1) 0)
                (let* ((point (previous-single-property-change (point) 'tab))
                       (tab-prop (when point
                                   (or (get-pos-property point 'tab)
                                       (and (setq point (previous-single-property-change point 'tab))
                                            (get-pos-property point 'tab)))))
                       (new-hscroll (when tab-prop
                                      (seq-position strings tab-prop
                                                    (lambda (str tab)
                                                      (eq (get-pos-property 1 'tab str) tab))))))
                  (when new-hscroll
                    (setq hscroll (float new-hscroll))
                    (set-window-parameter nil 'tab-line-hscroll hscroll)))
              (setq hscroll nil)
              (set-window-parameter nil 'tab-line-hscroll hscroll)))
           (t
            ;; Check if the selected tab is already visible
            (erase-buffer)
            (apply 'insert (seq-subseq strings (truncate hscroll) (1+ selected)))
            (goto-char (point-min))
            (add-face-text-property (point-min) (point-max) 'tab-line)
            (when (> (vertical-motion 1) 0)
              ;; Not visible already
              (erase-buffer)
              (apply 'insert (reverse (seq-subseq strings 0 (1+ selected))))
              (goto-char (point-min))
              (add-face-text-property (point-min) (point-max) 'tab-line)
              (when (> (vertical-motion 1) 0)
                (let* ((point (previous-single-property-change (point) 'tab))
                       (tab-prop (when point
                                   (or (get-pos-property point 'tab)
                                       (and (setq point (previous-single-property-change point 'tab))
                                            (get-pos-property point 'tab)))))
                       (new-hscroll (when tab-prop
                                      (seq-position strings tab-prop
                                                    (lambda (str tab)
                                                      (eq (get-pos-property 1 'tab str) tab))))))
                  (when new-hscroll
                    (setq hscroll (float new-hscroll))
                    (set-window-parameter nil 'tab-line-hscroll hscroll)))))))))
      (list show-arrows hscroll))))

\f
(defun tab-line-hscroll (&optional arg window)
  (let* ((hscroll (window-parameter window 'tab-line-hscroll))
         (tabs (if window
                   (with-selected-window window (funcall tab-line-tabs-function))
                 (funcall tab-line-tabs-function))))
    (set-window-parameter
     window 'tab-line-hscroll
     (max 0 (min (+ (if (numberp hscroll) (truncate hscroll) 0) (or arg 1))
                 (1- (length tabs)))))
    (when window
      (force-mode-line-update t))))

(defun tab-line-hscroll-right (&optional arg mouse-event)
  (interactive (list current-prefix-arg last-nonmenu-event))
  (let ((window (and (listp mouse-event) (posn-window (event-start mouse-event)))))
    (tab-line-hscroll arg window)
    (force-mode-line-update window)))

(defun tab-line-hscroll-left (&optional arg mouse-event)
  (interactive (list current-prefix-arg last-nonmenu-event))
  (let ((window (and (listp mouse-event) (posn-window (event-start mouse-event)))))
    (tab-line-hscroll (- (or arg 1)) window)
    (force-mode-line-update window)))

\f
(defun tab-line-new-tab (&optional mouse-event)
  "Add a new tab to the tab line.
Usually is invoked by clicking on the plus-shaped button.
But any switching to other buffer also adds a new tab
corresponding to the switched buffer."
  (interactive (list last-nonmenu-event))
  (if (functionp tab-line-new-tab-choice)
      (funcall tab-line-new-tab-choice)
    (let ((tab-line-tabs-buffer-groups mouse-buffer-menu-mode-groups))
      (if (and (listp mouse-event) window-system) ; (display-popup-menus-p)
          (mouse-buffer-menu mouse-event) ; like (buffer-menu-open)
        ;; tty menu doesn't support mouse clicks, so use tmm
        (tmm-prompt (mouse-buffer-menu-keymap))))))

(defun tab-line-select-tab (&optional e)
  "Switch to the selected tab.
This command maintains the original order of prev/next buffers.
So for example, switching to a previous tab is equivalent to
using the `previous-buffer' command."
  (interactive "e")
  (let* ((posnp (event-start e))
         (tab (get-pos-property 1 'tab (car (posn-string posnp))))
         (buffer (if (bufferp tab) tab (cdr (assq 'buffer tab)))))
    (if buffer
        (tab-line-select-tab-buffer buffer (posn-window posnp))
      (let ((select (cdr (assq 'select tab))))
        (when (functionp select)
          (with-selected-window (posn-window posnp)
            (funcall select)
            (force-mode-line-update)))))))

(defun tab-line-select-tab-buffer (buffer &optional window)
  (let* ((window-buffer (window-buffer window))
         (next-buffers (seq-remove (lambda (b) (eq b window-buffer))
                                   (window-next-buffers window)))
         (prev-buffers (seq-remove (lambda (b) (eq b window-buffer))
                                   (mapcar #'car (window-prev-buffers window))))
         ;; Remove next-buffers from prev-buffers
         (prev-buffers (seq-difference prev-buffers next-buffers)))
    (cond
     ((and (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
           (memq buffer next-buffers))
      (dotimes (_ (1+ (seq-position next-buffers buffer)))
        (switch-to-next-buffer window)))
     ((and (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
           (memq buffer prev-buffers))
      (dotimes (_ (1+ (seq-position prev-buffers buffer)))
        (switch-to-prev-buffer window)))
     (t
      (with-selected-window window
        (switch-to-buffer buffer))))))

(defun tab-line-switch-to-prev-tab (&optional mouse-event)
  "Switch to the previous tab.
Its effect is the same as using the `previous-buffer' command
(\\[previous-buffer])."
  (interactive (list last-nonmenu-event))
  (let ((window (and (listp mouse-event) (posn-window (event-start mouse-event)))))
    (if (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
        (switch-to-prev-buffer window)
      (with-selected-window (or window (selected-window))
        (let* ((tabs (funcall tab-line-tabs-function))
               (tab (nth (1- (seq-position
                              tabs (current-buffer)
                              (lambda (tab buffer)
                                (if (bufferp tab)
                                    (eq buffer tab)
                                  (eq buffer (cdr (assq 'buffer tab)))))))
                         tabs))
               (buffer (if (bufferp tab) tab (cdr (assq 'buffer tab)))))
          (when (bufferp buffer)
            (switch-to-buffer buffer)))))))

(defun tab-line-switch-to-next-tab (&optional mouse-event)
  "Switch to the next tab.
Its effect is the same as using the `next-buffer' command
(\\[next-buffer])."
  (interactive (list last-nonmenu-event))
  (let ((window (and (listp mouse-event) (posn-window (event-start mouse-event)))))
    (if (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
        (switch-to-next-buffer window)
      (with-selected-window (or window (selected-window))
        (let* ((tabs (funcall tab-line-tabs-function))
               (tab (nth (1+ (seq-position
                              tabs (current-buffer)
                              (lambda (tab buffer)
                                (if (bufferp tab)
                                    (eq buffer tab)
                                  (eq buffer (cdr (assq 'buffer tab)))))))
                         tabs))
               (buffer (if (bufferp tab) tab (cdr (assq 'buffer tab)))))
          (when (bufferp buffer)
            (switch-to-buffer buffer)))))))

\f
(defcustom tab-line-close-tab-function 'bury-buffer
  "Defines what to do on closing the tab.
If `bury-buffer', put the tab's buffer at the end of the list of all
buffers that effectively hides the buffer's tab from the tab line.
If `kill-buffer', kills the tab's buffer.
When a function, it is called with the tab as its argument.
This option is useful when `tab-line-tabs-function' has the value
`tab-line-tabs-window-buffers'."
  :type '(choice (const :tag "Bury buffer" bury-buffer)
                 (const :tag "Kill buffer" kill-buffer)
                 (function :tag "Function"))
  :group 'tab-line
  :version "27.1")

(defun tab-line-close-tab (&optional mouse-event)
  "Close the selected tab.
Usually is invoked by clicking on the close button on the right side
of the tab.  This command buries the buffer, so it goes out of sight
from the tab line."
  (interactive (list last-nonmenu-event))
  (let* ((posnp (and (listp mouse-event) (event-start mouse-event)))
         (window (and posnp (posn-window posnp)))
         (tab (get-pos-property 1 'tab (car (posn-string posnp))))
         (buffer (if (bufferp tab) tab (cdr (assq 'buffer tab))))
         (close-function (unless (bufferp tab) (cdr (assq 'close tab)))))
    (with-selected-window (or window (selected-window))
      (cond
       ((functionp close-function)
        (funcall close-function))
       ((eq tab-line-close-tab-function 'kill-buffer)
        (kill-buffer buffer))
       ((eq tab-line-close-tab-function 'bury-buffer)
        (if (eq buffer (current-buffer))
            (bury-buffer)
          (set-window-prev-buffers nil (assq-delete-all buffer (window-prev-buffers)))
          (set-window-next-buffers nil (delq buffer (window-next-buffers)))))
       ((functionp tab-line-close-tab-function)
        (funcall tab-line-close-tab-function tab)))
      (force-mode-line-update))))

\f
;;;###autoload
(define-minor-mode tab-line-mode
  "Toggle display of window tab line in the buffer."
  :lighter nil
  (setq tab-line-format (when tab-line-mode '(:eval (tab-line-format)))))

(defcustom tab-line-exclude-modes
  '(completion-list-mode)
  "List of major modes in which the tab line is not enabled."
  :type '(repeat symbol)
  :group 'tab-line
  :version "27.1")

;;;###autoload
(defvar tab-line-exclude nil)
;;;###autoload
(make-variable-buffer-local 'tab-line-exclude)

(defun tab-line-mode--turn-on ()
  "Turn on `tab-line-mode'."
  (unless (or (minibufferp)
              (string-match-p "\\` " (buffer-name))
              (memq major-mode tab-line-exclude-modes)
              (get major-mode 'tab-line-exclude)
              (buffer-local-value 'tab-line-exclude (current-buffer)))
    (tab-line-mode 1)))

;;;###autoload
(define-globalized-minor-mode global-tab-line-mode
  tab-line-mode tab-line-mode--turn-on
  :group 'tab-line
  :version "27.1")

\f
(global-set-key [tab-line mouse-4]    'tab-line-hscroll-left)
(global-set-key [tab-line mouse-5]    'tab-line-hscroll-right)
(global-set-key [tab-line wheel-up]   'tab-line-hscroll-left)
(global-set-key [tab-line wheel-down] 'tab-line-hscroll-right)

(global-set-key [tab-line S-mouse-4]    'tab-line-switch-to-prev-tab)
(global-set-key [tab-line S-mouse-5]    'tab-line-switch-to-next-tab)
(global-set-key [tab-line S-wheel-up]   'tab-line-switch-to-prev-tab)
(global-set-key [tab-line S-wheel-down] 'tab-line-switch-to-next-tab)

\f
(provide 'tab-line)
;;; tab-line.el ends here