;;; display-line-numbers.el --- interface for display-line-numbers -*- lexical-binding: t -*-

;; Copyright (C) 2017-2022 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; Keywords: convenience

;; 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 a minor mode interface for `display-line-numbers'.
;;
;; Toggle display of line numbers with M-x display-line-numbers-mode.
;; To enable line numbering in all buffers, use M-x
;; global-display-line-numbers-mode.  To change the default type of
;; line numbers displayed, customize display-line-numbers-type.

;; NOTE: Customization variables for `display-line-numbers' itself are
;; defined in cus-start.el.

;;; Code:

(defgroup display-line-numbers nil
  "Display line numbers in the buffer."
  :group 'convenience
  :group 'display)

(defcustom display-line-numbers-type t
  "The default type of line numbers to use in `display-line-numbers-mode'.
See `display-line-numbers' for value options."
  :group 'display-line-numbers
  :type '(choice (const :tag "Relative line numbers" relative)
                 (const :tag "Relative visual line numbers" visual)
                 (other :tag "Absolute line numbers" t))
  :version "26.1")

(defcustom display-line-numbers-grow-only nil
  "If non-nil, do not shrink line number width."
  :group 'display-line-numbers
  :type 'boolean
  :version "26.1")

(defcustom display-line-numbers-width-start nil
  "If non-nil, count number of lines to use for line number width.
When `display-line-numbers-mode' is turned on, if this option is
non-nil, `display-line-numbers-width' is set up front to a width
necessary to display all line numbers in the buffer.  If the value
is a positive number, it is interpreted as extra lines to account
for when computing the required width; this should be set to the
number of lines in the tallest window in which you want to prevent
the line-number width from changing."
  :group 'display-line-numbers
  :type '(choice (boolean :tag "Minimum width for buffer's line count")
                 (integer :tag "Number of extra lines to account for"))
  :version "28.1")

(defun display-line-numbers-update-width ()
  "Prevent the line number width from shrinking."
  (let ((width (line-number-display-width)))
    (when (> width (or display-line-numbers-width 1))
      (setq display-line-numbers-width width))))

;;;###autoload
(define-minor-mode display-line-numbers-mode
  "Toggle display of line numbers in the buffer.
This uses `display-line-numbers' internally.

To change the type of line numbers displayed by default,
customize `display-line-numbers-type'.  To change the type while
the mode is on, set `display-line-numbers' directly."
  :lighter nil
  (if display-line-numbers-mode
      (progn
        (when display-line-numbers-width-start
          (setq display-line-numbers-width
                (length (number-to-string
                         (+ (count-lines (point-min) (point-max))
                            (if (and (numberp display-line-numbers-width-start)
                                     (> display-line-numbers-width-start 0))
                                display-line-numbers-width-start
                              0))))))
        (when display-line-numbers-grow-only
          (add-hook 'pre-command-hook #'display-line-numbers-update-width nil t))
        (setq display-line-numbers display-line-numbers-type))
    (remove-hook 'pre-command-hook #'display-line-numbers-update-width t)
    (setq display-line-numbers nil)))

(defun display-line-numbers--turn-on ()
  "Turn on `display-line-numbers-mode'."
  (unless (or (minibufferp)
              (string-match-p "\\` " (buffer-name)))
    (display-line-numbers-mode)))

;;;###autoload
(define-globalized-minor-mode global-display-line-numbers-mode
  display-line-numbers-mode display-line-numbers--turn-on)

\f

;;;###autoload
(defvar header-line-indent ""
  "String to indent at the start if the header line.
This is used in `header-line-indent-mode', and buffers that have
this switched on should have a `header-line-format' that look like:

  (\"\" header-line-indent THE-REST...)

Also see `header-line-indent-width'.")

;;;###autoload
(defvar header-line-indent-width 0
  "The width of the current line numbers displayed.
This is updated when `header-line-indent-mode' is switched on.

Also see `header-line-indent'.")

(defun header-line-indent--line-number-width ()
  "Return the width taken by `display-line-numbers' in the current buffer."
  ;; line-number-display-width returns the value for the selected
  ;; window, which might not be the window in which the current buffer
  ;; is displayed.
  (if (not display-line-numbers)
      0
    (let ((cbuf-window (get-buffer-window (current-buffer) t)))
      (if (window-live-p cbuf-window)
          (with-selected-window cbuf-window
            (truncate (line-number-display-width 'columns)))
        4))))

(defun header-line-indent--watch-line-number-width (_window)
  (let ((width (header-line-indent--line-number-width)))
    (setq header-line-indent-width width)
    (unless (= (length header-line-indent) width)
      (setq header-line-indent (make-string width ?\s)))))

(defun header-line-indent--window-scroll-function (window _start)
  (let ((width (with-selected-window window
                 (truncate (line-number-display-width 'columns)))))
    (setq header-line-indent-width width)
    (unless (= (length header-line-indent) width)
      (setq header-line-indent (make-string width ?\s)))))

;;;###autoload
(define-minor-mode header-line-indent-mode
  "Mode to indent the header line in `display-line-numbers-mode' buffers.
This means that the header line will be kept indented so that it
has blank space that's as wide as the displayed line numbers in
the buffer.

Buffers that have this switched on should have a
`header-line-format' that look like:

  (\"\" header-line-indent THE-REST...)

The `header-line-indent-width' variable is also kept updated, and
has the width of `header-line-format'.  This can be used, for
instance, in `:align-to' specs, like:

  (space :align-to (+ header-line-indent-width 10))"
  :lighter nil
  (if header-line-indent-mode
      (progn
        (setq-local header-line-indent ""
                    header-line-indent-width 0)
        (add-hook 'pre-redisplay-functions
                  #'header-line-indent--watch-line-number-width nil t)
        (add-hook 'window-scroll-functions
                  #'header-line-indent--window-scroll-function nil t))
    (setq-local header-line-indent ""
                header-line-indent-width 0)
    (remove-hook 'pre-redisplay-functions
                 #'header-line-indent--watch-line-number-width t)
    (remove-hook 'window-scroll-functions
                 #'header-line-indent--window-scroll-function t)))

(provide 'display-line-numbers)

;;; display-line-numbers.el ends here