.emacs.d/init.d/basics/buffers.el

;;; buffers.el --- Default settings for buffers. -*- lexical-binding: t; -*-

;;; Commentary:
;; * Setup scratch buffer.
;; * Set fill-column.
;; * Define which buffers should be ignored.
;; * Enable auto-fill-mode.

;;; Code:

(require 'basics/package-management)
(require 'misc/libs)
(require 'misc/completion)

(use-package emacs
  :straight (:type built-in)
  :demand t
  :custom ((initial-scratch-message nil)   ; Make scratch buffer empty,
           (initial-major-mode 'text-mode)) ; and select mode.
  :config (progn
            (defvar my/skippable-buffers
              '("^\\*" "^magit[:-]" "^Pfuture-Callback")
              "Buffer names ignored by `next-buffer' and `previous-buffer'.")
            (defvar my/never-skippable-buffers
              '("^\\*scratch\\*$" "^\\*Easy-hugo\\*$")
              "Buffer names never ignored by `next-buffer' and `previous-buffer'.")
            (defun my/buffer-predicate (buffer)
              "Return nil if buffer-name matches expression in `my/skippable-buffers'."
              (catch 'return
                ;; Return t if buffer-name is on never-skippable list.
                (dolist (expression my/never-skippable-buffers)
                  (if (string-match expression (buffer-name buffer))
                      (throw 'return t)))
                ;; Return nil if buffer-name is on skippable list.
                (dolist (expression my/skippable-buffers)
                  (if (string-match expression (buffer-name buffer))
                      (throw 'return nil)))
                t))
            (set-frame-parameter nil 'buffer-predicate 'my/buffer-predicate)
            ; Doesn't work with use-package?
            (add-hook 'after-make-frame-functions
                      (lambda (frame)
                        (set-frame-parameter
                         frame 'buffer-predicate 'my/buffer-predicate)))

            (defun my/truncate-lines ()
              "Truncate lines in local buffer instead of wrapping them."
              (setq-local truncate-lines t)))
  :bind (("M-<left>"  . previous-buffer)
         ("M-<right>" . next-buffer))
  :hook ((prog-mode . my/truncate-lines)
         (conf-mode . my/truncate-lines)
         (emacs-startup . (lambda () (with-current-buffer "*scratch*"
                                       (turn-off-auto-fill))))))

;; Show and select buffers. Minimal interface for recovery situations.
(use-package bs
  :bind ("C-x C-b" . bs-show))

;; Delete old buffers.
;; https://www.emacswiki.org/emacs/CleanBufferList
(use-package midnight
  :straight (:type built-in)
  :defer 4
  :init (setq midnight-delay 30                ; 30 seconds after “midnight”.
              midnight-period (* 2 60 60))     ; Clean every 2 hours.
  :custom ((clean-buffer-list-delay-general 1) ; Clean normal bufs after 1d,
           (clean-buffer-list-delay-special (* 30 60)) ; special after 30m.
           (clean-buffer-list-kill-regexps '("^ ?\\*" ; These are “special”.
                                             "^magit-?.*:"
                                             ("\\.log$" . 3600)
                                             "^Pfuture-Callback")))
  :config (midnight-mode t))

;; Dedicate windows to “purposes”.
(use-package window-purpose
  :demand t                             ; projectile depends on window-purpose.
  :diminish purpose-mode
  :defines (purpose-x-popwin-major-modes)
  :custom (purpose-x-popwin-position 'right)
  :config (progn
            (purpose-mode)
            (add-to-list 'purpose-user-mode-purposes '(c++-mode . cpp))
            (add-to-list 'purpose-user-mode-purposes '(qml-mode . cpp))
            (add-to-list 'purpose-user-mode-purposes '(emacs-lisp-mode . elisp))
            (add-to-list 'purpose-user-mode-purposes '(ebuild-mode . ebuild))
            (add-to-list 'purpose-user-mode-purposes '(adoc-mode . adoc))
            (add-to-list 'purpose-user-mode-purposes '(markdown-mode . md))
            (add-to-list 'purpose-user-mode-purposes '(gfm-mode . md))
            (add-to-list 'purpose-user-mode-purposes '(Man-mode . help-buf))
            (add-to-list 'purpose-user-mode-purposes '(help-mode . help-buf))
            (add-to-list 'purpose-user-mode-purposes '(info-mode . help-buf))
            (add-to-list 'purpose-user-mode-purposes
                         '(compilation-mode . compile))

            (add-to-list 'purpose-special-action-sequences
                         '(help-buf purpose-display-reuse-window-buffer))
            (purpose-compile-user-configuration)

            (require 'window-purpose-x)
            ;; Assign all Magit buffers the same purpose.
            (purpose-x-magit-single-on)
            (purpose-x-kill-setup)   ; Replace killed buffers with same purpose.

            (purpose-x-popwin-setup)
            (push 'Man-mode purpose-x-popwin-major-modes)
            (purpose-x-popwin-update-conf))
  :bind (("<f2>" . purpose-toggle-window-purpose-dedicated)
         ("C-<f2>" . purpose-toggle-window-buffer-dedicated)
         ("M-<f2>" . purpose-load-window-layout)))

(use-package ivy-purpose
  :after (ivy window-purpose)
  :config (ivy-purpose-setup)
  :bind (:map purpose-mode-map
              ("C-x b" . ivy-switch-buffer)))

;; Visual feedback on some operations by highlighting region.
(use-package volatile-highlights
  :diminish volatile-highlights-mode
  :after (doom-themes display-line-numbers)
  :config (progn
            (defun my/volatile-highlights-reset-color ()
              (set-face-background 'vhl/default-face
                                   (hexrgb-increment-equal-rgb
                                    (face-background 'default) 2 8)))
            (my/volatile-highlights-reset-color))
  :hook (window-setup . volatile-highlights-mode))

(provide 'basics/buffers)
;;; buffers.el ends here