;;; vimish-fold.el --- Fold text like in Vim -*- lexical-binding: t; -*-
;;
;; Copyright © 2015–2017 Mark Karpov <markkarpov92@gmail.com>
;; Copyright © 2012–2013 Magnar Sveen <magnars@gmail.com>
;;
;; Author: Mark Karpov <markkarpov92@gmail.com>
;; Author: Magnar Sveen <magnars@gmail.com>
;; URL: https://github.com/mrkkrp/vimish-fold
;; Version: 0.2.3
;; Package-Requires: ((emacs "24.4") (cl-lib "0.5") (f "0.18.0"))
;; Keywords: convenience
;;
;; This file is not part of GNU Emacs.
;;
;; This program 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.
;;
;; This program 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 this program. If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This is a package to perform text folding like in Vim.  It has the
;; following features:
;;
;; * folding of active regions;
;;
;; * good visual feedback: it's obvious which part of text is folded;
;;
;; * persistence by default: when you kill a buffer your folds don't
;;   disappear;
;;
;; * persistence scales well, you can work on hundreds of files with lots of
;;   folds without adverse effects;
;;
;; * it does not break indentation;
;;
;; * folds can be toggled from folded state to unfolded and back very
;;   easily;
;;
;; * quick navigation between existing folds;
;;
;; * you can use mouse to unfold folds (good for beginners and not only for
;;   them);
;;
;; * for fans of `avy' package: you can use `avy' to fold text with minimal
;;   number of key strokes!

;;; Code:

(require 'cl-lib)
(require 'f)

(defgroup vimish-fold nil
  "Fold text like in Vim"
  :group  'text
  :tag    "Vimish Fold"
  :prefix "vimish-fold-"
  :link   '(url-link :tag "GitHub" "https://github.com/mrkkrp/vimish-fold"))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Basic functionality

(defface vimish-fold-overlay
  '((t (:inherit highlight)))
  "Face used to highlight the fold overlay.")

(defface vimish-fold-mouse-face
  '((t (:inherit highlight :weight bold)))
  "Face to use when mouse hovers over folded text.")

(defface vimish-fold-fringe
  '((t (:inherit font-lock-function-name-face)))
  "Face used to indicate folded text on fringe.")

(defcustom vimish-fold-indication-mode 'left-fringe
  "The indication mode for folded text areas.

This variable may have one of the following values:
`left-fringe', `right-fringe', or NIL.

If set to `left-fringe' or `right-fringe', indicate folded text
via icons in the left and right fringe respectively.

If set to NIL, do not indicate folded text, just highlight it."
  :tag "Indication on folded text"
  :type '(choice (const :tag "Indicate in the left fringe" left-fringe)
                 (const :tag "Indicate in the right fringe" right-fringe)
                 (const :tag "Do not indicate" nil)))

(defcustom vimish-fold-blank-fold-header "<blank fold>"
  "The string is used as fold header when it consists of blank characters."
  :tag  "Header of Blank Fold"
  :type 'string)

(defcustom vimish-fold-header-width 80
  "Width of header of folded region.

This can be a number or NIL.  If it's NIL value returned of
`window-width' will be used."
  :tag  "Width of header of folded region"
  :type '(choice (const   :tag "use window width")
                 (integer :tag "width of fold header")))

(defcustom vimish-fold-show-lines t
  "Whether to show number of lines folded in fold header."
  :tag  "Show number of lines folded"
  :type 'boolean)

(defcustom vimish-fold-include-last-empty-line nil
  "Whether to include last empty line in selection into created fold."
  :tag  "Include last empty line into created fold"
  :type 'boolean
  :package-version '(vimish-fold . "0.2.1"))

(defcustom vimish-fold-persist-on-saving t
  "Whether to save folds on buffer saving.

Other than on saving, folds are also saved on buffer killing and
when user quits Emacs.  Turn this option off if the additional
overhead is undesirable."
  :tag "Save folds on buffer saving."
  :type 'boolean
  :package-version '(vimish-fold . "0.2.3"))

(defvar vimish-fold-folded-keymap (make-sparse-keymap)
  "Keymap which is active when point is placed on folded text.")

(defvar vimish-fold-unfolded-keymap (make-sparse-keymap)
  "Keymap which is active when point is placed on unfolded text.")

(defun vimish-fold--correct-region (beg end)
  "Return a cons of corrected BEG and END.

We only support folding by whole lines, so we should make sure
that beginning and end positions are correct.  Also, sometimes
users select region including last newline into it, they don't
really want to include it, we correct this here."
  (cl-destructuring-bind (beg . end)
      (if (>= end beg)
          (cons beg end)
        (cons end beg))
    (save-excursion
      (let* ((beg* (progn (goto-char beg)
                          (line-beginning-position)))
             (end* (progn (goto-char end)
                          (if (and (zerop (current-column))
                                   (/= end beg*)
                                   (not vimish-fold-include-last-empty-line))
                              (1- end)
                            (line-end-position)))))
        (cons beg* end*)))))

(defun vimish-fold--read-only (on beg end)
  "If ON is non-NIL, make text between BEG and END read-only.

If ON is NIL, make the text editable again."
  (let ((inhibit-read-only t))
    (with-silent-modifications
      (funcall
       (if on #'add-text-properties #'remove-text-properties)
       beg end (list 'read-only on)))))

(defun vimish-fold--get-header (beg end)
  "Extract folding header from region between BEG and END in BUFFER.

If BUFFER is NIL, current buffer is used."
  (let ((info (when vimish-fold-show-lines
                (format "    %d lines" (count-lines beg end)))))
    (save-excursion
      (goto-char beg)
      (re-search-forward "^\\([[:blank:]]*.+\\)$")
      (concat
       (truncate-string-to-width
        (if (and (>= (match-beginning 1) beg)
                 (<= (match-end 1)       end))
            (match-string-no-properties 1)
          vimish-fold-blank-fold-header)
        (- (or vimish-fold-header-width
               (window-width))
           (length info))
        nil
        32 ; space
        "…")
       info))))

(defun vimish-fold--setup-fringe (overlay &optional prefix)
  "Setup fringe for OVERLAY according to user settings.

If PREFIX is not NIL, setup fringe for every line."
  (when vimish-fold-indication-mode
    (unless (memq vimish-fold-indication-mode
                  '(left-fringe right-fringe))
      (error "Invalid fringe side: %S"
             vimish-fold-indication-mode))
    (overlay-put overlay (if prefix 'line-prefix 'before-string)
                 (propertize "…" 'display
                             (list vimish-fold-indication-mode
                                   'empty-line
                                   'vimish-fold-fringe)))))

(defun vimish-fold--apply-cosmetic (overlay header)
  "Make OVERLAY look according to user's settings displaying HEADER.

This includes fringe bitmaps and faces."
  (overlay-put overlay 'display
               (propertize header 'face 'vimish-fold-overlay))
  (overlay-put overlay 'pointer 'hand)
  (overlay-put overlay 'mouse-face 'vimish-fold-mouse-face)
  (overlay-put overlay 'help-echo "Click to unfold the text")
  (vimish-fold--setup-fringe overlay))

(defun vimish-fold--vimish-overlay-p (overlay)
  "Detect if given OVERLAY is created by this package."
  (memq (overlay-get overlay 'type)
        '(vimish-fold--folded
          vimish-fold--unfolded)))

;;;###autoload
(defun vimish-fold (beg end)
  "Fold active region staring at BEG, ending at END."
  (interactive "r")
  (deactivate-mark)
  (cl-destructuring-bind (beg . end) (vimish-fold--correct-region beg end)
    (when (< (count-lines beg end) 2)
      (error "Nothing to fold"))
    (dolist (overlay (overlays-in beg end))
      (when (vimish-fold--vimish-overlay-p overlay)
        (goto-char (overlay-start overlay))
        (error "Fold already exists here")))
    (vimish-fold--read-only t (max 1 (1- beg)) end)
    (let ((overlay (make-overlay beg end nil t nil)))
      (overlay-put overlay 'type 'vimish-fold--folded)
      (overlay-put overlay 'evaporate t)
      (overlay-put overlay 'keymap vimish-fold-folded-keymap)
      (vimish-fold--apply-cosmetic overlay (vimish-fold--get-header beg end)))
    (goto-char beg)))

(defun vimish-fold--unfold (overlay)
  "Unfold fold found by its OVERLAY type `vimish-fold--folded'."
  (when (eq (overlay-get overlay 'type) 'vimish-fold--folded)
    (let ((beg (overlay-start overlay))
          (end (overlay-end   overlay)))
      (vimish-fold--read-only nil (max 1 (1- beg)) end)
      (delete-overlay overlay)
      (let ((unfolded (make-overlay beg end nil t nil)))
        (overlay-put unfolded 'type 'vimish-fold--unfolded)
        (overlay-put unfolded 'evaporate t)
        (overlay-put unfolded 'keymap vimish-fold-unfolded-keymap)
        (vimish-fold--setup-fringe unfolded t)))))

;;;###autoload
(defun vimish-fold-unfold ()
  "Delete all `vimish-fold--folded' overlays at point."
  (interactive)
  (mapc #'vimish-fold--unfold (overlays-at (point))))

(define-key vimish-fold-folded-keymap (kbd "<mouse-1>") #'vimish-fold-unfold)
(define-key vimish-fold-folded-keymap (kbd "C-`")       #'vimish-fold-unfold)

(defun vimish-fold--refold (overlay)
  "Refold fold found by its OVERLAY type `vimish-fold--unfolded'."
  (when (eq (overlay-get overlay 'type) 'vimish-fold--unfolded)
    (let* ((beg (overlay-start overlay))
           (end (overlay-end   overlay)))
      (delete-overlay overlay)
      (vimish-fold beg end))))

;;;###autoload
(defun vimish-fold-refold ()
  "Refold unfolded fold at point."
  (interactive)
  (mapc #'vimish-fold--refold (overlays-at (point))))

(define-key vimish-fold-unfolded-keymap (kbd "C-`") #'vimish-fold-refold)

(defun vimish-fold--delete (overlay)
  "Internal function used to delete folds represented by OVERLAY.

If OVERLAY does not represent a fold, it's ignored."
  (when (vimish-fold--vimish-overlay-p overlay)
    (when (eq (overlay-get overlay 'type)
              'vimish-fold--folded)
      (vimish-fold--read-only
       nil
       (max 1 (1- (overlay-start overlay)))
       (overlay-end overlay)))
    (delete-overlay overlay)))

;;;###autoload
(defun vimish-fold-delete ()
  "Delete fold at point."
  (interactive)
  (mapc #'vimish-fold--delete (overlays-at (point))))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Extra features

(defun vimish-fold--folds-in (beg end)
  "Return all folds exiting between BEG and END in current buffer."
  (cl-remove-if-not
   #'vimish-fold--vimish-overlay-p
   (overlays-in beg end)))

;;;###autoload
(defun vimish-fold-unfold-all ()
  "Unfold all folds in current buffer."
  (interactive)
  (mapc #'vimish-fold--unfold
        (vimish-fold--folds-in
         (point-min)
         (point-max))))

;;;###autoload
(defun vimish-fold-refold-all ()
  "Refold all closed folds in current buffer."
  (interactive)
  (save-excursion ; after folding cursor jumps to beginning of fold
    (mapc #'vimish-fold--refold
          (vimish-fold--folds-in
           (point-min)
           (point-max)))))

;;;###autoload
(defun vimish-fold-delete-all ()
  "Delete all folds in current buffer."
  (interactive)
  (mapc #'vimish-fold--delete
        (vimish-fold--folds-in
         (point-min)
         (point-max))))

(defun vimish-fold--toggle (overlay)
  "Unfold or refold fold represented by OVERLAY depending on its type."
  (when (vimish-fold--vimish-overlay-p overlay)
    (save-excursion
      (goto-char (overlay-start overlay))
      (if (eq (overlay-get overlay 'type)
              'vimish-fold--folded)
          (vimish-fold-unfold)
        (vimish-fold-refold)))))

;;;###autoload
(defun vimish-fold-toggle ()
  "Toggle fold at point."
  (interactive)
  (mapc #'vimish-fold--toggle (overlays-at (point))))

;;;###autoload
(defun vimish-fold-toggle-all ()
  "Toggle all folds in current buffer."
  (interactive)
  (mapc #'vimish-fold--toggle
        (vimish-fold--folds-in
         (point-min)
         (point-max))))

(declare-function avy-goto-line "ext:avy")

;;;###autoload
(defun vimish-fold-avy ()
  "Fold region of text between point and line selected with avy.

This feature needs `avy' package."
  (interactive)
  (if (require 'avy nil t)
      (let ((beg (point))
            (end (let (avy-all-windows)
                   (ignore avy-all-windows)
                   (call-interactively #'avy-goto-line)
                   (point))))
        (vimish-fold beg end))
    (message "Package ‘avy’ is unavailable")))

;;;###autoload
(defun vimish-fold-next-fold ()
  "Jump to next folded region in current buffer."
  (interactive)
  (let ((folds-after-point
         (cl-nset-difference
          (vimish-fold--folds-in (point) (point-max))
          (overlays-at (point)))))
    (if folds-after-point
        (goto-char
         (cl-reduce
          #'min
          (mapcar
           #'overlay-start
           folds-after-point)))
      (message "No more folds after point"))))

;;;###autoload
(defun vimish-fold-previous-fold ()
  "Jump to previous folded region in current buffer."
  (interactive)
  (let ((folds-before-point
         (cl-nset-difference
          (vimish-fold--folds-in (point-min) (point))
          (overlays-at (point)))))
    (if folds-before-point
        (goto-char
         (cl-reduce
          #'max
          (mapcar
           #'overlay-start
           folds-before-point)))
      (message "No more folds before point"))))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Persistence

(defcustom vimish-fold-dir
  (file-name-as-directory (f-expand "vimish-fold" user-emacs-directory))
  "The directory where Vimish Fold keeps its files.

The string should end with a slash.  If it doesn't exist, it will
be created automatically."
  :tag   "Directory for Folding Info"
  :type  'directory)

(defun vimish-fold--make-file-name (file)
  "Return path to file where information about folding in FILE is written."
  (f-expand
   (replace-regexp-in-string
    (regexp-opt (list (f-path-separator) ":")) "!" file)
   vimish-fold-dir))

(defun vimish-fold--restore-from (list)
  "Restore folds in current buffer form LIST.

Elements of LIST should be of the following form:

  (BEG END &optional UNFOLDED)"
  (save-excursion
    (dolist (item list)
      (cl-destructuring-bind (beg end . rest) item
        (funcall #'vimish-fold beg end)
        (when (car rest)
          (goto-char beg)
          (vimish-fold-unfold))))))

(defun vimish-fold--save-folds (&optional buffer-or-name)
  "Save folds in BUFFER-OR-NAME, which should have associated file.

BUFFER-OR-NAME defaults to current buffer."
  (with-current-buffer (or buffer-or-name (current-buffer))
    (let ((filename (buffer-file-name))
          regions)
      (when filename
        (dolist (overlay (overlays-in (point-min) (point-max)))
          (when (vimish-fold--vimish-overlay-p overlay)
            (push (list (overlay-start overlay)
                        (overlay-end   overlay)
                        (eq (overlay-get overlay 'type)
                            'vimish-fold--unfolded))
                  regions)))
        (let ((fold-file (vimish-fold--make-file-name filename)))
          (if regions
              (with-temp-buffer
                (pp regions (current-buffer))
                (let ((version-control 'never))
                  (condition-case nil
                      (progn
                        (apply #'f-mkdir (f-split vimish-fold-dir))
                        (write-region (point-min) (point-max) fold-file)
                        (message nil))
                    (file-error
                     (message "Vimish Fold: can't write %s" fold-file)))
                  (kill-buffer (current-buffer))))
            (when (f-exists? fold-file)
              (f-delete fold-file))))))))

(defun vimish-fold--restore-folds (&optional buffer-or-name)
  "Restore folds in BUFFER-OR-NAME, if they have been saved.

BUFFER-OR-NAME defaults to current buffer.

Return T is some folds have been restored and NIL otherwise."
  (with-current-buffer (or buffer-or-name (current-buffer))
    (let ((filename (buffer-file-name)))
      (when (and filename
                 (null (vimish-fold--folds-in
                        (point-min)
                        (point-max))))
        (let ((fold-file (vimish-fold--make-file-name filename)))
          (when (and fold-file (f-readable? fold-file))
            (vimish-fold--restore-from
             (with-temp-buffer
               (insert-file-contents fold-file)
               (read (buffer-string))))))))))

(defun vimish-fold--kill-emacs-hook ()
  "Traverse all buffers and try to save their folds."
  (mapc #'vimish-fold--save-folds (buffer-list)))

;;;###autoload
(define-minor-mode vimish-fold-mode
  "Toggle `vimish-fold-mode' minor mode.

With a prefix argument ARG, enable `vimish-fold-mode' mode if ARG
is positive, and disable it otherwise.  If called from Lisp,
enable the mode if ARG is omitted or NIL, and toggle it if ARG is
`toggle'.

This minor mode sets hooks so when you `find-file' it calls
`vimish-fold--restore-folds' and when you kill a file it calls
`vimish-fold--save-folds'.

For globalized version of this mode see `vimish-gold-global-mode'."
  :global nil
  (let ((fnc (if vimish-fold-mode #'add-hook #'remove-hook)))
    (funcall fnc 'find-file-hook   #'vimish-fold--restore-folds)
    (funcall fnc 'kill-buffer-hook #'vimish-fold--save-folds)
    (funcall fnc 'kill-emacs-hook  #'vimish-fold--kill-emacs-hook)
    (when vimish-fold-persist-on-saving
      (funcall fnc 'before-save-hook #'vimish-fold--save-folds))))

;;;###autoload
(define-globalized-minor-mode vimish-fold-global-mode
  vimish-fold-mode vimish-fold-mode)

(provide 'vimish-fold)

;;; vimish-fold.el ends here