;;; org-fold.el --- Folding of Org entries -*- lexical-binding: t; -*-
;;
;; Copyright (C) 2020-2020 Free Software Foundation, Inc.
;;
;; Author: Ihor Radchenko <yantar92 at gmail dot com>
;; Keywords: folding, invisible text
;; URL: https://orgmode.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:

;; This file contains code handling temporary invisibility (folding
;; and unfolding) of text in org buffers.

;; The folding is implemented using generic org-fold-core library.  This file
;; contains org-specific implementation of the folding.  Also, various
;; useful functions from org-fold-core are aliased under shorted `org-fold'
;; prefix.

;; The following features are implemented:
;; - Folding/unfolding various Org mode elements and regions of Org buffers:
;;   + Region before first heading;
;;   + Org headings, their text, children (subtree), siblings, parents, etc;
;;   + Org blocks and drawers
;; - Revealing Org structure around invisible point location
;; - Revealing folded Org elements broken by user edits

;;; Code:

(require 'org-macs)
(org-assert-version)

(require 'org-macs)
(require 'org-fold-core)

(defvar org-inlinetask-min-level)
(defvar org-link--link-folding-spec)
(defvar org-link--description-folding-spec)
(defvar org-odd-levels-only)
(defvar org-drawer-regexp)
(defvar org-property-end-re)
(defvar org-link-descriptive)
(defvar org-outline-regexp-bol)
(defvar org-archive-tag)
(defvar org-custom-properties-overlays)
(defvar org-element-headline-re)

(declare-function isearch-filter-visible "isearch" (beg end))
(declare-function org-element-type "org-element" (element))
(declare-function org-element-at-point "org-element" (&optional pom cached-only))
(declare-function org-element-property "org-element" (property element))
(declare-function org-element--current-element "org-element" (limit &optional granularity mode structure))
(declare-function org-element--cache-active-p "org-element" ())
(declare-function org-toggle-custom-properties-visibility "org" ())
(declare-function org-item-re "org-list" ())
(declare-function org-up-heading-safe "org" ())
(declare-function org-get-tags "org" (&optional pos local fontify))
(declare-function org-get-valid-level "org" (level &optional change))
(declare-function org-before-first-heading-p "org" ())
(declare-function org-goto-sibling "org" (&optional previous))
(declare-function org-block-map "org" (function &optional start end))
(declare-function org-map-region "org" (fun beg end))
(declare-function org-end-of-subtree "org" (&optional invisible-ok to-heading))
(declare-function org-back-to-heading-or-point-min "org" (&optional invisible-ok))
(declare-function org-back-to-heading "org" (&optional invisible-ok))
(declare-function org-at-heading-p "org" (&optional invisible-not-ok))
(declare-function org-cycle-hide-drawers "org-cycle" (state))

(declare-function outline-show-branches "outline" ())
(declare-function outline-hide-sublevels "outline" (levels))
(declare-function outline-get-next-sibling "outline" ())
(declare-function outline-invisible-p "outline" (&optional pos))
(declare-function outline-next-heading "outline" ())

;;; Customization

(defgroup org-fold-reveal-location nil
  "Options about how to make context of a location visible."
  :tag "Org Reveal Location"
  :group 'org-structure)

(defcustom org-fold-show-context-detail '((agenda . local)
				  (bookmark-jump . lineage)
				  (isearch . lineage)
				  (default . ancestors))
  "Alist between context and visibility span when revealing a location.

\\<org-mode-map>Some actions may move point into invisible
locations.  As a consequence, Org always exposes a neighborhood
around point.  How much is shown depends on the initial action,
or context.  Valid contexts are

  agenda         when exposing an entry from the agenda
  org-goto       when using the command `org-goto' (`\\[org-goto]')
  occur-tree     when using the command `org-occur' (`\\[org-sparse-tree] /')
  tags-tree      when constructing a sparse tree based on tags matches
  link-search    when exposing search matches associated with a link
  mark-goto      when exposing the jump goal of a mark
  bookmark-jump  when exposing a bookmark location
  isearch        when exiting from an incremental search
  default        default for all contexts not set explicitly

Allowed visibility spans are

  minimal        show current headline; if point is not on headline,
                 also show entry

  local          show current headline, entry and next headline

  ancestors      show current headline and its direct ancestors; if
                 point is not on headline, also show entry

  ancestors-full show current subtree and its direct ancestors

  lineage        show current headline, its direct ancestors and all
                 their children; if point is not on headline, also show
                 entry and first child

  tree           show current headline, its direct ancestors and all
                 their children; if point is not on headline, also show
                 entry and all children

  canonical      show current headline, its direct ancestors along with
                 their entries and children; if point is not located on
                 the headline, also show current entry and all children

As special cases, a nil or t value means show all contexts in
`minimal' or `canonical' view, respectively.

Some views can make displayed information very compact, but also
make it harder to edit the location of the match.  In such
a case, use the command `org-fold-reveal' (`\\[org-fold-reveal]') to show
more context."
  :group 'org-fold-reveal-location
  :version "26.1"
  :package-version '(Org . "9.0")
  :type '(choice
	  (const :tag "Canonical" t)
	  (const :tag "Minimal" nil)
	  (repeat :greedy t :tag "Individual contexts"
		  (cons
		   (choice :tag "Context"
			   (const agenda)
			   (const org-goto)
			   (const occur-tree)
			   (const tags-tree)
			   (const link-search)
			   (const mark-goto)
			   (const bookmark-jump)
			   (const isearch)
			   (const default))
		   (choice :tag "Detail level"
			   (const minimal)
			   (const local)
			   (const ancestors)
                           (const ancestors-full)
			   (const lineage)
			   (const tree)
			   (const canonical))))))

(defvar org-fold-reveal-start-hook nil
  "Hook run before revealing a location.")

(defcustom org-fold-catch-invisible-edits 'smart
  "Check if in invisible region before inserting or deleting a character.
Valid values are:

nil              Do not check, so just do invisible edits.
error            Throw an error and do nothing.
show             Make point visible, and do the requested edit.
show-and-error   Make point visible, then throw an error and abort the edit.
smart            Make point visible, and do insertion/deletion if it is
                 adjacent to visible text and the change feels predictable.
                 Never delete a previously invisible character or add in the
                 middle or right after an invisible region.  Basically, this
                 allows insertion and backward-delete right before ellipses.
                 FIXME: maybe in this case we should not even show?"
  :group 'org-edit-structure
  :version "24.1"
  :type '(choice
	  (const :tag "Do not check" nil)
	  (const :tag "Throw error when trying to edit" error)
	  (const :tag "Unhide, but do not do the edit" show-and-error)
	  (const :tag "Show invisible part and do the edit" show)
	  (const :tag "Be smart and do the right thing" smart)))

;;; Core functionality

;;; API

;;;; Modifying folding specs

(defalias 'org-fold-folding-spec-p #'org-fold-core-folding-spec-p)
(defalias 'org-fold-add-folding-spec #'org-fold-core-add-folding-spec)
(defalias 'org-fold-remove-folding-spec #'org-fold-core-remove-folding-spec)

(defun org-fold-initialize (ellipsis)
  "Setup folding in current Org buffer."
  (setq-local org-fold-core-isearch-open-function #'org-fold--isearch-reveal)
  (setq-local org-fold-core-extend-changed-region-functions (list #'org-fold--extend-changed-region))
  ;; FIXME: Converting org-link + org-description to overlays when
  ;; search matches hidden "[[" part of the link, reverses priority of
  ;; link and description and hides the whole link.  Working around
  ;; this until there will be no need to convert text properties to
  ;; overlays for isearch.
  (setq-local org-fold-core--isearch-special-specs '(org-link))
  (org-fold-core-initialize
   `((,(if (eq org-fold-core-style 'text-properties) 'org-fold-outline 'outline)
      (:ellipsis . ,ellipsis)
      (:fragile . ,#'org-fold--reveal-outline-maybe)
      (:isearch-open . t)
      ;; This is needed to make sure that inserting a
      ;; new planning line in folded heading is not
      ;; revealed.  Also, the below combination of :front-sticky and
      ;; :rear-sticky conforms to the overlay properties in outline.el
      ;; and the older Org versions as in `outline-flag-region'.
      (:front-sticky . t)
      (:rear-sticky . nil)
      (:alias . (headline heading outline inlinetask plain-list)))
     (,(if (eq org-fold-core-style 'text-properties) 'org-fold-block 'org-hide-block)
      (:ellipsis . ,ellipsis)
      (:fragile . ,#'org-fold--reveal-drawer-or-block-maybe)
      (:isearch-open . t)
      (:front-sticky . t)
      (:alias . ( block center-block comment-block
                  dynamic-block example-block export-block
                  quote-block special-block src-block
                  verse-block)))
     (,(if (eq org-fold-core-style 'text-properties) 'org-fold-drawer 'org-hide-drawer)
      (:ellipsis . ,ellipsis)
      (:fragile . ,#'org-fold--reveal-drawer-or-block-maybe)
      (:isearch-open . t)
      (:front-sticky . t)
      (:alias . (drawer property-drawer)))
     ,org-link--description-folding-spec
     ,org-link--link-folding-spec)))

;;;; Searching and examining folded text

(defalias 'org-fold-folded-p #'org-fold-core-folded-p)
(defalias 'org-fold-get-folding-spec #'org-fold-core-get-folding-spec)
(defalias 'org-fold-get-folding-specs-in-region #'org-fold-core-get-folding-specs-in-region)
(defalias 'org-fold-get-region-at-point #'org-fold-core-get-region-at-point)
(defalias 'org-fold-get-regions #'org-fold-core-get-regions)
(defalias 'org-fold-next-visibility-change #'org-fold-core-next-visibility-change)
(defalias 'org-fold-previous-visibility-change #'org-fold-core-previous-visibility-change)
(defalias 'org-fold-next-folding-state-change #'org-fold-core-next-folding-state-change)
(defalias 'org-fold-previous-folding-state-change #'org-fold-core-previous-folding-state-change)
(defalias 'org-fold-search-forward #'org-fold-core-search-forward)

;;;;; Macros

(defalias 'org-fold-save-outline-visibility #'org-fold-core-save-visibility)

;;;; Changing visibility (regions, blocks, drawers, headlines)

;;;;; Region visibility

(defalias 'org-fold-region #'org-fold-core-region)
(defalias 'org-fold-regions #'org-fold-core-regions)

(defun org-fold-show-all (&optional types)
  "Show all contents in the visible part of the buffer.
By default, the function expands headings, blocks and drawers.
When optional argument TYPES is a list of symbols among `blocks',
`drawers' and `headings', to only expand one specific type."
  (interactive)
  (dolist (type (or types '(blocks drawers headings)))
    (org-fold-region (point-min) (point-max) nil
	     (pcase type
	       (`blocks 'block)
	       (`drawers 'drawer)
	       (`headings 'headline)
	       (_ (error "Invalid type: %S" type))))))

(defun org-fold-flag-above-first-heading (&optional arg)
  "Hide from bob up to the first heading.
Move point to the beginning of first heading or end of buffer."
  (goto-char (point-min))
  (unless (org-at-heading-p)
    (outline-next-heading))
  (unless (bobp)
    (org-fold-region 1 (1- (point)) (not arg) 'outline)))

;;;;; Heading visibility

(defun org-fold-heading (flag &optional entry)
  "Fold/unfold the current heading.  FLAG non-nil means make invisible.
When ENTRY is non-nil, show the entire entry."
  (save-excursion
    (org-back-to-heading t)
    ;; Check if we should show the entire entry
    (if (not entry)
	(org-fold-region
	 (line-end-position 0) (line-end-position) flag 'outline)
      (org-fold-show-entry)
      (save-excursion
	;; FIXME: potentially catches inlinetasks
	(and (outline-next-heading)
	     (org-fold-heading nil))))))

(defun org-fold-hide-entry ()
  "Hide the body directly following this heading."
  (interactive)
  (save-excursion
    (org-back-to-heading-or-point-min t)
    (when (org-at-heading-p) (end-of-line))
    (unless (eobp) ; Current headline is empty and ends at the end of buffer.
      (org-fold-region
       (line-end-position)
       (save-excursion
         (if (re-search-forward
              (concat "[\r\n]" (org-get-limited-outline-regexp)) nil t)
             (line-end-position 0)
           (point-max)))
       t
       'outline))))

(defun org-fold-subtree (flag)
  (save-excursion
    (org-back-to-heading t)
    (org-fold-region
     (line-end-position)
     (progn (org-end-of-subtree t) (point))
     flag
     'outline)))

;; Replaces `outline-hide-subtree'.
(defun org-fold-hide-subtree ()
  "Hide everything after this heading at deeper levels."
  (interactive)
  (org-fold-subtree t))

;; Replaces `outline-hide-sublevels'
(defun org-fold-hide-sublevels (levels)
  "Hide everything but the top LEVELS levels of headers, in whole buffer.
This also unhides the top heading-less body, if any.

Interactively, the prefix argument supplies the value of LEVELS.
When invoked without a prefix argument, LEVELS defaults to the level
of the current heading, or to 1 if the current line is not a heading."
  (interactive (list
		(cond
		 (current-prefix-arg (prefix-numeric-value current-prefix-arg))
		 ((save-excursion (beginning-of-line)
				  (looking-at outline-regexp))
		  (funcall outline-level))
		 (t 1))))
  (if (< levels 1)
      (error "Must keep at least one level of headers"))
  (save-excursion
    (let* ((beg (progn
                  (goto-char (point-min))
                  ;; Skip the prelude, if any.
                  (unless (org-at-heading-p) (outline-next-heading))
                  (point)))
           (end (progn
                  (goto-char (point-max))
                  ;; Keep empty last line, if available.
                  (max (point-min) (if (bolp) (1- (point)) (point))))))
      (if (< end beg)
	  (setq beg (prog1 end (setq end beg))))
      ;; First hide everything.
      (org-fold-region beg end t 'headline)
      ;; Then unhide the top level headers.
      (org-map-region
       (lambda ()
	 (when (<= (funcall outline-level) levels)
           (org-fold-heading nil)))
       beg end)
      ;; Finally unhide any trailing newline.
      (goto-char (point-max))
      (if (and (bolp) (not (bobp)) (outline-invisible-p (1- (point))))
          (org-fold-region (max (point-min) (1- (point))) (point) nil)))))

(defun org-fold-show-entry (&optional hide-drawers)
  "Show the body directly following its heading.
Show the heading too, if it is currently invisible."
  (interactive)
  (save-excursion
    (org-back-to-heading-or-point-min t)
    (org-fold-region
     (line-end-position 0)
     (save-excursion
       (if (re-search-forward
            (concat "[\r\n]\\(" (org-get-limited-outline-regexp) "\\)") nil t)
           (match-beginning 1)
         (point-max)))
     nil
     'outline)
    (when hide-drawers (org-cycle-hide-drawers 'children))))

(defalias 'org-fold-show-hidden-entry #'org-fold-show-entry
  "Show an entry where even the heading is hidden.")

(defun org-fold-show-siblings ()
  "Show all siblings of the current headline."
  (save-excursion
    (while (org-goto-sibling) (org-fold-heading nil)))
  (save-excursion
    (while (org-goto-sibling 'previous)
      (org-fold-heading nil))))

(defun org-fold-show-children (&optional level)
  "Show all direct subheadings of this heading.
Prefix arg LEVEL is how many levels below the current level
should be shown.  Default is enough to cause the following
heading to appear."
  (interactive "p")
  (unless (org-before-first-heading-p)
    (save-excursion
      (org-with-limited-levels (org-back-to-heading t))
      (let* ((current-level (funcall outline-level))
             (max-level (org-get-valid-level
                         current-level
                         (if level (prefix-numeric-value level) 1)))
             (end (save-excursion (org-end-of-subtree t t)))
             (regexp-fmt "^\\*\\{%d,%s\\}\\(?: \\|$\\)")
             (past-first-child nil)
             ;; Make sure to skip inlinetasks.
             (re (format regexp-fmt
                         current-level
                         (cond
                          ((not (featurep 'org-inlinetask)) "")
                          (org-odd-levels-only (- (* 2 org-inlinetask-min-level)
                                                  3))
                          (t (1- org-inlinetask-min-level))))))
        ;; Display parent heading.
        (org-fold-heading nil)
        (forward-line)
        ;; Display children.  First child may be deeper than expected
        ;; MAX-LEVEL.  Since we want to display it anyway, adjust
        ;; MAX-LEVEL accordingly.
        (while (re-search-forward re end t)
          (unless past-first-child
            (setq re (format regexp-fmt
                             current-level
                             (max (funcall outline-level) max-level)))
            (setq past-first-child t))
          (org-fold-heading nil))))))

(defun org-fold-show-subtree ()
  "Show everything after this heading at deeper levels."
  (interactive)
  (org-fold-region
   (point) (save-excursion (org-end-of-subtree t t)) nil 'outline))

(defun org-fold-show-branches ()
  "Show all subheadings of this heading, but not their bodies."
  (interactive)
  (org-fold-show-children 1000))

(defun org-fold-show-branches-buffer ()
  "Show all branches in the buffer."
  (org-fold-flag-above-first-heading)
  (org-fold-hide-sublevels 1)
  (unless (eobp)
    (org-fold-show-branches)
    (while (outline-get-next-sibling)
      (org-fold-show-branches)))
  (goto-char (point-min)))

;;;;; Blocks and drawers visibility

(defun org-fold--hide-wrapper-toggle (element category force no-error)
  "Toggle visibility for ELEMENT.

ELEMENT is a block or drawer type parsed element.  CATEGORY is
either `block' or `drawer'.  When FORCE is `off', show the block
or drawer.  If it is non-nil, hide it unconditionally.  Throw an
error when not at a block or drawer, unless NO-ERROR is non-nil.

Return a non-nil value when toggling is successful."
  (let ((type (org-element-type element)))
    (cond
     ((memq type
            (pcase category
              (`drawer '(drawer property-drawer))
              (`block '(center-block
                        comment-block dynamic-block example-block export-block
                        quote-block special-block src-block verse-block))
              (_ (error "Unknown category: %S" category))))
      (let* ((post (org-element-property :post-affiliated element))
             (start (save-excursion
                      (goto-char post)
                      (line-end-position)))
             (end (save-excursion
                    (goto-char (org-element-property :end element))
                    (skip-chars-backward " \t\n")
                    (line-end-position))))
        ;; Do nothing when not before or at the block opening line or
        ;; at the block closing line.
        (unless (let ((eol (line-end-position)))
                  (and (> eol start) (/= eol end)))
          (org-fold-region start end
                   (cond ((eq force 'off) nil)
                         (force t)
                         ((org-fold-folded-p start category) nil)
                         (t t))
                   category)
          ;; When the block is hidden away, make sure point is left in
          ;; a visible part of the buffer.
          (when (invisible-p (max (1- (point)) (point-min)))
            (goto-char post))
          ;; Signal success.
          t)))
     (no-error nil)
     (t
      (user-error (format "%s@%s: %s"
                          (buffer-file-name (buffer-base-buffer))
                          (point)
                          (if (eq category 'drawer)
	                      "Not at a drawer"
	                    "Not at a block")))))))

(defun org-fold-hide-block-toggle (&optional force no-error element)
  "Toggle the visibility of the current block.

When optional argument FORCE is `off', make block visible.  If it
is non-nil, hide it unconditionally.  Throw an error when not at
a block, unless NO-ERROR is non-nil.  When optional argument
ELEMENT is provided, consider it instead of the current block.

Return a non-nil value when toggling is successful."
  (interactive)
  (org-fold--hide-wrapper-toggle
   (or element (org-element-at-point)) 'block force no-error))

(defun org-fold-hide-drawer-toggle (&optional force no-error element)
  "Toggle the visibility of the current drawer.

When optional argument FORCE is `off', make drawer visible.  If
it is non-nil, hide it unconditionally.  Throw an error when not
at a drawer, unless NO-ERROR is non-nil.  When optional argument
ELEMENT is provided, consider it instead of the current drawer.

Return a non-nil value when toggling is successful."
  (interactive)
  (org-fold--hide-wrapper-toggle
   (or element (org-element-at-point)) 'drawer force no-error))

(defun org-fold-hide-block-all ()
  "Fold all blocks in the current buffer."
  (interactive)
  (org-block-map (apply-partially #'org-fold-hide-block-toggle 'hide)))

(defun org-fold-hide-drawer-all ()
  "Fold all drawers in the current buffer."
  (let ((begin (point-min))
        (end (point-max)))
    (org-fold--hide-drawers begin end)))

(defun org-fold--hide-drawers (begin end)
  "Hide all drawers between BEGIN and END."
  (save-excursion
    (goto-char begin)
    (while (and (< (point) end)
                (re-search-forward org-drawer-regexp end t))
      ;; Skip folded drawers
      (if (org-fold-folded-p nil 'drawer)
          (goto-char (org-fold-next-folding-state-change 'drawer nil end))
        (let* ((drawer (org-element-at-point))
               (type (org-element-type drawer)))
          (when (memq type '(drawer property-drawer))
            (org-fold-hide-drawer-toggle t nil drawer)
            ;; Make sure to skip drawer entirely or we might flag it
            ;; another time when matching its ending line with
            ;; `org-drawer-regexp'.
            (goto-char (org-element-property :end drawer))))))))

(defun org-fold-hide-archived-subtrees (beg end)
  "Re-hide all archived subtrees after a visibility state change."
  (org-with-wide-buffer
   (let ((case-fold-search nil)
	 (re (concat org-outline-regexp-bol ".*:" org-archive-tag ":")))
     (goto-char beg)
     ;; Include headline point is currently on.
     (beginning-of-line)
     (while (and (< (point) end) (re-search-forward re end t))
       (when (member org-archive-tag (org-get-tags nil t))
	 (org-fold-subtree t)
	 (org-end-of-subtree t))))))

;;;;; Reveal point location

(defun org-fold-show-context (&optional key)
  "Make sure point and context are visible.
Optional argument KEY, when non-nil, is a symbol.  See
`org-fold-show-context-detail' for allowed values and how much is to
be shown."
  (org-fold-show-set-visibility
   (cond ((symbolp org-fold-show-context-detail) org-fold-show-context-detail)
	 ((cdr (assq key org-fold-show-context-detail)))
	 (t (cdr (assq 'default org-fold-show-context-detail))))))


(defvar org-hide-emphasis-markers); Defined in org.el
(defvar org-pretty-entities); Defined in org.el
(defun org-fold-show-set-visibility (detail)
  "Set visibility around point according to DETAIL.
DETAIL is either nil, `minimal', `local', `ancestors',
`ancestors-full', `lineage', `tree', `canonical' or t.  See
`org-show-context-detail' for more information."
  ;; Show current heading and possibly its entry, following headline
  ;; or all children.
  (if (and (org-at-heading-p) (not (eq detail 'local)))
      (org-fold-heading nil)
    (org-fold-show-entry)
    ;; If point is hidden make sure to expose it.
    (when (org-invisible-p)
      ;; FIXME: No clue why, but otherwise the following might not work.
      (redisplay)
      (let ((region (org-fold-get-region-at-point)))
        ;; Reveal emphasis markers.
        (when (eq detail 'local)
          (let (org-hide-emphasis-markers
                org-link-descriptive
                org-pretty-entities
                (org-hide-macro-markers nil)
                (region (or (org-find-text-property-region (point) 'org-emphasis)
                            (org-find-text-property-region (point) 'org-macro)
                            (org-find-text-property-region (point) 'invisible)
                            region)))
            ;; Silence byte-compiler.
            (ignore org-hide-macro-markers)
            (when region
              (org-with-point-at (car region)
                (beginning-of-line)
                (let (font-lock-extend-region-functions)
                  (font-lock-fontify-region (max (point-min) (1- (car region))) (cdr region))))))
          ;; Unfold links.
          (when region
            (dolist (spec '(org-link org-link-description))
              (org-fold-region (car region) (cdr region) nil spec))))
        (when region
          (dolist (spec (org-fold-core-folding-spec-list))
            ;; Links are taken care by above.
            (unless (memq spec '(org-link org-link-description))
              (org-fold-region (car region) (cdr region) nil spec))))))
    (unless (org-before-first-heading-p)
      (org-with-limited-levels
       (cl-case detail
	 ((tree canonical t) (org-fold-show-children))
	 ((nil minimal ancestors ancestors-full))
	 (t (save-excursion
	      (outline-next-heading)
	      (org-fold-heading nil)))))))
  ;; Show whole subtree.
  (when (eq detail 'ancestors-full) (org-fold-show-subtree))
  ;; Show all siblings.
  (when (eq detail 'lineage) (org-fold-show-siblings))
  ;; Show ancestors, possibly with their children.
  (when (memq detail '(ancestors ancestors-full lineage tree canonical t))
    (save-excursion
      (while (org-up-heading-safe)
	(org-fold-heading nil)
	(when (memq detail '(canonical t)) (org-fold-show-entry))
	(when (memq detail '(tree canonical t)) (org-fold-show-children))))))

(defun org-fold-reveal (&optional siblings)
  "Show current entry, hierarchy above it, and the following headline.

This can be used to show a consistent set of context around
locations exposed with `org-fold-show-context'.

With optional argument SIBLINGS, on each level of the hierarchy all
siblings are shown.  This repairs the tree structure to what it would
look like when opened with hierarchical calls to `org-cycle'.

With a \\[universal-argument] \\[universal-argument] prefix, \
go to the parent and show the entire tree."
  (interactive "P")
  (run-hooks 'org-fold-reveal-start-hook)
  (cond ((equal siblings '(4)) (org-fold-show-set-visibility 'canonical))
	((equal siblings '(16))
	 (save-excursion
	   (when (org-up-heading-safe)
	     (org-fold-show-subtree)
	     (run-hook-with-args 'org-cycle-hook 'subtree))))
	(t (org-fold-show-set-visibility 'lineage))))

;;; Make isearch search in some text hidden via text properties.

(defun org-fold--isearch-reveal (&rest _)
  "Reveal text at POS found by isearch."
  (org-fold-show-context 'isearch))

;;; Handling changes in folded elements

(defun org-fold--extend-changed-region (from to)
  "Consider folded regions in the next/previous line when fixing
region visibility.
This function is intended to be used as a member of
`org-fold-core-extend-changed-region-functions'."
  ;; If the edit is done in the first line of a folded drawer/block,
  ;; the folded text is only starting from the next line and needs to
  ;; be checked.
  (setq to (save-excursion (goto-char to) (line-beginning-position 2)))
  ;; If the ":END:" line of the drawer is deleted, the folded text is
  ;; only ending at the previous line and needs to be checked.
  (setq from (save-excursion (goto-char from) (line-beginning-position 0)))
  (cons from to))

(defun org-fold--reveal-headline-at-point ()
  "Reveal header line and empty contents inside.
Reveal the header line and, if present, also reveal its contents, when
the contents consists of blank lines.

Assume that point is located at the header line."
  (org-with-wide-buffer
   (beginning-of-line)
   (org-fold-region
    (max (point-min) (1- (point)))
    (let ((endl (line-end-position)))
      (save-excursion
        (goto-char endl)
        (skip-chars-forward "\n\t\r ")
        ;; Unfold blank lines after newly inserted headline.
        (if (equal (point)
                   (save-excursion
                     (goto-char endl)
                     (org-end-of-subtree)
                     (skip-chars-forward "\n\t\r ")))
            (point)
          endl)))
    nil 'headline)))

(defun org-fold--reveal-outline-maybe (region _)
  "Reveal folded outline in REGION when needed.

This function is intended to be used as :fragile property of
`org-fold-outline' spec.  See `org-fold-core--specs' for details."
  (save-match-data
    (org-with-wide-buffer
     (goto-char (car region))
     ;; The line before beginning of the fold should be either a
     ;; headline or a list item.
     (backward-char)
     (beginning-of-line)
     ;; Make sure that headline is not partially hidden.
     (unless (org-fold-folded-p nil 'headline)
       (org-fold--reveal-headline-at-point))
     ;; Never hide level 1 headlines
     (save-excursion
       (goto-char (line-end-position))
       (unless (>= (point) (cdr region))
         (when (re-search-forward (rx bol "* ") (cdr region) t)
           (org-fold--reveal-headline-at-point))))
     ;; Make sure that headline after is not partially hidden.
     (goto-char (cdr region))
     (beginning-of-line)
     (unless (org-fold-folded-p nil 'headline)
       (when (looking-at-p org-element-headline-re)
         (org-fold--reveal-headline-at-point)))
     ;; Check the validity of headline
     (goto-char (car region))
     (backward-char)
     (beginning-of-line)
     (unless (let ((case-fold-search t))
	       (looking-at (rx-to-string
                            `(or (regex ,(org-item-re))
			         (regex ,org-outline-regexp-bol)))))
       t))))

(defun org-fold--reveal-drawer-or-block-maybe (region spec)
  "Reveal folded drawer/block (according to SPEC) in REGION when needed.

This function is intended to be used as :fragile property of
`org-fold-drawer' or `org-fold-block' spec."
  (let ((begin-re (cond
		   ((eq spec (org-fold-core-get-folding-spec-from-alias 'drawer))
		    org-drawer-regexp)
		   ;; Group one below contains the type of the block.
		   ((eq spec (org-fold-core-get-folding-spec-from-alias 'block))
		    (rx bol (zero-or-more (any " " "\t"))
			"#+begin"
			(or ":"
			    (seq "_"
				 (group (one-or-more (not (syntax whitespace))))))))))
        ;; To be determined later. May depend on `begin-re' match (i.e. for blocks).
        end-re)
    (save-match-data ; we should not clobber match-data in after-change-functions
      (let ((fold-begin (car region))
	    (fold-end (cdr region)))
	(let (unfold?)
	  (catch :exit
	    ;; The line before folded text should be beginning of
	    ;; the drawer/block.
	    (save-excursion
	      (goto-char fold-begin)
	      ;; The line before beginning of the fold should be the
	      ;; first line of the drawer/block.
	      (backward-char)
	      (beginning-of-line)
	      (unless (let ((case-fold-search t))
			(looking-at begin-re)) ; the match-data will be used later
		(throw :exit (setq unfold? t))))
            ;; Set `end-re' for the current drawer/block.
            (setq end-re
		  (cond
		   ((eq spec (org-fold-core-get-folding-spec-from-alias 'drawer))
                    org-property-end-re)
		   ((eq spec (org-fold-core-get-folding-spec-from-alias 'block))
		    (let ((block-type (match-string 1))) ; the last match is from `begin-re'
		      (concat (rx bol (zero-or-more (any " " "\t")) "#+end")
			      (if block-type
				  (concat "_"
					  (regexp-quote block-type)
					  (rx (zero-or-more (any " " "\t")) eol))
				(rx (opt ":") (zero-or-more (any " " "\t")) eol)))))))
	    ;; The last line of the folded text should match `end-re'.
	    (save-excursion
	      (goto-char fold-end)
	      (beginning-of-line)
	      (unless (let ((case-fold-search t))
			(looking-at end-re))
		(throw :exit (setq unfold? t))))
	    ;; There should be no `end-re' or
	    ;; `org-outline-regexp-bol' anywhere in the
	    ;; drawer/block body.
	    (save-excursion
	      (goto-char fold-begin)
	      (when (save-excursion
		      (let ((case-fold-search t))
			(re-search-forward (rx-to-string `(or (regex ,end-re)
						              (regex ,org-outline-regexp-bol)))
					   (max (point)
						(1- (save-excursion
						      (goto-char fold-end)
						      (line-beginning-position))))
					   t)))
		(throw :exit (setq unfold? t)))))
          unfold?)))))

;; Catching user edits inside invisible text
(defun org-fold-check-before-invisible-edit (kind)
  "Check if editing KIND is dangerous with invisible text around.
The detailed reaction depends on the user option
`org-fold-catch-invisible-edits'."
  ;; First, try to get out of here as quickly as possible, to reduce overhead
  (when (and org-fold-catch-invisible-edits
	     (or (not (boundp 'visible-mode)) (not visible-mode))
	     (or (org-invisible-p)
		 (org-invisible-p (max (point-min) (1- (point))))))
    ;; OK, we need to take a closer look.  Only consider invisibility
    ;; caused by folding of headlines, drawers, and blocks.  Edits
    ;; inside links will be handled by font-lock.
    (let* ((invisible-at-point (org-fold-folded-p (point) '(headline drawer block)))
	   (invisible-before-point
	    (and (not (bobp))
	         (org-fold-folded-p (1- (point)) '(headline drawer block))))
	   (border-and-ok-direction
	    (or
	     ;; Check if we are acting predictably before invisible
	     ;; text.
	     (and invisible-at-point (not invisible-before-point)
		  (memq kind '(insert delete-backward)))
             ;; Check if we are acting predictably after invisible text
             ;; This works not well, and I have turned it off.  It seems
             ;; better to always show and stop after invisible text.
             ;; (and (not invisible-at-point) invisible-before-point
             ;;  (memq kind '(insert delete)))
             )))
      (when (or invisible-at-point invisible-before-point)
	(when (eq org-fold-catch-invisible-edits 'error)
	  (user-error "Editing in invisible areas is prohibited, make them visible first"))
	(if (and org-custom-properties-overlays
		 (y-or-n-p "Display invisible properties in this buffer? "))
	    (org-toggle-custom-properties-visibility)
	  ;; Make the area visible
          (save-excursion
	    (org-fold-show-set-visibility 'local))
          (when invisible-before-point
            (org-with-point-at (1- (point)) (org-fold-show-set-visibility 'local)))
	  (cond
	   ((eq org-fold-catch-invisible-edits 'show)
	    ;; That's it, we do the edit after showing
	    (message
	     "Unfolding invisible region around point before editing")
	    (sit-for 1))
	   ((and (eq org-fold-catch-invisible-edits 'smart)
		 border-and-ok-direction)
	    (message "Unfolding invisible region around point before editing"))
	   (t
	    ;; Don't do the edit, make the user repeat it in full visibility
	    (user-error "Edit in invisible region aborted, repeat to confirm with text visible"))))))))

(provide 'org-fold)

;;; org-fold.el ends here