;;; ox-my-html.el --- HTML Derived Backend -*- lexical-binding: t; -*-

;; Copyright (C) 2011-2023 Free Software Foundation, Inc.

;; Author: Carsten Dominik <carsten.dominik AT gmail DOT com>
;;         Nicolas Goaziou <n.goaziou AT gmail DOT com>
;; Maintainer: Gerard Vermeulen <gerard.vermeulen AT posteo DOT net>
;; Keywords: org, hypermedia

;; 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 library implements a HTML derived backend for Org export:
;; 1. The Org ox-beamer library shows how to code derived backends.
;; 2. The function org-my-html-link is an edited org-html-link copy.
;; 3. It borrows code from https://emacs.stackexchange.com/a/57433 to
;;    embed SVG images in exported HTML files.

;;; Code:

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

(require 'cl-lib)
(require 'ox-html)
(require 'nxml-mode)


;;; Define Backend

(org-export-define-derived-backend 'my-html 'html
  :menu-entry
  '(?h 1
       ((?M "As my-HTML buffer" org-my-html-export-as-html)
        (?m "As my-HTML file" org-my-html-export-to-html)
        (?O "As my-HTML file and open"
            (lambda (a s v b)
              (if a (org-my-html-export-to-html t s v b)
                (org-open-file (org-my-html-export-to-html nil s v b)))))))
  :options-alist
  '((:my-html-embed-svg "HTML_EMBED_SVG" nil nil t))
  :translate-alist
  '((link . org-my-html-link)))


;;; User Configuration Variables

;;;; Links :: Embed SVG

(defcustom org-my-html-embed-svg t
  "Non-nil means embed SVG images into exported my-HTML pages,
otherwise link to SVG images from exported my-HTML pages."
  :group 'org-export-html
  :version "30.0"
  :type 'boolean)


;;; Transcode Functions

;;;; Link

(defun org--my-html-embed-svg-p (link)
  "Check whether LINK links to an SVG file to embed."
  (and (not (org-element-contents link))
       (let ((case-fold-search t))
         (string-match-p ".svg\\'" (org-element-property :path link)))))

(defun org--my-html-svg-contents (path)
  "Return the SVG contents of the file named PATH."
  ;; https://emacs.stackexchange.com/a/57433
  (with-temp-buffer
    (insert-file-contents path)
    (with-syntax-table nxml-mode-syntax-table
      ;; Barf if contents contains no valid SVG.
      (while (and (search-forward "<svg")
                  (nth 8 (syntax-ppss)))))
    (delete-region (point-min) (match-beginning 0))
    (buffer-string)))

(defun org-my-html-link (link desc info)
  "Transcode a LINK object from Org to MY-HTML.
DESC is the description part of the link, or the empty string.
INFO is a plist holding contextual information.  See
`org-export-data'.   This function can embed or link SVG images
contrary to `org-html-link' which can only link such images."
  (let* ((html-ext (plist-get info :html-extension))
	 (dot (when (> (length html-ext) 0) "."))
	 (link-org-files-as-html-maybe
	  (lambda (raw-path info)
	    ;; Treat links to `file.org' as links to `file.html', if
	    ;; needed.  See `org-html-link-org-files-as-html'.
            (save-match-data
	      (cond
	       ((and (plist-get info :html-link-org-files-as-html)
                     (let ((case-fold-search t))
                       (string-match "\\(.+\\)\\.org\\(?:\\.gpg\\)?$" raw-path)))
	        (concat (match-string 1 raw-path) dot html-ext))
	       (t raw-path)))))
	 (type (org-element-property :type link))
	 (raw-path (org-element-property :path link))
	 ;; Ensure DESC really exists, or set it to nil.
	 (desc (org-string-nw-p desc))
	 (path
	  (cond
	   ((member type '("http" "https" "ftp" "mailto" "news"))
	    (url-encode-url (concat type ":" raw-path)))
	   ((string= "file" type)
	    ;; During publishing, turn absolute file names belonging
	    ;; to base directory into relative file names.  Otherwise,
	    ;; append "file" protocol to absolute file name.
	    (setq raw-path
		  (org-export-file-uri
		   (org-publish-file-relative-name raw-path info)))
	    ;; Possibly append `:html-link-home' to relative file
	    ;; name.
	    (let ((home (and (plist-get info :html-link-home)
			     (org-trim (plist-get info :html-link-home)))))
	      (when (and home
			 (plist-get info :html-link-use-abs-url)
			 (file-name-absolute-p raw-path))
		(setq raw-path (concat (file-name-as-directory home) raw-path))))
	    ;; Maybe turn ".org" into ".html".
	    (setq raw-path (funcall link-org-files-as-html-maybe raw-path info))
	    ;; Add search option, if any.  A search option can be
	    ;; relative to a custom-id, a headline title, a name or
	    ;; a target.
	    (let ((option (org-element-property :search-option link)))
	      (if (not option) raw-path
		(let ((path (org-element-property :path link)))
		  (concat raw-path
			  "#"
			  (org-publish-resolve-external-link option path t))))))
	   (t raw-path)))
	 (attributes-plist
	  (org-combine-plists
	   ;; Extract attributes from parent's paragraph.  HACK: Only
	   ;; do this for the first link in parent (inner image link
	   ;; for inline images).  This is needed as long as
	   ;; attributes cannot be set on a per link basis.
	   (let* ((parent (org-export-get-parent-element link))
		  (link (let ((container (org-export-get-parent link)))
			  (if (and (eq 'link (org-element-type container))
				   (org-html-inline-image-p link info))
			      container
			    link))))
	     (and (eq link (org-element-map parent 'link #'identity info t))
		  (org-export-read-attribute :attr_html parent)))
	   ;; Also add attributes from link itself.  Currently, those
	   ;; need to be added programmatically before `org-my-html-link'
	   ;; is invoked, for example, by backends building upon HTML
	   ;; export.
	   (org-export-read-attribute :attr_html link)))
	 (attributes
	  (let ((attr (org-html--make-attribute-string attributes-plist)))
	    (if (org-string-nw-p attr) (concat " " attr) ""))))
    (cond
     ;; Link type is handled by a special function.
     ((org-export-custom-protocol-maybe link desc 'html info))
     ;; Embed SVG.
     ((and (plist-get info :my-html-embed-svg)
           (org--my-html-embed-svg-p link))
      (org--my-html-svg-contents path))
     ;; Image file.
     ((and (plist-get info :html-inline-images)
	   (org-export-inline-image-p
	    link (plist-get info :html-inline-image-rules)))
      (org-html--format-image path attributes-plist info))
     ;; Radio target: Transcode target's contents and use them as
     ;; link's description.
     ((string= type "radio")
      (let ((destination (org-export-resolve-radio-link link info)))
	(if (not destination) desc
	  (format "<a href=\"#%s\"%s>%s</a>"
		  (org-export-get-reference destination info)
		  attributes
		  desc))))
     ;; Links pointing to a headline: Find destination and build
     ;; appropriate referencing command.
     ((member type '("custom-id" "fuzzy" "id"))
      (let ((destination (if (string= type "fuzzy")
			     (org-export-resolve-fuzzy-link link info)
			   (org-export-resolve-id-link link info))))
	(pcase (org-element-type destination)
	  ;; ID link points to an external file.
	  (`plain-text
	   (let ((fragment (concat org-html--id-attr-prefix path))
		 ;; Treat links to ".org" files as ".html", if needed.
		 (path (funcall link-org-files-as-html-maybe
				destination info)))
	     (format "<a href=\"%s#%s\"%s>%s</a>"
		     path fragment attributes (or desc destination))))
	  ;; Fuzzy link points nowhere.
	  (`nil
	   (format "<i>%s</i>"
		   (or desc
		       (org-export-data
			(org-element-property :raw-link link) info))))
	  ;; Link points to a headline.
	  (`headline
	   (let ((href (org-html--reference destination info))
		 ;; What description to use?
		 (desc
		  ;; Case 1: Headline is numbered and LINK has no
		  ;; description.  Display section number.
		  (if (and (org-export-numbered-headline-p destination info)
			   (not desc))
		      (mapconcat #'number-to-string
				 (org-export-get-headline-number
				  destination info) ".")
		    ;; Case 2: Either the headline is un-numbered or
		    ;; LINK has a custom description.  Display LINK's
		    ;; description or headline's title.
		    (or desc
			(org-export-data
			 (org-element-property :title destination) info)))))
	     (format "<a href=\"#%s\"%s>%s</a>" href attributes desc)))
	  ;; Fuzzy link points to a target or an element.
	  (_
           (if (and destination
                    (memq (plist-get info :with-latex) '(mathjax t))
                    (eq 'latex-environment (org-element-type destination))
                    (eq 'math (org-latex--environment-type destination)))
               ;; Caption and labels are introduced within LaTeX
	       ;; environment.  Use "ref" or "eqref" macro, depending on user
               ;; preference to refer to those in the document.
               (format (plist-get info :html-equation-reference-format)
                       (org-html--reference destination info))
             (let* ((ref (org-html--reference destination info))
                    (org-html-standalone-image-predicate
                     #'org-html--has-caption-p)
                    (counter-predicate
                     (if (eq 'latex-environment (org-element-type destination))
                         #'org-html--math-environment-p
                       #'org-html--has-caption-p))
                    (number
		     (cond
		      (desc nil)
		      ((org-html-standalone-image-p destination info)
		       (org-export-get-ordinal
			(org-element-map destination 'link #'identity info t)
			info '(link) 'org-html-standalone-image-p))
		      (t (org-export-get-ordinal
			  destination info nil counter-predicate))))
                    (desc
		     (cond (desc)
			   ((not number) "No description for this link")
			   ((numberp number) (number-to-string number))
			   (t (mapconcat #'number-to-string number ".")))))
               (format "<a href=\"#%s\"%s>%s</a>" ref attributes desc)))))))
     ;; Coderef: replace link with the reference name or the
     ;; equivalent line number.
     ((string= type "coderef")
      (let ((fragment (concat "coderef-" (org-html-encode-plain-text path))))
	(format "<a href=\"#%s\" %s%s>%s</a>"
		fragment
		(format "class=\"coderef\" onmouseover=\"CodeHighlightOn(this, \
'%s');\" onmouseout=\"CodeHighlightOff(this, '%s');\""
			fragment fragment)
		attributes
		(format (org-export-get-coderef-format path desc)
			(org-export-resolve-coderef path info)))))
     ;; External link with a description part.
     ((and path desc)
      (format "<a href=\"%s\"%s>%s</a>"
	      (org-html-encode-plain-text path)
	      attributes
	      desc))
     ;; External link without a description part.
     (path
      (let ((path (org-html-encode-plain-text path)))
	(format "<a href=\"%s\"%s>%s</a>" path attributes path)))
     ;; No path, only description.  Try to do something useful.
     (t
      (format "<i>%s</i>" desc)))))


;;; End-user functions

;;;###autoload
(defun org-my-html-export-as-html
    (&optional async subtreep visible-only body-only ext-plist)
  "Export current buffer to a MY-HTML buffer.

If narrowing is active in the current buffer, only export its
narrowed part.

If a region is active, export that region.

A non-nil optional argument ASYNC means the process should happen
asynchronously.  The resulting buffer should be accessible
through the `org-export-stack' interface.

When optional argument SUBTREEP is non-nil, export the sub-tree
at point, extracting information from the headline properties
first.

When optional argument VISIBLE-ONLY is non-nil, don't export
contents of hidden elements.

When optional argument BODY-ONLY is non-nil, only write code
between \"<body>\" and \"</body>\" tags.

EXT-PLIST, when provided, is a property list with external
parameters overriding Org default settings, but still inferior to
file-local settings.

Export is done in a buffer named \"*Org HTML PLUS Export*\", which
will be displayed when `org-export-show-temporary-export-buffer'
is non-nil."
  (interactive)
  (org-export-to-buffer 'my-html "*Org MY-HTML Export*"
    async subtreep visible-only body-only ext-plist
    (lambda () (set-auto-mode t))))

;;;###autoload
(defun org-my-html-export-to-html
    (&optional async subtreep visible-only body-only ext-plist)
  "Export current buffer to a MY-HTML file.

If narrowing is active in the current buffer, only export its
narrowed part.

If a region is active, export that region.

A non-nil optional argument ASYNC means the process should happen
asynchronously.  The resulting file should be accessible through
the `org-export-stack' interface.

When optional argument SUBTREEP is non-nil, export the sub-tree
at point, extracting information from the headline properties
first.

When optional argument VISIBLE-ONLY is non-nil, don't export
contents of hidden elements.

When optional argument BODY-ONLY is non-nil, only write code
between \"<body>\" and \"</body>\" tags.

EXT-PLIST, when provided, is a property list with external
parameters overriding Org default settings, but still inferior to
file-local settings.

Return output file's name."
  (interactive)
  (let* ((extension (concat
		     (when (> (length org-html-extension) 0) ".")
		     (or (plist-get ext-plist :html-extension)
			 org-html-extension
			 "html")))
	 (file (org-export-output-file-name extension subtreep))
	 (org-export-coding-system org-html-coding-system))
    (org-export-to-file 'my-html file
      async subtreep visible-only body-only ext-plist)))

(provide 'ox-my-html)

;;; ox-my-html.el ends here