;;; xwwp-follow-link.el --- Link navigation in `xwidget-webkit' sessions -*- lexical-binding: t; -*-

;; Copyright (C) 2020 Damien Merenne <dam@cosinux.org>

;; This file is NOT part of GNU Emacs.

;;; License:

;; 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Add support for navigating web pages in `xwidget-webkit' sessions using the
;; minibuffer completion.

;;; Code:

(require 'xwidget)
(require 'xwwp)
(require 'eieio)
(require 'cl-lib)
(require 'ido)

(defgroup xwwp-follow-link nil
  "`xwidget-webkit' follow link customizations."
  :group 'xwwp)

(defcustom xwwp-follow-link-completion-system 'default
  "The completion system to be used by xwidget plus.

Custom function should be a function that takes no arguments and
returns an instance of an eieio class extending
`xwwp-follow-link-completion-backend'."
  :group 'xwwp-follow-link
  :type '(radio
          (const :tag "Ido" ido)
          (const :tag "Helm" helm)
          (const :tag "Ivy" ivy)
          (const :tag "Default" default)
          (function :tag "Custom function")))

(defcustom xwwp-follow-link-candidate-style '(("border" . "1px dashed blue")
                                              ("background" . "#0000ff20"))
  "Style to apply to candidate links."
  :type '(list (cons string string))
  :group 'xwwp-follow-link)

(defcustom xwwp-follow-link-selected-style '(("border" . "1px dashed red")
                                             ("background" . "#ff000020"))
  "Style to apply to currently selected link."
  :type '(list (cons string string))
  :group 'xwwp-follow-link)

(defun xwwp-follow-link-style-definition ()
  "Return the css definitions for the follow link feature."
  (concat (xwwp-css-make-class "xwwp-follow-link-candidate" xwwp-follow-link-candidate-style)
          (xwwp-css-make-class "xwwp-follow-link-selected" xwwp-follow-link-selected-style)))

(xwwp-js-def follow-link cleanup ()
  "Remove all custom class from links.""
document.querySelectorAll('a').forEach(a => {
    a.classList.remove('xwwp-follow-link-candidate', 'xwwp-follow-link-selected');
});
")

(xwwp-js-def follow-link highlight (ids selected)
  "Highlight IDS as candidate and SELECTED as selected.""
document.querySelectorAll('a').forEach((a, id) => {
    a.classList.remove('xwwp-follow-link-candidate', 'xwwp-follow-link-selected');
    if (selected == id) {
        a.classList.add('xwwp-follow-link-selected');
        a.scrollIntoView({behavior: 'smooth', block: 'center'});
    } else if (ids && ids.includes(id)) {
        a.classList.add('xwwp-follow-link-candidate');
    }
});
")

(xwwp-js-def follow-link action (link-id)
  "Click on the link identified by LINK-ID""
__xwidget_plus_follow_link_cleanup();
document.querySelectorAll('a')[link_id].click();
")

(xwwp-js-def follow-link fetch-links ()
  "Fetch all visible, non empty links from the current page.""
var r = {};
document.querySelectorAll('a').forEach((a, i) => {
    if (a.offsetWidth || a.offsetHeight || a.getClientRects().length) {
        if (a.innerText.match(/\\\\S/))
            r[i] = a.innerText;
    }
});
return r;
")


;; Completion backend class
(defclass xwwp-follow-link-completion-backend () ((collection) (text)))

(cl-defmethod xwwp-follow-link-candidates ((_backend xwwp-follow-link-completion-backend))
  "Return the BACKEND selected link and the candidates.

The return value is a list whose first element is the selected id
link and the rest are the candidates ids.

Return nil if the backend does not support narrowing selection list.")

(cl-defmethod xwwp-follow-link-read ((_backend xwwp-follow-link-completion-backend)
                                     _prompt _collection _action _update-fn)
  "Use BACKEND to PROMPT the user for a link in COLLECTION.

ACTION should be called with the resulting link.

UPDATE-FN is a function that can be called when the candidates
list is narrowed.It will highlight the link list in the
browser.")


;; Default backend using completing-read
(defclass xwwp-follow-link-completion-backend-default (xwwp-follow-link-completion-backend) ())

(cl-defmethod xwwp-follow-link-candidates ((backend xwwp-follow-link-completion-backend-default))
  "Return the BACKEND selected link and the candidates.

The return value is a list whose first element is the selected id
link and the rest are the candidates ids.

Return nil if the backend does not support narrowing selection list."
  (let* ((collection (oref backend collection))
         (text (oref backend text))
         (matches (seq-filter (lambda (i) (string-match-p (concat "^" (regexp-quote text)) (car i))) collection))
         (matches (seq-map #'cdr matches)))
    (if (= 1 (length matches))
        matches
      (cons nil matches))))

(cl-defmethod xwwp-follow-link-read ((backend xwwp-follow-link-completion-backend-default) prompt collection action update-fn)
  "Use BACKEND to PROMPT the user for a link in COLLECTION.

ACTION should be called with the resulting link.

UPDATE-FN is a function that can be called when the candidates
list is narrowed.It will highlight the link list in the
browser."
  (funcall action (cdr (assoc (completing-read prompt (lambda (str pred _)
                                                        (oset backend text str)
                                                        (funcall update-fn)
                                                        (try-completion str collection pred))
                                               nil t)
                              collection))))

(declare-function xwwp-follow-link-completion-backend-ido "xwwp-follow-link-ido")
(declare-function xwwp-follow-link-completion-backend-ivy "xwwp-follow-link-ivy")
(declare-function xwwp-follow-link-completion-backend-helm "xwwp-follow-link-helm")

(defun xwwp-follow-link-make-backend ()
  "Instanciate a completion backend."
  (cond ((eq xwwp-follow-link-completion-system 'default)
         #'xwwp-follow-link-completion-backend-default)
        ((eq xwwp-follow-link-completion-system 'ivy)
         (unless (require 'xwwp-follow-link-ivy nil t)
           (user-error "Install the `xwwp-follow-link-ivy' package to use `xwwp-follow-link' with `ivy'"))
         #'xwwp-follow-link-completion-backend-ivy)
        ((eq xwwp-follow-link-completion-system 'helm)
         (unless (require 'xwwp-follow-link-helm nil t)
           (user-error "Install the `xwwp-follow-link-helm' package to use `xwwp-follow-link' with `helm'"))
         #'xwwp-follow-link-completion-backend-helm)
        ((eq xwwp-follow-link-completion-system 'ido)
         (require 'xwwp-follow-link-ido)
         #'xwwp-follow-link-completion-backend-ido)
        ((eq xwwp-follow-link-completion-system 'default)
         #'xwwp-follow-link-completion-backend-default)
        (t xwwp-follow-link-completion-system)))


(defvar xwwp-follow-link-completion-backend-instance '())

(defun xwwp-follow-link-update (xwidget)
  "Highligh LINKS in XWIDGET buffer when updating candidates."
  (let ((links (xwwp-follow-link-candidates xwwp-follow-link-completion-backend-instance)))
    (when links
      (let* ((selected (car links))
             (candidates (cdr links)))
        (xwwp-follow-link-highlight xwidget candidates selected)))))

(defun xwwp-follow-link-trigger-action (xwidget selected)
  "Activate link matching SELECTED in XWIDGET LINKS."
  (xwwp-follow-link-action xwidget selected))

(defun xwwp-follow-link-format-link (str)
  "Format link title STR."
  (setq str (replace-regexp-in-string "^[[:space:][:cntrl:]]+" "" str))
  (setq str (replace-regexp-in-string "[[:space:][:cntrl:]]+$" "" str))
  (setq str (replace-regexp-in-string "[[:cntrl:]]+" "/" str))
  (replace-regexp-in-string "[[:space:]]+" " " str))

(defun xwwp-follow-link-prepare-links (links)
  "Prepare the alist of LINKS."
  (seq-sort-by (lambda (v) (cdr v)) #'<
               (seq-map (lambda (v) (cons (xwwp-follow-link-format-link (cdr v)) (string-to-number (car v))))
                        links)))

(defun xwwp-follow-link-callback (links)
  "Ask for a link belonging to the alist LINKS."
  (let* ((xwidget (xwidget-webkit-current-session))
         (links (xwwp-follow-link-prepare-links links)))
    (oset xwwp-follow-link-completion-backend-instance collection links)
    (condition-case nil
        (xwwp-follow-link-read xwwp-follow-link-completion-backend-instance
                               "Link: " links
                               (apply-partially #'xwwp-follow-link-trigger-action xwidget)
                               (apply-partially #'xwwp-follow-link-update xwidget))
      (quit (xwwp-follow-link-cleanup xwidget)))
    (oset xwwp-follow-link-completion-backend-instance collection nil)))

;;;###autoload
(defun xwwp-follow-link (&optional xwidget)
  "Ask for a link in the XWIDGET session or the current one and follow it."
  (interactive)
  (setq xwwp-follow-link-completion-backend-instance (funcall (xwwp-follow-link-make-backend)))
  (let ((xwidget (or xwidget (xwidget-webkit-current-session))))
    (xwwp-html-inject-style xwidget "__xwidget_plus_follow_link_style" (xwwp-follow-link-style-definition))
    (xwwp-js-inject xwidget 'follow-link)
    (xwwp-follow-link-fetch-links xwidget #'xwwp-follow-link-callback)))

;; Local Variables:
;; eval: (mmm-mode)
;; eval: (mmm-add-group 'elisp-js '((elisp-rawjs :submode js-mode
;;                                               :face mmm-code-submode-face
;;                                               :delimiter-mode nil
;;                                               :front "xwwp--js \"" :back "\" js--")
;;                                  (elisp-defjs :submode js-mode
;;                                               :face mmm-code-submode-face
;;                                               :delimiter-mode nil
;;                                               :front "xwwp-js-def .*\n.*\"\"\n" :back "\")\n")))
;; mmm-classes: elisp-js
;; End:

(provide 'xwwp-follow-link)
;;; xwwp-follow-link.el ends here