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;;; pancake.el --- Pancake browser interface -*- lexical-binding: t; -*-

;; Copyright (C) 2017 defanor

;; Author: defanor <defanor@uberspace.net>
;; Maintainer: defanor <defanor@uberspace.net>
;; Created: 2017-10-28
;; Keywords: pandoc, web, gopher, browser
;; Homepage: https://defanor.uberspace.net/projects/pancake/
;; Version: 0.1.7

;; 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 rather simple interface to the pancake browser.

;;; Code:

(require 'seq)


;;;; Settings

(defgroup pancake nil
  "Pancake browser interface."
  :prefix "pancake-"
  :group 'applications)

(defface pancake-color-black-foreground
  '((((type graphic) (class color) (background dark)) :foreground "grey")
    (((type graphic) (class color) (background light)) :foreground "black")
    (t :foreground "black"))
  "Foreground face for black color."
  :group 'pancake)

(defface pancake-color-red-foreground
  '((((type graphic) (class color) (background dark)) :foreground "light coral")
    (((type graphic) (class color) (background light)) :foreground "dark red")
    (t :foreground "red"))
  "Foreground face for red color."
  :group 'pancake)

(defface pancake-color-green-foreground
  '((((type graphic) (class color) (background dark)) :foreground "dark sea green")
    (((type graphic) (class color) (background light)) :foreground "dark green")
    (t :foreground "green"))
  "Foreground face for green color."
  :group 'pancake)

(defface pancake-color-yellow-foreground
  '((((type graphic) (class color) (background dark)) :foreground "light yellow")
    (((type graphic) (class color) (background light)) :foreground "yellow4")
    (t :foreground "yellow"))
  "Foreground face for yellow color."
  :group 'pancake)

(defface pancake-color-blue-foreground
  '((((type graphic) (class color) (background dark)) :foreground "light blue")
    (((type graphic) (class color) (background light)) :foreground "dark blue")
    (t :foreground "blue"))
  "Foreground face for blue color."
  :group 'pancake)

(defface pancake-color-magenta-foreground
  '((((type graphic) (class color) (background dark)) :foreground "pink")
    (((type graphic) (class color) (background light)) :foreground "magenta4")
    (t :foreground "magenta"))
  "Foreground face for magenta color."
  :group 'pancake)

(defface pancake-color-cyan-foreground
  '((((type graphic) (class color) (background dark)) :foreground "DarkSlateGray3")
    (((type graphic) (class color) (background light)) :foreground "dark cyan")
    (t :foreground "cyan"))
  "Foreground face for cyan color."
  :group 'pancake)

(defface pancake-color-white-foreground
  '((((type graphic) (class color) (background dark)) :foreground "white")
    (((type graphic) (class color) (background light)) :foreground "grey")
    (t :foreground "white"))
  "Foreground face for white color."
  :group 'pancake)

(defface pancake-strike-through
  '((t :strike-through t))
  "A strike-through face."
  :group 'pancake)

(defcustom pancake-command '("pancake" "--embedded")
  "A command that runs pancake, along with its arguments"
  :type '(list string)
  :group 'pancake)

(defcustom pancake-display-hook nil
  "Hook run after displaying a page in pancake."
  :type 'hook
  :group 'pancake)

(defvar pancake-buffers '()
  "A list of pancake browser buffers, used to find a buffer to
  use by the `pancake' command.")

(defvar pancake-headings '()
  "A list of headings with their levels.")
(make-variable-buffer-local 'pancake-headings)

(defvar pancake-process-output ""
  "Pancake process's stdout collector.")
(make-variable-buffer-local 'pancake-process-output)

(defvar pancake-process-stderr-output ""
  "Pancake process's stderr collector.")
(make-variable-buffer-local 'pancake-process-stderr-output)

(defvar pancake-process nil
  "Pancake browser process.")
(make-variable-buffer-local 'pancake-process)

(defvar pancake-uri-history '()
  "History of visited URIs, limited by `history-length'.")
(make-variable-buffer-local 'pancake-uri-history)


;;;; Functions

;;;###autoload
(defun pancake-new ()
  "Run a new pancake session."
  (interactive)
  (let ((p-buf (generate-new-buffer "*pancake*")))
    (display-buffer p-buf)
    (with-current-buffer p-buf
      (pancake-mode)
      (setq pancake-process
            (let ((process-environment
                   (append
                    (list (format "TERM=%s" (if window-system "xterm"
                                              (or (getenv "TERM") "dumb")))
                          (format "INSIDE_EMACS=%s,pancake" emacs-version)
                          (format "COLUMNS=%d" (1- (window-width))))
                    process-environment)))
              (make-process
               :name "pancake"
               :buffer p-buf
               :command pancake-command
               :stderr (make-pipe-process
                        :name "pancake-stderr"
                        :buffer (generate-new-buffer "*pancake-stderr*")
                        :filter 'pancake-process-stderr-filter
                        :sentinel 'pancake-process-stderr-sentinel)
               :filter 'pancake-process-filter
               :sentinel 'pancake-process-sentinel)))
      (push p-buf pancake-buffers)
      (read-only-mode 1))))

;;;###autoload
(defun pancake (&optional url new-session)
  "Browse an URL with pancake, suitable for setting as
`browse-url-browser-function'. Or simply display a pancake buffer
if no URL is provided."
  (interactive)
  (when (or new-session (not (consp pancake-buffers)))
    (pancake-new))
  (let ((buffer (if (eq major-mode 'pancake-mode)
                    (current-buffer)
                  (car pancake-buffers))))
    (with-current-buffer buffer
      (when url (pancake-process-send url))
      (display-buffer (current-buffer)))))

(defun pancake-goto-line (&optional line)
  "Go to LINE. This is mostly to avoid `goto-line' warnings,
while avoiding code duplication."
  (when line
    (goto-char (point-min))
    (forward-line (1- line))))

(defun pancake-translate-color (name attr)
  "Translate pancake colors into emacs faces."
  (intern (concat "pancake-color-"
                  (downcase (symbol-name name))
                  "-"
                  (symbol-name attr))))

(defun pancake-button-action (button)
  "An action to be invoked on button activation."
  (funcall 'browse-url (or (button-get button 'pancake-link)
                           (button-get button 'pancake-image))))

(defun pancake-print-elem (element)
  "Translate ELEMENT into a string."
  (if (stringp element)
      (insert element)
    (let ((start (point)))
      (pcase element
        (`(fg ,color . ,rest)
         (pancake-print-line rest)
         (add-face-text-property
          start (point) (pancake-translate-color color 'foreground) t))
        (`(style strikethrough . ,rest)
         (pancake-print-line rest)
         (add-face-text-property start (point) 'pancake-strike-through t))
        (`(style ,face . ,rest)
         (pancake-print-line rest)
         (add-face-text-property start (point) face t))
        (`(subscript . ,rest)
         (pancake-print-line rest)
         (add-text-properties start (point) '(display (raise -0.2))))
        (`(superscript . ,rest)
         (pancake-print-line rest)
         (add-text-properties start (point) '(display (raise 0.2))))
        (`(denotation (math . ,_formula) . ,rest)
         (pancake-print-line rest))
        (`(denotation (link . ,uri) . ,rest)
         (pancake-print-line rest)
         (make-text-button start (point)
                           'pancake-link uri
                           'help-echo uri
                           'follow-link t
                           'action #'pancake-button-action))
        (`(denotation (image . ,uri) . ,rest)
         (pancake-print-line rest)
         (make-text-button start (point)
                           'pancake-image uri
                           'help-echo uri
                           'follow-link t
                           'action #'pancake-button-action))
        (`(denotation (heading . ,level) . ,rest)
         (pancake-print-line rest)
         (add-to-list 'pancake-headings (cons (line-number-at-pos) level))
         (add-text-properties start (point)
                              `(display (height ,(1+ (/ 0.5 level))))))
        (_ (format "Unexpected element: %S" element))))))

(defun pancake-print-line (line)
  "Translate LINE (a list of elements) into a string"
  (mapc 'pancake-print-elem line))

(defun pancake-line-p (string)
  "Return t if STRING ends with a newline character."
  (char-equal (elt string (- (length string) 1)) ?\n))

(defun pancake-uri-history-add (uri)
  "Adds URI into `pancake-uri-history', or simply moves it into
the list's `car' if it is already present."
  (setq pancake-uri-history
        (seq-take (cons uri (seq-remove (lambda (e) (string-equal e uri))
                                        pancake-uri-history))
                  history-length)))

(defun pancake-traverse-image-buttons (function)
  "Traverse image buttons, applying FUNCTION to each. The
function arguments must be a button and its pancake-image
property. Returns a list of collected values."
  (save-excursion
    (goto-char (point-min))
    (let ((inhibit-read-only t)
          (ret nil)
          (btn (next-button (point) t)))
      (while btn
        (let ((btn-image (button-get btn 'pancake-image)))
          (goto-char btn)
          (when btn-image
            (push (apply function (list btn btn-image)) ret)))
        (setq btn (next-button (point))))
      (reverse ret))))

(defun pancake-insert-image (uri path)
  "Inserts a saved image."
  (pancake-traverse-image-buttons
   (lambda (_btn btn-image)
     (when (string-equal btn-image uri)
       (let ((img (create-image path)))
         ;; todo: might be better to slice images, but it seems to be
         ;; a bit glitchy and breaks line numbering. Handling local
         ;; references completely in emacs would help with the latter.
         (insert-image img))))))

(defun pancake-load-images ()
  "Requests all the images to be loaded."
  (interactive)
  (mapc (lambda (uri) (pancake-process-send (concat "save " uri)))
        (seq-uniq (pancake-traverse-image-buttons
                   (lambda (_btn btn-image) btn-image))
                  'string-equal)))

(defun pancake-process-filter (proc string)
  "Pancake process filter for stdout."
  (when (buffer-live-p (process-buffer proc))
    (with-current-buffer (process-buffer proc)
      (setq pancake-process-output (concat pancake-process-output string))
      (when (pancake-line-p pancake-process-output)
        (let ((raw-lines (split-string pancake-process-output "\n")))
          (setq pancake-process-output "")
          ;; there may be multiple lines, processing separately
          (dolist (raw-line raw-lines)
            (unless (string-empty-p raw-line)
              (let ((output (read raw-line)))
                (pcase output
                  (`(render . ,alist)
                   ;; todo: maybe store identifiers and links for
                   ;; further manipulation
                   (let ((inhibit-read-only t))
                     (delete-region (point-min) (point-max))
                     (setq pancake-headings '())
                     (pancake-uri-history-add (alist-get 'uri alist))
                     (dolist (line (alist-get 'lines alist))
                       (pancake-print-line line)
                       (newline))
                     (goto-char (point-min)))
                   (run-hooks 'pancake-display-hook))
                  (`(goto ,line) (pancake-goto-line line))
                  ;; todo: check if the images were requested
                  ;; explicitly, don't just show all the images that get
                  ;; saved
                  (`(saved ,uri ,path) (pancake-insert-image uri path)))))))))))

(defun pancake-process-stderr-filter (_proc string)
  "Pancake process filter for stderr."
  (setq pancake-process-stderr-output
        (concat pancake-process-stderr-output string))
  (when (pancake-line-p pancake-process-stderr-output)
    (message "pancake: %s" (string-trim pancake-process-stderr-output))
    (setq pancake-process-stderr-output "")))

(defun pancake-process-sentinel (process _event)
  "Pancake process sentinel for stdout."
  (let ((buf (process-buffer process)))
    (when (and (not (process-live-p process))
               (buffer-live-p (process-buffer process)))
      (kill-buffer buf))
    (setq pancake-buffers
          (seq-remove (lambda (x) (eq x buf)) pancake-buffers))))

(defun pancake-process-stderr-sentinel (process _event)
  "Pancake process sentinel for stderr."
  (when (and (not (process-live-p process))
             (buffer-live-p (process-buffer process)))
    (kill-buffer (process-buffer process))))

(defun pancake-interrupt ()
  "Send SIGINT to the process."
  (interactive)
  (interrupt-process pancake-process))

(defun pancake-yank ()
  "Insert a string."
  (interactive)
  (funcall (pancake-input (current-kill 0))))

(defun pancake-yank-primary ()
  "Insert a string from the primary selection."
  (interactive)
  (funcall (pancake-input (gui-get-primary-selection))))

(defun pancake-width-adjust (&optional width)
  "Sets the width (in columns) that the pancake process should
use. Current window width is used if none is provided."
  (interactive)
  ;; Not using `pancake-process-send' here, since it itself would call
  ;; this function.
  (process-send-string pancake-process
                       (format "set width %d\n"
                               (or width (1- (window-width))))))

(defun pancake-process-send (line)
  "Send LINE to the pancake process."
  (pancake-width-adjust)
  (process-send-string pancake-process (concat line "\n")))

(defun pancake-go-backward ()
  "Go backward in history."
  (interactive)
  (pancake-process-send "["))

(defun pancake-go-forward ()
  "Go forward in history."
  (interactive)
  (pancake-process-send "]"))

(defun pancake-quit ()
  "Quit pancake."
  (interactive)
  (pancake-process-send "quit"))

(defun pancake-reload ()
  "Reload the current document."
  (interactive)
  (pancake-process-send ","))

(defun pancake-display-current-uri ()
  "Display current URI and put it into the kill ring."
  (interactive)
  (when (consp pancake-uri-history)
    (message "%s" (car pancake-uri-history))
    (kill-new (car pancake-uri-history))))

(defun pancake-next-button ()
  "Moves cursor to the next button."
  (interactive)
  (let ((next (next-button (point))))
    (when next
      (goto-char next))))

(defun pancake-previous-button ()
  "Moves cursor to the previous button."
  (interactive)
  (let ((prev (previous-button (point))))
    (when prev
      (goto-char prev))))

(defun pancake-previous-heading ()
  "Moves cursor to the previous heading."
  (interactive)
  (let ((line (seq-find (lambda (x) (< x (line-number-at-pos)))
                        (mapcar 'car pancake-headings))))
    (when line
      (pancake-goto-line line))))

(defun pancake-next-heading ()
  "Moves cursor to the next heading."
  (interactive)
  (let ((line (seq-find (lambda (x) (> x (line-number-at-pos)))
                        (reverse (mapcar 'car pancake-headings)))))
    (when line
      (pancake-goto-line line))))

(defun pancake-minibuffer-setup ()
  "Removes itself from `minibuffer-setup-hook' and unsets SPC in
that minibuffer, since there's usually no need to complete words,
yet shortcuts should be entered easily."
  (remove-hook 'minibuffer-setup-hook #'pancake-minibuffer-setup)
  (local-unset-key (kbd "SPC")))

(defun pancake-prompt (&optional string)
  "Prompts for input, passes it to `pancake-process'. Similar to
`pancake-input', but runs immediately."
  (interactive)
  (add-hook 'minibuffer-setup-hook #'pancake-minibuffer-setup)
  (pancake-process-send
   (completing-read "pancake> " pancake-uri-history nil nil string)))

(defun pancake-input (string)
  "Pancake input handler: opens minibuffer for input.
Sets the initial contents to STRING, reads the rest, and passes
it to `pancake-process' as input."
  (lambda ()
    (interactive)
    (pancake-prompt string)))

(defvar pancake-mode-map
  (let ((map (make-sparse-keymap))
        (chars (append (list ?? ?. ?/ ?# ?* ?,)
                       (number-sequence ?0 ?9)
                       (number-sequence ?a ?z))))
    (dolist (char chars)
      (let ((str (char-to-string char)))
        (define-key map (kbd str) (pancake-input str))))
    (define-key map (kbd "C-y") 'pancake-yank)
    (define-key map (kbd "<mouse-2>") 'pancake-yank-primary)
    (define-key map (kbd "<mouse-8>") 'pancake-go-backward)
    (define-key map (kbd "<mouse-9>") 'pancake-go-forward)
    (define-key map (kbd "TAB") 'pancake-next-button)
    (define-key map (kbd "<backtab>") 'pancake-previous-button)
    (define-key map (kbd "RET") 'pancake-prompt)
    (define-key map (kbd "C-c C-c") 'pancake-interrupt)
    (define-key map (kbd "C-c C-u") 'pancake-display-current-uri)
    (define-key map (kbd "C-M-e") 'pancake-next-heading)
    (define-key map (kbd "C-M-a") 'pancake-previous-heading)
    (define-key map (kbd "[") 'pancake-go-backward)
    (define-key map (kbd "]") 'pancake-go-forward)
    (define-key map (kbd "Q") 'pancake-quit)
    (define-key map (kbd "R") 'pancake-reload)
    (define-key map (kbd "I") 'pancake-load-images)
    map)
  "Keymap for `pancake-mode'.")

(define-derived-mode pancake-mode nil "Pancake"
  "A basic emacs interface to the pancake browser.")

(provide 'pancake)

;;; pancake.el ends here