;;; elopher.el --- gopher client

;;; Commentary:

;; Simple gopher client in elisp.

;;; Code:

;;; Customization group
;;

(defgroup elopher nil
  "A simple gopher client."
  :group 'applications)

(defcustom elopher-index-face '(foreground-color . "cyan")
  "Face used for index records.")
(defcustom elopher-text-face '(foreground-color . "white")
  "Face used for text records.")
(defcustom elopher-info-face '(foreground-color . "gray")
  "Face used for info records.")
(defcustom elopher-image-face '(foreground-color . "green")
  "Face used for image records.")
(defcustom elopher-unknown-face '(foreground-color . "red")
  "Face used for unknown record types.")

;;; Model
;;

(defun elopher-make-node (parent address &optional content)
  (list parent address cache))

(defun elopher-node-parent (node)
  (car node))

(defun elopher-node-address (node)
  (cadr node))

(defun elopher-node-content (node)
  (caddr node))

(defun elopher-reload-node (node after)
  ())

;;; Global constants
;;

(defconst elopher-version "1.0.0"
  "Current version of elopher.")

(defconst elopher-margin-width 6
  "Width of left-hand margin used when rendering indicies.")

(defconst elopher-start-page
  (concat "i\tfake\tfake\t1\r\n"
          "i--------------------------------------------\tfake\tfake\t1\r\n"
          "i          Elopher Gopher Client             \tfake\tfake\t1\r\n"
          (format "i              version %s\tfake\tfake\t1\r\n" elopher-version)
          "i--------------------------------------------\tfake\tfake\t1\r\n"
          "i\tfake\tfake\t1\r\n"
          "iBasic usage:\tfake\tfake\t1\r\n"
          "i - tab/shift-tab: next/prev directory entry\tfake\tfake\t1\r\n"
          "i - RET/mouse-1: open directory entry\tfake\tfake\t1\r\n"
          "i - u: return to parent directory entry\tfake\tfake\t1\r\n"
          "i - g: go to a particular site\tfake\tfake\t1\r\n"
          "i\tfake\tfake\t1\r\n"
          "iPlaces to start exploring Gopherspace:\tfake\tfake\t1\r\n"
          "1Floodgap Systems Gopher Server\t\tgopher.floodgap.com\t70\r\n"
          "1Super-Dimensional Fortress\t\tsdf.org\t70\r\n"
          "i\tfake\tfake\t1\r\n"
          "iTest entries:\tfake\tfake\t1\r\n"
          "pXKCD comic image\t/fun/xkcd/comics/2130/2137/text_entry.png\tgopher.floodgap.com\t70\r\n"))

;;; Mode and keymap
;;

(setq elopher-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "<tab>") 'elopher-next-link)
    (define-key map (kbd "<S-tab>") 'elopher-prev-link)
    (define-key map (kbd "u") 'elopher-pop-history)
    (define-key map (kbd "g") 'elopher-go)
    (define-key map (kbd "r") 'elopher-reload)
    (when (require 'evil nil t)
      (evil-define-key 'normal map
        (kbd "C-]") 'elopher-follow-closest-link
        (kbd "C-t") 'elopher-pop-history
        (kbd "u") 'elopher-pop-history
        (kbd "g") 'elopher-go
        (kbd "r") 'elopher-reload))
    map))
  ;; "Keymap for gopher client.")

(define-derived-mode elopher-mode special-mode "elopher"
  "Major mode for elopher, an elisp gopher client.")


;;; Index rendering
;;

(defun elopher-insert-index (string)
  "Inserts the index corresponding to STRING into the current buffer."
  (dolist (line (split-string string "\r\n"))
    (elopher-insert-index-record line)))

(defun elopher-insert-margin (&optional type-name)
  (if type-name
      (insert (format (concat "%" (number-to-string elopher-margin-width) "s"
                              (concat
                               (propertize "[" 'face '(foreground-color . "blue"))
                               (propertize type-name 'face '(foreground-color . "white"))
                               (propertize "]" 'face '(foreground-color . "blue"))))))
    (insert (make-string elopher-margin-width ?\s))))

(defun elopher-insert-index-record (line)
  "Inserts the index record corresponding to LINE into the current buffer."
  (let* ((type (elt line 0))
         (fields (split-string (substring line 1) "\t"))
         (display-string (elt fields 0))
         (selector (elt fields 1))
         (hostname (elt fields 2))
         (port (elt fields 3))
         (address (list selector hostname port)))
    (pcase type
      (?i (elopher-insert-margin)
          (insert (propertize display-string
                              'face elopher-info-face)))
      (?0 (elopher-insert-margin "T")
          (insert-text-button display-string
                              'face elopher-text-face
                              'link-getter #'elopher-get-text
                              'link-address address
                              'action #'elopher-click-link
                              'follow-link t))
      (?1 (elopher-insert-margin "/")
          (insert-text-button display-string
                              'face elopher-index-face
                              'link-getter #'elopher-get-index
                              'link-address address
                              'action #'elopher-click-link
                              'follow-link t))
      (?p (elopher-insert-margin "img")
          (insert-text-button display-string
                             'face elopher-image-face
                             'link-getter #'elopher-get-image
                             'link-address address
                             'action #'elopher-click-link
                             'follow-link t))
      (?.) ; Occurs at end of index, can safely ignore.
      (tp (elopher-insert-margin (concat (char-to-string tp) "?"))
          (insert (propertize display-string
                              'face elopher-unknown-face))))
    (insert "\n")))

;;; History management
;;

(defvar elopher-history nil
  "List of pages in elopher history.")

(defvar elopher-place-history nil
  "List of objects describing how to access pages in history.")

(defvar elopher-current-place nil
  "How to access current page.")

(defun elopher-push-history ()
  "Add current contents of buffer, including point, to history."
  (unless (string-empty-p (buffer-string))
    (push
     (list (buffer-string)
           (point))
     elopher-history)
    (push
     elopher-current-place
     elopher-place-history)))

(defun elopher-pop-history ()
  "Restore most recent page from history."
  (interactive)
  (if (get-buffer "*elopher*")
      (if elopher-history
          (let* ((inhibit-read-only t)
                 (prev-page (pop elopher-history))
                 (page-string (car prev-page))
                 (page-point (cadr prev-page)))
            (switch-to-buffer "*elopher*")
            (erase-buffer)
            (insert page-string)
            (goto-char page-point)
            (setq elopher-current-place (pop elopher-place-history)))
        (message "Already at start of history."))
    (message "No elopher buffer found.")))


;;; Selector retrieval (all kinds)
;;

(defun elopher-get-selector (selector host port filter &optional sentinel)
  (switch-to-buffer "*elopher*")
  (elopher-mode)
  (elopher-push-history)
  (let ((inhibit-read-only t))
    (erase-buffer))
  (make-network-process
   :name "elopher-process"
   :host host
   :service (if port port 70)
   :filter filter
   :sentinel sentinel)
  (process-send-string "elopher-process" (concat selector "\n")))

;; Index retrieval

(defun elopher-index-filter (proc string)
  (let ((marker (process-mark proc))
        (inhibit-read-only t))
    (if (not (marker-position marker))
        (set-marker marker 0 (current-buffer)))
    (save-excursion
      (goto-char marker)
      (elopher-render-complete-records string)
      (set-marker marker (point)))))

(defun elopher-get-index (selector host port)
  (setq elopher-incomplete-record "")
  (elopher-get-selector selector host port
                        #'elopher-index-filter))

;; Text retrieval

(defun elopher-text-filter (proc string)
  (let ((marker (process-mark proc))
        (inhibit-read-only t))
    (if (not (marker-position marker))
        (set-marker marker 0 (current-buffer)))
    (save-excursion
      (goto-char marker)
      (dolist (line (split-string string "\r"))
        (insert line))
      (set-marker marker (point)))))

(defun elopher-get-text (selector host port)
  (elopher-get-selector selector host port
                        #'elopher-text-filter))

;; Image retrieval

(defvar elopher-image-buffer "")

(defun elopher-image-filter (proc string)
  (setq elopher-image-buffer (concat elopher-image-buffer string)))

(defun elopher-image-sentinel (proc event)
  (let ((inhibit-read-only t))
    (insert-image (create-image elopher-image-buffer))))

(defun elopher-get-image (selector host port)
  (setq elopher-image-buffer "")
  (elopher-get-selector selector host port
                        #'elopher-image-filter
                        #'elopher-image-sentinel))

;; Start page retrieval

(defun elopher-get-start-page (&optional selector host port)
  "Display start page.  SELECTOR, HOST and PORT are unused."
  (let ((inhibit-read-only t))
    (erase-buffer)
    (save-excursion
      (elopher-render-complete-records elopher-start-page))))

;;; Navigation methods
;;

(defun elopher-next-link ()
  (interactive)
  (forward-button 1))

(defun elopher-prev-link ()
  (interactive)
  (backward-button 1))

(defun elopher-click-link (button)
  (apply (button-get button 'link-getter) (button-get button 'link-address))
  (setq elopher-current-place (list link-getter link-address)))

(defun elopher-follow-closest-link ()
  (interactive)
  (push-button))

(defun elopher-go ()
  "Go to a particular gopher site."
  (interactive)
  (let* ((selector "")
         (hostname (read-from-minibuffer "Gopher host: "))
         (port 70)
         (address (list selector hostname port)))
    (elopher-get-index "" (read-from-minibuffer "Gopher host: ") 70)i
    (setq elopher-current-place (list #'elopher-get-index address))))

(defun  elopher-reload ()
  "Reload current page."
  (interactive)
  (if elopher-current-place
      (let ((link-getter (car elopher-current-place))
            (address (cadr elopher-current-place)))
        (apply link-getter address))
    (elopher-get-start-page)))

;;; Main start procedure
;;

(defun elopher ()
  "Start elopher with default landing page."
  (interactive)
  (switch-to-buffer "*elopher*")
  (elopher-mode)
  (setq elopher-history nil)
  (setq elopher-place-history nil)
  (setq elopher-current-place nil)
  (elopher-get-start-page))


;;; elopher.el ends here