;;; hnreader.el --- A hackernews reader -*- lexical-binding: t; -*-

;; Copyright (C) 2019  Thanh Vuong

;; Author: Thanh Vuong <thanhvg@gmail.com>
;; URL: https://github.com/thanhvg/emacs-hnreader/
;; Package-Requires: ((emacs "25.1") (promise "1.1") (request "0.3.0") (org "9.2"))
;; Version: 0.1

;; 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 package renders hackernews website at https://news.ycombinator.com/ in
;; an org buffer. Almost everything works. Features that are not supported are
;; account related features. You cannot add comment, downvote or upvote.

;;; Dependencies
;; `promise' and `request' are required.
;; user must have `org-mode' 9.2 or later installed also.

;;; Commands
;; hnreader-news: Load news page.
;; hnreader-past: Load past page.
;; hnreader-ask: Load ask page.
;; hnreader-show: Load show page.
;; hnreader-more: Load more.
;; hnreader-back: Go back to previous page.

;;; Customization
;; hnreader-history-max: max number history items to remember.

;;; Code:
(require 'promise)
(require 'request)
(require 'shr)
(require 'dom)
(require 'cl-lib)
(require 'org)

;; public variables
(defgroup hnreader nil
  "Search and read stackoverflow and sisters's sites."
  :group 'extensions
  :group 'convenience
  :version "25.1"
  :link '(emacs-commentary-link "hnreader.el"))

(defcustom hnreader-history-max 100
  "Max history to remember."
  :type 'number
  :group 'hnreader)

;; internal stuff
(defvar hnreader--buffer "*HN*"
  "Buffer for HN pages.")

(defvar hnreader--comment-buffer "*HNComments*"
  "Comment buffer.")

(defvar hnreader--indent 40
  "Tab value which is the width of an indent.
top level commnet is 0 indent
second one is 40
third one is 80.")

(defvar hnreader--history '()
  "History list.")

(defvar hnreader--more-link nil
  "Load more link.")

;;;###autoload
(defun hnreader-back ()
  "Go back to previous location in history."
  (let ((link (nth 1 hnreader--history)))
    (if link
        (progn
          (setq hnreader--history (cdr hnreader--history))
          (when (> (length hnreader--history) hnreader-history-max)
            (setq hnreader--history (seq-take hnreader--history hnreader-history-max)))
          (hnreader-read-page-back link))
      (message "Nothing to go back."))))

(defun hnreader--get-hn-buffer ()
  "Get hn buffer."
  (get-buffer-create hnreader--buffer))

(defun hnreader--get-hn-comment-buffer ()
  "Get hn commnet buffer."
  (get-buffer-create hnreader--comment-buffer))

(defun hnreader--promise-dom (url)
  "Promise (url . dom) from URL with curl."
  (promise-new
   (lambda (resolve reject)
     (request url
              :parser (lambda ()
                        (goto-char (point-min))
                        (while (re-search-forward ">\\*" nil t)
                          (replace-match ">-"))
                        (libxml-parse-html-region (point-min) (point-max)))
              :error (cl-function (lambda (&rest args &key error-thrown &allow-other-keys)
                                    (funcall reject  error-thrown)))
              :success (cl-function (lambda (&key data &allow-other-keys)
                                      (funcall resolve data)))))))

(defun hnreader--prepare-buffer (buf &optional msg)
  "Print MSG message and prepare window for BUF buffer."
  (when (not (equal (window-buffer) buf))
    (switch-to-buffer-other-window buf))
  ;; (display-buffer buf '(display-buffer-use-some-window (inhibit-same-window . t))))
  (with-current-buffer buf
    (read-only-mode -1)
    (erase-buffer)
    (insert (if msg
                msg
              "Loading...")))
  buf)

(defun hnreader--print-frontpage-item (thing subtext)
  "Print THING dom and SUBTEXT dom."
  (let ((id (dom-attr thing 'id))
        (story-link (dom-attr (dom-by-class thing "^storylink$") 'href)))
    (insert (format "\n* %s %s (%s) [%s]\n"
                    ;; rank
                    (dom-text (dom-by-class thing "^rank$"))
                    ;; title
                    (dom-text (dom-by-class thing "^storylink$"))
                    ;; points
                    (dom-text (dom-by-class subtext "^score$"))
                    ;; comments
                    (dom-text (last (dom-by-tag subtext 'a)))))
    ;; (setq thanh subtext)
    ;; link
    (insert (format "%s\n[[eww:%s][view story in eww]]\n" story-link story-link))
    ;; comment link
    (insert (format "[[elisp:(hnreader-comment %s)][https://news.ycombinator.com/item?id=%s]]"
                    id
                    id))))

(defun hnreader--get-morelink (dom)
  "Get more link from DOM."
  (let* ((more-link (dom-by-class dom "morelink"))
         (full-more-link (concat "https://news.ycombinator.com/"
                                 (dom-attr more-link 'href))))
    (setq hnreader--more-link full-more-link)
    (format "[[elisp:(hnreader-read-page \"https://news.ycombinator.com/%s\")][More]]"
            full-more-link)))

(defun hnreader--get-time-top-link (node)
  "Get date link in route /past from NODE."
  (let ((a-link (dom-attr (dom-by-tag node 'a) 'href))
        (text (dom-texts node)))
    (format "[[elisp:(hnreader-read-page \"https://news.ycombinator.com/%s\")][%s]]"
            a-link
            text)))

(defun hnreader--past-time-top-links (node-list)
  "Get date, month and year links from NODE-LIST."
  (if (= 3 (length node-list))
      (concat (seq-reduce (lambda (acc it)
                            (concat acc (hnreader--get-time-top-link it) " "))
                          node-list
                          "- Go back to a "))
    (concat (seq-reduce (lambda (acc it)
                          (concat acc (hnreader--get-time-top-link it) " "))
                        (seq-take node-list 3)
                        "- Go back to a ")
            (seq-reduce (lambda (acc it)
                          (concat acc (hnreader--get-time-top-link it) " "))
                        (seq-drop node-list 3)
                        "- Go forward to a "))))

(defun hnreader--get-route-top-info (dom)
  "Get top info of route like title, date of hn routes such as front, past from DOM."
  (let* ((space-page (dom-by-id dom "^pagespace$"))
         (title (dom-attr space-page 'title))
         (hn-more (dom-by-class dom "^hnmore$")))
    (if hn-more
        (format "\n%s %s"
                title
                (hnreader--past-time-top-links hn-more))
      (format "\n%s" title))))

(defun hnreader--print-frontpage (dom buf url)
  "Print raw DOM and URL on BUF."
  (let ((things (dom-by-class dom "^athing$"))
        (subtexts (dom-by-class dom "^subtext$")))
    (with-current-buffer buf
      (read-only-mode -1)
      (erase-buffer)
      (insert "#+STARTUP: overview indent\n")
      (insert (hnreader--get-route-top-info dom))
      (cl-mapcar #'hnreader--print-frontpage-item things subtexts)
      ;; (setq-local org-confirm-elisp-link-function nil)
      (if hnreader--history
          (insert "\n* "(format "[[elisp:(hnreader-back)][< Back]]" ) " | ")
        (insert "\n* "))
      (insert (hnreader--get-morelink dom) " | ")
      (insert (format "[[elisp:(hnreader-read-page-back \"%s\")][Reload]]" url) )
      (org-mode)
      (goto-char (point-min))
      (forward-line 2))))

(defun hnreader--get-title (dom)
  "Get title and link from DOM comment page."
  (let ((a-link (dom-by-class dom "^storylink$")))
    (cons (dom-text a-link) (dom-attr a-link 'href))))

(defun hnreader--get-post-info (dom)
  "Get top info about the DOM comment page."
  (let* ((fat-item (dom-by-class dom "^fatitem$"))
         (user (dom-by-class fat-item "^hnuser$"))
         (score (dom-by-class fat-item "^score$"))
         (tr-tag (dom-by-tag fat-item 'tr))
         (comment-count (last (dom-by-tag (dom-by-class fat-item "^subtext$") 'a)))
         (intro (if (= (length tr-tag) 6)
                    (nth 3 tr-tag)
                  nil)))
    ;; (setq thanh tr-tag)
    ;; (setq thanh-fat fat-item)
    (cons
     (format "%s | by %s | %s\n"
             (dom-text score)
             (dom-text user)
             (dom-text comment-count))
     intro)))

(defun hnreader--print-node (node)
  "Print the NODE with extra options."
  (let ((shr-width 80)
        (shr-use-fonts nil))
    (shr-insert-document node)))

(defun hnreader--print-comments (dom id)
  "Print DOM comment and ID to buffer."
  (let ((comments (dom-by-class  dom "^athing comtr $"))
        (title (hnreader--get-title dom))
        (info (hnreader--get-post-info dom)))
    (with-current-buffer (hnreader--get-hn-comment-buffer)
      (read-only-mode -1)
      (erase-buffer)
      (insert "#+STARTUP: overview indent\n")
      (insert "#+TITLE: " (car title))
      (insert (format "\n%s\n[[eww:%s][view story in eww]]\n" (cdr title) (cdr title)))
      (insert (car info))
      (when (cdr info)
        (insert "\n")
        (hnreader--print-node (cdr info)))
      (dolist (comment comments)
        ;; (setq thanh comment)
        (insert (format "%s %s\n"
                        (hnreader--get-indent
                         (hnreader--get-img-tag-width comment))
                        (hnreader--get-comment-owner comment)))
        (hnreader--print-node (hnreader--get-comment comment)))
      (insert "\n* " (format  "[[elisp:(hnreader-comment %s)][Reload]]" id))
      (org-mode)
      ;; (org-shifttab 3)
      (goto-char (point-min))
      (forward-line 2))))

(defun hnreader--get-img-tag-width (comment-dom)
  "Get width attribute of img tag in COMMENT-DOM."
  (string-to-number
   (dom-attr (dom-by-tag (dom-by-class comment-dom "^ind$") 'img)
             'width)))

(defun hnreader--get-indent (width)
  "Return headline star string from WIDTH of img tag."
  (let ((stars "\n*")) (dotimes (_ (round (/ width hnreader--indent)) stars)
                         (setq stars (concat stars "*")))))

(defun hnreader--get-comment-owner (comment-dom)
  "Return user who wrote this COMMENT-DOM."
  (dom-text (dom-by-class comment-dom "^hnuser$")))

(defun hnreader--get-comment (comment-dom)
  "Get comment dom from COMMENT-DOM."
  (dom-by-class comment-dom "^commtext"))

(defun hnreader-readpage-promise (url)
  "Promise HN URL."
  (hnreader--prepare-buffer (hnreader--get-hn-buffer))
  (promise-chain (hnreader--promise-dom url)
    (then (lambda (result)
            (hnreader--print-frontpage result (hnreader--get-hn-buffer) url)))
    (promise-catch (lambda (reason)
                     (message "catch error in promise prontpage: %s" reason)))))

(defun hnreader-read-page-back (url)
  "Print HN URL page and won't change the history."
  (interactive "sLink: ")
  (hnreader-readpage-promise url)
  nil)

(defun hnreader-read-page (url)
  "Print HN URL page.
Also upate `hnreader--history'."
  (interactive "sLink: ")
  (setq hnreader--history (cons url hnreader--history))
  (hnreader-readpage-promise url)
  nil)

;;;###autoload
(defun hnreader-news()
  "Read front page."
  (interactive)
  (hnreader-read-page "https://news.ycombinator.com/news"))

;;;###autoload
(defun hnreader-past()
  "Read past page."
  (interactive)
  (hnreader-read-page "https://news.ycombinator.com/front"))

;;;###autoload
(defun hnreader-ask ()
  "Read ask page."
  (interactive)
  (hnreader-read-page "https://news.ycombinator.com/ask"))

;;;###autoload
(defun hnreader-show ()
  "Read show page."
  (interactive)
  (hnreader-read-page "https://news.ycombinator.com/show"))

;;;###autoload
(defun hnreader-jobs ()
  "Read jobs page."
  (interactive)
  (hnreader-read-page "https://news.ycombinator.com/jobs"))

;;;###autoload
(defun hnreader-more()
  "Load more."
  (interactive)
  (if hnreader--more-link
      (hnreader-read-page hnreader--more-link)
    (message "no more link.")))

(defun hnreader-promise-comment (comment-id)
  "Promise to print hn COMMENT-ID page to buffer."
  (hnreader--prepare-buffer (hnreader--get-hn-comment-buffer))
  (promise-chain (hnreader--promise-dom (format "https://news.ycombinator.com/item?id=%s" comment-id))
    (then (lambda (dom)
            (hnreader--print-comments dom comment-id)))
    (promise-catch (lambda (reason)
                     (message "catch error in promise comments: %s" reason)))))

(defun hnreader-comment (comment-id)
  "Print hn COMMENT-ID page to buffer."
  (interactive "sComment ID: ")
  (hnreader-promise-comment comment-id)
  nil)

(provide 'hnreader)
;;; hnreader.el ends here