;;; sx-question-list.el --- Major-mode for navigating questions list.  -*- lexical-binding: t; -*-

;; Copyright (C) 2014  Artur Malabarba

;; Author: Artur Malabarba <bruce.connor.am@gmail.com>

;; 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:

;;; Code:
(require 'tabulated-list)
(require 'cl-lib)

(require 'sx)
(require 'sx-time)
(require 'sx-site)
(require 'sx-question)
(require 'sx-question-mode)
(require 'sx-favorites)


;;; Customization
(defcustom sx-question-list-height 12
  "Height, in lines, of stack-mode's *question-list* buffer."
  :type 'integer
  :group 'sx-question-list)

(defface sx-question-list-parent
  '((t :inherit default))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-answers
  '((((background light)) :foreground "SeaGreen4"
     :height 1.0 :inherit sx-question-list-parent)
    (((background dark))  :foreground "#D1FA71"
     :height 1.0 :inherit sx-question-list-parent)
    (t :inherit sx-question-list-parent))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-answers-accepted
  '((t :underline t :overline t :inherit sx-question-list-answers))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-score
  '((t :height 1.0 :inherit sx-question-list-parent))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-score-upvoted
  '((t :weight bold
       :inherit sx-question-list-score))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-tags
  '((t :inherit sx-question-mode-tags))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-date
  '((t :inherit font-lock-comment-face))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-read-question
  '((t :height 1.0 :inherit sx-question-list-parent))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-unread-question
  '((t :weight bold :inherit sx-question-list-read-question))
  ""
  :group 'sx-question-list-faces)

(defface sx-question-list-favorite
  '((t :inherit sx-question-list-score-upvoted))
  ""
  :group 'sx-question-list-faces)


;;; Mode Definition
(define-derived-mode sx-question-list-mode tabulated-list-mode "Question List"
  "Major mode for browsing a list of questions from StackExchange.
Letters do not insert themselves; instead, they are commands.
\\<sx-question-list>
\\{sx-question-list}"
  (hl-line-mode 1)
  (sx-question-list--update-mode-line)
  (setq tabulated-list-format
        [("  V" 3 t :right-align t)
         ("  A" 3 t :right-align t)
         ("Title" 0 sx-question-list--date-more-recent-p)])
  (setq tabulated-list-padding 1)
  ;; Sorting by title actually sorts by date. It's what we want, but
  ;; it's not terribly intuitive.
  (setq tabulated-list-sort-key '("Title" . nil))
  (add-hook 'tabulated-list-revert-hook
            #'sx-question-list-refresh nil t)
  (add-hook 'tabulated-list-revert-hook
            #'sx-question-list--update-mode-line nil t)
  (tabulated-list-init-header))

(defcustom sx-question-list-date-sort-method 'last_activity_date
  "Parameter which controls date sorting."
  ;; This should be made into a (choice ...) of constants.
  :type 'symbol
  ;; Add a setter to protect the value.
  :group 'sx-question-list)

(defun sx-question-list--date-more-recent-p (x y)
  "Non-nil if tabulated-entry X is newer than Y."
  (sx--<
   sx-question-list-date-sort-method
   (car x) (car y) #'>))

(mapc
 (lambda (x) (define-key sx-question-list-mode-map
          (car x) (cadr x)))
 '(("n" sx-question-list-next)
   ("p" sx-question-list-previous)
   ("j" sx-question-list-view-next)
   ("k" sx-question-list-view-previous)
   ("g" sx-question-list-refresh)
   (":" sx-question-list-switch-site)
   ("v" sx-question-list-visit)
   ("h" sx-question-list-hide)
   ("m" sx-question-list-mark-read)
   ([?\r] sx-question-list-display-question)))

(defun sx-question-list-hide (data)
  "Hide question under point.
Non-interactively, DATA is a question alist."
  (interactive
   (list (if (derived-mode-p 'sx-question-list-mode)
             (tabulated-list-get-id)
           (user-error "Not in `sx-question-list-mode'"))))
  (sx-question--mark-hidden data)
  (when (called-interactively-p 'any)
    (sx-question-list-refresh 'redisplay 'noupdate)))

(defun sx-question-list-mark-read (data)
  "Mark as read question under point.
Non-interactively, DATA is a question alist."
  (interactive
   (list (if (derived-mode-p 'sx-question-list-mode)
             (tabulated-list-get-id)
           (user-error "Not in `sx-question-list-mode'"))))
  (sx-question--mark-read data)
  (sx-question-list-next 1)
  (when (called-interactively-p 'any)
    (sx-question-list-refresh 'redisplay 'noupdate)))

(defvar sx-question-list--current-page "Latest"
  ;; @TODO Other values (once we implement them) are "Top Voted",
  ;; "Unanswered", etc.
  "Variable describing current page being viewed.")

(defvar sx-question-list--unread-count 0
  "Holds the number of unread questions in the current buffer.")
(make-variable-buffer-local 'sx-question-list--unread-count)

(defvar sx-question-list--total-count 0
  "Holds the total number of questions in the current buffer.")
(make-variable-buffer-local 'sx-question-list--total-count)

(defconst sx-question-list--mode-line-format
  '("  "
    mode-name
    " "
    (:propertize sx-question-list--current-page
                 face mode-line-buffer-id)
    " ["
    "Unread: "
    (:propertize
     (:eval (int-to-string sx-question-list--unread-count))
     face mode-line-buffer-id)
    ", "
    "Total: "
    (:propertize
     (:eval (int-to-string sx-question-list--total-count))
     face mode-line-buffer-id)
    "] ")
  "Mode-line construct to use in question-list buffers.")

(defun sx-question-list--update-mode-line ()
  "Fill the mode-line with useful information."
  ;; All the data we need is right in the buffer.
  (when (derived-mode-p 'sx-question-list-mode)
    (setq mode-line-format
          sx-question-list--mode-line-format)
    (setq sx-question-list--total-count
          (length tabulated-list-entries))))

(defvar sx-question-list--current-site "emacs"
  "Site being displayed in the *question-list* buffer.")

(defvar sx-question-list--current-dataset nil
  "The logical data behind the displayed list of questions.
This dataset contains even questions that are hidden by the user,
and thus not displayed in the list of questions.")

(defun sx-question-list-refresh (&optional redisplay no-update)
  "Update the list of questions.
If REDISPLAY is non-nil (or if interactive), also call `tabulated-list-print'.
If the prefix argument NO-UPDATE is nil, query StackExchange for
a new list before redisplaying."
  (interactive "p\nP")
  ;; Reset the mode-line unread count (we rebuild it here).
  (setq sx-question-list--unread-count 0)
  (let ((question-list
         (if (and no-update sx-question-list--current-dataset)
             sx-question-list--current-dataset
           (sx-question-get-questions
            sx-question-list--current-site))))
    (setq sx-question-list--current-dataset question-list)
    ;; Print the result.
    (setq tabulated-list-entries
          (mapcar #'sx-question-list--print-info
                  (cl-remove-if #'sx-question--hidden-p question-list))))
  (when redisplay (tabulated-list-print 'remember)))

(defun sx-question-list-visit (&optional data)
  "Visits question under point (or from DATA) using `browse-url'."
  (interactive)
  (unless data (setq data (tabulated-list-get-id)))
  (unless data (error "No question here!"))
  (sx-assoc-let data
    (browse-url .link))
  (sx-question--mark-read data)
  (sx-question-list-refresh 'redisplay 'no-update))

(defcustom sx-question-list-ago-string " ago"
  "String appended to descriptions of the time since something happened.
Used in the questions list to indicate a question was updated
\"4d ago\"."
  :type 'string
  :group 'sx-question-list)

(defun sx-question-list--print-info (question-data)
  "Convert `json-read' QUESTION-DATA into tabulated-list format.
See `sx-question-list-refresh'."
  (sx-assoc-let question-data
    (let ((favorite (if (member .question_id
                                (assoc .site
                                       sx-favorites--user-favorite-list))
                        (if (char-displayable-p ?\x2b26) "\x2b26" "*") " ")))
      (list
       question-data
       (vector
        (list (int-to-string .score)
              'face (if .upvoted 'sx-question-list-score-upvoted
                      'sx-question-list-score))
        (list (int-to-string .answer_count)
              'face (if (sx-question--accepted-answer-id question-data)
                        'sx-question-list-answers-accepted
                      'sx-question-list-answers))
        (concat
         (propertize
          .title
          'face (if (sx-question--read-p question-data)
                    'sx-question-list-read-question
                  ;; Increment `sx-question-list--unread-count' for
                  ;; the mode-line.
                  (cl-incf sx-question-list--unread-count)
                  'sx-question-list-unread-question))
         (propertize " " 'display "\n   ")
         (propertize favorite 'face 'sx-question-list-favorite)
         "     "
         (propertize (concat (sx-time-since .last_activity_date)
                             sx-question-list-ago-string)
                     'face 'sx-question-list-date)
         " "
         (propertize (mapconcat #'sx-question--tag-format .tags " ")
                     'face 'sx-question-list-tags)
         (propertize " " 'display "\n")))))))

(defun sx-question-list-view-previous (n)
  "Move cursor up N questions up and display this question.
Displayed in `sx-question-mode--window', replacing any question
that may currently be there."
  (interactive "p")
  (sx-question-list-view-next (- n)))

(defun sx-question-list-view-next (n)
  "Move cursor down N questions and display this question.
Displayed in `sx-question-mode--window', replacing any question
that may currently be there."
  (interactive "p")
  (sx-question-list-next n)
  (sx-question-list-display-question))

(defun sx-question-list-next (n)
  "Move cursor down N questions.
This does not update `sx-question-mode--window'."
  (interactive "p")
  (forward-line n))

(defun sx-question-list-previous (n)
  "Move cursor up N questions.
This does not update `sx-question-mode--window'."
  (interactive "p")
  (sx-question-list-next (- n)))

(defun sx-question-list-display-question (&optional data focus)
  "Display question given by DATA.
When DATA is nil, display question under point.  When FOCUS is
non-nil (the default when called interactively), also focus the
relevant window."
  (interactive '(nil t))
  (unless data (setq data (tabulated-list-get-id)))
  (unless data (error "No question here!"))
  (unless (sx-question--read-p data)
    (cl-decf sx-question-list--unread-count)
    (sx-question--mark-read data)
    (sx-question-list-refresh 'redisplay 'no-update))
  (unless (and (window-live-p sx-question-mode--window)
               (null (equal sx-question-mode--window (selected-window))))
    (setq sx-question-mode--window
          (condition-case er
              (split-window (selected-window) sx-question-list-height 'below)
            (error
             ;; If the window is too small to split, use current one.
             (if (string-match
                  "Window #<window .*> too small for splitting"
                  (car (cdr-safe er)))
                 nil
               (error (cdr er)))))))
  ;; Display the question.
  (sx-question-mode--display data sx-question-mode--window)
  ;; Configure the window to be closed on `q'.
  (set-window-prev-buffers sx-question-mode--window nil)
  (set-window-parameter
   sx-question-mode--window
   'quit-restore
   ;; See (info "(elisp) Window Parameters")
   `(window window ,(selected-window) ,sx-question-mode--buffer))
  (when focus
    (if sx-question-mode--window
        (select-window sx-question-mode--window)
      (switch-to-buffer sx-question-mode--buffer))))

(defun sx-question-list-switch-site (site)
  "Switch the current site to SITE and display its questions.
Uses `ido-completing-read' if variable `ido-mode' is active.  Retrieves
completions from `sx-site-get-api-tokens'.  Sets
`sx-question-list--current-site' and then
`sx-question-list-refresh' with `redisplay'."
  (interactive
   (list (funcall (if ido-mode #'ido-completing-read #'completing-read)
          "Switch to site: " (sx-site-get-api-tokens)
          (lambda (site)
            (not (equal site sx-question-list--current-site)))
          t)))
  (setq sx-question-list--current-site site)
  (sx-question-list-refresh 'redisplay))

(defvar sx-question-list--buffer nil
  "Buffer where the list of questions is displayed.")

(defun list-questions (no-update)
  "Display a list of StackExchange questions.
NO-UPDATE is passed to `sx-question-list-refresh'."
  (interactive "P")
  (sx-initialize)
  (unless (buffer-live-p sx-question-list--buffer)
    (setq sx-question-list--buffer
          (generate-new-buffer "*question-list*")))
  (with-current-buffer sx-question-list--buffer
    (sx-question-list-mode)
    (sx-question-list-refresh 'redisplay no-update))
  (switch-to-buffer sx-question-list--buffer))

(defalias 'sx-list-questions #'list-questions)

(provide 'sx-question-list)
;;; sx-question-list.el ends here