;;; wiki-engine.el -- client to wiki engines -*- lexical-binding: t -*-

;; Copyright (C) 2023  Free Software Foundation, Inc.

;; Author: Yuchen Pei <id@ypei.org>

;; This file is part of wiki.el.

;; wiki.el is free software: you can redistribute it and/or modify it under
;; the terms of the GNU Affero General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; wiki.el 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 Affero General
;; Public License for more details.

;; You should have received a copy of the GNU Affero General Public
;; License along with wiki.el.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; client to wiki engines, wiki server software. Each engine defines
;; how Emacs interacts with the remote server, including how to
;; construct a url to fetch from.

;;; Code:
(require 'wiki-utils)
(require 'wiki-markup)

;; TODO: make this a defcustom
(defvar wiki-default-engine 'mediawiki
  "The default wiki engine, when one is not supplied.")

(defun wiki-engine-html-url (site title)
  "Return the url of the html webpage of TITLE on SITE."
  (format "%s%s" (plist-get (alist-get site wiki-sites) :base-url)
          title))

(defun wiki-current-html-url ()
  "Return the url of the html webpage of the current wiki buffer."
  (unless (and wiki-site wiki-title)
    (error "Nil wiki-site or wiki-title!"))
  (wiki-engine-html-url wiki-site wiki-title))

(defun wiki-fetch-url (url title &optional dir callback)
  "Fetch URL asynchronously to a file in DIR.

Then call CALLBACK which is a closure taking no argument.

A non-nil TITLE overrides title inferred from the url."
  (let ((cb (lambda (status)
              (wiki-save-fetched-and-switch status title dir)
              (when callback (funcall callback)))))
    (url-retrieve url cb))
  )

(defun wiki-save-string-and-switch (to-insert title dir)
  "Insert string TO-INSERT to TITLE under DIR and switch to buffer."
  (let ((buffer (wiki-find-file title dir t))
        (coding-system-for-write 'utf-8))
    (with-current-buffer buffer
      (insert to-insert)
      (goto-char (point-min))
      (save-buffer)
      (revert-buffer t t))
    (switch-to-buffer buffer)))

(defun wiki-save-fetched-and-switch (status title dir)
  "If STATUS is ok, insert response payload to TITLE under DIR.

And switch to the corresponding buffer."
  (when (plist-get status :error)
    (error "Wiki fetch failed: %s" (plist-get status :error)))
  (wiki-delete-http-header)
  (let ((to-insert (buffer-string))
        (_ (kill-buffer)))
    (wiki-save-string-and-switch to-insert title dir)))

(defun wiki-compute-engine (site-info)
  "Return :engine of SITE-INFO, or the default engine."
  (or (plist-get site-info :engine) wiki-default-engine))

(defun wiki-engine-wiki-url (site title)
  "Construct the url to fetch wiki of TITLE from SITE."
  (let* ((site-info (alist-get site wiki-sites))
         (engine (wiki-compute-engine site-info))
         (base-url (plist-get site-info :base-url)))
    (pcase engine
      ('mediawiki (format "%s%s?action=raw" base-url title))
      ('moinmoin (format "%s%s?action=raw" base-url title))
      ('oddmuse (format "%s?action=download;id=%s" base-url title))
      (_ (error "Unknown engine: %s" engine)))))

(defun wiki-engine-simple-fetch (site-id title)
  "A simple method to fetch TITLE from site with SITE-ID.

If the site has a `local' engine, \"fetch\" locally. Otherwise,
if `wiki-fetch-prefer-local' is non-nil, try fetching locally,
and if the title cannot be found locally, fetch remotely."
  (when (string-empty-p title) (setq title "Main Page"))
  (let* ((engine (wiki-compute-engine (alist-get site-id wiki-sites)))
         (found-local
          (when (or wiki-fetch-prefer-local (eq engine 'local))
            (wiki-find-file title (wiki-locate-dir site-id)
                            (eq engine 'local)))))
    (if found-local
        (switch-to-buffer found-local)
      (wiki-fetch-url
       (wiki-engine-wiki-url site-id title)
       title
       (wiki-locate-dir site-id)
       (lambda ()
         (wiki-mode)
         (setq-local wiki-site site-id
                     wiki-title title))))))

(defun wiki-engine-mediawiki-api-wiki (base-url title)
  (wiki-url-fetch-json
   (format
    "%sapi.php?action=query&format=json&titles=%s&prop=revisions&rvprop=content&rvslots=main"
    base-url title)))

(defun wiki-engine-mediawiki-api-fetch (site-id title)
  "Fetch TITLE from site with SITE-ID using mediawiki api."
  (when (string-empty-p title) (setq title "Main Page"))
  (let* ((engine (wiki-compute-engine (alist-get site-id wiki-sites)))
         (base-url (plist-get (alist-get site-id wiki-sites) :base-url))
         (found-local
          (when (or wiki-fetch-prefer-local (eq engine 'local))
            (wiki-find-file title (wiki-locate-dir site-id)
                            (eq engine 'local)))))
    (if found-local
        (switch-to-buffer found-local)
      (wiki-save-string-and-switch
       (alist-get
        '* (alist-get
            'main (alist-get
                   'slots (elt
                           (alist-get
                            'revisions
                            (cdr
                             (car
                              (alist-get
                               'pages (alist-get
                                       'query
                                       (wiki-url-fetch-json
                                        (wiki-engine-mediawiki-api-wiki
                                         base-url title)
                                        ))))))
                           0))))
       title
       (wiki-locate-dir site-id))
      (wiki-mode)
      (setq-local wiki-site site-id
                  wiki-title title))))

(defun wiki-locate-dir (site-id)
  "Locate the directory for a SITE-ID."
  (expand-file-name (format "%s" site-id) wiki-local-dir))

(defun wiki-find-file (title &optional dir create-if-not-exists)
  "Find local TITLE in DIR. Do not switch to buffer.

Return the buffer if success, and nil otherwise. If
CREATE-IF-NOT-EXISTS is non-nil, creates the file is not found.
DIR defaults to `default-directory'."
  (interactive (list (read-file-name "Find wiki file: ")))
  (unless dir (setq dir default-directory))
  (let ((file-name (expand-file-name
                    (concat title wiki-extension)
                    dir)))
    (when (or (file-exists-p file-name) create-if-not-exists)
      (setq dir (file-name-directory file-name))
      (unless (file-exists-p dir) (make-directory dir t))
      (with-current-buffer (find-file-noselect file-name)
        (wiki-mode)
        (buffer-name)))))

(defmacro defun-wiki-fetchers ()
  "Defines all wiki fetcher functions."
  (cons 'progn
        (mapcar
         (lambda (pair)
           (pcase-let ((`(,id . ,info) pair))
             (let ((engine-fetcher
                    (or (plist-get info :fetcher)
                        'wiki-engine-simple-fetch)))
               `(defun ,(wiki-site-fetcher id) (title)
                  (interactive ,(format "sFetch title for %s: "
                                        (plist-get info :display-name)))
                  (,engine-fetcher ',id title)))))
         (seq-filter #'cdr wiki-sites)
         )))

(defun-wiki-fetchers)

(defun wiki-open-url (url)
  "Open the raw wiki corresponding to the URL of a html wiki page.

If URL points to html title, open the corresponding raw title."
  (interactive "sURL: ")
  (when-let
      ((found-site
        (seq-find
         (lambda (site-pair)
           (when-let ((base-url (plist-get (cdr site-pair) :base-url)))
             (string-prefix-p base-url url)))
         wiki-sites)))
    (pcase-let ((`(,site-id . ,site-info) found-site))
      (funcall (wiki-site-fetcher site-id)
               (string-remove-prefix (plist-get site-info :base-url) url))))
  )

(provide 'wiki-engine)
;;; wiki-engine.el ends here