怎样把 MediaWiki 的 wikitext 转换为 GitHub 风格的 markdown

想把本站内容发布到微信公众号，复制 wikitext 过去手动编辑，肯定是麻烦的。只有寻求 wikitext 到微信公众号的自动化方法。本文提供一个简明的 wikitext 转 markdown 工具，需要在 Emacs 中使用。

1. wikitext 直达微信公众平台，此路人少，难以走通
2. markdown 直达微信公众平台，此路人多，很易走通

问题于是变成，怎样让 wikitext 较为完美地转换为 markdown。试过 pandoc，不太靠谱。在 ChatGPT 的帮助下，自己写了一个。

以上转换规则，果断放弃了表格转换，因为表格太费事了，复杂度逆天，不如直接放截图。果断放弃了图片地址转换，因为辛苦找图床，不如直接单独另传至微信公众号后台图床。把有序列表 # 转换为 *，是因为 # 在 markdown 里被当成一级标题，肯定不符合我们的意图；而把它转换为 *，是因为偷懒，挨个加数字序号可不是我有耐心去干的，干脆有序变无序。至于无序列表 *、预设格式 pre，wikitext 与 markdown 里两边相同，所以不需要理它们。

;; wikitext -> gfm converter
;;
;; 设计原则：
;; 1 所有规则按顺序执行
;; 2 每条规则对应一段代码
;; 3 不做抽象，优先可读性
;;
;; 规则：
;; 1 <code> 和 </code> -> ```
;; 2 <syntaxhighlight> -> ```
;; 3 # -> *
;; 4 ====== -> ######
;; 5 ===== -> #####
;; 6 ==== -> ####
;; 7 === -> ###
;; 8 == -> ##
;; 9 <del> -> ~~
;; 10 ---- -> ---

(defun wikitext-convert-all (&optional start end)
  "Convert simple wikitext to GFM markdown."

  (interactive
   (if (use-region-p)
       (list (region-beginning) (region-end))
     (list (point-min) (point-max))))

  (save-excursion
    (save-restriction
      (narrow-to-region start end)

      ;; --------------------------------------------------
      ;; 1. inline <code>
      ;; --------------------------------------------------

      (goto-char (point-min))
      (while (re-search-forward "<code>\\([^<\n]*\\)</code>" nil t)
        (replace-match (concat "`" (match-string 1) "`") t t))

      (goto-char (point-min))
      (while (re-search-forward "<code>" nil t)
        (replace-match "`"))

      (goto-char (point-min))
      (while (re-search-forward "</code>" nil t)
        (replace-match "`"))

      ;; --------------------------------------------------
      ;; 2. syntaxhighlight
      ;; --------------------------------------------------

      (goto-char (point-min))
      (while (re-search-forward "<syntaxhighlight\\s-+lang=[\"']\\([^\"']+\\)[\"'][^>]*>" nil t)
        (replace-match (concat "```" (match-string 1)) t t))

      (goto-char (point-min))
      (while (re-search-forward "</syntaxhighlight>" nil t)
        (replace-match "```"))

      ;; --------------------------------------------------
      ;; 3. 列表 # → *
      ;; --------------------------------------------------

      (let ((in-code-block nil))
        (goto-char (point-min))
        (while (not (eobp))

          (let ((line (thing-at-point 'line t)))

            (when (string-match "^```" line)
              (setq in-code-block (not in-code-block)))

            (unless in-code-block
              (beginning-of-line)
              (while (search-forward "#" (line-end-position) t)
                (replace-match "*"))))

          (forward-line 1)))

      ;; --------------------------------------------------
      ;; 4. headings
      ;; --------------------------------------------------

      (dolist (n '(6 5 4 3 2))
        (goto-char (point-min))
        (let ((pat (format "^=\\{%d\\}[ \t]*\\(.*?\\S-\\)[ \t]*=\\{%d\\}[ \t]*$" n n))
              (rep (concat (make-string n ?#) " \\1")))
          (while (re-search-forward pat nil t)
            (replace-match rep))))

      ;; --------------------------------------------------
      ;; 5. other
      ;; --------------------------------------------------

      (goto-char (point-min))
      (while (re-search-forward "<del>" nil t)
        (replace-match "~~"))

      (goto-char (point-min))
      (while (re-search-forward "</del>" nil t)
        (replace-match "~~"))

      (goto-char (point-min))
      (while (re-search-forward "^----[ \t]*$" nil t)
        (replace-match "---"))

      (widen))))