markdown-it-replace-link.mts

import path from "path"
import type Md from "markdown-it"
import type Token from "markdown-it/lib/token"

export default (md: Md, options: { baseUrl: string; root: string }): void => {
  const base = options.baseUrl
  const root = path.resolve(options.root)

  /** Normalize href */
  function normalizeHref(curr: string, href: string) {
    let absolutePath
    let hash = ""
    if (/\.md(?:#.*)?$/.test(href)) {
      hash = /\.md(#.*)?$/.exec(href)![1] || ""
      absolutePath = path.join(
        path.dirname(curr),
        hash ? href.slice(0, -hash.length) : href,
      )
    } else {
      // hash only
      absolutePath = curr
      hash = href
    }

    return `${base}/${path
      .relative(root, absolutePath)
      .replace(/README\.md$/, "")
      .replace(/\.md$/, "")}/${hash}`
      .replace(/\\/gu, "/")
      .replace(/\/+/gu, "/")
  }

  md.renderer.rules.link_open = (tokens, idx, options, env, self) => {
    const token = tokens[idx]
    const hrefIndex = token.attrIndex("href")
    if (hrefIndex >= 0) {
      const link = token.attrs![hrefIndex]
      const href = link[1]
      if (/^https?:/.test(href)) {
        const proxyToken = {
          ...token,
          attrs: [
            ...token.attrs!,
            ["target", "_blank"],
            ["rel", "noopener noreferrer"],
          ],
        } as Token
        return self.renderToken([proxyToken], 0, options)
      } else if (/\.md(?:#.*)?$/.test(href) || /^#.*$/.test(href)) {
        const proxyToken = {
          ...token,
          attrs: [
            ...token.attrs!.slice(0, hrefIndex - 1),
            [link[0], normalizeHref(env.id, href)],
            ...token.attrs!.slice(hrefIndex + 1),
          ],
        } as Token
        return self.renderToken([proxyToken], 0, options)
      }
    }
    return self.renderToken(tokens, idx, options)
  }
}