markdownlint-rule-relative-links/src/index.js

"use strict"

const { pathToFileURL } = require("node:url")
const fs = require("node:fs")

const {
  filterTokens,
  addError,
  convertHeadingToHTMLFragment,
  getMarkdownHeadings,
} = require("./utils.js")

const customRule = {
  names: ["relative-links"],
  description: "Relative links should be valid",
  tags: ["links"],
  function: (params, onError) => {
    filterTokens(params, "inline", (token) => {
      for (const child of token.children) {
        const { lineNumber, type, attrs } = child

        /** @type {string | null} */
        let hrefSrc = null

        if (type === "link_open") {
          for (const attr of attrs) {
            if (attr[0] === "href") {
              hrefSrc = attr[1]
              break
            }
          }
        }

        if (type === "image") {
          for (const attr of attrs) {
            if (attr[0] === "src") {
              hrefSrc = attr[1]
              break
            }
          }
        }

        if (hrefSrc != null) {
          const url = new URL(hrefSrc, pathToFileURL(params.name))
          const isRelative =
            url.protocol === "file:" && !hrefSrc.startsWith("/")
          if (isRelative) {
            const detail = `Link "${hrefSrc}"`

            if (!fs.existsSync(url)) {
              addError(
                onError,
                lineNumber,
                `${detail} should exist in the file system`,
              )
              continue
            }

            if (type === "link_open" && url.hash !== "") {
              const fileContent = fs.readFileSync(url, { encoding: "utf8" })
              const headings = getMarkdownHeadings(fileContent)

              /** @type {Map<string, number>} */
              const fragments = new Map()

              const headingsHTMLFragments = headings.map((heading) => {
                const fragment = convertHeadingToHTMLFragment(heading)
                const count = fragments.get(fragment) ?? 0
                fragments.set(fragment, count + 1)
                if (count !== 0) {
                  return `${fragment}-${count}`
                }
                return fragment
              })

              if (!headingsHTMLFragments.includes(url.hash)) {
                addError(
                  onError,
                  lineNumber,
                  `${detail} should have a valid fragment`,
                )
              }
            }
          }
        }
      }
    })
  },
}

module.exports = customRule