@jsenv/import-map/src/internal/urlToRelativeUrl.js

Helpers to implement importmaps.

import { getCommonPathname } from "./getCommonPathname.js"
import { pathnameToParentPathname } from "./pathnameToParentPathname.js"

export const urlToRelativeUrl = (urlArg, baseUrlArg) => {
  const url = new URL(urlArg)
  const baseUrl = new URL(baseUrlArg)

  if (url.protocol !== baseUrl.protocol) {
    return urlArg
  }

  if (url.username !== baseUrl.username || url.password !== baseUrl.password) {
    return urlArg.slice(url.protocol.length)
  }

  if (url.host !== baseUrl.host) {
    return urlArg.slice(url.protocol.length)
  }

  const { pathname, hash, search } = url
  if (pathname === "/") {
    return baseUrl.pathname.slice(1)
  }

  const { pathname: basePathname } = baseUrl

  const commonPathname = getCommonPathname(pathname, basePathname)
  if (!commonPathname) {
    return urlArg
  }

  const specificPathname = pathname.slice(commonPathname.length)
  const baseSpecificPathname = basePathname.slice(commonPathname.length)
  if (baseSpecificPathname.includes("/")) {
    const baseSpecificParentPathname = pathnameToParentPathname(baseSpecificPathname)
    const relativeDirectoriesNotation = baseSpecificParentPathname.replace(/.*?\//g, "../")
    return `${relativeDirectoriesNotation}${specificPathname}${search}${hash}`
  }
  return `${specificPathname}${search}${hash}`
}