Function rewriteUrls

packages/@tailwindcss-node/src/urls.ts:37–93

({
  css,
  base,
  root,
}: {
  css: string
  base: string
  root: string
})

}

export async function rewriteUrls({
  css,
  base,
  root,
}: {
  css: string
  base: string
  root: string
}) {
  if (!css.includes('url(') && !css.includes('image-set(')) {
    return css
  }

  let ast = parse(css)

  let promises: Promise<void>[] = []

  function replacerForDeclaration(url: string) {
    if (url[0] === '/') return url

    let absoluteUrl = path.posix.join(normalizePath(base), url)
    let relativeUrl = path.posix.relative(normalizePath(root), absoluteUrl)

    // If the path points to a file in the same directory, `path.relative` will
    // remove the leading `./` and we need to add it back in order to still
    // consider the path relative
    if (!relativeUrl.startsWith('.')) {
      relativeUrl = './' + relativeUrl
    }

    return relativeUrl
  }

  walk(ast, (node) => {
    if (node.kind !== 'declaration') return
    if (!node.value) return

    let isCssUrl = cssUrlRE.test(node.value)
    let isCssImageSet = cssImageSetRE.test(node.value)

    if (isCssUrl || isCssImageSet) {
      let rewriterToUse = isCssImageSet ? rewriteCssImageSet : rewriteCssUrls

      promises.push(
        rewriterToUse(node.value, replacerForDeclaration).then((url) => {
          node.value = url
        }),
      )
    }
  })

  if (promises.length) {
    await Promise.all(promises)
  }

  return toCss(ast)
}