function parseMetadata (metadata) {
  // 1. Let result be the empty set.
  /** @type {{ algo: string, hash: string }[]} */
  const result = []

  // 2. Let empty be equal to true.
  let empty = true

  // 3. For each token returned by splitting metadata on spaces:
  for (const token of metadata.split(' ')) {
    // 1. Set empty to false.
    empty = false

    // 2. Parse token as a hash-with-options.
    const parsedToken = parseHashWithOptions.exec(token)

    // 3. If token does not parse, continue to the next token.
    if (
      parsedToken === null ||
      parsedToken.groups === undefined ||
      parsedToken.groups.algo === undefined
    ) {
      // Note: Chromium blocks the request at this point, but Firefox
      // gives a warning that an invalid integrity was given. The
      // correct behavior is to ignore these, and subsequently not
      // check the integrity of the resource.
      continue
    }

    // 4. Let algorithm be the hash-algo component of token.
    const algorithm = parsedToken.groups.algo.toLowerCase()

    // 5. If algorithm is a hash function recognized by the user
    //    agent, add the parsed token to result.
    if (supportedHashes.includes(algorithm)) {
      result.push(parsedToken.groups)
    }
  }

  // 4. Return no metadata if empty is true, otherwise return result.
  if (empty === true) {
    return 'no metadata'
  }

  return result
}
@see https://w3c.github.io/webappsec-subresource-integrity/#parse-metadata
@param {string} metadata