getEntryIndices = (entries) => {
  const indices = entries.reduce((result, entry) => {
    const firstFile = entry.files[0]
    const index = firstFile.index
    if (!result.includes(index)) {
      result.push(index)
    }
    return result
  }, [])

  return indices
}
@param {object} entries
@returns {string[]} Indices