function* parseMetadata(metadata) {
  for (const [key, entry] of Object.entries(metadata)) {
    entry.textUris = entry.formaturi
      .filter(uri => extensionIn(uri, ['.txt', '.utf-8']))
      .map(stripPGHost)
    entry.pictures = entry.formaturi
      .filter(uri => extensionIn(uri, ['.jpg', 'png']))
      .map(stripPGHost)
    delete entry.formaturi
    entry.id = key
    yield entry
  }
}

function extensionIn(path, endings) {
  return endings.some(ending => path.endsWith(ending))
}
function stripPGHost(uri) {
  return uri.replace('http://www.gutenberg.org', '')
}

module.exports = { parseMetadata }