class Bundler::CompactIndexClient::Updater

def checksum_for_file(path)
  return nil unless path.file?
  Digest::MD5.file(path).hexdigest
end

def etag_for(path)
  sum = checksum_for_file(path)
  sum ? '"' << sum << '"' : nil
end

def initialize(fetcher)
  @fetcher = fetcher
end

def update(local_path, remote_path, retrying = nil)
  headers = {}
  if local_path.file?
    headers["If-None-Match"] = etag_for(local_path)
    headers["Range"] = "bytes=#{local_path.size}-"
  else
    # Fastly ignores Range when Accept-Encoding: gzip is set
    headers["Accept-Encoding"] = "gzip"
  end
  response = @fetcher.call(remote_path, headers)
  return if response.is_a?(Net::HTTPNotModified)
  content = response.body
  if response["Content-Encoding"] == "gzip"
    content = Zlib::GzipReader.new(StringIO.new(content)).read
  end
  mode = response.is_a?(Net::HTTPPartialContent) ? "a" : "w"
  local_path.open(mode) {|f| f << content }
  return if etag_for(local_path) == response["ETag"]
  if retrying.nil?
    local_path.delete
    update(local_path, remote_path, :retrying)
  else
    raise MisMatchedChecksumError, "Checksum of /#{remote_path} " \
      "does not match the checksum provided by server! Something is wrong."
  end
end