class Inspec::TarProvider

def initialize(path)
  @path = path
  @contents = {}
  @files = []
  walk_tar(@path) do |tar|
    @files = tar.find_all(&:file?)
    # delete all entries with no name
    @files = @files.find_all { |x| !x.full_name.empty? }
    # delete all entries that have a PaxHeader
    @files = @files.delete_if { |x| x.full_name.include?('PaxHeader/') }
    # replace all items of the array simply with the relative filename of the file
    @files.map! { |x| Pathname.new(x.full_name).relative_path_from(Pathname.new('.')).to_s }
  end
end

def read(file)
  @contents[file] ||= read_from_tar(file)
end

def read_from_tar(file)
  return nil unless @files.include?(file)
  res = nil
  # NB `TarReader` includes `Enumerable` beginning with Ruby 2.x
  walk_tar(@path) do |tar|
    tar.each do |entry|
      next unless entry.file? && [file, "./#{file}"].include?(entry.full_name)
      res = entry.read
      break
    end
  end
  res
end

def walk_tar(path, &callback)
  Gem::Package::TarReader.new(Zlib::GzipReader.open(path), &callback)
end