import tarfile
from util.registry.gzipwrap import GzipWrap


class TarImageFormatter(object):
  """
  Base class for classes which produce a tar containing image and layer data.
  """

  def build_stream(self, namespace, repository, tag, repo_image, synthetic_image_id,
                   get_image_iterator, get_layer_iterator):
    """
    Builds and streams a synthetic .tar.gz that represents the formatted tar created by this class's
    implementation.
    """
    return GzipWrap(self.stream_generator(namespace, repository, tag, repo_image,
                                          synthetic_image_id, get_image_iterator,
                                          get_layer_iterator))

  def stream_generator(self, namespace, repository, tag, repo_image, synthetic_image_id,
                       get_image_iterator, get_layer_iterator):
    raise NotImplementedError

  def tar_file(self, name, contents, mtime=None):
    """
    Returns the tar binary representation for a file with the given name and file contents.
    """
    length = len(contents)
    tar_data = self.tar_file_header(name, length, mtime=mtime)
    tar_data += contents
    tar_data += self.tar_file_padding(length)
    return tar_data

  def tar_file_padding(self, length):
    """
    Returns tar file padding for file data of the given length.
    """
    if length % 512 != 0:
      return '\0' * (512 - (length % 512))

    return ''

  def tar_file_header(self, name, file_size, mtime=None):
    """
    Returns tar file header data for a file with the given name and size.
    """
    info = tarfile.TarInfo(name=name)
    info.type = tarfile.REGTYPE
    info.size = file_size

    if mtime is not None:
      info.mtime = mtime
    return info.tobuf()

  def tar_folder(self, name, mtime=None):
    """
    Returns tar file header data for a folder with the given name.
    """
    info = tarfile.TarInfo(name=name)
    info.type = tarfile.DIRTYPE

    if mtime is not None:
      info.mtime = mtime

    # allow the directory to be readable by non-root users
    info.mode = 0755
    return info.tobuf()