import tempfile


class StoragePaths(object):
  shared_images = 'sharedimages'

  @staticmethod
  def temp_store_handler():
    tmpf = tempfile.TemporaryFile()

    def fn(buf):
      try:
        tmpf.write(buf)
      except IOError:
        pass

    return tmpf, fn

  def image_path(self, storage_uuid):
    return '{0}/{1}/'.format(self.shared_images, storage_uuid)

  def image_json_path(self, storage_uuid):
    base_path = self.image_path(storage_uuid)
    return '{0}json'.format(base_path)

  def image_layer_path(self, storage_uuid):
    base_path = self.image_path(storage_uuid)
    return '{0}layer'.format(base_path)

  def image_ancestry_path(self, storage_uuid):
    base_path = self.image_path(storage_uuid)
    return '{0}ancestry'.format(base_path)

  def image_file_trie_path(self, storage_uuid):
    base_path = self.image_path(storage_uuid)
    return '{0}files.trie'.format(base_path)

  def image_file_diffs_path(self, storage_uuid):
    base_path = self.image_path(storage_uuid)
    return '{0}diffs.json'.format(base_path)


class BaseStorage(StoragePaths):
  """Storage is organized as follow:
  $ROOT/images/<image_id>/json
  $ROOT/images/<image_id>/layer
  $ROOT/repositories/<namespace>/<repository_name>/<tag_name>
  """

  # Useful if we want to change those locations later without rewriting
  # the code which uses Storage
  repositories = 'repositories'
  images = 'images'
  # Set the IO buffer to 64kB
  buffer_size = 64 * 1024

  def setup(self):
    """ Called to perform any storage system setup. """
    pass

  def get_direct_download_url(self, path, expires_in=60, requires_cors=False):
    return None

  def get_direct_upload_url(self, path, mime_type, requires_cors=True):
    return None

  def get_supports_resumable_downloads(self):
    return False

  def get_content(self, path):
    raise NotImplementedError

  def put_content(self, path, content):
    raise NotImplementedError

  def stream_read(self, path):
    raise NotImplementedError

  def stream_read_file(self, path):
    raise NotImplementedError

  def stream_write(self, path, fp, content_type=None, content_encoding=None):
    raise NotImplementedError

  def list_directory(self, path=None):
    raise NotImplementedError

  def exists(self, path):
    raise NotImplementedError

  def remove(self, path):
    raise NotImplementedError

  def get_checksum(self, path):
    raise NotImplementedError


class DigestInvalidException(RuntimeError):
  pass


class BaseStorageV2(BaseStorage):
  def initiate_chunked_upload(self):
    """ Start a new chunked upload, and return a handle with which the upload can be referenced.
    """
    raise NotImplementedError

  def stream_upload_chunk(self, uuid, offset, length, in_fp):
    """ Upload the specified amount of data from the given file pointer to the chunked destination
        specified, starting at the given offset. Returns the number of bytes written.
    """
    raise NotImplementedError

  def complete_chunked_upload(self, uuid, final_path, digest_to_verify):
    """ Complete the chunked upload and store the final results in the path indicated.
    """
    raise NotImplementedError