import json
import tarfile

from cachetools import lru_cache
from io import BytesIO

from image.docker.interfaces import ContentRetriever

class ContentRetrieverForTesting(ContentRetriever):
  def __init__(self, digests=None):
    self.digests = digests or {}

  def add_digest(self, digest, content):
    self.digests[digest] = content

  def get_manifest_bytes_with_digest(self, digest):
    return self.digests.get(digest)

  def get_blob_bytes_with_digest(self, digest):
    return self.digests.get(digest)

  @classmethod
  def for_config(cls, config_obj, digest, size):
    config_str = json.dumps(config_obj)
    padded_string = config_str + ' ' * (size - len(config_str))
    digests = {}
    digests[digest] = padded_string
    return ContentRetrieverForTesting(digests)


@lru_cache(maxsize=1)
def generate_empty_layer_data():
  """ Generates the layer data for an "empty" layer. """
  with BytesIO() as f:
    tar_file = tarfile.open(fileobj=f, mode='w|gw')
    tar_file.close()
    return f.getvalue()