import hashlib
import logging
import tarfile


TarError = tarfile.TarError
logger = logging.getLogger(__name__)


def sha256_file(fp, data=None):
  h = hashlib.sha256(data or '')
  if not fp:
    return h.hexdigest()
  while True:
    buf = fp.read(4096)
    if not buf:
      break
    h.update(buf)
  return h.hexdigest()


def sha256_string(s):
  return hashlib.sha256(s).hexdigest()


def compute_tarsum(fp, json_data):
  header_fields = ('name', 'mode', 'uid', 'gid', 'size', 'mtime',
                   'type', 'linkname', 'uname', 'gname', 'devmajor',
                   'devminor')
  tar = None
  hashes = []
  try:
    tar = tarfile.open(mode='r|*', fileobj=fp)
    for member in tar:
      header = ''
      for field in header_fields:
        value = getattr(member, field)
        if field == 'type':
          field = 'typeflag'
        elif field == 'name':
          if member.isdir() and not value.endswith('/'):
            value += '/'
        header += '{0}{1}'.format(field, value)
      h = None
      try:
        if member.size > 0:
          f = tar.extractfile(member)
          h = sha256_file(f, header)
        else:
          h = sha256_string(header)
      except KeyError:
        h = sha256_string(header)
      hashes.append(h)
    hashes.sort()
  except tarfile.ReadError as e:
    if e.message != 'empty file':
      # NOTE(samalba): ignore empty tarfiles but still let the tarsum
      # compute with json data
      raise
  finally:
    if tar:
      tar.close()
  data = json_data + ''.join(hashes)
  tarsum = 'tarsum+sha256:{0}'.format(sha256_string(data))
  logger.debug('checksums.compute_tarsum: return %s', tarsum)
  return tarsum


def simple_checksum_handler(json_data):
  h = hashlib.sha256(json_data.encode('utf8') + '\n')

  def fn(buf):
    h.update(buf)
  return h, fn


def content_checksum_handler():
  h = hashlib.sha256()

  def fn(buf):
    h.update(buf)
  return h, fn


def compute_simple(fp, json_data):
  data = json_data + '\n'
  return 'sha256:{0}'.format(sha256_file(fp, data))


if __name__ == '__main__':
  import sys
  if len(sys.argv) < 3:
    print 'Usage: {0} json_file layer_file'.format(sys.argv[0])
    sys.exit(1)
  json_data = file(sys.argv[1]).read()
  fp = open(sys.argv[2])
  print compute_simple(fp, json_data)
  print compute_tarsum(fp, json_data)