# -*- coding: utf-8 -*- #
# Copyright 2017 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Helpers for digesting a file."""

from __future__ import absolute_import
from __future__ import division
from __future__ import unicode_literals

import hashlib
from googlecloudsdk.api_lib.cloudkms import base as cloudkms_base
from googlecloudsdk.calliope import exceptions
from googlecloudsdk.core.util import files

_READ_SIZE = 4 * 1024 * 1024


def _ChunkReader(file_, chunk_size=_READ_SIZE):
  while True:
    chunk = file_.read(chunk_size)
    if not chunk:
      break
    yield chunk


_DIGEST_ALGORITHMS = {
    'sha256': hashlib.sha256,
    'sha384': hashlib.sha384,
    'sha512': hashlib.sha512,
}


# TODO(b/77481291) Refactor this to allow reading from stdin.
def GetDigest(digest_algorithm, filename):
  """Digest the file at filename based on digest_algorithm.

  Args:
    digest_algorithm: The algorithm used to digest the file, can be one of
      'sha256', 'sha384', or 'sha512'.
    filename: A valid file path over which a digest will be calculated.

  Returns:
    The digest of the provided file.

  Raises:
    InvalidArgumentException: The provided digest_algorithm is invalid.
  """
  with files.BinaryFileReader(filename) as f:
    return GetDigestOfFile(digest_algorithm, f)


def GetDigestOfFile(digest_algorithm, file_to_digest):
  """Digest the file_to_digest based on digest_algorithm.

  Args:
    digest_algorithm: The algorithm used to digest the file, can be one of
      'sha256', 'sha384', or 'sha512'.
    file_to_digest: A valid file handle.

  Returns:
    The digest of the provided file.

  Raises:
    InvalidArgumentException: The provided digest_algorithm is invalid.
  """
  messages = cloudkms_base.GetMessagesModule()
  algorithm = _DIGEST_ALGORITHMS.get(digest_algorithm)
  if not algorithm:
    raise exceptions.InvalidArgumentException('digest',
                                              'digest_algorithm is invalid.')
  digest = algorithm()
  for chunk in _ChunkReader(file_to_digest):
    digest.update(chunk)
  kwargs = {digest_algorithm: digest.digest()}
  return messages.Digest(**kwargs)
