# Copyright 2017 Amazon.com, Inc. or its affiliates. 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. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file 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.
"""Example showing basic encryption and decryption of a value already in memory."""
import aws_encryption_sdk
from aws_encryption_sdk import CommitmentPolicy


def cycle_string(key_arn, source_plaintext, botocore_session=None):
    """Encrypts and then decrypts a string under a KMS customer master key (CMK).

    :param str key_arn: Amazon Resource Name (ARN) of the KMS CMK
    :param bytes source_plaintext: Data to encrypt
    :param botocore_session: existing botocore session instance
    :type botocore_session: botocore.session.Session
    """
    # Set up an encryption client with an explicit commitment policy. Note that if you do not explicitly choose a
    # commitment policy, REQUIRE_ENCRYPT_REQUIRE_DECRYPT is used by default.
    client = aws_encryption_sdk.EncryptionSDKClient(commitment_policy=CommitmentPolicy.REQUIRE_ENCRYPT_REQUIRE_DECRYPT)

    # Create a KMS master key provider. Note that because we are planning on decrypting using this same provider,
    # we MUST provide the ARN of the KMS Key. If we provide a raw key id or a key alias, decryption will fail.
    kms_kwargs = dict(key_ids=[key_arn])
    if botocore_session is not None:
        kms_kwargs["botocore_session"] = botocore_session
    master_key_provider = aws_encryption_sdk.StrictAwsKmsMasterKeyProvider(**kms_kwargs)

    # Encrypt the plaintext source data
    ciphertext, encryptor_header = client.encrypt(source=source_plaintext, key_provider=master_key_provider)

    # Decrypt the ciphertext
    cycled_plaintext, decrypted_header = client.decrypt(source=ciphertext, key_provider=master_key_provider)

    # Verify that the "cycled" (encrypted, then decrypted) plaintext is identical to the source plaintext
    assert cycled_plaintext == source_plaintext

    # Verify that the encryption context used in the decrypt operation includes all key pairs from
    # the encrypt operation. (The SDK can add pairs, so don't require an exact match.)
    #
    # In production, always use a meaningful encryption context. In this sample, we omit the
    # encryption context (no key pairs).
    assert all(
        pair in decrypted_header.encryption_context.items() for pair in encryptor_header.encryption_context.items()
    )