# Copyright 2019 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 how to customize the AWS KMS Client."""
import boto3
from botocore.config import Config

import aws_encryption_sdk
from aws_encryption_sdk import CommitmentPolicy


# Create a new class that extends the AWS KMS Provider you need to use
class CustomKMSClientMasterKeyProvider(aws_encryption_sdk.StrictAwsKmsMasterKeyProvider):
    """Custom region-specific client which extends the StrictAwsKmsMasterKeyProvider"""

    # Override `add_regional_client` to use whatever configuration you need
    def add_regional_client(self, region_name):
        """Adds a regional client for the specified region if it does not already exist.
        :param str region_name: AWS Region ID (ex: us-east-1)
        """
        if region_name not in self._regional_clients:
            session = boto3.session.Session(botocore_session=self.config.botocore_session)
            client = session.client(
                'kms',
                region_name=region_name,
                # Add additional custom client configuration here
                config=Config(connection_timeout=10).merge(self._user_agent_adding_config)
            )
            self._register_client(client, region_name)
            self._regional_clients[region_name] = client


# This is just an example of using the above master key provider
def encrypt_decrypt(key_arn, source_plaintext, botocore_session=None):
    """Encrypts and then decrypts a string under one 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
    """
    kwargs = dict(key_ids=[key_arn])

    if botocore_session is not None:
        kwargs["botocore_session"] = botocore_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 the custom master key provider using the ARN of the key and the session (botocore_session)
    kms_key_provider = CustomKMSClientMasterKeyProvider(**kwargs)

    # Encrypt the plaintext using the AWS Encryption SDK. It returns the encrypted message and the header. Note: in
    # order for decrypt to succeed, the key_ids value must be the key ARN of the CMK.
    ciphertext, encrypted_message_header = client.encrypt(source=source_plaintext, key_provider=kms_key_provider)

    # Decrypt the encrypted message using the AWS Encryption SDK. It returns the decrypted message and the header
    plaintext, decrypted_message_header = client.decrypt(source=ciphertext, key_provider=kms_key_provider)

    # Check if the original message and the decrypted message are the same
    assert source_plaintext == plaintext

    # Check if the headers of the encrypted message and decrypted message match
    assert all(
        pair in encrypted_message_header.encryption_context.items()
        for pair in decrypted_message_header.encryption_context.items()
    )