# Copyright 2021 Google LLC
#
# 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.
# [START envelope-example]
"""A command-line utility for encrypting small files using envelope encryption with GCP."""

from absl import app
from absl import flags
from absl import logging
import tink
from tink import aead
from tink.integration import gcpkms


FLAGS = flags.FLAGS

flags.DEFINE_enum(
    'mode', None, ['encrypt', 'decrypt'], 'The operation to perform.'
)
flags.DEFINE_string(
    'kek_uri', None, 'The Cloud KMS URI of the key encryption key.'
)
flags.DEFINE_string(
    'gcp_credential_path', None, 'Path to the GCP credentials JSON file.'
)
flags.DEFINE_string('input_path', None, 'Path to the input file.')
flags.DEFINE_string('output_path', None, 'Path to the output file.')
flags.DEFINE_string(
    'associated_data', None, 'Optional associated data used for the encryption.'
)


def main(argv):
  del argv  # Unused.

  associated_data = (
      b''
      if not FLAGS.associated_data
      else bytes(FLAGS.associated_data, 'utf-8')
  )

  # Initialise Tink
  aead.register()

  try:
    # Read the GCP credentials and setup client
    client = gcpkms.GcpKmsClient(FLAGS.kek_uri, FLAGS.gcp_credential_path)
  except tink.TinkError as e:
    logging.exception('Error creating GCP KMS client: %s', e)
    return 1

  # Create envelope AEAD primitive using AES256 GCM for encrypting the data
  try:
    remote_aead = client.get_aead(FLAGS.kek_uri)
    env_aead = aead.KmsEnvelopeAead(
        aead.aead_key_templates.AES256_GCM, remote_aead
    )
  except tink.TinkError as e:
    logging.exception('Error creating primitive: %s', e)
    return 1

  with open(FLAGS.input_path, 'rb') as input_file:
    input_data = input_file.read()
    if FLAGS.mode == 'decrypt':
      output_data = env_aead.decrypt(input_data, associated_data)
    elif FLAGS.mode == 'encrypt':
      output_data = env_aead.encrypt(input_data, associated_data)
    else:
      logging.error(
          'Unsupported mode %s. Please choose "encrypt" or "decrypt".',
          FLAGS.mode,
      )
      return 1

    with open(FLAGS.output_path, 'wb') as output_file:
      output_file.write(output_data)


if __name__ == '__main__':
  flags.mark_flags_as_required(
      ['mode', 'kek_uri', 'gcp_credential_path', 'input_path', 'output_path']
  )
  app.run(main)
# [END envelope-example]