# Source code for sqlalchemy_utils.types.encrypted.encrypted_type

    # -*- coding: utf-8 -*-
    import base64
    import datetime
    import os

    import six
    from sqlalchemy.types import LargeBinary, String, TypeDecorator

    from sqlalchemy_utils.exceptions import ImproperlyConfigured
    from sqlalchemy_utils.types.encrypted.padding import PADDING_MECHANISM
    from sqlalchemy_utils.types.scalar_coercible import ScalarCoercible

    cryptography = None
    try:
        import cryptography
        from cryptography.hazmat.backends import default_backend
        from cryptography.hazmat.primitives import hashes
        from cryptography.hazmat.primitives.ciphers import (
            Cipher, algorithms, modes
        )
        from cryptography.fernet import Fernet
        from cryptography.exceptions import InvalidTag
    except ImportError:
        pass

    dateutil = None
    try:
        import dateutil
        from dateutil.parser import parse as datetime_parse
    except ImportError:
        pass

    class InvalidCiphertextError(Exception):
        pass

    class EncryptionDecryptionBaseEngine(object):
        """A base encryption and decryption engine.

        This class must be sub-classed in order to create
        new engines.
        """

        def _update_key(self, key):
            if isinstance(key, six.string_types):
                key = key.encode()
            digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
            digest.update(key)
            engine_key = digest.finalize()

            self._initialize_engine(engine_key)

        def encrypt(self, value):
            raise NotImplementedError('Subclasses must implement this!')

        def decrypt(self, value):
            raise NotImplementedError('Subclasses must implement this!')

    class AesEngine(EncryptionDecryptionBaseEngine):
        """Provide AES encryption and decryption methods.

        You may also consider using the AesGcmEngine instead -- that may be
        a better fit for some cases.

        You should NOT use the AesGcmEngine if you want to be able to search
        for a row based on the value of an encrypted column. Use AesEngine
        instead, since that allows you to perform such searches.

        If you don't need to search by the value of an encypted column, the
        AesGcmEngine provides better security.
        """

        BLOCK_SIZE = 16

        def _initialize_engine(self, parent_class_key):
            self.secret_key = parent_class_key
            self.iv = self.secret_key[:16]
            self.cipher = Cipher(
                algorithms.AES(self.secret_key),
                modes.CBC(self.iv),
                backend=default_backend()
            )

        def _set_padding_mechanism(self, padding_mechanism=None):
            """Set the padding mechanism."""
            if isinstance(padding_mechanism, six.string_types):
                if padding_mechanism not in PADDING_MECHANISM.keys():
                    raise ImproperlyConfigured(
                        "There is not padding mechanism with name {}".format(
                            padding_mechanism
                        )
                    )

            if padding_mechanism is None:
                padding_mechanism = 'naive'

            padding_class = PADDING_MECHANISM[padding_mechanism]
            self.padding_engine = padding_class(self.BLOCK_SIZE)

        def encrypt(self, value):
            if not isinstance(value, six.string_types):
                value = repr(value)
            if isinstance(value, six.text_type):
                value = str(value)
            value = value.encode()
            value = self.padding_engine.pad(value)
            encryptor = self.cipher.encryptor()
            encrypted = encryptor.update(value) + encryptor.finalize()
            encrypted = base64.b64encode(encrypted)
            return encrypted

        def decrypt(self, value):
            if isinstance(value, six.text_type):
                value = str(value)
            decryptor = self.cipher.decryptor()
            decrypted = base64.b64decode(value)
            decrypted = decryptor.update(decrypted) + decryptor.finalize()
            decrypted = self.padding_engine.unpad(decrypted)
            if not isinstance(decrypted, six.string_types):
                try:
                    decrypted = decrypted.decode('utf-8')
                except UnicodeDecodeError:
                    raise ValueError('Invalid decryption key')
            return decrypted

    class AesGcmEngine(EncryptionDecryptionBaseEngine):
        """Provide AES/GCM encryption and decryption methods.

        You may also consider using the AesEngine instead -- that may be
        a better fit for some cases.

        You should NOT use this AesGcmEngine if you want to be able to search
        for a row based on the value of an encrypted column. Use AesEngine
        instead, since that allows you to perform such searches.

        If you don't need to search by the value of an encypted column, the
        AesGcmEngine provides better security.
        """

        BLOCK_SIZE = 16
        IV_BYTES_NEEDED = 12
        TAG_SIZE_BYTES = BLOCK_SIZE

        def _initialize_engine(self, parent_class_key):
            self.secret_key = parent_class_key

        def encrypt(self, value):
            if not isinstance(value, six.string_types):
                value = repr(value)
            if isinstance(value, six.text_type):
                value = str(value)
            value = value.encode()
            iv = os.urandom(self.IV_BYTES_NEEDED)
            cipher = Cipher(
                algorithms.AES(self.secret_key),
                modes.GCM(iv),
                backend=default_backend()
            )
            encryptor = cipher.encryptor()
            encrypted = encryptor.update(value) + encryptor.finalize()
            assert len(encryptor.tag) == self.TAG_SIZE_BYTES
            encrypted = base64.b64encode(iv + encryptor.tag + encrypted)
            return encrypted

        def decrypt(self, value):
            if isinstance(value, six.text_type):
                value = str(value)
            decrypted = base64.b64decode(value)
            if len(decrypted) < self.IV_BYTES_NEEDED + self.TAG_SIZE_BYTES:
                raise InvalidCiphertextError()
            iv = decrypted[:self.IV_BYTES_NEEDED]
            tag = decrypted[self.IV_BYTES_NEEDED:
                            self.IV_BYTES_NEEDED + self.TAG_SIZE_BYTES]
            decrypted = decrypted[self.IV_BYTES_NEEDED + self.TAG_SIZE_BYTES:]
            cipher = Cipher(
                algorithms.AES(self.secret_key),
                modes.GCM(iv, tag),
                backend=default_backend()
            )
            decryptor = cipher.decryptor()
            try:
                decrypted = decryptor.update(decrypted) + decryptor.finalize()
            except InvalidTag:
                raise InvalidCiphertextError()
            if not isinstance(decrypted, six.string_types):
                try:
                    decrypted = decrypted.decode('utf-8')
                except UnicodeDecodeError:
                    raise InvalidCiphertextError()
            return decrypted

    class FernetEngine(EncryptionDecryptionBaseEngine):
        """Provide Fernet encryption and decryption methods."""

        def _initialize_engine(self, parent_class_key):
            self.secret_key = base64.urlsafe_b64encode(parent_class_key)
            self.fernet = Fernet(self.secret_key)

        def encrypt(self, value):
            if not isinstance(value, six.string_types):
                value = repr(value)
            if isinstance(value, six.text_type):
                value = str(value)
            value = value.encode()
            encrypted = self.fernet.encrypt(value)
            return encrypted

        def decrypt(self, value):
            if isinstance(value, six.text_type):
                value = str(value)
            decrypted = self.fernet.decrypt(value)
            if not isinstance(decrypted, six.string_types):
                decrypted = decrypted.decode('utf-8')
            return decrypted

    class EncryptedType(TypeDecorator, ScalarCoercible):
        """
        EncryptedType provides a way to encrypt and decrypt values,
        to and from databases, that their type is a basic SQLAlchemy type.
        For example Unicode, String or even Boolean.
        On the way in, the value is encrypted and on the way out the stored value
        is decrypted.

        EncryptedType needs Cryptography_ library in order to work.

        When declaring a column which will be of type EncryptedType
        it is better to be as precise as possible and follow the pattern
        below.

        .. _Cryptography: https://cryptography.io/en/latest/

        ::

            a_column = sa.Column(EncryptedType(sa.Unicode,
                                               secret_key,
                                               FernetEngine))

            another_column = sa.Column(EncryptedType(sa.Unicode,
                                               secret_key,
                                               AesEngine,
                                               'pkcs5'))

        A more complete example is given below.

        ::

            import sqlalchemy as sa
            from sqlalchemy import create_engine
            from sqlalchemy.ext.declarative import declarative_base
            from sqlalchemy.orm import sessionmaker

            from sqlalchemy_utils import EncryptedType
            from sqlalchemy_utils.types.encrypted.encrypted_type import AesEngine

            secret_key = 'secretkey1234'
            # setup
            engine = create_engine('sqlite:///:memory:')
            connection = engine.connect()
            Base = declarative_base()

            class User(Base):
                __tablename__ = "user"
                id = sa.Column(sa.Integer, primary_key=True)
                username = sa.Column(EncryptedType(sa.Unicode,
                                                   secret_key,
                                                   AesEngine,
                                                   'pkcs5'))
                access_token = sa.Column(EncryptedType(sa.String,
                                                       secret_key,
                                                       AesEngine,
                                                       'pkcs5'))
                is_active = sa.Column(EncryptedType(sa.Boolean,
                                                    secret_key,
                                                    AesEngine,
                                                    'zeroes'))
                number_of_accounts = sa.Column(EncryptedType(sa.Integer,
                                                             secret_key,
                                                             AesEngine,
                                                             'oneandzeroes'))

            sa.orm.configure_mappers()
            Base.metadata.create_all(connection)

            # create a configured "Session" class
            Session = sessionmaker(bind=connection)

            # create a Session
            session = Session()

            # example
            user_name = u'secret_user'
            test_token = 'atesttoken'
            active = True
            num_of_accounts = 2

            user = User(username=user_name, access_token=test_token,
                        is_active=active, number_of_accounts=num_of_accounts)
            session.add(user)
            session.commit()

            user_id = user.id

            session.expunge_all()

            user_instance = session.query(User).get(user_id)

            print('id: {}'.format(user_instance.id))
            print('username: {}'.format(user_instance.username))
            print('token: {}'.format(user_instance.access_token))
            print('active: {}'.format(user_instance.is_active))
            print('accounts: {}'.format(user_instance.number_of_accounts))

            # teardown
            session.close_all()
            Base.metadata.drop_all(connection)
            connection.close()
            engine.dispose()

        The key parameter accepts a callable to allow for the key to change
        per-row instead of being fixed for the whole table.

        ::

            def get_key():
                return 'dynamic-key'

            class User(Base):
                __tablename__ = 'user'
                id = sa.Column(sa.Integer, primary_key=True)
                username = sa.Column(EncryptedType(
                    sa.Unicode, get_key))

        """

        impl = LargeBinary

        def __init__(self, type_in=None, key=None,
                     engine=None, padding=None, **kwargs):
            """Initialization."""
            if not cryptography:
                raise ImproperlyConfigured(
                    "'cryptography' is required to use EncryptedType"
                )
            super(EncryptedType, self).__init__(**kwargs)
            # set the underlying type
            if type_in is None:
                type_in = String()
            elif isinstance(type_in, type):
                type_in = type_in()
            self.underlying_type = type_in
            self._key = key
            if not engine:
                engine = AesEngine
            self.engine = engine()
            if isinstance(self.engine, AesEngine):
                self.engine._set_padding_mechanism(padding)

        @property
        def key(self):
            return self._key

        @key.setter
        def key(self, value):
            self._key = value

        def _update_key(self):
            key = self._key() if callable(self._key) else self._key
            self.engine._update_key(key)

        def process_bind_param(self, value, dialect):
            """Encrypt a value on the way in."""
            if value is not None:
                self._update_key()

                try:
                    value = self.underlying_type.process_bind_param(
                        value, dialect
                    )

                except AttributeError:
                    # Doesn't have 'process_bind_param'

                    # Handle 'boolean' and 'dates'
                    type_ = self.underlying_type.python_type
                    if issubclass(type_, bool):
                        value = 'true' if value else 'false'

                    elif issubclass(type_, (datetime.date, datetime.time)):
                        value = value.isoformat()

                return self.engine.encrypt(value)

        def process_result_value(self, value, dialect):
            """Decrypt value on the way out."""
            if value is not None:
                self._update_key()
                decrypted_value = self.engine.decrypt(value)

                try:
                    return self.underlying_type.process_result_value(
                        decrypted_value, dialect
                    )

                except AttributeError:
                    # Doesn't have 'process_result_value'

                    # Handle 'boolean' and 'dates'
                    type_ = self.underlying_type.python_type
                    date_types = [datetime.datetime, datetime.time, datetime.date]

                    if issubclass(type_, bool):
                        return decrypted_value == 'true'

                    elif type_ in date_types:
                        return DatetimeHandler.process_value(
                            decrypted_value, type_
                        )

                    # Handle all others
                    return self.underlying_type.python_type(decrypted_value)

        def _coerce(self, value):
            if isinstance(self.underlying_type, ScalarCoercible):
                return self.underlying_type._coerce(value)

            return value

    class DatetimeHandler(object):
        """
        DatetimeHandler is responsible for parsing strings and
        returning the appropriate date, datetime or time objects.
        """

        @classmethod
        def process_value(cls, value, python_type):
            """
            process_value returns a datetime, date
            or time object according to a given string
            value and a python type.
            """
            if not dateutil:
                raise ImproperlyConfigured(
                    "'python-dateutil' is required to process datetimes"
                )

            return_value = datetime_parse(value)

            if issubclass(python_type, datetime.datetime):
                return return_value
            elif issubclass(python_type, datetime.time):
                return return_value.time()
            elif issubclass(python_type, datetime.date):
                return return_value.date()