# SPDX-FileCopyrightText: 2014 Legrandin <helderijs@gmail.com>
# SPDX-License-Identifier: BSD-2-Clause

"""
OpenPGP mode.
"""

from __future__ import annotations

from typing import TYPE_CHECKING, Union

__all__ = ["OpenPgpMode"]
from Crypto.Random import get_random_bytes
from Crypto.Util._raw_api import is_buffer

if TYPE_CHECKING:
    from types import ModuleType

Buffer = Union[bytes, bytearray, memoryview]


class OpenPgpMode:
    """OpenPGP mode.

    This mode is a variant of CFB, and it is only used in PGP and
    OpenPGP_ applications. If in doubt, use another mode.

    An Initialization Vector (*IV*) is required.

    Unlike CFB, the *encrypted* IV (not the IV itself) is
    transmitted to the receiver.

    The IV is a random data block. For legacy reasons, two of its bytes are
    duplicated to act as a checksum for the correctness of the key, which is now
    known to be insecure and is ignored. The encrypted IV is therefore 2 bytes
    longer than the clean IV.

    .. _OpenPGP: https://www.rfc-editor.org/rfc/rfc4880
    """

    def __init__(self, factory: ModuleType, key: Buffer, iv: Buffer, cipher_params: dict) -> None:
        #: The block size of the underlying cipher, in bytes.
        self.block_size = factory.block_size

        self._done_first_block = False  # True after the first encryption

        # Instantiate a temporary cipher to process the IV
        IV_cipher = factory.new(
            key,
            factory.MODE_CFB,
            IV=b"\x00" * self.block_size,
            segment_size=self.block_size * 8,
            **cipher_params,
        )

        if not is_buffer(iv):
            raise TypeError("IV must be bytes, bytearray or memoryview")
        iv = bytes(iv)

        # The cipher will be used for...
        if len(iv) == self.block_size:
            # ... encryption
            self._encrypted_IV = IV_cipher.encrypt(iv + iv[-2:])
        elif len(iv) == self.block_size + 2:
            # ... decryption
            self._encrypted_IV = iv
            # Last two bytes are for a deprecated "quick check" feature that
            # should not be used. (https://eprint.iacr.org/2005/033)
            iv = IV_cipher.decrypt(iv)[:-2]
        else:
            raise ValueError(
                "Length of IV must be %d or %d bytes"
                " for MODE_OPENPGP" % (self.block_size, self.block_size + 2)
            )

        self.iv = iv
        """The Initialization Vector originally used to create the object
        (without the two extra bytes used for decryption)."""

        self.IV = iv
        """Alias for `iv`"""

        # Instantiate the cipher for the real PGP data
        self._cipher = factory.new(
            key,
            factory.MODE_CFB,
            IV=self._encrypted_IV[-self.block_size :],
            segment_size=self.block_size * 8,
            **cipher_params,
        )

    def encrypt(self, plaintext: Buffer) -> bytes:
        """Encrypt data with the key and the parameters set at initialization.

        A cipher object is stateful: once you have encrypted a message
        you cannot encrypt (or decrypt) another message using the same
        object.

        The data to encrypt can be broken up in two or
        more pieces and `encrypt` can be called multiple times.

        That is, the statement:

            >>> c.encrypt(a) + c.encrypt(b)

        is equivalent to:

             >>> c.encrypt(a+b)

        This function does not add any padding to the plaintext.

        Args:
            plaintext (bytes/bytearray/memoryview):
                The piece of data to encrypt.

        Returns:
            the encrypted data, as a byte string.
            It is as long as *plaintext* with one exception:
            when encrypting the first message chunk,
            the encypted IV is prepended to the returned ciphertext.
        """

        res = self._cipher.encrypt(plaintext)
        if not self._done_first_block:
            res = self._encrypted_IV + res
            self._done_first_block = True
        return res

    def decrypt(self, ciphertext: Buffer) -> bytes:
        """Decrypt data with the key and the parameters set at initialization.

        A cipher object is stateful: once you have decrypted a message
        you cannot decrypt (or encrypt) another message with the same
        object.

        The data to decrypt can be broken up in two or
        more pieces and `decrypt` can be called multiple times.

        That is, the statement:

            >>> c.decrypt(a) + c.decrypt(b)

        is equivalent to:

             >>> c.decrypt(a+b)

        This function does not remove any padding from the plaintext.

        Args:
            ciphertext (bytes/bytearray/memoryview):
                The piece of data to decrypt.

        Returns:
            the decrypted data (byte string).
        """

        return self._cipher.decrypt(ciphertext)


def _create_openpgp_cipher(factory, **kwargs):
    """Create a new block cipher, configured in OpenPGP mode.

    Args:
        factory (module):
            The module.

    Keyword Args:
        key (bytes/bytearray/memoryview):
            The secret key to use in the symmetric cipher.

        IV (bytes/bytearray/memoryview):
            The initialization vector to use for encryption or decryption.

            For encryption, the IV must be as long as the cipher block size.

            For decryption, it must be 2 bytes longer (it is actually the
            *encrypted* IV which was prefixed to the ciphertext).
    """

    iv = kwargs.pop("IV", None)
    IV = kwargs.pop("iv", None)

    if (iv, IV) == (None, None):
        iv = get_random_bytes(factory.block_size)
    if iv is not None:
        if IV is not None:
            raise TypeError("You must either use 'iv' or 'IV', not both")
    else:
        iv = IV

    try:
        key = kwargs.pop("key")
    except KeyError as e:
        raise TypeError("Missing component: " + str(e))

    return OpenPgpMode(factory, key, iv, kwargs)