#
#  Cipher/mode_ofb.py : OFB mode
#
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# the extent that dedication to the public domain is not available,
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"""
Output Feedback (CFB) mode.
"""

from __future__ import annotations

from typing import Optional, Union, overload

__all__ = ["OfbMode"]
from Crypto.Cipher._state_machine import Method
from Crypto.Random import get_random_bytes
from Crypto.Util._raw_api import (
    SmartPointer,
    VoidPointer,
    c_size_t,
    c_uint8_ptr_len,
    c_uint8_ptr_out,
    create_output_buffer,
    get_raw_buffer,
    is_writeable_buffer,
    load_pycryptodome_raw_lib,
)

Buffer = Union[bytes, bytearray, memoryview]

raw_ofb_lib = load_pycryptodome_raw_lib(
    "Crypto.Cipher._raw_ofb",
    """
                        int OFB_start_operation(void *cipher,
                                                const uint8_t iv[],
                                                size_t iv_len,
                                                void **pResult);
                        int OFB_encrypt(void *ofbState,
                                        const uint8_t *in,
                                        uint8_t *out,
                                        size_t data_len);
                        int OFB_decrypt(void *ofbState,
                                        const uint8_t *in,
                                        uint8_t *out,
                                        size_t data_len);
                        int OFB_stop_operation(void *state);
                        """,
)


class OfbMode:
    """*Output FeedBack (OFB)*.

    This mode is very similar to CBC, but it
    transforms the underlying block cipher into a stream cipher.

    The keystream is the iterated block encryption of the
    previous ciphertext block.

    An Initialization Vector (*IV*) is required.

    See `NIST SP800-38A`_ , Section 6.4.

    .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
    """

    def __init__(self, block_cipher: SmartPointer, iv: Buffer) -> None:
        """Create a new block cipher, configured in OFB mode.

        Args:
            block_cipher (C pointer):
                A smart pointer to the low-level block cipher instance.

            iv (bytes/bytearray/memoryview):
                The initialization vector to use for encryption or decryption.
                It is as long as the cipher block.

                **The IV must be a nonce, to to be reused for any other
                message**. It shall be a nonce or a random value.

                Reusing the *IV* for encryptions performed with the same key
                compromises confidentiality.
        """

        state = VoidPointer()
        iv_ptr, iv_len = c_uint8_ptr_len(iv)
        result = raw_ofb_lib.OFB_start_operation(
            block_cipher.get(), iv_ptr, c_size_t(iv_len), state.address_of()
        )
        if result:
            raise ValueError("Error %d while instantiating the OFB mode" % result)

        # Ensure that object disposal of this Python object will (eventually)
        # free the memory allocated by the raw library for the cipher mode
        self._state = SmartPointer(state.get(), raw_ofb_lib.OFB_stop_operation)

        # Memory allocated for the underlying block cipher is now owed
        # by the cipher mode
        block_cipher.release()

        self.block_size = len(iv)
        """The block size of the underlying cipher, in bytes."""

        self.iv = bytes(iv)
        """The Initialization Vector originally used to create the object.
        The value does not change."""

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

        self._next = [Method.ENCRYPT, Method.DECRYPT]

    @overload
    def encrypt(self, plaintext: Buffer) -> bytes: ...

    @overload
    def encrypt(self, plaintext: Buffer, output: Union[bytearray, memoryview]) -> None: ...

    def encrypt(
        self, plaintext: Buffer, output: Optional[Union[bytearray, memoryview]] = None
    ) -> Optional[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.
                It can be of any length.
        Keyword Args:
            output (bytearray/memoryview):
                The location where the ciphertext must be written to.
                If ``None``, the ciphertext is returned.
        Returns:
            If ``output`` is ``None``, the ciphertext is returned as ``bytes``.
            Otherwise, ``None``.
        """

        if Method.ENCRYPT not in self._next:
            raise TypeError("encrypt() cannot be called after decrypt()")
        self._next = [Method.ENCRYPT]

        if output is None:
            ciphertext = create_output_buffer(len(plaintext))
        else:
            ciphertext = output

            if not is_writeable_buffer(output):
                raise TypeError("output must be a bytearray or a writeable memoryview")

            if len(plaintext) != len(output):
                raise ValueError("output must have the same length as the input  (%d bytes)" % len(plaintext))

        with c_uint8_ptr_out(ciphertext) as ciphertext_ptr:
            plaintext_ptr, plaintext_len = c_uint8_ptr_len(plaintext)
            # Check the lengths of the buffers that C code gets
            if len(ciphertext_ptr) != plaintext_len:
                raise ValueError("output must have the same length as the input  (%d bytes)" % plaintext_len)
            result = raw_ofb_lib.OFB_encrypt(
                self._state.get(), plaintext_ptr, ciphertext_ptr, c_size_t(plaintext_len)
            )
        if result:
            raise ValueError("Error %d while encrypting in OFB mode" % result)

        if output is None:
            return get_raw_buffer(ciphertext)
        else:
            return None

    @overload
    def decrypt(self, ciphertext: Buffer) -> bytes: ...

    @overload
    def decrypt(self, ciphertext: Buffer, output: Union[bytearray, memoryview]) -> None: ...

    def decrypt(
        self, ciphertext: Buffer, output: Optional[Union[bytearray, memoryview]] = None
    ) -> Optional[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.
                It can be of any length.
        Keyword Args:
            output (bytearray/memoryview):
                The location where the plaintext is written to.
                If ``None``, the plaintext is returned.
        Returns:
            If ``output`` is ``None``, the plaintext is returned as ``bytes``.
            Otherwise, ``None``.
        """

        if Method.DECRYPT not in self._next:
            raise TypeError("decrypt() cannot be called after encrypt()")
        self._next = [Method.DECRYPT]

        if output is None:
            plaintext = create_output_buffer(len(ciphertext))
        else:
            plaintext = output

            if not is_writeable_buffer(output):
                raise TypeError("output must be a bytearray or a writeable memoryview")

            if len(ciphertext) != len(output):
                raise ValueError("output must have the same length as the input  (%d bytes)" % len(plaintext))

        with c_uint8_ptr_out(plaintext) as plaintext_ptr:
            ciphertext_ptr, ciphertext_len = c_uint8_ptr_len(ciphertext)
            # Check the lengths of the buffers that C code gets
            if len(plaintext_ptr) != ciphertext_len:
                raise ValueError("output must have the same length as the input  (%d bytes)" % ciphertext_len)
            result = raw_ofb_lib.OFB_decrypt(
                self._state.get(), ciphertext_ptr, plaintext_ptr, c_size_t(ciphertext_len)
            )
        if result:
            raise ValueError("Error %d while decrypting in OFB mode" % result)

        if output is None:
            return get_raw_buffer(plaintext)
        else:
            return None


def _create_ofb_cipher(factory, **kwargs):
    """Instantiate a cipher object that performs OFB encryption/decryption.

    Args:
        factory (module):
            The underlying block cipher, a module from ``Crypto.Cipher``.

    Keyword Args:
        iv (bytes/bytearray/memoryview):
            The IV to use for OFB.

        IV (bytes/bytearray/memoryview):
            Alias for ``iv``.

    Any other keyword will be passed to the underlying block cipher.
    See the relevant documentation for details (at least ``key`` will need
    to be present).
    """

    cipher_state = factory._create_base_cipher(kwargs)
    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

    if len(iv) != factory.block_size:
        raise ValueError("Incorrect IV length (it must be %d bytes long)" % factory.block_size)

    if kwargs:
        raise TypeError("Unknown parameters for OFB: %s" % str(kwargs))

    return OfbMode(cipher_state, iv)