# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.

from __future__ import absolute_import, division, print_function

import math

from cryptography import utils
from cryptography.exceptions import (
    AlreadyFinalized, InvalidSignature, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import (
    AsymmetricSignatureContext, AsymmetricVerificationContext, rsa
)
from cryptography.hazmat.primitives.asymmetric.padding import (
    AsymmetricPadding, MGF1, OAEP, PKCS1v15, PSS
)
from cryptography.hazmat.primitives.asymmetric.rsa import (
    RSAPrivateKeyWithSerialization, RSAPublicKeyWithSerialization
)


def _get_rsa_pss_salt_length(pss, key_size, digest_size):
    salt = pss._salt_length

    if salt is MGF1.MAX_LENGTH or salt is PSS.MAX_LENGTH:
        # bit length - 1 per RFC 3447
        emlen = int(math.ceil((key_size - 1) / 8.0))
        salt_length = emlen - digest_size - 2
        assert salt_length >= 0
        return salt_length
    else:
        return salt


def _enc_dec_rsa(backend, key, data, padding):
    if not isinstance(padding, AsymmetricPadding):
        raise TypeError("Padding must be an instance of AsymmetricPadding.")

    if isinstance(padding, PKCS1v15):
        padding_enum = backend._lib.RSA_PKCS1_PADDING
    elif isinstance(padding, OAEP):
        padding_enum = backend._lib.RSA_PKCS1_OAEP_PADDING
        if not isinstance(padding._mgf, MGF1):
            raise UnsupportedAlgorithm(
                "Only MGF1 is supported by this backend.",
                _Reasons.UNSUPPORTED_MGF
            )

        if not isinstance(padding._mgf._algorithm, hashes.SHA1):
            raise UnsupportedAlgorithm(
                "This backend supports only SHA1 inside MGF1 when "
                "using OAEP.",
                _Reasons.UNSUPPORTED_HASH
            )

        if padding._label is not None and padding._label != b"":
            raise ValueError("This backend does not support OAEP labels.")

        if not isinstance(padding._algorithm, hashes.SHA1):
            raise UnsupportedAlgorithm(
                "This backend only supports SHA1 when using OAEP.",
                _Reasons.UNSUPPORTED_HASH
            )
    else:
        raise UnsupportedAlgorithm(
            "{0} is not supported by this backend.".format(
                padding.name
            ),
            _Reasons.UNSUPPORTED_PADDING
        )

    if backend._lib.Cryptography_HAS_PKEY_CTX:
        return _enc_dec_rsa_pkey_ctx(backend, key, data, padding_enum)
    else:
        return _enc_dec_rsa_098(backend, key, data, padding_enum)


def _enc_dec_rsa_pkey_ctx(backend, key, data, padding_enum):
    if isinstance(key, _RSAPublicKey):
        init = backend._lib.EVP_PKEY_encrypt_init
        crypt = backend._lib.Cryptography_EVP_PKEY_encrypt
    else:
        init = backend._lib.EVP_PKEY_decrypt_init
        crypt = backend._lib.Cryptography_EVP_PKEY_decrypt

    pkey_ctx = backend._lib.EVP_PKEY_CTX_new(
        key._evp_pkey, backend._ffi.NULL
    )
    assert pkey_ctx != backend._ffi.NULL
    pkey_ctx = backend._ffi.gc(pkey_ctx, backend._lib.EVP_PKEY_CTX_free)
    res = init(pkey_ctx)
    assert res == 1
    res = backend._lib.EVP_PKEY_CTX_set_rsa_padding(
        pkey_ctx, padding_enum)
    assert res > 0
    buf_size = backend._lib.EVP_PKEY_size(key._evp_pkey)
    assert buf_size > 0
    outlen = backend._ffi.new("size_t *", buf_size)
    buf = backend._ffi.new("char[]", buf_size)
    res = crypt(pkey_ctx, buf, outlen, data, len(data))
    if res <= 0:
        _handle_rsa_enc_dec_error(backend, key)

    return backend._ffi.buffer(buf)[:outlen[0]]


def _enc_dec_rsa_098(backend, key, data, padding_enum):
    if isinstance(key, _RSAPublicKey):
        crypt = backend._lib.RSA_public_encrypt
    else:
        crypt = backend._lib.RSA_private_decrypt

    key_size = backend._lib.RSA_size(key._rsa_cdata)
    assert key_size > 0
    buf = backend._ffi.new("unsigned char[]", key_size)
    res = crypt(len(data), data, buf, key._rsa_cdata, padding_enum)
    if res < 0:
        _handle_rsa_enc_dec_error(backend, key)

    return backend._ffi.buffer(buf)[:res]


def _handle_rsa_enc_dec_error(backend, key):
    errors = backend._consume_errors()
    assert errors
    assert errors[0].lib == backend._lib.ERR_LIB_RSA
    if isinstance(key, _RSAPublicKey):
        assert (errors[0].reason ==
                backend._lib.RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE)
        raise ValueError(
            "Data too long for key size. Encrypt less data or use a "
            "larger key size."
        )
    else:
        decoding_errors = [
            backend._lib.RSA_R_BLOCK_TYPE_IS_NOT_01,
            backend._lib.RSA_R_BLOCK_TYPE_IS_NOT_02,
        ]