# 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.

import typing

from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives import hashes


if typing.TYPE_CHECKING:
    from cryptography.hazmat.backends.openssl.backend import Backend


class _HashContext(hashes.HashContext):
    def __init__(
        self, backend: "Backend", algorithm: hashes.HashAlgorithm, ctx=None
    ) -> None:
        self._algorithm = algorithm

        self._backend = backend

        if ctx is None:
            ctx = self._backend._lib.EVP_MD_CTX_new()
            ctx = self._backend._ffi.gc(
                ctx, self._backend._lib.EVP_MD_CTX_free
            )
            evp_md = self._backend._evp_md_from_algorithm(algorithm)
            if evp_md == self._backend._ffi.NULL:
                raise UnsupportedAlgorithm(
                    "{} is not a supported hash on this backend.".format(
                        algorithm.name
                    ),
                    _Reasons.UNSUPPORTED_HASH,
                )
            res = self._backend._lib.EVP_DigestInit_ex(
                ctx, evp_md, self._backend._ffi.NULL
            )
            self._backend.openssl_assert(res != 0)

        self._ctx = ctx

    @property
    def algorithm(self) -> hashes.HashAlgorithm:
        return self._algorithm

    def copy(self) -> "_HashContext":
        copied_ctx = self._backend._lib.EVP_MD_CTX_new()
        copied_ctx = self._backend._ffi.gc(
            copied_ctx, self._backend._lib.EVP_MD_CTX_free
        )
        res = self._backend._lib.EVP_MD_CTX_copy_ex(copied_ctx, self._ctx)
        self._backend.openssl_assert(res != 0)
        return _HashContext(self._backend, self.algorithm, ctx=copied_ctx)

    def update(self, data: bytes) -> None:
        data_ptr = self._backend._ffi.from_buffer(data)
        res = self._backend._lib.EVP_DigestUpdate(
            self._ctx, data_ptr, len(data)
        )
        self._backend.openssl_assert(res != 0)

    def finalize(self) -> bytes:
        if isinstance(self.algorithm, hashes.ExtendableOutputFunction):
            # extendable output functions use a different finalize
            return self._finalize_xof()
        else:
            buf = self._backend._ffi.new(
                "unsigned char[]", self._backend._lib.EVP_MAX_MD_SIZE
            )
            outlen = self._backend._ffi.new("unsigned int *")
            res = self._backend._lib.EVP_DigestFinal_ex(self._ctx, buf, outlen)
            self._backend.openssl_assert(res != 0)
            self._backend.openssl_assert(
                outlen[0] == self.algorithm.digest_size
            )
            return self._backend._ffi.buffer(buf)[: outlen[0]]

    def _finalize_xof(self) -> bytes:
        buf = self._backend._ffi.new(
            "unsigned char[]", self.algorithm.digest_size
        )
        res = self._backend._lib.EVP_DigestFinalXOF(
            self._ctx, buf, self.algorithm.digest_size
        )
        self._backend.openssl_assert(res != 0)
        return self._backend._ffi.buffer(buf)[: self.algorithm.digest_size]
