"""HMAC (Keyed-Hashing for Message Authentication) module.

Implements the HMAC algorithm as described by RFC 2104.
"""

import warnings as _warnings
try:
    import _hashlib as _hashopenssl
except ImportError:
    _hashopenssl = None
    _functype = None
    from _operator import _compare_digest as compare_digest
else:
    compare_digest = _hashopenssl.compare_digest
    _functype = type(_hashopenssl.openssl_sha256)  # builtin type

import hashlib as _hashlib

trans_5C = bytes((x ^ 0x5C) for x in range(256))
trans_36 = bytes((x ^ 0x36) for x in range(256))

# The size of the digests returned by HMAC depends on the underlying
# hashing module used.  Use digest_size from the instance of HMAC instead.
digest_size = None


class HMAC:
    """RFC 2104 HMAC class.  Also complies with RFC 4231.

    This supports the API for Cryptographic Hash Functions (PEP 247).
    """
    blocksize = 64  # 512-bit HMAC; can be changed in subclasses.

    __slots__ = (
        "_hmac", "_inner", "_outer", "block_size", "digest_size"
    )

    def __init__(self, key, msg=None, digestmod=''):
        """Create a new HMAC object.

        key: bytes or buffer, key for the keyed hash object.
        msg: bytes or buffer, Initial input for the hash or None.
        digestmod: A hash name suitable for hashlib.new(). *OR*
                   A hashlib constructor returning a new hash object. *OR*
                   A module supporting PEP 247.

                   Required as of 3.8, despite its position after the optional
                   msg argument.  Passing it as a keyword argument is
                   recommended, though not required for legacy API reasons.
        """

        if not isinstance(key, (bytes, bytearray)):
            raise TypeError("key: expected bytes or bytearray, but got %r" % type(key).__name__)

        if not digestmod:
            raise TypeError("Missing required parameter 'digestmod'.")

        if _hashopenssl and isinstance(digestmod, (str, _functype)):
            try:
                self._init_hmac(key, msg, digestmod)
            except _hashopenssl.UnsupportedDigestmodError:
                self._init_old(key, msg, digestmod)
        else:
            self._init_old(key, msg, digestmod)

    def _init_hmac(self, key, msg, digestmod):
        self._hmac = _hashopenssl.hmac_new(key, msg, digestmod=digestmod)
        self.digest_size = self._hmac.digest_size
        self.block_size = self._hmac.block_size

    def _init_old(self, key, msg, digestmod):
        if callable(digestmod):
            digest_cons = digestmod
        elif isinstance(digestmod, str):
            digest_cons = lambda d=b'': _hashlib.new(digestmod, d)
        else:
            digest_cons = lambda d=b'': digestmod.new(d)

        self._hmac = None
        self._outer = digest_cons()
        self._inner = digest_cons()
        self.digest_size = self._inner.digest_size

        if hasattr(self._inner, 'block_size'):
            blocksize = self._inner.block_size
            if blocksize < 16:
                _warnings.warn('block_size of %d seems too small; using our '
                               'default of %d.' % (blocksize, self.blocksize),
                               RuntimeWarning, 2)
                blocksize = self.blocksize
        else:
            _warnings.warn('No block_size attribute on given digest object; '
                           'Assuming %d.' % (self.blocksize),
                           RuntimeWarning, 2)
            blocksize = self.blocksize

        if len(key) > blocksize:
            key = digest_cons(key).digest()

        # self.blocksize is the default blocksize. self.block_size is
        # effective block size as well as the public API attribute.
        self.block_size = blocksize

        key = key.ljust(blocksize, b'\0')
        self._outer.update(key.translate(trans_5C))
        self._inner.update(key.translate(trans_36))
        if msg is not None:
            self.update(msg)

    @property
    def name(self):
        if self._hmac:
            return self._hmac.name
        else:
            return f"hmac-{self._inner.name}"

    def update(self, msg):
        """Feed data from msg into this hashing object."""
        inst = self._hmac or self._inner
        inst.update(msg)

    def copy(self):
        """Return a separate copy of this hashing object.

        An update to this copy won't affect the original object.
        """
        # Call __new__ directly to avoid the expensive __init__.
        other = self.__class__.__new__(self.__class__)
        other.digest_size = self.digest_size
        if self._hmac:
            other._hmac = self._hmac.copy()
            other._inner = other._outer = None
        else:
            other._hmac = None
            other._inner = self._inner.copy()
            other._outer = self._outer.copy()
        return other