"""JSON Web Algorithms.

https://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-40

"""
import abc
import logging
from collections.abc import Hashable
from typing import Any, Callable, Dict

import cryptography.exceptions
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes, hmac
from cryptography.hazmat.primitives.asymmetric import ec, padding, rsa
from cryptography.hazmat.primitives.asymmetric.utils import (
    decode_dss_signature,
    encode_dss_signature,
)
from cryptography.hazmat.primitives.hashes import HashAlgorithm

from josepy import errors, interfaces, jwk

logger = logging.getLogger(__name__)


class JWA(interfaces.JSONDeSerializable):
    # for some reason disable=abstract-method has to be on the line
    # above...
    """JSON Web Algorithm."""


class JWASignature(JWA, Hashable):
    """Base class for JSON Web Signature Algorithms."""
    SIGNATURES: Dict[str, 'JWASignature'] = {}
    kty: Any

    def __init__(self, name: str) -> None:
        self.name = name

    def __eq__(self, other: Any) -> bool:
        if not isinstance(other, JWASignature):
            return NotImplemented
        return self.name == other.name

    def __hash__(self) -> int:
        return hash((self.__class__, self.name))

    @classmethod
    def register(cls, signature_cls: 'JWASignature') -> 'JWASignature':
        """Register class for JSON deserialization."""
        cls.SIGNATURES[signature_cls.name] = signature_cls
        return signature_cls

    def to_partial_json(self) -> Any:
        return self.name

    @classmethod
    def from_json(cls, jobj: Any) -> 'JWASignature':
        return cls.SIGNATURES[jobj]

    @abc.abstractmethod
    def sign(self, key: Any, msg: bytes) -> bytes:  # pragma: no cover
        """Sign the ``msg`` using ``key``."""
        raise NotImplementedError()

    @abc.abstractmethod
    def verify(self, key: Any, msg: bytes, sig: bytes) -> bool:  # pragma: no cover
        """Verify the ``msg`` and ``sig`` using ``key``."""
        raise NotImplementedError()

    def __repr__(self) -> str:
        return self.name


class _JWAHS(JWASignature):
    kty = jwk.JWKOct

    def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]):
        super().__init__(name)
        self.hash = hash_()

    def sign(self, key: bytes, msg: bytes) -> bytes:
        signer = hmac.HMAC(key, self.hash, backend=default_backend())
        signer.update(msg)
        return signer.finalize()

    def verify(self, key: bytes, msg: bytes, sig: bytes) -> bool:
        verifier = hmac.HMAC(key, self.hash, backend=default_backend())
        verifier.update(msg)
        try:
            verifier.verify(sig)
        except cryptography.exceptions.InvalidSignature as error:
            logger.debug(error, exc_info=True)
            return False
        else:
            return True


class _JWARSA:
    kty = jwk.JWKRSA
    padding: Any = NotImplemented
    hash: HashAlgorithm = NotImplemented

    def sign(self, key: rsa.RSAPrivateKey, msg: bytes) -> bytes:
        """Sign the ``msg`` using ``key``."""
        try:
            return key.sign(msg, self.padding, self.hash)
        except AttributeError as error:
            logger.debug(error, exc_info=True)
            raise errors.Error("Public key cannot be used for signing")
        except ValueError as error:  # digest too large
            logger.debug(error, exc_info=True)
            raise errors.Error(str(error))

    def verify(self, key: rsa.RSAPublicKey, msg: bytes, sig: bytes) -> bool:
        """Verify the ``msg` and ``sig`` using ``key``."""
        try:
            key.verify(sig, msg, self.padding, self.hash)
        except cryptography.exceptions.InvalidSignature as error:
            logger.debug(error, exc_info=True)
            return False
        else:
            return True


class _JWARS(_JWARSA, JWASignature):

    def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]) -> None:
        super().__init__(name)
        self.padding = padding.PKCS1v15()
        self.hash = hash_()


class _JWAPS(_JWARSA, JWASignature):

    def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]) -> None:
        super().__init__(name)
        self.padding = padding.PSS(
            mgf=padding.MGF1(hash_()),
            salt_length=padding.PSS.MAX_LENGTH)
        self.hash = hash_()


class _JWAEC(JWASignature):
    kty = jwk.JWKEC

    def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]):
        super().__init__(name)
        self.hash = hash_()

    def sign(self, key: ec.EllipticCurvePrivateKey, msg: bytes) -> bytes:
        """Sign the ``msg`` using ``key``."""
        sig = self._sign(key, msg)
        dr, ds = decode_dss_signature(sig)
        length = jwk.JWKEC.expected_length_for_curve(key.curve)
        return (dr.to_bytes(length=length, byteorder='big') +
                ds.to_bytes(length=length, byteorder='big'))

    def _sign(self, key: ec.EllipticCurvePrivateKey, msg: bytes) -> bytes:
        try:
            return key.sign(msg, ec.ECDSA(self.hash))
        except AttributeError as error:
            logger.debug(error, exc_info=True)
            raise errors.Error('Public key cannot be used for signing')
        except ValueError as error:  # digest too large
            logger.debug(error, exc_info=True)
            raise errors.Error(str(error))

    def verify(self, key: ec.EllipticCurvePublicKey, msg: bytes, sig: bytes) -> bool:
        """Verify the ``msg` and ``sig`` using ``key``."""
        rlen = jwk.JWKEC.expected_length_for_curve(key.curve)
        if len(sig) != 2 * rlen:
            # Format error - rfc7518 - 3.4 … MUST NOT be shortened to omit any leading zero octets
            return False
        asn1sig = encode_dss_signature(
            int.from_bytes(sig[0:rlen], byteorder='big'),
            int.from_bytes(sig[rlen:], byteorder='big')
        )
        return self._verify(key, msg, asn1sig)

    def _verify(self, key: ec.EllipticCurvePublicKey, msg: bytes, asn1sig: bytes) -> bool:
        try:
            key.verify(asn1sig, msg, ec.ECDSA(self.hash))
        except cryptography.exceptions.InvalidSignature as error:
            logger.debug(error, exc_info=True)
            return False
        else:
            return True


#: HMAC using SHA-256
HS256 = JWASignature.register(_JWAHS('HS256', hashes.SHA256))
#: HMAC using SHA-384
HS384 = JWASignature.register(_JWAHS('HS384', hashes.SHA384))
#: HMAC using SHA-512
HS512 = JWASignature.register(_JWAHS('HS512', hashes.SHA512))

#: RSASSA-PKCS-v1_5 using SHA-256
RS256 = JWASignature.register(_JWARS('RS256', hashes.SHA256))
#: RSASSA-PKCS-v1_5 using SHA-384
RS384 = JWASignature.register(_JWARS('RS384', hashes.SHA384))
#: RSASSA-PKCS-v1_5 using SHA-512
RS512 = JWASignature.register(_JWARS('RS512', hashes.SHA512))

#: RSASSA-PSS using SHA-256 and MGF1 with SHA-256
PS256 = JWASignature.register(_JWAPS('PS256', hashes.SHA256))
#: RSASSA-PSS using SHA-384 and MGF1 with SHA-384
PS384 = JWASignature.register(_JWAPS('PS384', hashes.SHA384))
#: RSASSA-PSS using SHA-512 and MGF1 with SHA-512
PS512 = JWASignature.register(_JWAPS('PS512', hashes.SHA512))

#: ECDSA using P-256 and SHA-256
ES256 = JWASignature.register(_JWAEC('ES256', hashes.SHA256))
#: ECDSA using P-384 and SHA-384
ES384 = JWASignature.register(_JWAEC('ES384', hashes.SHA384))
#: ECDSA using P-521 and SHA-512
ES512 = JWASignature.register(_JWAEC('ES512', hashes.SHA512))