"""Proof of Possession Identifier Validation Challenge."""
import logging
import os

from cryptography import x509
from cryptography.hazmat.backends import default_backend
import zope.component

from acme import challenges
from acme import jose
from acme import other

from letsencrypt import interfaces
from letsencrypt.display import util as display_util


logger = logging.getLogger(__name__)


class ProofOfPossession(object): # pylint: disable=too-few-public-methods
    """Proof of Possession Identifier Validation Challenge.

    Based on draft-barnes-acme, section 6.5.

    :ivar installer: Installer object
    :type installer: :class:`~letsencrypt.interfaces.IInstaller`

    """
    def __init__(self, installer):
        self.installer = installer

    def perform(self, achall):
        """Perform the Proof of Possession Challenge.

        :param achall: Proof of Possession Challenge
        :type achall: :class:`letsencrypt.achallenges.ProofOfPossession`

        :returns: Response or None/False if the challenge cannot be completed
        :rtype: :class:`acme.challenges.ProofOfPossessionResponse`
            or False

        """
        if (achall.alg in [jose.HS256, jose.HS384, jose.HS512] or
                not isinstance(achall.hints.jwk, achall.alg.kty)):
            return None

        for cert, key, _ in self.installer.get_all_certs_keys():
            with open(cert) as cert_file:
                cert_data = cert_file.read()
            try:
                cert_obj = x509.load_pem_x509_certificate(
                    cert_data, default_backend())
            except ValueError:
                try:
                    cert_obj = x509.load_der_x509_certificate(
                        cert_data, default_backend())
                except ValueError:
                    logger.warn("Certificate is neither PER nor DER: %s", cert)

            cert_key = achall.alg.kty(key=cert_obj.public_key())
            if cert_key == achall.hints.jwk:
                return self._gen_response(achall, key)

        # Is there are different prompt we should give the user?
        code, key = zope.component.getUtility(
            interfaces.IDisplay).input(
                "Path to private key for identifier: %s " % achall.domain)
        if code != display_util.CANCEL:
            return self._gen_response(achall, key)

        # If we get here, the key wasn't found
        return False

    def _gen_response(self, achall, key_path): # pylint: disable=no-self-use
        """Create the response to the Proof of Possession Challenge.

        :param achall: Proof of Possession Challenge
        :type achall: :class:`letsencrypt.achallenges.ProofOfPossession`

        :param str key_path: Path to the key corresponding to the hinted to
            public key.

        :returns: Response or False if the challenge cannot be completed
        :rtype: :class:`acme.challenges.ProofOfPossessionResponse`
            or False

        """
        if os.path.isfile(key_path):
            with open(key_path, 'rb') as key:
                try:
                    # Needs to be changed if JWKES doesn't have a key attribute
                    jwk = achall.alg.kty.load(key.read())
                    sig = other.Signature.from_msg(achall.nonce, jwk.key,
                                                   alg=achall.alg)
                except (IndexError, ValueError, TypeError, jose.errors.Error):
                    return False
            return challenges.ProofOfPossessionResponse(nonce=achall.nonce,
                                                        signature=sig)
        return False
