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import time
import datetime
import uuid
import base64
import binascii
import re

import jwt

from .constants import Jwt
from .log import Logger
from .adal_error import AdalError

def _get_date_now():
    return datetime.datetime.now()

def _get_new_jwt_id():
    return str(uuid.uuid4())

def _create_x5t_value(thumbprint):
    hex_val = binascii.a2b_hex(thumbprint)
    return base64.urlsafe_b64encode(hex_val).decode()

def _sign_jwt(header, payload, certificate):
    try:
        encoded_jwt = _encode_jwt(payload, certificate, header)
    except Exception as exp:
        raise AdalError("Error:Invalid Certificate: Expected Start of Certificate to be '-----BEGIN RSA PRIVATE KEY-----'", exp)
    _raise_on_invalid_jwt_signature(encoded_jwt)
    return encoded_jwt

def _encode_jwt(payload, certificate, header):
    return jwt.encode(payload, certificate, algorithm='RS256', headers=header).decode()

def _raise_on_invalid_jwt_signature(encoded_jwt):
    segments = encoded_jwt.split('.')
    if len(segments) < 3 or not segments[2]:    
        raise AdalError('Failed to sign JWT. This is most likely due to an invalid certificate.')

class SelfSignedJwt(object):

    NumCharIn128BitHexString = 128/8*2
    numCharIn160BitHexString = 160/8*2
    ThumbprintRegEx = r"^[a-f\d]*$"

    def __init__(self, call_context, authority, client_id):
        self._log = Logger('SelfSignedJwt', call_context['log_context'])
        self._call_context = call_context

        self._authortiy = authority
        self._token_endpoint = authority.token_endpoint
        self._client_id = client_id

    def _create_header(self, thumbprint):
        x5t = _create_x5t_value(thumbprint)
        header = {'typ':'JWT', 'alg':'RS256', 'x5t':x5t}

        self._log.debug("Creating self signed JWT header. x5t: %(x5t)s",
                        {"x5t": x5t})

        return header

    def _create_payload(self):
        now = _get_date_now()
        minutes = datetime.timedelta(0, 0, 0, 0, Jwt.SELF_SIGNED_JWT_LIFETIME)
        expires = now + minutes

        self._log.debug(
            'Creating self signed JWT payload. Expires: %(expires)s NotBefore: %(nbf)s',
            {"expires": expires, "nbf": now})

        jwt_payload = {}
        jwt_payload[Jwt.AUDIENCE] = self._token_endpoint
        jwt_payload[Jwt.ISSUER] = self._client_id
        jwt_payload[Jwt.SUBJECT] = self._client_id
        jwt_payload[Jwt.NOT_BEFORE] = int(time.mktime(now.timetuple()))
        jwt_payload[Jwt.EXPIRES_ON] = int(time.mktime(expires.timetuple()))
        jwt_payload[Jwt.JWT_ID] = _get_new_jwt_id()

        return jwt_payload

    def _raise_on_invalid_thumbprint(self, thumbprint):
        thumbprint_sizes = [self.NumCharIn128BitHexString, self.numCharIn160BitHexString]
        size_ok = len(thumbprint) in thumbprint_sizes
        if not size_ok or not re.search(self.ThumbprintRegEx, thumbprint):
            raise AdalError("The thumbprint does not match a known format")

    def _reduce_thumbprint(self, thumbprint):
        canonical = thumbprint.lower().replace(' ', '').replace(':', '')
        self._raise_on_invalid_thumbprint(canonical)
        return canonical

    def create(self, certificate, thumbprint):
        thumbprint = self._reduce_thumbprint(thumbprint)
        header = self._create_header(thumbprint)
        payload = self._create_payload()
        return _sign_jwt(header, payload, certificate)