import json

from jwkest import BadSignature

from jwkest.jwk import SYMKey
from jwkest.jws import NoSuitableSigningKeys
from jwkest.jwt import JWT
from oic.oic import OIDCONF_PATTERN
from oic.oic.message import IdToken, ProviderConfigurationResponse
from oic.utils.keyio import KeyJar, KeyBundle
import requests


class IDTokenVerificationError(Exception):
    pass


def verify_signed_id_token(token, key=None, jwks=None):
    jwt = JWT().unpack(token)
    payload = jwt.payload()
    issuer = payload['iss']
    provider_keys = None

    if jwt.headers['alg'].startswith('HS') and not key:
        raise IDTokenVerificationError(
            'No symmetric key provided for signature using \'{}\' algorithm.'.format(
                jwt.headers['alg']))

    if key:
        provider_keys = KeyJar()
        key = SYMKey(use='sig', k=key)
        kb = KeyBundle(keytype='oct')
        kb.append(key)
        provider_keys[issuer] = [kb]
    elif jwks:
        provider_keys = _parse_provider_keys_from_jwks(issuer, jwks)
    elif jwt.headers['alg'] != 'none':  # don't fetch keys for unsigned JWT
        provider_keys = _fetch_provider_keys(issuer)

    try:
        return IdToken().from_jwt(token, keyjar=provider_keys).to_json()
    except (BadSignature, NoSuitableSigningKeys) as e:
        raise IDTokenVerificationError(
            'No key that could be used to verify the signature could be found.')


def _fetch_provider_keys(issuer):
    try:
        provider_config = ProviderConfigurationResponse(
            **requests.get(OIDCONF_PATTERN % issuer).json())
    except requests.exceptions.RequestException:
        raise IDTokenVerificationError('The providers configuration could not be fetched.')
    assert issuer == provider_config['issuer']

    provider_keys = KeyJar()
    keybundle = provider_keys.add(issuer, provider_config['jwks_uri'])

    try:
        keybundle.update()  # force fetch of remote keys from jwks_uri
    except requests.exceptions.RequestException:
        raise IDTokenVerificationError('Keys could not be fetched from the providers \'jwks_uri\'.')

    return provider_keys


def _parse_provider_keys_from_jwks(issuer, jwks):
    keys = json.loads(jwks)['keys']
    provider_keys = KeyJar()
    provider_keys[issuer] = [KeyBundle(keys=keys)]
    return provider_keys

import json

from jwkest import BadSignature

from jwkest.jwk import SYMKey
from jwkest.jws import NoSuitableSigningKeys
from jwkest.jwt import JWT
from oic.oic import OIDCONF_PATTERN
from oic.oic.message import IdToken, ProviderConfigurationResponse
from oic.utils.keyio import KeyJar, KeyBundle
import requests


class IDTokenVerificationError(Exception):
    pass


def verify_signed_id_token(token, key=None, jwks=None):
    jwt = JWT().unpack(token)
    payload = jwt.payload()
    issuer = payload['iss']
    provider_keys = None

    if jwt.headers['alg'].startswith('HS') and not key:
        raise IDTokenVerificationError(
            'No symmetric key provided for signature using \'{}\' algorithm.'.format(
                jwt.headers['alg']))

    if key:
        provider_keys = _create_symmetric_key(issuer, key)
    elif jwks:
        provider_keys = _parse_provider_keys_from_jwks(issuer, jwks)
    elif jwt.headers['alg'] != 'none':  # don't fetch keys for unsigned JWT
        provider_keys = _fetch_provider_keys(issuer)

    try:
        return IdToken().from_jwt(token, keyjar=provider_keys).to_json()
    except (BadSignature, NoSuitableSigningKeys) as e:
        raise IDTokenVerificationError(
            'No key that could be used to verify the signature could be found.')


def _fetch_provider_keys(issuer):
    try:
        provider_config = ProviderConfigurationResponse(
            **requests.get(OIDCONF_PATTERN % issuer).json())
    except requests.exceptions.RequestException:
        raise IDTokenVerificationError('The providers configuration could not be fetched.')
    assert issuer == provider_config['issuer']

    provider_keys = KeyJar()
    keybundle = provider_keys.add(issuer, provider_config['jwks_uri'])

    try:
        keybundle.update()  # force fetch of remote keys from jwks_uri
    except requests.exceptions.RequestException:
        raise IDTokenVerificationError('Keys could not be fetched from the providers \'jwks_uri\'.')

    return provider_keys


def _parse_provider_keys_from_jwks(issuer, jwks):
    keys = json.loads(jwks)['keys']
    provider_keys = KeyJar()
    provider_keys[issuer] = [KeyBundle(keys=keys)]
    return provider_keys


def _create_symmetric_key(issuer, key):
    provider_keys = KeyJar()
    key = SYMKey(use='sig', k=key)
    kb = KeyBundle(keytype='oct')
    kb.append(key)
    provider_keys[issuer] = [kb]

    return provider_keys

Refactor symmetric key instantiation to separate function.