# bijoe - BI dashboard
# Copyright (C) 2015  Entr'ouvert
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import base64
import datetime
import hashlib
import hmac
import logging
import random
import urllib

from django.utils import six
from django.utils.encoding import force_bytes, smart_bytes
from django.utils.http import quote, urlencode
from django.utils.six.moves.urllib import parse as urlparse

'''Simple signature scheme for query strings'''
# from http://repos.entrouvert.org/portail-citoyen.git/tree/portail_citoyen/apps/data_source_plugin/signature.py


def sign_url(url, key, algo='sha256', timestamp=None, nonce=None):
    parsed = urlparse.urlparse(url)
    new_query = sign_query(parsed.query, key, algo, timestamp, nonce)
    return urlparse.urlunparse(parsed[:4] + (new_query,) + parsed[5:])


def sign_query(query, key, algo='sha256', timestamp=None, nonce=None):
    if timestamp is None:
        timestamp = datetime.datetime.utcnow()
    timestamp = timestamp.strftime('%Y-%m-%dT%H:%M:%SZ')
    if nonce is None:
        nonce = hex(random.getrandbits(128))[2:]
    new_query = query
    if new_query:
        new_query += '&'
    new_query += urlencode((('algo', algo), ('timestamp', timestamp), ('nonce', nonce)))
    signature = base64.b64encode(sign_string(new_query, key, algo=algo))
    new_query += '&signature=' + quote(signature)
    return new_query


def sign_string(s, key, algo='sha256', timedelta=30):
    digestmod = getattr(hashlib, algo)
    hash = hmac.HMAC(smart_bytes(key), digestmod=digestmod, msg=smart_bytes(s))
    return hash.digest()


def check_url(url, key, known_nonce=None, timedelta=30):
    parsed = urlparse.urlparse(url, 'https')
    return check_query(parsed.query, key)


def check_query(query, key, known_nonce=None, timedelta=30):
    res, error = check_query2(query, key, known_nonce=known_nonce, timedelta=timedelta)
    if not res:
        key_hash = 'md5:%s' % hashlib.md5(force_bytes(key)).hexdigest()[:6]
        logging.getLogger(__name__).warning(
            'could not check signature of query %r with key %s: %s', query, key_hash, error
        )
    return res


def check_query2(query, key, known_nonce, timedelta):
    parsed = urlparse.parse_qs(query)
    try:
        signature = parsed['signature'][0]
        algo = parsed['algo'][0]
        timestamp = parsed['timestamp'][0]
        nonce = parsed['nonce'][0]
    except KeyError as e:
        return False, 'missing required field %r' % e.args[0]
    try:
        signature = base64.b64decode(parsed['signature'][0])
    except Exception as e:
        return False, 'could not decode base64 signature (%s)' % e

    if algo not in hashlib.algorithms_guaranteed:
        return False, 'hash algorithm %s is not supported' % algo

    try:
        timestamp = datetime.datetime.strptime(timestamp, '%Y-%m-%dT%H:%M:%SZ')
    except Exception as e:
        return False, 'could not parse the timestamp %s' % timestamp
    unsigned_query = query.split('&signature=')[0]
    if known_nonce is not None and known_nonce(nonce):
        return False, 'used nonce'
    if abs(datetime.datetime.utcnow() - timestamp) > datetime.timedelta(seconds=timedelta):
        return False, 'timestamp is older than %d seconds' % timedelta
    if not check_string(unsigned_query, signature, key, algo=algo):
        return False, 'signature does not match'
    return True, None


def check_string(s, signature, key, algo='sha256'):
    # constant time compare
    signature2 = sign_string(s, key, algo=algo)
    if len(signature2) != len(signature):
        return False
    res = 0
    for a, b in zip(signature, signature2):
        res |= a ^ b
    return res == 0