# Copyright 2013-present MongoDB, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Authentication helpers."""

import functools
import hashlib
import hmac
import os
import socket
from base64 import standard_b64decode, standard_b64encode
from collections import namedtuple
from typing import Callable, Mapping
from urllib.parse import quote

from bson.binary import Binary
from bson.son import SON
from pymongo.auth_aws import _authenticate_aws
from pymongo.errors import ConfigurationError, OperationFailure
from pymongo.saslprep import saslprep

HAVE_KERBEROS = True
_USE_PRINCIPAL = False
try:
    import winkerberos as kerberos

    if tuple(map(int, kerberos.__version__.split(".")[:2])) >= (0, 5):
        _USE_PRINCIPAL = True
except ImportError:
    try:
        import kerberos
    except ImportError:
        HAVE_KERBEROS = False


MECHANISMS = frozenset(
    [
        "GSSAPI",
        "MONGODB-CR",
        "MONGODB-X509",
        "MONGODB-AWS",
        "PLAIN",
        "SCRAM-SHA-1",
        "SCRAM-SHA-256",
        "DEFAULT",
    ]
)
"""The authentication mechanisms supported by PyMongo."""


class _Cache(object):
    __slots__ = ("data",)

    _hash_val = hash("_Cache")

    def __init__(self):
        self.data = None

    def __eq__(self, other):
        # Two instances must always compare equal.
        if isinstance(other, _Cache):
            return True
        return NotImplemented

    def __ne__(self, other):
        if isinstance(other, _Cache):
            return False
        return NotImplemented

    def __hash__(self):
        return self._hash_val


MongoCredential = namedtuple(
    "MongoCredential",
    ["mechanism", "source", "username", "password", "mechanism_properties", "cache"],
)
"""A hashable namedtuple of values used for authentication."""


GSSAPIProperties = namedtuple(
    "GSSAPIProperties", ["service_name", "canonicalize_host_name", "service_realm"]
)
"""Mechanism properties for GSSAPI authentication."""


_AWSProperties = namedtuple("_AWSProperties", ["aws_session_token"])
"""Mechanism properties for MONGODB-AWS authentication."""


def _build_credentials_tuple(mech, source, user, passwd, extra, database):
    """Build and return a mechanism specific credentials tuple."""
    if mech not in ("MONGODB-X509", "MONGODB-AWS") and user is None:
        raise ConfigurationError("%s requires a username." % (mech,))
    if mech == "GSSAPI":
        if source is not None and source != "$external":
            raise ValueError("authentication source must be $external or None for GSSAPI")
        properties = extra.get("authmechanismproperties", {})
        service_name = properties.get("SERVICE_NAME", "mongodb")
        canonicalize = properties.get("CANONICALIZE_HOST_NAME", False)
        service_realm = properties.get("SERVICE_REALM")
        props = GSSAPIProperties(
            service_name=service_name,
            canonicalize_host_name=canonicalize,
            service_realm=service_realm,
        )
        # Source is always $external.
        return MongoCredential(mech, "$external", user, passwd, props, None)
    elif mech == "MONGODB-X509":
        if passwd is not None:
            raise ConfigurationError("Passwords are not supported by MONGODB-X509")
        if source is not None and source != "$external":
            raise ValueError("authentication source must be $external or None for MONGODB-X509")
        # Source is always $external, user can be None.
        return MongoCredential(mech, "$external", user, None, None, None)
    elif mech == "MONGODB-AWS":
        if user is not None and passwd is None:
            raise ConfigurationError("username without a password is not supported by MONGODB-AWS")
        if source is not None and source != "$external":
            raise ConfigurationError(
                "authentication source must be $external or None for MONGODB-AWS"
            )

        properties = extra.get("authmechanismproperties", {})
        aws_session_token = properties.get("AWS_SESSION_TOKEN")
        aws_props = _AWSProperties(aws_session_token=aws_session_token)
        # user can be None for temporary link-local EC2 credentials.
        return MongoCredential(mech, "$external", user, passwd, aws_props, None)
    elif mech == "PLAIN":
        source_database = source or database or "$external"
        return MongoCredential(mech, source_database, user, passwd, None, None)
    else:
        source_database = source or database or "admin"
        if passwd is None:
            raise ConfigurationError("A password is required.")
        return MongoCredential(mech, source_database, user, passwd, None, _Cache())


def _xor(fir, sec):
    """XOR two byte strings together (python 3.x)."""
    return b"".join([bytes([x ^ y]) for x, y in zip(fir, sec)])


def _parse_scram_response(response):
    """Split a scram response into key, value pairs."""
    return dict(item.split(b"=", 1) for item in response.split(b","))


def _authenticate_scram_start(credentials, mechanism):
    username = credentials.username
    user = username.encode("utf-8").replace(b"=", b"=3D").replace(b",", b"=2C")
    nonce = standard_b64encode(os.urandom(32))
    first_bare = b"n=" + user + b",r=" + nonce

    cmd = SON(
        [
            ("saslStart", 1),
            ("mechanism", mechanism),
            ("payload", Binary(b"n,," + first_bare)),
            ("autoAuthorize", 1),
            ("options", {"skipEmptyExchange": True}),
        ]
    )
    return nonce, first_bare, cmd


def _authenticate_scram(credentials, sock_info, mechanism):
    """Authenticate using SCRAM."""
    username = credentials.username
    if mechanism == "SCRAM-SHA-256":
        digest = "sha256"
        digestmod = hashlib.sha256
        data = saslprep(credentials.password).encode("utf-8")
    else:
        digest = "sha1"
        digestmod = hashlib.sha1
        data = _password_digest(username, credentials.password).encode("utf-8")
    source = credentials.source
    cache = credentials.cache

    # Make local
    _hmac = hmac.HMAC

    ctx = sock_info.auth_ctx
    if ctx and ctx.speculate_succeeded():
        nonce, first_bare = ctx.scram_data
        res = ctx.speculative_authenticate
    else:
        nonce, first_bare, cmd = _authenticate_scram_start(credentials, mechanism)
        res = sock_info.command(source, cmd)

    server_first = res["payload"]
    parsed = _parse_scram_response(server_first)
    iterations = int(parsed[b"i"])
    if iterations < 4096:
        raise OperationFailure("Server returned an invalid iteration count.")
    salt = parsed[b"s"]
    rnonce = parsed[b"r"]
    if not rnonce.startswith(nonce):
        raise OperationFailure("Server returned an invalid nonce.")

    without_proof = b"c=biws,r=" + rnonce
    if cache.data:
        client_key, server_key, csalt, citerations = cache.data
    else:
        client_key, server_key, csalt, citerations = None, None, None, None

    # Salt and / or iterations could change for a number of different
    # reasons. Either changing invalidates the cache.
    if not client_key or salt != csalt or iterations != citerations:
        salted_pass = hashlib.pbkdf2_hmac(digest, data, standard_b64decode(salt), iterations)
        client_key = _hmac(salted_pass, b"Client Key", digestmod).digest()
        server_key = _hmac(salted_pass, b"Server Key", digestmod).digest()
        cache.data = (client_key, server_key, salt, iterations)
    stored_key = digestmod(client_key).digest()
    auth_msg = b",".join((first_bare, server_first, without_proof))
    client_sig = _hmac(stored_key, auth_msg, digestmod).digest()
    client_proof = b"p=" + standard_b64encode(_xor(client_key, client_sig))
    client_final = b",".join((without_proof, client_proof))

    server_sig = standard_b64encode(_hmac(server_key, auth_msg, digestmod).digest())

    cmd = SON(
        [
            ("saslContinue", 1),
            ("conversationId", res["conversationId"]),
            ("payload", Binary(client_final)),
        ]
    )
    res = sock_info.command(source, cmd)

    parsed = _parse_scram_response(res["payload"])
    if not hmac.compare_digest(parsed[b"v"], server_sig):
        raise OperationFailure("Server returned an invalid signature.")

    # A third empty challenge may be required if the server does not support
    # skipEmptyExchange: SERVER-44857.
    if not res["done"]:
        cmd = SON(
            [
                ("saslContinue", 1),
                ("conversationId", res["conversationId"]),
                ("payload", Binary(b"")),
            ]
        )
        res = sock_info.command(source, cmd)
        if not res["done"]:
            raise OperationFailure("SASL conversation failed to complete.")


def _password_digest(username, password):
    """Get a password digest to use for authentication."""
    if not isinstance(password, str):
        raise TypeError("password must be an instance of str")
    if len(password) == 0:
        raise ValueError("password can't be empty")
    if not isinstance(username, str):
        raise TypeError("username must be an instance of str")

    md5hash = hashlib.md5()
    data = "%s:mongo:%s" % (username, password)
    md5hash.update(data.encode("utf-8"))
    return md5hash.hexdigest()


def _auth_key(nonce, username, password):
    """Get an auth key to use for authentication."""
    digest = _password_digest(username, password)
    md5hash = hashlib.md5()
    data = "%s%s%s" % (nonce, username, digest)
    md5hash.update(data.encode("utf-8"))
    return md5hash.hexdigest()


def _canonicalize_hostname(hostname):
    """Canonicalize hostname following MIT-krb5 behavior."""
    # https://github.com/krb5/krb5/blob/d406afa363554097ac48646a29249c04f498c88e/src/util/k5test.py#L505-L520
    af, socktype, proto, canonname, sockaddr = socket.getaddrinfo(
        hostname, None, 0, 0, socket.IPPROTO_TCP, socket.AI_CANONNAME
    )[0]

    try:
        name = socket.getnameinfo(sockaddr, socket.NI_NAMEREQD)
    except socket.gaierror:
        return canonname.lower()

    return name[0].lower()


def _authenticate_gssapi(credentials, sock_info):
    """Authenticate using GSSAPI."""
    if not HAVE_KERBEROS:
        raise ConfigurationError(
            'The "kerberos" module must be installed to use GSSAPI authentication.'
        )

    try:
        username = credentials.username
        password = credentials.password
        props = credentials.mechanism_properties
        # Starting here and continuing through the while loop below - establish
        # the security context. See RFC 4752, Section 3.1, first paragraph.
        host = sock_info.address[0]
        if props.canonicalize_host_name:
            host = _canonicalize_hostname(host)
        service = props.service_name + "@" + host
        if props.service_realm is not None:
            service = service + "@" + props.service_realm

        if password is not None:
            if _USE_PRINCIPAL:
                # Note that, though we use unquote_plus for unquoting URI
                # options, we use quote here. Microsoft's UrlUnescape (used
                # by WinKerberos) doesn't support +.
                principal = ":".join((quote(username), quote(password)))
                result, ctx = kerberos.authGSSClientInit(
                    service, principal, gssflags=kerberos.GSS_C_MUTUAL_FLAG
                )
            else:
                if "@" in username:
                    user, domain = username.split("@", 1)
                else:
                    user, domain = username, None
                result, ctx = kerberos.authGSSClientInit(
                    service,
                    gssflags=kerberos.GSS_C_MUTUAL_FLAG,
                    user=user,
                    domain=domain,
                    password=password,
                )
        else:
            result, ctx = kerberos.authGSSClientInit(service, gssflags=kerberos.GSS_C_MUTUAL_FLAG)

        if result != kerberos.AUTH_GSS_COMPLETE:
            raise OperationFailure("Kerberos context failed to initialize.")

        try:
            # pykerberos uses a weird mix of exceptions and return values
            # to indicate errors.
            # 0 == continue, 1 == complete, -1 == error
            # Only authGSSClientStep can return 0.
            if kerberos.authGSSClientStep(ctx, "") != 0:
                raise OperationFailure("Unknown kerberos failure in step function.")

            # Start a SASL conversation with mongod/s
            # Note: pykerberos deals with base64 encoded byte strings.
            # Since mongo accepts base64 strings as the payload we don't
            # have to use bson.binary.Binary.
            payload = kerberos.authGSSClientResponse(ctx)
            cmd = SON(
                [
                    ("saslStart", 1),
                    ("mechanism", "GSSAPI"),
                    ("payload", payload),
                    ("autoAuthorize", 1),
                ]
            )
            response = sock_info.command("$external", cmd)

            # Limit how many times we loop to catch protocol / library issues
            for _ in range(10):
                result = kerberos.authGSSClientStep(ctx, str(response["payload"]))
                if result == -1:
                    raise OperationFailure("Unknown kerberos failure in step function.")

                payload = kerberos.authGSSClientResponse(ctx) or ""

                cmd = SON(
                    [
                        ("saslContinue", 1),
                        ("conversationId", response["conversationId"]),
                        ("payload", payload),
                    ]
                )
                response = sock_info.command("$external", cmd)

                if result == kerberos.AUTH_GSS_COMPLETE:
                    break
            else:
                raise OperationFailure("Kerberos authentication failed to complete.")

            # Once the security context is established actually authenticate.
            # See RFC 4752, Section 3.1, last two paragraphs.
            if kerberos.authGSSClientUnwrap(ctx, str(response["payload"])) != 1:
                raise OperationFailure("Unknown kerberos failure during GSS_Unwrap step.")

            if kerberos.authGSSClientWrap(ctx, kerberos.authGSSClientResponse(ctx), username) != 1:
                raise OperationFailure("Unknown kerberos failure during GSS_Wrap step.")

            payload = kerberos.authGSSClientResponse(ctx)
            cmd = SON(
                [
                    ("saslContinue", 1),
                    ("conversationId", response["conversationId"]),
                    ("payload", payload),
                ]
            )
            sock_info.command("$external", cmd)

        finally:
            kerberos.authGSSClientClean(ctx)

    except kerberos.KrbError as exc:
        raise OperationFailure(str(exc))


def _authenticate_plain(credentials, sock_info):
    """Authenticate using SASL PLAIN (RFC 4616)"""
    source = credentials.source
    username = credentials.username
    password = credentials.password
    payload = ("\x00%s\x00%s" % (username, password)).encode("utf-8")
    cmd = SON(
        [
            ("saslStart", 1),
            ("mechanism", "PLAIN"),
            ("payload", Binary(payload)),
            ("autoAuthorize", 1),
        ]
    )
    sock_info.command(source, cmd)


def _authenticate_x509(credentials, sock_info):
    """Authenticate using MONGODB-X509."""
    ctx = sock_info.auth_ctx
    if ctx and ctx.speculate_succeeded():
        # MONGODB-X509 is done after the speculative auth step.
        return

    cmd = _X509Context(credentials).speculate_command()
    sock_info.command("$external", cmd)


def _authenticate_mongo_cr(credentials, sock_info):
    """Authenticate using MONGODB-CR."""
    source = credentials.source
    username = credentials.username
    password = credentials.password
    # Get a nonce
    response = sock_info.command(source, {"getnonce": 1})
    nonce = response["nonce"]
    key = _auth_key(nonce, username, password)

    # Actually authenticate
    query = SON([("authenticate", 1), ("user", username), ("nonce", nonce), ("key", key)])
    sock_info.command(source, query)


def _authenticate_default(credentials, sock_info):
    if sock_info.max_wire_version >= 7:
        if sock_info.negotiated_mechs:
            mechs = sock_info.negotiated_mechs
        else:
            source = credentials.source
            cmd = sock_info.hello_cmd()
            cmd["saslSupportedMechs"] = source + "." + credentials.username
            mechs = sock_info.command(source, cmd, publish_events=False).get(
                "saslSupportedMechs", []
            )
        if "SCRAM-SHA-256" in mechs:
            return _authenticate_scram(credentials, sock_info, "SCRAM-SHA-256")
        else:
            return _authenticate_scram(credentials, sock_info, "SCRAM-SHA-1")
    else:
        return _authenticate_scram(credentials, sock_info, "SCRAM-SHA-1")


_AUTH_MAP: Mapping[str, Callable] = {
    "GSSAPI": _authenticate_gssapi,
    "MONGODB-CR": _authenticate_mongo_cr,
    "MONGODB-X509": _authenticate_x509,
    "MONGODB-AWS": _authenticate_aws,
    "PLAIN": _authenticate_plain,
    "SCRAM-SHA-1": functools.partial(_authenticate_scram, mechanism="SCRAM-SHA-1"),
    "SCRAM-SHA-256": functools.partial(_authenticate_scram, mechanism="SCRAM-SHA-256"),
    "DEFAULT": _authenticate_default,
}


class _AuthContext(object):
    def __init__(self, credentials):
        self.credentials = credentials
        self.speculative_authenticate = None

    @staticmethod
    def from_credentials(creds):
        spec_cls = _SPECULATIVE_AUTH_MAP.get(creds.mechanism)
        if spec_cls:
            return spec_cls(creds)
        return None

    def speculate_command(self):
        raise NotImplementedError

    def parse_response(self, hello):
        self.speculative_authenticate = hello.speculative_authenticate

    def speculate_succeeded(self):
        return bool(self.speculative_authenticate)


class _ScramContext(_AuthContext):
    def __init__(self, credentials, mechanism):
        super(_ScramContext, self).__init__(credentials)
        self.scram_data = None
        self.mechanism = mechanism

    def speculate_command(self):
        nonce, first_bare, cmd = _authenticate_scram_start(self.credentials, self.mechanism)
        # The 'db' field is included only on the speculative command.
        cmd["db"] = self.credentials.source
        # Save for later use.
        self.scram_data = (nonce, first_bare)
        return cmd


class _X509Context(_AuthContext):
    def speculate_command(self):
        cmd = SON([("authenticate", 1), ("mechanism", "MONGODB-X509")])
        if self.credentials.username is not None:
            cmd["user"] = self.credentials.username
        return cmd


_SPECULATIVE_AUTH_MAP: Mapping[str, Callable] = {
    "MONGODB-X509": _X509Context,
    "SCRAM-SHA-1": functools.partial(_ScramContext, mechanism="SCRAM-SHA-1"),
    "SCRAM-SHA-256": functools.partial(_ScramContext, mechanism="SCRAM-SHA-256"),
    "DEFAULT": functools.partial(_ScramContext, mechanism="SCRAM-SHA-256"),
}


def authenticate(credentials, sock_info):
    """Authenticate sock_info."""
    mechanism = credentials.mechanism
    auth_func = _AUTH_MAP[mechanism]
    auth_func(credentials, sock_info)
