#--depends-on config

import base64, hashlib, hmac, typing, uuid
from src import ModuleManager, utils
from . import scram

CAP = utils.irc.Capability("sasl")

USERPASS_MECHANISMS = [
    "SCRAM-SHA-512",
    "SCRAM-SHA-256",
    "SCRAM-SHA-1",
    "PLAIN"
]
ALL_MECHANISMS = USERPASS_MECHANISMS+["EXTERNAL"]

def _parse(value):
    mechanism, _, arguments = value.partition(" ")
    mechanism = mechanism.upper()

    if mechanism in ALL_MECHANISMS:
        return {"mechanism": mechanism.upper(), "args": arguments}
    else:
        raise utils.settings.SettingParseException(
            "Unknown SASL mechanism '%s'" % mechanism)

SASL_TIMEOUT = 15 # 15 seconds

HARDFAIL = utils.BoolSetting("sasl-hard-fail",
    "Set whether a SASL failure should cause a disconnect")

@utils.export("serverset", utils.FunctionSetting(_parse, "sasl",
    "Set the sasl username/password for this server",
    example="PLAIN BitBot:hunter2", format=utils.sensitive_format))
@utils.export("serverset", HARDFAIL)
@utils.export("botset", HARDFAIL)
class Module(ModuleManager.BaseModule):
    @utils.hook("new.server")
    def new_server(self, event):
        event["server"]._sasl_timeout = None
        event["server"]._sasl_retry = False

    def _best_userpass_mechanism(self, mechanisms):
        for potential_mechanism in USERPASS_MECHANISMS:
            if potential_mechanism in mechanisms:
                return potential_mechanism

    def _mech_match(self, server, server_mechanisms):
        our_sasl = server.get_setting("sasl", None)
        if not our_sasl:
            return None

        our_mechanism = our_sasl["mechanism"].upper()

        if not server_mechanisms and our_mechanism in ALL_MECHANISMS:
            return our_mechanism
        elif our_mechanism in server_mechanisms:
            return our_mechanism
        elif our_mechanism == "USERPASS":
            if server_mechanisms:
                return self._best_userpass_mechanism(server_mechanisms)
            else:
                return USERPASS_MECHANISMS[0]
        return None

    @utils.hook("received.cap.new")
    @utils.hook("received.cap.ls")
    def on_cap(self, event):
        has_sasl = "sasl" in event["capabilities"]
        if has_sasl:
            server_mechanisms = event["capabilities"]["sasl"]
            if server_mechanisms:
                server_mechanisms = server_mechanisms.split(",")
            else:
                server_mechanisms = []

            mechanism = self._mech_match(event["server"], server_mechanisms)

            if mechanism:
                cap = CAP.copy()
                cap.on_ack(
                    lambda: self._sasl_ack(event["server"], mechanism))
                return cap

    def _sasl_ack(self, server, mechanism):
        server.send_authenticate(mechanism)
        server._sasl_timeout = self.timers.add("sasl-timeout",
            self._sasl_timeout, SASL_TIMEOUT, server=server)
        server._sasl_mechanism = mechanism

        server.wait_for_capability("sasl")

    def _sasl_timeout(self, timer):
        server = timer.kwargs["server"]
        self._panic(server, "SASL handshake timed out")

    @utils.hook("received.authenticate")
    def on_authenticate(self, event):
        sasl = event["server"].get_setting("sasl")
        mechanism = event["server"]._sasl_mechanism

        auth_text = None
        if mechanism == "PLAIN":
            if event["message"] != "+":
                event["server"].send_authenticate("*")
            else:
                sasl_username, sasl_password = sasl["args"].split(":", 1)
                auth_text = ("%s\0%s\0%s" % (
                    sasl_username, sasl_username, sasl_password)).encode("utf8")

        elif mechanism == "EXTERNAL":
            if event["message"] != "+":
                event["server"].send_authenticate("*")
            else:
                auth_text = "+"

        elif mechanism.startswith("SCRAM-"):

            if event["message"] == "+":
                # start SCRAM handshake

                # create SCRAM helper
                sasl_username, sasl_password = sasl["args"].split(":", 1)
                algo = mechanism.split("SCRAM-", 1)[1]
                event["server"]._scram = scram.SCRAM(
                    algo, sasl_username, sasl_password)

                # generate client-first-message
                auth_text = event["server"]._scram.client_first()
            else:
                current_scram = event["server"]._scram
                data = base64.b64decode(event["message"])
                if current_scram.state == scram.SCRAMState.ClientFirst:
                    # use server-first-message to generate client-final-message
                    auth_text = current_scram.server_first(data)
                elif current_scram.state == scram.SCRAMState.ClientFinal:
                    # use server-final-message to check server proof
                    verified = current_scram.server_final(data)
                    del event["server"]._scram

                    if verified:
                        auth_text = "+"
                    else:
                        if current_scram.state == scram.SCRAMState.VerifyFailed:
                            # server gave a bad verification so we should panic
                            self._panic(event["server"], "SCRAM VerifyFailed")

        else:
            raise ValueError("unknown sasl mechanism '%s'" % mechanism)

        if not auth_text == None:
            if not auth_text == "+":
                auth_text = base64.b64encode(auth_text)
                auth_text = auth_text.decode("utf8")
            event["server"].send_authenticate(auth_text)

    def _end_sasl(self, server):
        server.capability_done("sasl")
        if not server._sasl_timeout == None:
            server._sasl_timeout.cancel()
            server._sasl_timeout = None

    @utils.hook("received.908")
    def sasl_mechanisms(self, event):
        server_mechanisms = event["line"].args[1].split(",")
        mechanism = self._mech_match(event["server"], server_mechanisms)
        if mechanism:
            event["server"]._sasl_mechanism = mechanism
            event["server"].send_authenticate(mechanism)
            event["server"]._sasl_retry = True

    @utils.hook("received.903")
    def sasl_success(self, event):
        self._end_sasl(event["server"])
    @utils.hook("received.904")
    def sasl_failure(self, event):
        if not event["server"]._sasl_retry:
            self._panic(event["server"], "ERR_SASLFAIL (%s)" %
                event["line"].args[1])
        else:
            event["server"]._sasl_retry = False

    @utils.hook("received.907")
    def sasl_already(self, event):
        self._end_sasl(event["server"])

    def _panic(self, server, message):
        if server.get_setting("sasl-hard-fail",
                self.bot.get_setting("sasl-hard-fail", False)):
            message = "SASL panic for %s: %s" % (str(server), message)
            self.log.error(message)
            self.bot.disconnect(server)
        else:
            self.log.warn("SASL failure for %s: %s" % (str(server), message))
            self._end_sasl(server)