# -*- coding: utf-8 -*-
# Copyright 2017 New Vector Ltd
#
# 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.

import gc
import logging
import signal
import sys
import traceback

import psutil
from daemonize import Daemonize

from twisted.internet import defer, error, reactor
from twisted.protocols.tls import TLSMemoryBIOFactory

import synapse
from synapse.app import check_bind_error
from synapse.crypto import context_factory
from synapse.util import PreserveLoggingContext
from synapse.util.async_helpers import Linearizer
from synapse.util.rlimit import change_resource_limit
from synapse.util.versionstring import get_version_string

logger = logging.getLogger(__name__)

_sighup_callbacks = []


def register_sighup(func):
    """
    Register a function to be called when a SIGHUP occurs.

    Args:
        func (function): Function to be called when sent a SIGHUP signal.
            Will be called with a single argument, the homeserver.
    """
    _sighup_callbacks.append(func)


def start_worker_reactor(appname, config):
    """ Run the reactor in the main process

    Daemonizes if necessary, and then configures some resources, before starting
    the reactor. Pulls configuration from the 'worker' settings in 'config'.

    Args:
        appname (str): application name which will be sent to syslog
        config (synapse.config.Config): config object
    """

    logger = logging.getLogger(config.worker_app)

    start_reactor(
        appname,
        soft_file_limit=config.soft_file_limit,
        gc_thresholds=config.gc_thresholds,
        pid_file=config.worker_pid_file,
        daemonize=config.worker_daemonize,
        cpu_affinity=config.worker_cpu_affinity,
        print_pidfile=config.print_pidfile,
        logger=logger,
    )


def start_reactor(
        appname,
        soft_file_limit,
        gc_thresholds,
        pid_file,
        daemonize,
        cpu_affinity,
        print_pidfile,
        logger,
):
    """ Run the reactor in the main process

    Daemonizes if necessary, and then configures some resources, before starting
    the reactor

    Args:
        appname (str): application name which will be sent to syslog
        soft_file_limit (int):
        gc_thresholds:
        pid_file (str): name of pid file to write to if daemonize is True
        daemonize (bool): true to run the reactor in a background process
        cpu_affinity (int|None): cpu affinity mask
        print_pidfile (bool): whether to print the pid file, if daemonize is True
        logger (logging.Logger): logger instance to pass to Daemonize
    """

    install_dns_limiter(reactor)

    def run():
        # make sure that we run the reactor with the sentinel log context,
        # otherwise other PreserveLoggingContext instances will get confused
        # and complain when they see the logcontext arbitrarily swapping
        # between the sentinel and `run` logcontexts.
        with PreserveLoggingContext():
            logger.info("Running")
            if cpu_affinity is not None:
                # Turn the bitmask into bits, reverse it so we go from 0 up
                mask_to_bits = bin(cpu_affinity)[2:][::-1]

                cpus = []
                cpu_num = 0

                for i in mask_to_bits:
                    if i == "1":
                        cpus.append(cpu_num)
                    cpu_num += 1

                p = psutil.Process()
                p.cpu_affinity(cpus)

            change_resource_limit(soft_file_limit)
            if gc_thresholds:
                gc.set_threshold(*gc_thresholds)
            reactor.run()

    if daemonize:
        if print_pidfile:
            print(pid_file)

        daemon = Daemonize(
            app=appname,
            pid=pid_file,
            action=run,
            auto_close_fds=False,
            verbose=True,
            logger=logger,
        )
        daemon.start()
    else:
        run()


def quit_with_error(error_string):
    message_lines = error_string.split("\n")
    line_length = max([len(l) for l in message_lines if len(l) < 80]) + 2
    sys.stderr.write("*" * line_length + '\n')
    for line in message_lines:
        sys.stderr.write(" %s\n" % (line.rstrip(),))
    sys.stderr.write("*" * line_length + '\n')
    sys.exit(1)


def listen_metrics(bind_addresses, port):
    """
    Start Prometheus metrics server.
    """
    from synapse.metrics import RegistryProxy
    from prometheus_client import start_http_server

    for host in bind_addresses:
        logger.info("Starting metrics listener on %s:%d", host, port)
        start_http_server(port, addr=host, registry=RegistryProxy)


def listen_tcp(bind_addresses, port, factory, reactor=reactor, backlog=50):
    """
    Create a TCP socket for a port and several addresses

    Returns:
        list[twisted.internet.tcp.Port]: listening for TCP connections
    """
    r = []
    for address in bind_addresses:
        try:
            r.append(
                reactor.listenTCP(
                    port,
                    factory,
                    backlog,
                    address
                )
            )
        except error.CannotListenError as e:
            check_bind_error(e, address, bind_addresses)

    return r


def listen_ssl(
    bind_addresses, port, factory, context_factory, reactor=reactor, backlog=50
):
    """
    Create an TLS-over-TCP socket for a port and several addresses

    Returns:
        list of twisted.internet.tcp.Port listening for TLS connections
    """
    r = []
    for address in bind_addresses:
        try:
            r.append(
                reactor.listenSSL(
                    port,
                    factory,
                    context_factory,
                    backlog,
                    address
                )
            )
        except error.CannotListenError as e:
            check_bind_error(e, address, bind_addresses)

    return r


def refresh_certificate(hs):
    """
    Refresh the TLS certificates that Synapse is using by re-reading them from
    disk and updating the TLS context factories to use them.
    """

    if not hs.config.has_tls_listener():
        # attempt to reload the certs for the good of the tls_fingerprints
        hs.config.read_certificate_from_disk(require_cert_and_key=False)
        return

    hs.config.read_certificate_from_disk(require_cert_and_key=True)
    hs.tls_server_context_factory = context_factory.ServerContextFactory(hs.config)

    if hs._listening_services:
        logger.info("Updating context factories...")
        for i in hs._listening_services:
            # When you listenSSL, it doesn't make an SSL port but a TCP one with
            # a TLS wrapping factory around the factory you actually want to get
            # requests. This factory attribute is public but missing from
            # Twisted's documentation.
            if isinstance(i.factory, TLSMemoryBIOFactory):
                addr = i.getHost()
                logger.info(
                    "Replacing TLS context factory on [%s]:%i", addr.host, addr.port,
                )
                # We want to replace TLS factories with a new one, with the new
                # TLS configuration. We do this by reaching in and pulling out
                # the wrappedFactory, and then re-wrapping it.
                i.factory = TLSMemoryBIOFactory(
                    hs.tls_server_context_factory,
                    False,
                    i.factory.wrappedFactory
                )
        logger.info("Context factories updated.")


def start(hs, listeners=None):
    """
    Start a Synapse server or worker.

    Args:
        hs (synapse.server.HomeServer)
        listeners (list[dict]): Listener configuration ('listeners' in homeserver.yaml)
    """
    try:
        # Set up the SIGHUP machinery.
        if hasattr(signal, "SIGHUP"):
            def handle_sighup(*args, **kwargs):
                for i in _sighup_callbacks:
                    i(hs)

            signal.signal(signal.SIGHUP, handle_sighup)

            register_sighup(refresh_certificate)

        # Load the certificate from disk.
        refresh_certificate(hs)

        # It is now safe to start your Synapse.
        hs.start_listening(listeners)
        hs.get_datastore().start_profiling()

        setup_sentry(hs)
    except Exception:
        traceback.print_exc(file=sys.stderr)
        reactor = hs.get_reactor()
        if reactor.running:
            reactor.stop()
        sys.exit(1)


def setup_sentry(hs):
    """Enable sentry integration, if enabled in configuration

    Args:
        hs (synapse.server.HomeServer)
    """

    if not hs.config.sentry_enabled:
        return

    import sentry_sdk
    sentry_sdk.init(
        dsn=hs.config.sentry_dsn,
        release=get_version_string(synapse),
    )

    # We set some default tags that give some context to this instance
    with sentry_sdk.configure_scope() as scope:
        scope.set_tag("matrix_server_name", hs.config.server_name)

        app = hs.config.worker_app if hs.config.worker_app else "synapse.app.homeserver"
        name = hs.config.worker_name if hs.config.worker_name else "master"
        scope.set_tag("worker_app", app)
        scope.set_tag("worker_name", name)


def install_dns_limiter(reactor, max_dns_requests_in_flight=100):
    """Replaces the resolver with one that limits the number of in flight DNS
    requests.

    This is to workaround https://twistedmatrix.com/trac/ticket/9620, where we
    can run out of file descriptors and infinite loop if we attempt to do too
    many DNS queries at once
    """
    new_resolver = _LimitedHostnameResolver(
        reactor.nameResolver, max_dns_requests_in_flight,
    )

    reactor.installNameResolver(new_resolver)


class _LimitedHostnameResolver(object):
    """Wraps a IHostnameResolver, limiting the number of in-flight DNS lookups.
    """

    def __init__(self, resolver, max_dns_requests_in_flight):
        self._resolver = resolver
        self._limiter = Linearizer(
            name="dns_client_limiter", max_count=max_dns_requests_in_flight,
        )

    def resolveHostName(self, resolutionReceiver, hostName, portNumber=0,
                        addressTypes=None, transportSemantics='TCP'):
        # Note this is happening deep within the reactor, so we don't need to
        # worry about log contexts.

        # We need this function to return `resolutionReceiver` so we do all the
        # actual logic involving deferreds in a separate function.
        self._resolve(
            resolutionReceiver, hostName, portNumber,
            addressTypes, transportSemantics,
        )

        return resolutionReceiver

    @defer.inlineCallbacks
    def _resolve(self, resolutionReceiver, hostName, portNumber=0,
                 addressTypes=None, transportSemantics='TCP'):

        with (yield self._limiter.queue(())):
            # resolveHostName doesn't return a Deferred, so we need to hook into
            # the receiver interface to get told when resolution has finished.

            deferred = defer.Deferred()
            receiver = _DeferredResolutionReceiver(resolutionReceiver, deferred)

            self._resolver.resolveHostName(
                receiver, hostName, portNumber,
                addressTypes, transportSemantics,
            )

            yield deferred


class _DeferredResolutionReceiver(object):
    """Wraps a IResolutionReceiver and simply resolves the given deferred when
    resolution is complete
    """

    def __init__(self, receiver, deferred):
        self._receiver = receiver
        self._deferred = deferred

    def resolutionBegan(self, resolutionInProgress):
        self._receiver.resolutionBegan(resolutionInProgress)

    def addressResolved(self, address):
        self._receiver.addressResolved(address)

    def resolutionComplete(self):
        self._deferred.callback(())
        self._receiver.resolutionComplete()
