# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# 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.
from typing import Optional

from twisted.internet import defer
from twisted.internet.defer import Deferred

from synapse.config.homeserver import HomeServerConfig
from synapse.config.ratelimiting import FederationRatelimitSettings
from synapse.util.ratelimitutils import FederationRateLimiter

from tests.server import ThreadedMemoryReactorClock, get_clock
from tests.unittest import TestCase
from tests.utils import default_config


class FederationRateLimiterTestCase(TestCase):
    def test_ratelimit(self) -> None:
        """A simple test with the default values"""
        reactor, clock = get_clock()
        rc_config = build_rc_config()
        ratelimiter = FederationRateLimiter(clock, rc_config)

        with ratelimiter.ratelimit("testhost") as d1:
            # shouldn't block
            self.successResultOf(d1)

    def test_concurrent_limit(self) -> None:
        """Test what happens when we hit the concurrent limit"""
        reactor, clock = get_clock()
        rc_config = build_rc_config({"rc_federation": {"concurrent": 2}})
        ratelimiter = FederationRateLimiter(clock, rc_config)

        with ratelimiter.ratelimit("testhost") as d1:
            # shouldn't block
            self.successResultOf(d1)

            cm2 = ratelimiter.ratelimit("testhost")
            d2 = cm2.__enter__()
            # also shouldn't block
            self.successResultOf(d2)

            cm3 = ratelimiter.ratelimit("testhost")
            d3 = cm3.__enter__()
            # this one should block, though ...
            self.assertNoResult(d3)

            # ... until we complete an earlier request
            cm2.__exit__(None, None, None)
            reactor.advance(0.0)
            self.successResultOf(d3)

    def test_sleep_limit(self) -> None:
        """Test what happens when we hit the sleep limit"""
        reactor, clock = get_clock()
        rc_config = build_rc_config(
            {"rc_federation": {"sleep_limit": 2, "sleep_delay": 500}}
        )
        ratelimiter = FederationRateLimiter(clock, rc_config)

        with ratelimiter.ratelimit("testhost") as d1:
            # shouldn't block
            self.successResultOf(d1)

        with ratelimiter.ratelimit("testhost") as d2:
            # nor this
            self.successResultOf(d2)

        with ratelimiter.ratelimit("testhost") as d3:
            # this one should block, though ...
            self.assertNoResult(d3)
            sleep_time = _await_resolution(reactor, d3)
            self.assertAlmostEqual(sleep_time, 500, places=3)

    def test_lots_of_queued_things(self) -> None:
        """Tests lots of synchronous things queued up behind a slow thing.

        The stack should *not* explode when the slow thing completes.
        """
        reactor, clock = get_clock()
        rc_config = build_rc_config(
            {
                "rc_federation": {
                    "sleep_limit": 1000000000,  # never sleep
                    "reject_limit": 1000000000,  # never reject requests
                    "concurrent": 1,
                }
            }
        )
        ratelimiter = FederationRateLimiter(clock, rc_config)

        with ratelimiter.ratelimit("testhost") as d:
            # shouldn't block
            self.successResultOf(d)

            async def task() -> None:
                with ratelimiter.ratelimit("testhost") as d:
                    await d

            for _ in range(1, 100):
                defer.ensureDeferred(task())

            last_task = defer.ensureDeferred(task())

            # Upon exiting the context manager, all the synchronous things will resume.
            # If a stack overflow occurs, the final task will not complete.

        # Wait for all the things to complete.
        reactor.advance(0.0)
        self.successResultOf(last_task)


def _await_resolution(reactor: ThreadedMemoryReactorClock, d: Deferred) -> float:
    """advance the clock until the deferred completes.

    Returns the number of milliseconds it took to complete.
    """
    start_time = reactor.seconds()
    while not d.called:
        reactor.advance(0.01)
    return (reactor.seconds() - start_time) * 1000


def build_rc_config(settings: Optional[dict] = None) -> FederationRatelimitSettings:
    config_dict = default_config("test")
    config_dict.update(settings or {})
    config = HomeServerConfig()
    config.parse_config_dict(config_dict, "", "")
    return config.ratelimiting.rc_federation