# Copyright 2014-2016 OpenMarket 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.

"""This module contains logic for storing HTTP PUT transactions. This is used
to ensure idempotency when performing PUTs using the REST API."""
import logging
from typing import TYPE_CHECKING, Awaitable, Callable, Dict, Hashable, Tuple

from typing_extensions import ParamSpec

from twisted.internet.defer import Deferred
from twisted.python.failure import Failure
from twisted.web.iweb import IRequest

from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.types import JsonDict, Requester
from synapse.util.async_helpers import ObservableDeferred

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)

CLEANUP_PERIOD_MS = 1000 * 60 * 30  # 30 mins


P = ParamSpec("P")


class HttpTransactionCache:
    def __init__(self, hs: "HomeServer"):
        self.hs = hs
        self.clock = self.hs.get_clock()
        # $txn_key: (ObservableDeferred<(res_code, res_json_body)>, timestamp)
        self.transactions: Dict[
            Hashable, Tuple[ObservableDeferred[Tuple[int, JsonDict]], int]
        ] = {}
        # Try to clean entries every 30 mins. This means entries will exist
        # for at *LEAST* 30 mins, and at *MOST* 60 mins.
        self.cleaner = self.clock.looping_call(self._cleanup, CLEANUP_PERIOD_MS)

        self._msc3970_enabled = hs.config.experimental.msc3970_enabled

    def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hashable:
        """A helper function which returns a transaction key that can be used
        with TransactionCache for idempotent requests.

        Idempotency is based on the returned key being the same for separate
        requests to the same endpoint. The key is formed from the HTTP request
        path and attributes from the requester: the access_token_id for regular users,
        the user ID for guest users, and the appservice ID for appservice users.
        With MSC3970, for regular users, the key is based on the user ID and device ID.

        Args:
            request: The incoming request.
            requester: The requester doing the request.
        Returns:
            A transaction key
        """
        assert request.path is not None
        path: str = request.path.decode("utf8")

        if requester.is_guest:
            assert requester.user is not None, "Guest requester must have a user ID set"
            return (path, "guest", requester.user)

        elif requester.app_service is not None:
            return (path, "appservice", requester.app_service.id)

        # With MSC3970, we use the user ID and device ID as the transaction key
        elif self._msc3970_enabled:
            assert requester.user, "Requester must have a user"
            assert requester.device_id, "Requester must have a device_id"
            return (path, "user", requester.user, requester.device_id)

        # Otherwise, the pre-MSC3970 behaviour is to use the access token ID
        else:
            assert (
                requester.access_token_id is not None
            ), "Requester must have an access_token_id"
            return (path, "user", requester.access_token_id)

    def fetch_or_execute_request(
        self,
        request: IRequest,
        requester: Requester,
        fn: Callable[P, Awaitable[Tuple[int, JsonDict]]],
        *args: P.args,
        **kwargs: P.kwargs,
    ) -> "Deferred[Tuple[int, JsonDict]]":
        """Fetches the response for this transaction, or executes the given function
        to produce a response for this transaction.

        Args:
            request:
            requester:
            fn: A function which returns a tuple of (response_code, response_dict).
            *args: Arguments to pass to fn.
            **kwargs: Keyword arguments to pass to fn.
        Returns:
            Deferred which resolves to a tuple of (response_code, response_dict).
        """
        txn_key = self._get_transaction_key(request, requester)
        if txn_key in self.transactions:
            observable = self.transactions[txn_key][0]
        else:
            # execute the function instead.
            deferred = run_in_background(fn, *args, **kwargs)

            observable = ObservableDeferred(deferred)
            self.transactions[txn_key] = (observable, self.clock.time_msec())

            # if the request fails with an exception, remove it
            # from the transaction map. This is done to ensure that we don't
            # cache transient errors like rate-limiting errors, etc.
            def remove_from_map(err: Failure) -> None:
                self.transactions.pop(txn_key, None)
                # we deliberately do not propagate the error any further, as we
                # expect the observers to have reported it.

            deferred.addErrback(remove_from_map)

        return make_deferred_yieldable(observable.observe())

    def _cleanup(self) -> None:
        now = self.clock.time_msec()
        for key in list(self.transactions):
            ts = self.transactions[key][1]
            if now > (ts + CLEANUP_PERIOD_MS):  # after cleanup period
                del self.transactions[key]
