# 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.
from typing import TYPE_CHECKING, List, Optional, Tuple

import attr
from frozendict import frozendict

from synapse.appservice import ApplicationService
from synapse.events import EventBase
from synapse.types import JsonDict, StateMap

if TYPE_CHECKING:
    from synapse.storage.controllers import StorageControllers
    from synapse.storage.databases.main import DataStore
    from synapse.types.state import StateFilter


@attr.s(slots=True, auto_attribs=True)
class EventContext:
    """
    Holds information relevant to persisting an event

    Attributes:
        rejected: A rejection reason if the event was rejected, else None

        _state_group: The ID of the state group for this event. Note that state events
            are persisted with a state group which includes the new event, so this is
            effectively the state *after* the event in question.

            For a *rejected* state event, where the state of the rejected event is
            ignored, this state_group should never make it into the
            event_to_state_groups table. Indeed, inspecting this value for a rejected
            state event is almost certainly incorrect.

            For an outlier, where we don't have the state at the event, this will be
            None.

            Note that this is a private attribute: it should be accessed via
            the ``state_group`` property.

        state_group_before_event: The ID of the state group representing the state
            of the room before this event.

            If this is a non-state event, this will be the same as ``state_group``. If
            it's a state event, it will be the same as ``prev_group``.

            If ``state_group`` is None (ie, the event is an outlier),
            ``state_group_before_event`` will always also be ``None``.

        state_delta_due_to_event: If `state_group` and `state_group_before_event` are not None
            then this is the delta of the state between the two groups.

        prev_group: If it is known, ``state_group``'s prev_group. Note that this being
            None does not necessarily mean that ``state_group`` does not have
            a prev_group!

            If the event is a state event, this is normally the same as
            ``state_group_before_event``.

            If ``state_group`` is None (ie, the event is an outlier), ``prev_group``
            will always also be ``None``.

            Note that this *not* (necessarily) the state group associated with
            ``_prev_state_ids``.

        delta_ids: If ``prev_group`` is not None, the state delta between ``prev_group``
            and ``state_group``.

        app_service: If this event is being sent by a (local) application service, that
            app service.

        partial_state: if True, we may be storing this event with a temporary,
            incomplete state.
    """

    _storage: "StorageControllers"
    rejected: Optional[str] = None
    _state_group: Optional[int] = None
    state_group_before_event: Optional[int] = None
    _state_delta_due_to_event: Optional[StateMap[str]] = None
    prev_group: Optional[int] = None
    delta_ids: Optional[StateMap[str]] = None
    app_service: Optional[ApplicationService] = None

    partial_state: bool = False

    @staticmethod
    def with_state(
        storage: "StorageControllers",
        state_group: Optional[int],
        state_group_before_event: Optional[int],
        state_delta_due_to_event: Optional[StateMap[str]],
        partial_state: bool,
        prev_group: Optional[int] = None,
        delta_ids: Optional[StateMap[str]] = None,
    ) -> "EventContext":
        return EventContext(
            storage=storage,
            state_group=state_group,
            state_group_before_event=state_group_before_event,
            state_delta_due_to_event=state_delta_due_to_event,
            prev_group=prev_group,
            delta_ids=delta_ids,
            partial_state=partial_state,
        )

    @staticmethod
    def for_outlier(
        storage: "StorageControllers",
    ) -> "EventContext":
        """Return an EventContext instance suitable for persisting an outlier event"""
        return EventContext(storage=storage)

    async def serialize(self, event: EventBase, store: "DataStore") -> JsonDict:
        """Converts self to a type that can be serialized as JSON, and then
        deserialized by `deserialize`

        Args:
            event: The event that this context relates to

        Returns:
            The serialized event.
        """

        return {
            "state_group": self._state_group,
            "state_group_before_event": self.state_group_before_event,
            "rejected": self.rejected,
            "prev_group": self.prev_group,
            "state_delta_due_to_event": _encode_state_dict(
                self._state_delta_due_to_event
            ),
            "delta_ids": _encode_state_dict(self.delta_ids),
            "app_service_id": self.app_service.id if self.app_service else None,
            "partial_state": self.partial_state,
        }

    @staticmethod
    def deserialize(storage: "StorageControllers", input: JsonDict) -> "EventContext":
        """Converts a dict that was produced by `serialize` back into a
        EventContext.

        Args:
            storage: Used to convert AS ID to AS object and fetch state.
            input: A dict produced by `serialize`

        Returns:
            The event context.
        """
        context = EventContext(
            # We use the state_group and prev_state_id stuff to pull the
            # current_state_ids out of the DB and construct prev_state_ids.
            storage=storage,
            state_group=input["state_group"],
            state_group_before_event=input["state_group_before_event"],
            prev_group=input["prev_group"],
            state_delta_due_to_event=_decode_state_dict(
                input["state_delta_due_to_event"]
            ),
            delta_ids=_decode_state_dict(input["delta_ids"]),
            rejected=input["rejected"],
            partial_state=input.get("partial_state", False),
        )

        app_service_id = input["app_service_id"]
        if app_service_id:
            context.app_service = storage.main.get_app_service_by_id(app_service_id)

        return context

    @property
    def state_group(self) -> Optional[int]:
        """The ID of the state group for this event.

        Note that state events are persisted with a state group which includes the new
        event, so this is effectively the state *after* the event in question.

        For an outlier, where we don't have the state at the event, this will be None.

        It is an error to access this for a rejected event, since rejected state should
        not make it into the room state. Accessing this property will raise an exception
        if ``rejected`` is set.
        """
        if self.rejected:
            raise RuntimeError("Attempt to access state_group of rejected event")

        return self._state_group

    async def get_current_state_ids(
        self, state_filter: Optional["StateFilter"] = None
    ) -> Optional[StateMap[str]]:
        """
        Gets the room state map, including this event - ie, the state in ``state_group``

        It is an error to access this for a rejected event, since rejected state should
        not make it into the room state. This method will raise an exception if
        ``rejected`` is set.

        Arg:
           state_filter: specifies the type of state event to fetch from DB, example: EventTypes.JoinRules

        Returns:
            Returns None if state_group is None, which happens when the associated
            event is an outlier.

            Maps a (type, state_key) to the event ID of the state event matching
            this tuple.
        """
        if self.rejected:
            raise RuntimeError("Attempt to access state_ids of rejected event")

        assert self._state_delta_due_to_event is not None

        prev_state_ids = await self.get_prev_state_ids(state_filter)

        if self._state_delta_due_to_event:
            prev_state_ids = dict(prev_state_ids)
            prev_state_ids.update(self._state_delta_due_to_event)

        return prev_state_ids

    async def get_prev_state_ids(
        self, state_filter: Optional["StateFilter"] = None
    ) -> StateMap[str]:
        """
        Gets the room state map, excluding this event.

        For a non-state event, this will be the same as get_current_state_ids().

        Args:
            state_filter: specifies the type of state event to fetch from DB, example: EventTypes.JoinRules

        Returns:
            Returns {} if state_group is None, which happens when the associated
            event is an outlier.

            Maps a (type, state_key) to the event ID of the state event matching
            this tuple.
        """
        assert self.state_group_before_event is not None
        return await self._storage.state.get_state_ids_for_group(
            self.state_group_before_event, state_filter
        )


def _encode_state_dict(
    state_dict: Optional[StateMap[str]],
) -> Optional[List[Tuple[str, str, str]]]:
    """Since dicts of (type, state_key) -> event_id cannot be serialized in
    JSON we need to convert them to a form that can.
    """
    if state_dict is None:
        return None

    return [(etype, state_key, v) for (etype, state_key), v in state_dict.items()]


def _decode_state_dict(
    input: Optional[List[Tuple[str, str, str]]]
) -> Optional[StateMap[str]]:
    """Decodes a state dict encoded using `_encode_state_dict` above"""
    if input is None:
        return None

    return frozendict({(etype, state_key): v for etype, state_key, v in input})
