# -*- coding: utf-8 -*-
# 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 six import iteritems

from frozendict import frozendict

from twisted.internet import defer

from synapse.util.logcontext import make_deferred_yieldable, run_in_background


class EventContext(object):
    """
    Attributes:
        state_group (int|None): state group id, if the state has been stored
            as a state group. This is usually only None if e.g. the event is
            an outlier.
        rejected (bool|str): A rejection reason if the event was rejected, else
            False

        push_actions (list[(str, list[object])]): list of (user_id, actions)
            tuples

        prev_group (int): Previously persisted state group. ``None`` for an
            outlier.
        delta_ids (dict[(str, str), str]): Delta from ``prev_group``.
            (type, state_key) -> event_id. ``None`` for an outlier.

        prev_state_events (?): XXX: is this ever set to anything other than
            the empty list?

        _current_state_ids (dict[(str, str), str]|None):
            The current state map including the current event. None if outlier
            or we haven't fetched the state from DB yet.
            (type, state_key) -> event_id

        _prev_state_ids (dict[(str, str), str]|None):
            The current state map excluding the current event. None if outlier
            or we haven't fetched the state from DB yet.
            (type, state_key) -> event_id

        _fetching_state_deferred (Deferred|None): Resolves when *_state_ids have
            been calculated. None if we haven't started calculating yet

        _event_type (str): The type of the event the context is associated with.
            Only set when state has not been fetched yet.

        _event_state_key (str|None): The state_key of the event the context is
            associated with. Only set when state has not been fetched yet.

        _prev_state_id (str|None): If the event associated with the context is
            a state event, then `_prev_state_id` is the event_id of the state
            that was replaced.
            Only set when state has not been fetched yet.
    """

    __slots__ = [
        "state_group",
        "rejected",
        "prev_group",
        "delta_ids",
        "prev_state_events",
        "app_service",
        "_current_state_ids",
        "_prev_state_ids",
        "_prev_state_id",
        "_event_type",
        "_event_state_key",
        "_fetching_state_deferred",
    ]

    def __init__(self):
        self.prev_state_events = []
        self.rejected = False
        self.app_service = None

    @staticmethod
    def with_state(state_group, current_state_ids, prev_state_ids,
                   prev_group=None, delta_ids=None):
        context = EventContext()

        # The current state including the current event
        context._current_state_ids = current_state_ids
        # The current state excluding the current event
        context._prev_state_ids = prev_state_ids
        context.state_group = state_group

        context._prev_state_id = None
        context._event_type = None
        context._event_state_key = None
        context._fetching_state_deferred = defer.succeed(None)

        # A previously persisted state group and a delta between that
        # and this state.
        context.prev_group = prev_group
        context.delta_ids = delta_ids

        return context

    @defer.inlineCallbacks
    def serialize(self, event, store):
        """Converts self to a type that can be serialized as JSON, and then
        deserialized by `deserialize`

        Args:
            event (FrozenEvent): The event that this context relates to

        Returns:
            dict
        """

        # We don't serialize the full state dicts, instead they get pulled out
        # of the DB on the other side. However, the other side can't figure out
        # the prev_state_ids, so if we're a state event we include the event
        # id that we replaced in the state.
        if event.is_state():
            prev_state_ids = yield self.get_prev_state_ids(store)
            prev_state_id = prev_state_ids.get((event.type, event.state_key))
        else:
            prev_state_id = None

        defer.returnValue({
            "prev_state_id": prev_state_id,
            "event_type": event.type,
            "event_state_key": event.state_key if event.is_state() else None,
            "state_group": self.state_group,
            "rejected": self.rejected,
            "prev_group": self.prev_group,
            "delta_ids": _encode_state_dict(self.delta_ids),
            "prev_state_events": self.prev_state_events,
            "app_service_id": self.app_service.id if self.app_service else None
        })

    @staticmethod
    def deserialize(store, input):
        """Converts a dict that was produced by `serialize` back into a
        EventContext.

        Args:
            store (DataStore): Used to convert AS ID to AS object
            input (dict): A dict produced by `serialize`

        Returns:
            EventContext
        """
        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.
        context._prev_state_id = input["prev_state_id"]
        context._event_type = input["event_type"]
        context._event_state_key = input["event_state_key"]

        context._current_state_ids = None
        context._prev_state_ids = None
        context._fetching_state_deferred = None

        context.state_group = input["state_group"]
        context.prev_group = input["prev_group"]
        context.delta_ids = _decode_state_dict(input["delta_ids"])

        context.rejected = input["rejected"]
        context.prev_state_events = input["prev_state_events"]

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

        return context

    @defer.inlineCallbacks
    def get_current_state_ids(self, store):
        """Gets the current state IDs

        Returns:
            Deferred[dict[(str, str), str]|None]: 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 not self._fetching_state_deferred:
            self._fetching_state_deferred = run_in_background(
                self._fill_out_state, store,
            )

        yield make_deferred_yieldable(self._fetching_state_deferred)

        defer.returnValue(self._current_state_ids)

    @defer.inlineCallbacks
    def get_prev_state_ids(self, store):
        """Gets the prev state IDs

        Returns:
            Deferred[dict[(str, str), str]|None]: 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 not self._fetching_state_deferred:
            self._fetching_state_deferred = run_in_background(
                self._fill_out_state, store,
            )

        yield make_deferred_yieldable(self._fetching_state_deferred)

        defer.returnValue(self._prev_state_ids)

    def get_cached_current_state_ids(self):
        """Gets the current state IDs if we have them already cached.

        Returns:
            dict[(str, str), str]|None: Returns None if we haven't cached the
            state or if state_group is None, which happens when the associated
            event is an outlier.
        """

        return self._current_state_ids

    @defer.inlineCallbacks
    def _fill_out_state(self, store):
        """Called to populate the _current_state_ids and _prev_state_ids
        attributes by loading from the database.
        """
        if self.state_group is None:
            return

        self._current_state_ids = yield store.get_state_ids_for_group(
            self.state_group,
        )
        if self._prev_state_id and self._event_state_key is not None:
            self._prev_state_ids = dict(self._current_state_ids)

            key = (self._event_type, self._event_state_key)
            self._prev_state_ids[key] = self._prev_state_id
        else:
            self._prev_state_ids = self._current_state_ids

    @defer.inlineCallbacks
    def update_state(self, state_group, prev_state_ids, current_state_ids,
                     prev_group, delta_ids):
        """Replace the state in the context
        """

        # We need to make sure we wait for any ongoing fetching of state
        # to complete so that the updated state doesn't get clobbered
        if self._fetching_state_deferred:
            yield make_deferred_yieldable(self._fetching_state_deferred)

        self.state_group = state_group
        self._prev_state_ids = prev_state_ids
        self.prev_group = prev_group
        self._current_state_ids = current_state_ids
        self.delta_ids = delta_ids

        # We need to ensure that that we've marked as having fetched the state
        self._fetching_state_deferred = defer.succeed(None)


def _encode_state_dict(state_dict):
    """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 iteritems(state_dict)
    ]


def _decode_state_dict(input):
    """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})
