# -*- coding: utf-8 -*-
# Copyright 2018 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 logging
from collections import namedtuple

from canonicaljson import json

from twisted.internet import defer

from synapse.api.errors import SynapseError
# these are only included to make the type annotations work
from synapse.events import EventBase  # noqa: F401
from synapse.events import FrozenEvent
from synapse.events.snapshot import EventContext  # noqa: F401
from synapse.events.utils import prune_event
from synapse.util.logcontext import (
    LoggingContext,
    PreserveLoggingContext,
    make_deferred_yieldable,
    run_in_background,
)
from synapse.util.metrics import Measure

from ._base import SQLBaseStore

logger = logging.getLogger(__name__)


# These values are used in the `enqueus_event` and `_do_fetch` methods to
# control how we batch/bulk fetch events from the database.
# The values are plucked out of thing air to make initial sync run faster
# on jki.re
# TODO: Make these configurable.
EVENT_QUEUE_THREADS = 3  # Max number of threads that will fetch events
EVENT_QUEUE_ITERATIONS = 3  # No. times we block waiting for requests for events
EVENT_QUEUE_TIMEOUT_S = 0.1  # Timeout when waiting for requests for events


_EventCacheEntry = namedtuple("_EventCacheEntry", ("event", "redacted_event"))


class EventsWorkerStore(SQLBaseStore):
    def get_received_ts(self, event_id):
        """Get received_ts (when it was persisted) for the event.

        Raises an exception for unknown events.

        Args:
            event_id (str)

        Returns:
            Deferred[int|None]: Timestamp in milliseconds, or None for events
            that were persisted before received_ts was implemented.
        """
        return self._simple_select_one_onecol(
            table="events",
            keyvalues={
                "event_id": event_id,
            },
            retcol="received_ts",
            desc="get_received_ts",
        )

    @defer.inlineCallbacks
    def get_event(self, event_id, check_redacted=True,
                  get_prev_content=False, allow_rejected=False,
                  allow_none=False):
        """Get an event from the database by event_id.

        Args:
            event_id (str): The event_id of the event to fetch
            check_redacted (bool): If True, check if event has been redacted
                and redact it.
            get_prev_content (bool): If True and event is a state event,
                include the previous states content in the unsigned field.
            allow_rejected (bool): If True return rejected events.
            allow_none (bool): If True, return None if no event found, if
                False throw an exception.

        Returns:
            Deferred : A FrozenEvent.
        """
        events = yield self._get_events(
            [event_id],
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        if not events and not allow_none:
            raise SynapseError(404, "Could not find event %s" % (event_id,))

        defer.returnValue(events[0] if events else None)

    @defer.inlineCallbacks
    def get_events(self, event_ids, check_redacted=True,
                   get_prev_content=False, allow_rejected=False):
        """Get events from the database

        Args:
            event_ids (list): The event_ids of the events to fetch
            check_redacted (bool): If True, check if event has been redacted
                and redact it.
            get_prev_content (bool): If True and event is a state event,
                include the previous states content in the unsigned field.
            allow_rejected (bool): If True return rejected events.

        Returns:
            Deferred : Dict from event_id to event.
        """
        events = yield self._get_events(
            event_ids,
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        defer.returnValue({e.event_id: e for e in events})

    @defer.inlineCallbacks
    def _get_events(self, event_ids, check_redacted=True,
                    get_prev_content=False, allow_rejected=False):
        if not event_ids:
            defer.returnValue([])

        event_id_list = event_ids
        event_ids = set(event_ids)

        event_entry_map = self._get_events_from_cache(
            event_ids,
            allow_rejected=allow_rejected,
        )

        missing_events_ids = [e for e in event_ids if e not in event_entry_map]

        if missing_events_ids:
            log_ctx = LoggingContext.current_context()
            log_ctx.record_event_fetch(len(missing_events_ids))

            missing_events = yield self._enqueue_events(
                missing_events_ids,
                check_redacted=check_redacted,
                allow_rejected=allow_rejected,
            )

            event_entry_map.update(missing_events)

        events = []
        for event_id in event_id_list:
            entry = event_entry_map.get(event_id, None)
            if not entry:
                continue

            if allow_rejected or not entry.event.rejected_reason:
                if check_redacted and entry.redacted_event:
                    event = entry.redacted_event
                else:
                    event = entry.event

                events.append(event)

                if get_prev_content:
                    if "replaces_state" in event.unsigned:
                        prev = yield self.get_event(
                            event.unsigned["replaces_state"],
                            get_prev_content=False,
                            allow_none=True,
                        )
                        if prev:
                            event.unsigned = dict(event.unsigned)
                            event.unsigned["prev_content"] = prev.content
                            event.unsigned["prev_sender"] = prev.sender

        defer.returnValue(events)

    def _invalidate_get_event_cache(self, event_id):
            self._get_event_cache.invalidate((event_id,))

    def _get_events_from_cache(self, events, allow_rejected, update_metrics=True):
        """Fetch events from the caches

        Args:
            events (list(str)): list of event_ids to fetch
            allow_rejected (bool): Whether to teturn events that were rejected
            update_metrics (bool): Whether to update the cache hit ratio metrics

        Returns:
            dict of event_id -> _EventCacheEntry for each event_id in cache. If
            allow_rejected is `False` then there will still be an entry but it
            will be `None`
        """
        event_map = {}

        for event_id in events:
            ret = self._get_event_cache.get(
                (event_id,), None,
                update_metrics=update_metrics,
            )
            if not ret:
                continue

            if allow_rejected or not ret.event.rejected_reason:
                event_map[event_id] = ret
            else:
                event_map[event_id] = None

        return event_map

    def _do_fetch(self, conn):
        """Takes a database connection and waits for requests for events from
        the _event_fetch_list queue.
        """
        i = 0
        while True:
            with self._event_fetch_lock:
                event_list = self._event_fetch_list
                self._event_fetch_list = []

                if not event_list:
                    single_threaded = self.database_engine.single_threaded
                    if single_threaded or i > EVENT_QUEUE_ITERATIONS:
                        self._event_fetch_ongoing -= 1
                        return
                    else:
                        self._event_fetch_lock.wait(EVENT_QUEUE_TIMEOUT_S)
                        i += 1
                        continue
                i = 0

            self._fetch_event_list(conn, event_list)

    def _fetch_event_list(self, conn, event_list):
        """Handle a load of requests from the _event_fetch_list queue

        Args:
            conn (twisted.enterprise.adbapi.Connection): database connection

            event_list (list[Tuple[list[str], Deferred]]):
                The fetch requests. Each entry consists of a list of event
                ids to be fetched, and a deferred to be completed once the
                events have been fetched.

        """
        with Measure(self._clock, "_fetch_event_list"):
            try:
                event_id_lists = zip(*event_list)[0]
                event_ids = [
                    item for sublist in event_id_lists for item in sublist
                ]

                rows = self._new_transaction(
                    conn, "do_fetch", [], [],
                    self._fetch_event_rows, event_ids,
                )

                row_dict = {
                    r["event_id"]: r
                    for r in rows
                }

                # We only want to resolve deferreds from the main thread
                def fire(lst, res):
                    for ids, d in lst:
                        if not d.called:
                            try:
                                with PreserveLoggingContext():
                                    d.callback([
                                        res[i]
                                        for i in ids
                                        if i in res
                                    ])
                            except Exception:
                                logger.exception("Failed to callback")
                with PreserveLoggingContext():
                    self.hs.get_reactor().callFromThread(fire, event_list, row_dict)
            except Exception as e:
                logger.exception("do_fetch")

                # We only want to resolve deferreds from the main thread
                def fire(evs):
                    for _, d in evs:
                        if not d.called:
                            with PreserveLoggingContext():
                                d.errback(e)

                with PreserveLoggingContext():
                    self.hs.get_reactor().callFromThread(fire, event_list)

    @defer.inlineCallbacks
    def _enqueue_events(self, events, check_redacted=True, allow_rejected=False):
        """Fetches events from the database using the _event_fetch_list. This
        allows batch and bulk fetching of events - it allows us to fetch events
        without having to create a new transaction for each request for events.
        """
        if not events:
            defer.returnValue({})

        events_d = defer.Deferred()
        with self._event_fetch_lock:
            self._event_fetch_list.append(
                (events, events_d)
            )

            self._event_fetch_lock.notify()

            if self._event_fetch_ongoing < EVENT_QUEUE_THREADS:
                self._event_fetch_ongoing += 1
                should_start = True
            else:
                should_start = False

        if should_start:
            with PreserveLoggingContext():
                self.runWithConnection(
                    self._do_fetch
                )

        logger.debug("Loading %d events", len(events))
        with PreserveLoggingContext():
            rows = yield events_d
        logger.debug("Loaded %d events (%d rows)", len(events), len(rows))

        if not allow_rejected:
            rows[:] = [r for r in rows if not r["rejects"]]

        res = yield make_deferred_yieldable(defer.gatherResults(
            [
                run_in_background(
                    self._get_event_from_row,
                    row["internal_metadata"], row["json"], row["redacts"],
                    rejected_reason=row["rejects"],
                )
                for row in rows
            ],
            consumeErrors=True
        ))

        defer.returnValue({
            e.event.event_id: e
            for e in res if e
        })

    def _fetch_event_rows(self, txn, events):
        rows = []
        N = 200
        for i in range(1 + len(events) // N):
            evs = events[i * N:(i + 1) * N]
            if not evs:
                break

            sql = (
                "SELECT "
                " e.event_id as event_id, "
                " e.internal_metadata,"
                " e.json,"
                " r.redacts as redacts,"
                " rej.event_id as rejects "
                " FROM event_json as e"
                " LEFT JOIN rejections as rej USING (event_id)"
                " LEFT JOIN redactions as r ON e.event_id = r.redacts"
                " WHERE e.event_id IN (%s)"
            ) % (",".join(["?"] * len(evs)),)

            txn.execute(sql, evs)
            rows.extend(self.cursor_to_dict(txn))

        return rows

    @defer.inlineCallbacks
    def _get_event_from_row(self, internal_metadata, js, redacted,
                            rejected_reason=None):
        with Measure(self._clock, "_get_event_from_row"):
            d = json.loads(js)
            internal_metadata = json.loads(internal_metadata)

            if rejected_reason:
                rejected_reason = yield self._simple_select_one_onecol(
                    table="rejections",
                    keyvalues={"event_id": rejected_reason},
                    retcol="reason",
                    desc="_get_event_from_row_rejected_reason",
                )

            original_ev = FrozenEvent(
                d,
                internal_metadata_dict=internal_metadata,
                rejected_reason=rejected_reason,
            )

            redacted_event = None
            if redacted:
                redacted_event = prune_event(original_ev)

                redaction_id = yield self._simple_select_one_onecol(
                    table="redactions",
                    keyvalues={"redacts": redacted_event.event_id},
                    retcol="event_id",
                    desc="_get_event_from_row_redactions",
                )

                redacted_event.unsigned["redacted_by"] = redaction_id
                # Get the redaction event.

                because = yield self.get_event(
                    redaction_id,
                    check_redacted=False,
                    allow_none=True,
                )

                if because:
                    # It's fine to do add the event directly, since get_pdu_json
                    # will serialise this field correctly
                    redacted_event.unsigned["redacted_because"] = because

            cache_entry = _EventCacheEntry(
                event=original_ev,
                redacted_event=redacted_event,
            )

            self._get_event_cache.prefill((original_ev.event_id,), cache_entry)

        defer.returnValue(cache_entry)
