# -*- 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.

import logging
from typing import Optional

from canonicaljson import json

from twisted.internet import defer

from synapse.metrics.background_process_metrics import run_as_background_process

from . import engines

logger = logging.getLogger(__name__)


class BackgroundUpdatePerformance(object):
    """Tracks the how long a background update is taking to update its items"""

    def __init__(self, name):
        self.name = name
        self.total_item_count = 0
        self.total_duration_ms = 0
        self.avg_item_count = 0
        self.avg_duration_ms = 0

    def update(self, item_count, duration_ms):
        """Update the stats after doing an update"""
        self.total_item_count += item_count
        self.total_duration_ms += duration_ms

        # Exponential moving averages for the number of items updated and
        # the duration.
        self.avg_item_count += 0.1 * (item_count - self.avg_item_count)
        self.avg_duration_ms += 0.1 * (duration_ms - self.avg_duration_ms)

    def average_items_per_ms(self):
        """An estimate of how long it takes to do a single update.
        Returns:
            A duration in ms as a float
        """
        if self.avg_duration_ms == 0:
            return 0
        elif self.total_item_count == 0:
            return None
        else:
            # Use the exponential moving average so that we can adapt to
            # changes in how long the update process takes.
            return float(self.avg_item_count) / float(self.avg_duration_ms)

    def total_items_per_ms(self):
        """An estimate of how long it takes to do a single update.
        Returns:
            A duration in ms as a float
        """
        if self.total_duration_ms == 0:
            return 0
        elif self.total_item_count == 0:
            return None
        else:
            return float(self.total_item_count) / float(self.total_duration_ms)


class BackgroundUpdater(object):
    """ Background updates are updates to the database that run in the
    background. Each update processes a batch of data at once. We attempt to
    limit the impact of each update by monitoring how long each batch takes to
    process and autotuning the batch size.
    """

    MINIMUM_BACKGROUND_BATCH_SIZE = 100
    DEFAULT_BACKGROUND_BATCH_SIZE = 100
    BACKGROUND_UPDATE_INTERVAL_MS = 1000
    BACKGROUND_UPDATE_DURATION_MS = 100

    def __init__(self, hs, database):
        self._clock = hs.get_clock()
        self.db = database

        self._background_update_performance = {}
        self._background_update_queue = []
        self._background_update_handlers = {}
        self._all_done = False

    def start_doing_background_updates(self):
        run_as_background_process("background_updates", self.run_background_updates)

    async def run_background_updates(self, sleep=True):
        logger.info("Starting background schema updates")
        while True:
            if sleep:
                await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)

            try:
                result = await self.do_next_background_update(
                    self.BACKGROUND_UPDATE_DURATION_MS
                )
            except Exception:
                logger.exception("Error doing update")
            else:
                if result is None:
                    logger.info(
                        "No more background updates to do."
                        " Unscheduling background update task."
                    )
                    self._all_done = True
                    return None

    @defer.inlineCallbacks
    def has_completed_background_updates(self):
        """Check if all the background updates have completed

        Returns:
            Deferred[bool]: True if all background updates have completed
        """
        # if we've previously determined that there is nothing left to do, that
        # is easy
        if self._all_done:
            return True

        # obviously, if we have things in our queue, we're not done.
        if self._background_update_queue:
            return False

        # otherwise, check if there are updates to be run. This is important,
        # as we may be running on a worker which doesn't perform the bg updates
        # itself, but still wants to wait for them to happen.
        updates = yield self.db.simple_select_onecol(
            "background_updates",
            keyvalues=None,
            retcol="1",
            desc="has_completed_background_updates",
        )
        if not updates:
            self._all_done = True
            return True

        return False

    async def has_completed_background_update(self, update_name) -> bool:
        """Check if the given background update has finished running.
        """

        if self._all_done:
            return True

        if update_name in self._background_update_queue:
            return False

        update_exists = await self.db.simple_select_one_onecol(
            "background_updates",
            keyvalues={"update_name": update_name},
            retcol="1",
            desc="has_completed_background_update",
            allow_none=True,
        )

        return not update_exists

    async def do_next_background_update(
        self, desired_duration_ms: float
    ) -> Optional[int]:
        """Does some amount of work on the next queued background update

        Returns once some amount of work is done.

        Args:
            desired_duration_ms(float): How long we want to spend
                updating.
        Returns:
            None if there is no more work to do, otherwise an int
        """
        if not self._background_update_queue:
            updates = await self.db.simple_select_list(
                "background_updates",
                keyvalues=None,
                retcols=("update_name", "depends_on"),
            )
            in_flight = set(update["update_name"] for update in updates)
            for update in updates:
                if update["depends_on"] not in in_flight:
                    self._background_update_queue.append(update["update_name"])

        if not self._background_update_queue:
            # no work left to do
            return None

        # pop from the front, and add back to the back
        update_name = self._background_update_queue.pop(0)
        self._background_update_queue.append(update_name)

        res = await self._do_background_update(update_name, desired_duration_ms)
        return res

    async def _do_background_update(
        self, update_name: str, desired_duration_ms: float
    ) -> int:
        logger.info("Starting update batch on background update '%s'", update_name)

        update_handler = self._background_update_handlers[update_name]

        performance = self._background_update_performance.get(update_name)

        if performance is None:
            performance = BackgroundUpdatePerformance(update_name)
            self._background_update_performance[update_name] = performance

        items_per_ms = performance.average_items_per_ms()

        if items_per_ms is not None:
            batch_size = int(desired_duration_ms * items_per_ms)
            # Clamp the batch size so that we always make progress
            batch_size = max(batch_size, self.MINIMUM_BACKGROUND_BATCH_SIZE)
        else:
            batch_size = self.DEFAULT_BACKGROUND_BATCH_SIZE

        progress_json = await self.db.simple_select_one_onecol(
            "background_updates",
            keyvalues={"update_name": update_name},
            retcol="progress_json",
        )

        progress = json.loads(progress_json)

        time_start = self._clock.time_msec()
        items_updated = await update_handler(progress, batch_size)
        time_stop = self._clock.time_msec()

        duration_ms = time_stop - time_start

        logger.info(
            "Running background update %r. Processed %r items in %rms."
            " (total_rate=%r/ms, current_rate=%r/ms, total_updated=%r, batch_size=%r)",
            update_name,
            items_updated,
            duration_ms,
            performance.total_items_per_ms(),
            performance.average_items_per_ms(),
            performance.total_item_count,
            batch_size,
        )

        performance.update(items_updated, duration_ms)

        return len(self._background_update_performance)

    def register_background_update_handler(self, update_name, update_handler):
        """Register a handler for doing a background update.

        The handler should take two arguments:

        * A dict of the current progress
        * An integer count of the number of items to update in this batch.

        The handler should return a deferred or coroutine which returns an integer count
        of items updated.

        The handler is responsible for updating the progress of the update.

        Args:
            update_name(str): The name of the update that this code handles.
            update_handler(function): The function that does the update.
        """
        self._background_update_handlers[update_name] = update_handler

    def register_noop_background_update(self, update_name):
        """Register a noop handler for a background update.

        This is useful when we previously did a background update, but no
        longer wish to do the update. In this case the background update should
        be removed from the schema delta files, but there may still be some
        users who have the background update queued, so this method should
        also be called to clear the update.

        Args:
            update_name (str): Name of update
        """

        @defer.inlineCallbacks
        def noop_update(progress, batch_size):
            yield self._end_background_update(update_name)
            return 1

        self.register_background_update_handler(update_name, noop_update)

    def register_background_index_update(
        self,
        update_name,
        index_name,
        table,
        columns,
        where_clause=None,
        unique=False,
        psql_only=False,
    ):
        """Helper for store classes to do a background index addition

        To use:

        1. use a schema delta file to add a background update. Example:
            INSERT INTO background_updates (update_name, progress_json) VALUES
                ('my_new_index', '{}');

        2. In the Store constructor, call this method

        Args:
            update_name (str): update_name to register for
            index_name (str): name of index to add
            table (str): table to add index to
            columns (list[str]): columns/expressions to include in index
            unique (bool): true to make a UNIQUE index
            psql_only: true to only create this index on psql databases (useful
                for virtual sqlite tables)
        """

        def create_index_psql(conn):
            conn.rollback()
            # postgres insists on autocommit for the index
            conn.set_session(autocommit=True)

            try:
                c = conn.cursor()

                # If a previous attempt to create the index was interrupted,
                # we may already have a half-built index. Let's just drop it
                # before trying to create it again.

                sql = "DROP INDEX IF EXISTS %s" % (index_name,)
                logger.debug("[SQL] %s", sql)
                c.execute(sql)

                sql = (
                    "CREATE %(unique)s INDEX CONCURRENTLY %(name)s"
                    " ON %(table)s"
                    " (%(columns)s) %(where_clause)s"
                ) % {
                    "unique": "UNIQUE" if unique else "",
                    "name": index_name,
                    "table": table,
                    "columns": ", ".join(columns),
                    "where_clause": "WHERE " + where_clause if where_clause else "",
                }
                logger.debug("[SQL] %s", sql)
                c.execute(sql)
            finally:
                conn.set_session(autocommit=False)

        def create_index_sqlite(conn):
            # Sqlite doesn't support concurrent creation of indexes.
            #
            # We don't use partial indices on SQLite as it wasn't introduced
            # until 3.8, and wheezy and CentOS 7 have 3.7
            #
            # We assume that sqlite doesn't give us invalid indices; however
            # we may still end up with the index existing but the
            # background_updates not having been recorded if synapse got shut
            # down at the wrong moment - hance we use IF NOT EXISTS. (SQLite
            # has supported CREATE TABLE|INDEX IF NOT EXISTS since 3.3.0.)
            sql = (
                "CREATE %(unique)s INDEX IF NOT EXISTS %(name)s ON %(table)s"
                " (%(columns)s)"
            ) % {
                "unique": "UNIQUE" if unique else "",
                "name": index_name,
                "table": table,
                "columns": ", ".join(columns),
            }

            c = conn.cursor()
            logger.debug("[SQL] %s", sql)
            c.execute(sql)

        if isinstance(self.db.engine, engines.PostgresEngine):
            runner = create_index_psql
        elif psql_only:
            runner = None
        else:
            runner = create_index_sqlite

        @defer.inlineCallbacks
        def updater(progress, batch_size):
            if runner is not None:
                logger.info("Adding index %s to %s", index_name, table)
                yield self.db.runWithConnection(runner)
            yield self._end_background_update(update_name)
            return 1

        self.register_background_update_handler(update_name, updater)

    def start_background_update(self, update_name, progress):
        """Starts a background update running.

        Args:
            update_name: The update to set running.
            progress: The initial state of the progress of the update.

        Returns:
            A deferred that completes once the task has been added to the
            queue.
        """
        # Clear the background update queue so that we will pick up the new
        # task on the next iteration of do_background_update.
        self._background_update_queue = []
        progress_json = json.dumps(progress)

        return self.db.simple_insert(
            "background_updates",
            {"update_name": update_name, "progress_json": progress_json},
        )

    def _end_background_update(self, update_name):
        """Removes a completed background update task from the queue.

        Args:
            update_name(str): The name of the completed task to remove
        Returns:
            A deferred that completes once the task is removed.
        """
        self._background_update_queue = [
            name for name in self._background_update_queue if name != update_name
        ]
        return self.db.simple_delete_one(
            "background_updates", keyvalues={"update_name": update_name}
        )

    def _background_update_progress(self, update_name: str, progress: dict):
        """Update the progress of a background update

        Args:
            update_name: The name of the background update task
            progress: The progress of the update.
        """

        return self.db.runInteraction(
            "background_update_progress",
            self._background_update_progress_txn,
            update_name,
            progress,
        )

    def _background_update_progress_txn(self, txn, update_name, progress):
        """Update the progress of a background update

        Args:
            txn(cursor): The transaction.
            update_name(str): The name of the background update task
            progress(dict): The progress of the update.
        """

        progress_json = json.dumps(progress)

        self.db.simple_update_one_txn(
            txn,
            "background_updates",
            keyvalues={"update_name": update_name},
            updatevalues={"progress_json": progress_json},
        )
