# -*- coding: utf-8 -*-
# Copyright 2019 Matrix.org Foundation C.I.C.
#
# 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 os
from typing import Callable, Dict

from ._base import Config, ConfigError

# The prefix for all cache factor-related environment variables
_CACHES = {}
_CACHE_PREFIX = "SYNAPSE_CACHE_FACTOR"
_DEFAULT_FACTOR_SIZE = 0.5
_DEFAULT_EVENT_CACHE_SIZE = "10K"


class CacheProperties(object):
    def __init__(self):
        # The default factor size for all caches
        self.default_factor_size = float(
            os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
        )
        self.resize_all_caches_func = None


properties = CacheProperties()


def add_resizable_cache(cache_name: str, cache_resize_callback: Callable):
    """Register a cache that's size can dynamically change

    Args:
        cache_name: A reference to the cache
        cache_resize_callback: A callback function that will be ran whenever
            the cache needs to be resized
    """
    _CACHES[cache_name.lower()] = cache_resize_callback

    # Ensure all loaded caches are sized appropriately
    #
    # This method should only run once the config has been read,
    # as it uses values read from it
    if properties.resize_all_caches_func:
        properties.resize_all_caches_func()


class CacheConfig(Config):
    section = "caches"
    _environ = os.environ

    @staticmethod
    def reset():
        """Resets the caches to their defaults. Used for tests."""
        properties.default_factor_size = float(
            os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
        )
        properties.resize_all_caches_func = None
        _CACHES.clear()

    def generate_config_section(self, **kwargs):
        return """\
        ## Caching ##

        # Caching can be configured through the following options.
        #
        # A cache 'factor' is a multiplier that can be applied to each of
        # Synapse's caches in order to increase or decrease the maximum
        # number of entries that can be stored.

        # The number of events to cache in memory. Not affected by
        # caches.global_factor.
        #
        #event_cache_size: 10K

        caches:
           # Controls the global cache factor, which is the default cache factor
           # for all caches if a specific factor for that cache is not otherwise
           # set.
           #
           # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
           # variable. Setting by environment variable takes priority over
           # setting through the config file.
           #
           # Defaults to 0.5, which will half the size of all caches.
           #
           #global_factor: 1.0

           # A dictionary of cache name to cache factor for that individual
           # cache. Overrides the global cache factor for a given cache.
           #
           # These can also be set through environment variables comprised
           # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
           # letters and underscores. Setting by environment variable
           # takes priority over setting through the config file.
           # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
           #
           per_cache_factors:
             #get_users_who_share_room_with_user: 2.0
        """

    def read_config(self, config, **kwargs):
        self.event_cache_size = self.parse_size(
            config.get("event_cache_size", _DEFAULT_EVENT_CACHE_SIZE)
        )
        self.cache_factors = {}  # type: Dict[str, float]

        cache_config = config.get("caches") or {}
        self.global_factor = cache_config.get(
            "global_factor", properties.default_factor_size
        )
        if not isinstance(self.global_factor, (int, float)):
            raise ConfigError("caches.global_factor must be a number.")

        # Set the global one so that it's reflected in new caches
        properties.default_factor_size = self.global_factor

        # Load cache factors from the config
        individual_factors = cache_config.get("per_cache_factors") or {}
        if not isinstance(individual_factors, dict):
            raise ConfigError("caches.per_cache_factors must be a dictionary")

        # Override factors from environment if necessary
        individual_factors.update(
            {
                key[len(_CACHE_PREFIX) + 1 :].lower(): float(val)
                for key, val in self._environ.items()
                if key.startswith(_CACHE_PREFIX + "_")
            }
        )

        for cache, factor in individual_factors.items():
            if not isinstance(factor, (int, float)):
                raise ConfigError(
                    "caches.per_cache_factors.%s must be a number" % (cache.lower(),)
                )
            self.cache_factors[cache.lower()] = factor

        # Resize all caches (if necessary) with the new factors we've loaded
        self.resize_all_caches()

        # Store this function so that it can be called from other classes without
        # needing an instance of Config
        properties.resize_all_caches_func = self.resize_all_caches

    def resize_all_caches(self):
        """Ensure all cache sizes are up to date

        For each cache, run the mapped callback function with either
        a specific cache factor or the default, global one.
        """
        for cache_name, callback in _CACHES.items():
            new_factor = self.cache_factors.get(cache_name, self.global_factor)
            callback(new_factor)
