import numbers
import uuid
from time import time

from flask import current_app
from flask_redis import FlaskRedis


def prepare_value(val):
    """
    Only bytes, strings and numbers (ints, longs and floats) are acceptable
    for keys and values. Previously redis-py attempted to cast other types
    to str() and store the result. This caused must confusion and frustration
    when passing boolean values (cast to 'True' and 'False') or None values
    (cast to 'None'). It is now the user's responsibility to cast all
    key names and values to bytes, strings or numbers before passing the
    value to redis-py.
    """
    # things redis-py natively supports
    if isinstance(
        val,
        (
            bytes,
            str,
            numbers.Number,
        ),
    ):
        return val
    # things we know we can safely cast to string
    elif isinstance(val, (uuid.UUID,)):
        return str(val)
    else:
        raise ValueError("cannot cast {} to a string".format(type(val)))


class RedisClient:
    redis_store = FlaskRedis()
    active = False
    scripts = {}

    def init_app(self, app):
        self.active = app.config.get("REDIS_ENABLED")
        if self.active:
            self.redis_store.init_app(app)

            self.register_scripts()

    def register_scripts(self):
        # delete keys matching a pattern supplied as a parameter. Does so in batches of 5000 to prevent unpack from
        # exceeding lua's stack limit, and also to prevent errors if no keys match the pattern.
        # Inspired by https://gist.github.com/ddre54/0a4751676272e0da8186
        self.scripts["delete-keys-by-pattern"] = self.redis_store.register_script(
            """
            local keys = redis.call('keys', ARGV[1])
            local deleted = 0
            for i=1, #keys, 5000 do
                deleted = deleted + redis.call('del', unpack(keys, i, math.min(i + 4999, #keys)))
            end
            return deleted
            """
        )

    def delete_by_pattern(self, pattern, raise_exception=False):
        r"""
        Deletes all keys matching a given pattern, and returns how many keys were deleted.
        Pattern is defined as in the KEYS command: https://redis.io/commands/keys

        * h?llo matches hello, hallo and hxllo
        * h*llo matches hllo and heeeello
        * h[ae]llo matches hello and hallo, but not hillo
        * h[^e]llo matches hallo, hbllo, ... but not hello
        * h[a-b]llo matches hallo and hbllo

        Use \ to escape special characters if you want to match them verbatim
        """
        if self.active:
            try:
                return self.scripts["delete-keys-by-pattern"](args=[pattern])
            except Exception as e:
                self.__handle_exception(
                    e, raise_exception, "delete-by-pattern", pattern
                )

        return 0

    def exceeded_rate_limit(self, cache_key, limit, interval, raise_exception=False):
        """
        Rate limiting.
        - Uses Redis sorted sets
        - Also uses redis "multi" which is abstracted into pipeline() by FlaskRedis/PyRedis
        - Sends all commands to redis as a group to be executed atomically

        Method:
        (1) Add event, scored by timestamp (zadd). The score determines order in set.
        (2) Use zremrangebyscore to delete all set members with a score between
            - Earliest entry (lowest score == earliest timestamp) - represented as '-inf'
                and
            - Current timestamp minus the interval
            - Leaves only relevant entries in the set (those between now and now - interval)
        (3) Count the set
        (4) If count > limit fail request
        (5) Ensure we expire the set key to preserve space

        Notes:
        - Failed requests count. If over the limit and keep making requests you'll stay over the limit.
        - The actual value in the set is just the timestamp, the same as the score. We don't store any requets details.
        - return value of pipe.execute() is an array containing the outcome of each call.
            - result[2] == outcome of pipe.zcard()
        - If redis is inactive, or we get an exception, allow the request

        :param cache_key:
        :param limit: Number of requests permitted within interval
        :param interval: Interval we measure requests in
        :param raise_exception: Should throw exception
        :return:
        """
        cache_key = prepare_value(cache_key)
        if self.active:
            try:
                pipe = self.redis_store.pipeline()
                when = time()
                pipe.zadd(cache_key, {when: when})
                pipe.zremrangebyscore(cache_key, "-inf", when - interval)
                pipe.zcard(cache_key)
                pipe.expire(cache_key, interval)
                result = pipe.execute()
                return result[2] > limit
            except Exception as e:
                self.__handle_exception(
                    e, raise_exception, "rate-limit-pipeline", cache_key
                )
                return False
        else:
            return False

    def set(
        self, key, value, ex=None, px=None, nx=False, xx=False, raise_exception=False
    ):
        key = prepare_value(key)
        value = prepare_value(value)
        if self.active:
            self.redis_store.set(key, value, ex, px, nx, xx)

    def incr(self, key, raise_exception=False):
        key = prepare_value(key)
        if self.active:
            try:
                return self.redis_store.incr(key)
            except Exception as e:
                self.__handle_exception(e, raise_exception, "incr", key)

    def get(self, key, raise_exception=False):
        key = prepare_value(key)
        if self.active:
            return self.redis_store.get(key)

        return None

    def delete(self, *keys, raise_exception=False):
        keys = [prepare_value(k) for k in keys]
        if self.active:
            try:
                self.redis_store.delete(*keys)
            except Exception as e:
                self.__handle_exception(e, raise_exception, "delete", ", ".join(keys))

    def __handle_exception(self, e, raise_exception, operation, key_name):
        current_app.logger.exception(
            "Redis error performing {} on {}".format(operation, key_name), exc_info=True
        )
        if raise_exception:
            raise e