"""
Asynchronous rate limiting strategies
"""

from abc import ABC, abstractmethod
from typing import cast

from ..limits import RateLimitItem
from ..storage import StorageTypes
from ..util import WindowStats
from .storage import MovingWindowSupport, Storage


class RateLimiter(ABC):
    def __init__(self, storage: StorageTypes):
        assert isinstance(storage, Storage)
        self.storage: Storage = storage

    @abstractmethod
    async def hit(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Consume the rate limit

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The cost of this hit, default 1
        """
        raise NotImplementedError

    @abstractmethod
    async def test(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Check if the rate limit can be consumed

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The expected cost to be consumed, default 1
        """
        raise NotImplementedError

    @abstractmethod
    async def get_window_stats(
        self, item: RateLimitItem, *identifiers: str
    ) -> WindowStats:
        """
        Query the reset time and remaining amount for the limit

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :return: (reset time, remaining))
        """
        raise NotImplementedError

    async def clear(self, item: RateLimitItem, *identifiers: str) -> None:
        return await self.storage.clear(item.key_for(*identifiers))


class MovingWindowRateLimiter(RateLimiter):
    """
    Reference: :ref:`strategies:moving window`
    """

    def __init__(self, storage: StorageTypes) -> None:
        if not (
            hasattr(storage, "acquire_entry") or hasattr(storage, "get_moving_window")
        ):
            raise NotImplementedError(
                "MovingWindowRateLimiting is not implemented for storage "
                "of type %s" % storage.__class__
            )
        super().__init__(storage)

    async def hit(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Consume the rate limit

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The cost of this hit, default 1
        """

        return await cast(MovingWindowSupport, self.storage).acquire_entry(
            item.key_for(*identifiers), item.amount, item.get_expiry(), amount=cost
        )

    async def test(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Check if the rate limit can be consumed

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The expected cost to be consumed, default 1
        """
        res = await cast(MovingWindowSupport, self.storage).get_moving_window(
            item.key_for(*identifiers),
            item.amount,
            item.get_expiry(),
        )
        amount = res[1]

        return amount <= item.amount - cost

    async def get_window_stats(
        self, item: RateLimitItem, *identifiers: str
    ) -> WindowStats:
        """
        returns the number of requests remaining within this limit.

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :return: (reset time, remaining)
        """
        window_start, window_items = await cast(
            MovingWindowSupport, self.storage
        ).get_moving_window(item.key_for(*identifiers), item.amount, item.get_expiry())
        reset = window_start + item.get_expiry()

        return WindowStats(reset, item.amount - window_items)


class FixedWindowRateLimiter(RateLimiter):
    """
    Reference: :ref:`strategies:fixed window`
    """

    async def hit(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Consume the rate limit

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The cost of this hit, default 1
        """

        return (
            await self.storage.incr(
                item.key_for(*identifiers),
                item.get_expiry(),
                elastic_expiry=False,
                amount=cost,
            )
            <= item.amount
        )

    async def test(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Check if the rate limit can be consumed

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The expected cost to be consumed, default 1
        """

        return (
            await self.storage.get(item.key_for(*identifiers)) < item.amount - cost + 1
        )

    async def get_window_stats(
        self, item: RateLimitItem, *identifiers: str
    ) -> WindowStats:
        """
        Query the reset time and remaining amount for the limit

        :param item: the rate limit item
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :return: reset time, remaining
        """
        remaining = max(
            0,
            item.amount - await self.storage.get(item.key_for(*identifiers)),
        )
        reset = await self.storage.get_expiry(item.key_for(*identifiers))

        return WindowStats(reset, remaining)


class FixedWindowElasticExpiryRateLimiter(FixedWindowRateLimiter):
    """
    Reference: :ref:`strategies:fixed window with elastic expiry`
    """

    async def hit(self, item: RateLimitItem, *identifiers: str, cost: int = 1) -> bool:
        """
        Consume the rate limit

        :param item: a :class:`limits.limits.RateLimitItem` instance
        :param identifiers: variable list of strings to uniquely identify the
         limit
        :param cost: The cost of this hit, default 1
        """
        amount = await self.storage.incr(
            item.key_for(*identifiers),
            item.get_expiry(),
            elastic_expiry=True,
            amount=cost,
        )

        return amount <= item.amount


STRATEGIES = {
    "fixed-window": FixedWindowRateLimiter,
    "fixed-window-elastic-expiry": FixedWindowElasticExpiryRateLimiter,
    "moving-window": MovingWindowRateLimiter,
}