from __future__ import annotations

import asyncio
import time


class RateLimiter:
    """Twitch 速率限制令牌桶

    默认 20msg/30s (known user)，Mod/VIP 切换至 100msg/30s。
    mod 模式 60 秒后自动切回 known 模式。
    """

    MOD_TIMEOUT = 60.0

    def __init__(self, limit: int = 20, window: float = 30.0, mod_limit: int = 100):
        self._default_limit = limit
        self._mod_limit = mod_limit
        self._current_limit = limit
        self._window = window
        self._tokens = float(limit)
        self._last_refill = time.monotonic()
        self._mod_until: float | None = None
        self._lock = asyncio.Lock()

    async def switch_to_mod(self) -> None:
        async with self._lock:
            if self._current_limit == self._mod_limit:
                return
            self._current_limit = self._mod_limit
            self._tokens = float(self._mod_limit)
            self._last_refill = time.monotonic()
            self._mod_until = time.monotonic() + self.MOD_TIMEOUT

    async def switch_to_known(self) -> None:
        async with self._lock:
            self._current_limit = self._default_limit
            self._tokens = float(self._default_limit)
            self._last_refill = time.monotonic()
            self._mod_until = None

    async def acquire(self) -> bool:
        async with self._lock:
            now = time.monotonic()

            if self._mod_until is not None and now >= self._mod_until:
                self._current_limit = self._default_limit
                self._mod_until = None

            elapsed = now - self._last_refill
            refill = elapsed * (self._current_limit / self._window)
            self._tokens = min(float(self._current_limit), self._tokens + refill)
            self._last_refill = now

            if self._tokens >= 1.0:
                self._tokens -= 1.0
                return True
            return False

    @property
    def available_tokens(self) -> float:
        return self._tokens