insightflow/backend/rate_limiter.py

#!/usr/bin/env python3
"""
InsightFlow Rate Limiter - Phase 6
API 限流中间件
支持基于内存的滑动窗口限流
"""

import asyncio
import time
from collections import defaultdict
from collections.abc import Callable
from dataclasses import dataclass
from functools import wraps


@dataclass
class RateLimitConfig:
    """限流配置"""

    requests_per_minute: int = 60
    burst_size: int = 10  # 突发请求数
    window_size: int = 60  # 窗口大小（秒）


@dataclass
class RateLimitInfo:
    """限流信息"""

    allowed: bool
    remaining: int
    reset_time: int  # 重置时间戳
    retry_after: int  # 需要等待的秒数


class SlidingWindowCounter:
    """滑动窗口计数器"""

    def __init__(self, window_size: int = 60):
        self.window_size = window_size
        self.requests: dict[int, int] = defaultdict(int)  # 秒级计数
        self._lock = asyncio.Lock()
        self._cleanup_lock = asyncio.Lock()

    async def add_request(self) -> int:
        """添加请求，返回当前窗口内的请求数"""
        async with self._lock:
            now = int(time.time())
            self.requests[now] += 1
            self._cleanup_old(now)
            return sum(self.requests.values())

    async def get_count(self) -> int:
        """获取当前窗口内的请求数"""
        async with self._lock:
            now = int(time.time())
            self._cleanup_old(now)
            return sum(self.requests.values())

    def _cleanup_old(self, now: int):
        """清理过期的请求记录 - 使用独立锁避免竞态条件"""
        cutoff = now - self.window_size
        old_keys = [k for k in list(self.requests.keys()) if k < cutoff]
        for k in old_keys:
            self.requests.pop(k, None)


class RateLimiter:
    """API 限流器"""

    def __init__(self):
        # key -> SlidingWindowCounter
        self.counters: dict[str, SlidingWindowCounter] = {}
        # key -> RateLimitConfig
        self.configs: dict[str, RateLimitConfig] = {}
        self._lock = asyncio.Lock()
        self._cleanup_lock = asyncio.Lock()

    async def is_allowed(self, key: str, config: RateLimitConfig | None = None) -> RateLimitInfo:
        """
        检查是否允许请求

        Args:
            key: 限流键（如 API Key ID）
            config: 限流配置，如果为 None 则使用默认配置

        Returns:
            RateLimitInfo
        """
        if config is None:
            config = RateLimitConfig()

        async with self._lock:
            if key not in self.counters:
                self.counters[key] = SlidingWindowCounter(config.window_size)
                self.configs[key] = config

        counter = self.counters[key]
        stored_config = self.configs.get(key, config)

        # 获取当前计数
        current_count = await counter.get_count()

        # 计算剩余配额
        remaining = max(0, stored_config.requests_per_minute - current_count)

        # 计算重置时间
        now = int(time.time())
        reset_time = now + stored_config.window_size

        # 检查是否超过限制
        if current_count >= stored_config.requests_per_minute:
            return RateLimitInfo(
                allowed=False, remaining=0, reset_time=reset_time, retry_after=stored_config.window_size
            )

        # 允许请求，增加计数
        await counter.add_request()

        return RateLimitInfo(allowed=True, remaining=remaining - 1, reset_time=reset_time, retry_after=0)

    async def get_limit_info(self, key: str) -> RateLimitInfo:
        """获取限流信息（不增加计数）"""
        if key not in self.counters:
            config = RateLimitConfig()
            return RateLimitInfo(
                allowed=True,
                remaining=config.requests_per_minute,
                reset_time=int(time.time()) + config.window_size,
                retry_after=0,
            )

        counter = self.counters[key]
        config = self.configs.get(key, RateLimitConfig())

        current_count = await counter.get_count()
        remaining = max(0, config.requests_per_minute - current_count)
        reset_time = int(time.time()) + config.window_size

        return RateLimitInfo(
            allowed=current_count < config.requests_per_minute,
            remaining=remaining,
            reset_time=reset_time,
            retry_after=max(0, config.window_size) if current_count >= config.requests_per_minute else 0,
        )

    def reset(self, key: str | None = None):
        """重置限流计数器"""
        if key:
            self.counters.pop(key, None)
            self.configs.pop(key, None)
        else:
            self.counters.clear()
            self.configs.clear()


# 全局限流器实例
_rate_limiter: RateLimiter | None = None


def get_rate_limiter() -> RateLimiter:
    """获取限流器实例"""
    global _rate_limiter
    if _rate_limiter is None:
        _rate_limiter = RateLimiter()
    return _rate_limiter


# 限流装饰器（用于函数级别限流）
def rate_limit(requests_per_minute: int = 60, key_func: Callable | None = None):
    """
    限流装饰器

    Args:
        requests_per_minute: 每分钟请求数限制
        key_func: 生成限流键的函数，默认为 None（使用函数名）
    """

    def decorator(func):
        limiter = get_rate_limiter()
        config = RateLimitConfig(requests_per_minute=requests_per_minute)

        @wraps(func)
        async def async_wrapper(*args, **kwargs):
            key = key_func(*args, **kwargs) if key_func else func.__name__
            info = await limiter.is_allowed(key, config)

            if not info.allowed:
                raise RateLimitExceeded(f"Rate limit exceeded. Try again in {info.retry_after} seconds.")

            return await func(*args, **kwargs)

        @wraps(func)
        def sync_wrapper(*args, **kwargs):
            key = key_func(*args, **kwargs) if key_func else func.__name__
            # 同步版本使用 asyncio.run
            info = asyncio.run(limiter.is_allowed(key, config))

            if not info.allowed:
                raise RateLimitExceeded(f"Rate limit exceeded. Try again in {info.retry_after} seconds.")

            return func(*args, **kwargs)

        return async_wrapper if asyncio.iscoroutinefunction(func) else sync_wrapper

    return decorator


class RateLimitExceeded(Exception):
    """限流异常"""