import threading
import time
from functools import wraps
from flask import current_app, jsonify, stream_with_context, Response, request


class ExecutionTimeoutMonitor:
    """监控请求执行时间，超时后释放信号量"""
    def __init__(self, timeout, semaphore):
        self.timeout = timeout
        self.semaphore = semaphore
        self.is_timeout = False
        self.thread = threading.Thread(target=self._monitor)
        self.thread.daemon = True

    def _monitor(self):
        """等待指定时间后标记为超时并释放信号量
        目前的超时机制是通过 ExecutionTimeoutMonitor 的标志位来通知生成器超时。
        但是，生成器只有在下一次 yield 时才会检查标志位，因此不会在当前执行的代码段中间强行中断。
        """
        time.sleep(self.timeout)
        self.is_timeout = True
        self.semaphore.release()  # 超时后释放信号量
        current_app.logger.error(f"Request execution exceeded {self.timeout} seconds and was terminated.")

    def start(self):
        self.thread.start()

def require_connection_limit(timeout=900):
    def decorator(f):
        @wraps(f)
        def wrapped(*args, **kwargs):
            blueprint = request.blueprint
            limiter = current_app.connection_limiters.get(blueprint, current_app.connection_limiters.get('default'))
            if limiter is None:
                current_app.logger.error(f"未为蓝图 '{blueprint}' 配置 ConnectionLimiter，并且未设置默认限流器。")
                return jsonify({'error': '服务器配置错误'}), 500

            # 获取信号量（阻塞）
            acquired = limiter.semaphore.acquire(blocking=True)
            if not acquired:
                current_app.logger.warning("并发连接过多")
                return jsonify({'error': '并发连接过多'}), 429

            try:
                # 启动执行超时监控器
                monitor = ExecutionTimeoutMonitor(timeout, limiter.semaphore)
                monitor.start()

                generator = f(*args, **kwargs)

                @stream_with_context
                def generator_wrapper():
                    try:
                        for item in generator:
                            if monitor.is_timeout:
                                current_app.logger.error("请求执行时间超过限制并被终止。")
                                break
                            yield item
                    finally:
                        if not monitor.is_timeout:
                            limiter.semaphore.release()  # 正常结束时释放信号量

                return Response(generator_wrapper(), mimetype='text/event-stream')
            except Exception as e:
                limiter.semaphore.release()  # 异常时释放信号量
                current_app.logger.error(f"路由处理异常: {e}")
                return jsonify({'error': '内部服务器错误'}), 500
        return wrapped
    return decorator

class ConnectionLimiter:
    def __init__(self, max_connections=1):
        self.semaphore = threading.Semaphore(max_connections)