"""
视频捕获锁模块

提供线程安全的 VideoCapture 操作，防止 FFmpeg 多线程解码崩溃。

改进：从全局锁改为每摄像头独立锁 + 超时机制。
- 每路摄像头使用独立的锁，不再互相阻塞
- 超时读帧：如果某路摄像头卡住，不会无限阻塞其他路
- 健康检查：记录每路流的状态（最近帧时间、连续错误数等）
"""

import threading
import time
from typing import Optional, Tuple, Dict
from dataclasses import dataclass, field


@dataclass
class StreamHealth:
    """流健康状态"""
    camera_id: str = ""
    last_frame_time: float = 0.0       # 最近成功读帧时间
    consecutive_errors: int = 0         # 连续错误数
    total_frames: int = 0               # 总帧数
    total_errors: int = 0               # 总错误数
    is_healthy: bool = True             # 是否健康
    avg_read_time_ms: float = 0.0      # 平均读帧耗时(ms)


class CameraLockManager:
    """
    每摄像头独立锁管理器
    
    替代全局锁，每路摄像头使用独立的锁，互不阻塞。
    FFmpeg 内部的 async_lock 问题仅在多个 VideoCapture 实例
    并发调用 read() 时触发。独立锁允许同一路的读操作串行化，
    而不同路之间完全并行。
    """
    
    def __init__(self):
        self._locks: Dict[str, threading.Lock] = {}
        self._health: Dict[str, StreamHealth] = {}
        self._global_lock = threading.Lock()  # 仅用于管理锁的创建
    
    def get_lock(self, camera_id: str) -> threading.Lock:
        """获取或创建指定摄像头的独立锁"""
        with self._global_lock:
            if camera_id not in self._locks:
                self._locks[camera_id] = threading.Lock()
                self._health[camera_id] = StreamHealth(camera_id=camera_id)
            return self._locks[camera_id]
    
    def get_health(self, camera_id: str) -> StreamHealth:
        """获取摄像头流健康状态"""
        with self._global_lock:
            return self._health.get(camera_id, StreamHealth(camera_id=camera_id))
    
    def update_health(self, camera_id: str, success: bool, read_time_ms: float = 0.0):
        """更新流健康状态"""
        with self._global_lock:
            health = self._health.get(camera_id)
            if health is None:
                health = StreamHealth(camera_id=camera_id)
                self._health[camera_id] = health
            
            if success:
                health.last_frame_time = time.time()
                health.consecutive_errors = 0
                health.total_frames += 1
                health.is_healthy = True
                # 指数移动平均计算读帧耗时
                alpha = 0.1
                health.avg_read_time_ms = alpha * read_time_ms + (1 - alpha) * health.avg_read_time_ms
            else:
                health.consecutive_errors += 1
                health.total_errors += 1
                if health.consecutive_errors > 50:
                    health.is_healthy = False


# 全局锁管理器实例
_manager = CameraLockManager()


def safe_read(cap, camera_id: str = "default", timeout: float = 5.0) -> Tuple[bool, Optional[object]]:
    """
    线程安全的 VideoCapture.read()，使用每摄像头独立锁。
    
    Args:
        cap: cv2.VideoCapture 实例
        camera_id: 摄像头标识，用于区分不同路的锁
        timeout: 读帧超时(秒)，超时返回 (False, None)
    
    Returns:
        (ret, frame) 与 cap.read() 相同格式
    """
    lock = _manager.get_lock(camera_id)
    acquired = lock.acquire(timeout=timeout)
    if not acquired:
        _manager.update_health(camera_id, False)
        return (False, None)
    
    try:
        start_time = time.time()
        ret, frame = cap.read()
        read_time_ms = (time.time() - start_time) * 1000
        _manager.update_health(camera_id, ret, read_time_ms)
        
        if not ret or frame is None:
            return (False, None)
        return (ret, frame)
    except Exception:
        _manager.update_health(camera_id, False)
        return (False, None)
    finally:
        lock.release()


def safe_is_opened(cap, camera_id: str = "default") -> bool:
    """
    线程安全的 VideoCapture.isOpened() 检查
    """
    lock = _manager.get_lock(camera_id)
    acquired = lock.acquire(timeout=2.0)
    if not acquired:
        return False
    try:
        return cap.isOpened()
    except Exception:
        return False
    finally:
        lock.release()


def get_stream_health(camera_id: str) -> StreamHealth:
    """获取指定摄像头流的健康状态"""
    return _manager.get_health(camera_id)


def get_all_health() -> Dict[str, StreamHealth]:
    """获取所有摄像头流的健康状态"""
    with _manager._global_lock:
        return dict(_manager._health)


# ============================================================
# 向后兼容：保留全局锁接口，但内部使用更安全的超时机制
# ============================================================

# 全局锁（向后兼容，用于不指定 camera_id 的场景）
_compatibility_lock = threading.Lock()


def safe_read_global(cap) -> Tuple[bool, Optional[object]]:
    """
    全局锁版本的 safe_read（向后兼容）
    新代码应使用 safe_read(cap, camera_id) 代替
    """
    acquired = _compatibility_lock.acquire(timeout=5.0)
    if not acquired:
        return (False, None)
    try:
        ret, frame = cap.read()
        if not ret or frame is None:
            return (False, None)
        return (ret, frame)
    except Exception:
        return (False, None)
    finally:
        _compatibility_lock.release()


def safe_is_opened_global(cap) -> bool:
    """
    全局锁版本的 safe_is_opened（向后兼容）
    新代码应使用 safe_is_opened(cap, camera_id) 代替
    """
    acquired = _compatibility_lock.acquire(timeout=2.0)
    if not acquired:
        return False
    try:
        return cap.isOpened()
    except Exception:
        return False
    finally:
        _compatibility_lock.release()