"""全屏截帧引擎，后台线程持续截图存为 PNG 帧序列。"""
from __future__ import annotations

import threading
import time
from pathlib import Path
from typing import Optional

import mss
import mss.tools


class ScreenRecorder:
    def __init__(
        self,
        frames_dir: str,
        fps: int = 10,
        monitor_index: Optional[int] = None,
    ):
        """
        Args:
            monitor_index: mss 显示器索引；None=monitors[0]（所有屏合并区域，
                          旧行为），1=主屏，2+=第 N 屏。多显示器场景推荐显式传 1。
        """
        self._frames_dir = Path(frames_dir)
        self._fps = fps
        self._monitor_index = monitor_index
        self._stop_event = threading.Event()
        self._thread: threading.Thread | None = None
        self._frame_count = 0

    def start(self) -> None:
        self._frames_dir.mkdir(parents=True, exist_ok=True)
        self._stop_event.clear()
        self._frame_count = 0
        self._thread = threading.Thread(target=self._capture_loop, daemon=True)
        self._thread.start()

    def stop(self) -> None:
        self._stop_event.set()
        if self._thread:
            self._thread.join(timeout=10)

    @property
    def frame_count(self) -> int:
        return self._frame_count

    def _capture_loop(self) -> None:
        interval = 1.0 / self._fps
        with mss.mss() as sct:
            idx = self._monitor_index if self._monitor_index is not None else 0
            if idx < 0 or idx >= len(sct.monitors):
                idx = 0  # 越界兜底
            monitor = sct.monitors[idx]
            while not self._stop_event.is_set():
                t0 = time.perf_counter()
                img = sct.grab(monitor)
                path = self._frames_dir / f"frame_{self._frame_count:06d}.png"
                mss.tools.to_png(img.rgb, img.size, output=str(path))
                self._frame_count += 1
                elapsed = time.perf_counter() - t0
                sleep = max(0.0, interval - elapsed)
                time.sleep(sleep)