// ============================================================
// useObservationMode — 观察模式 Hook
// 职责：定时采帧 → 关键帧检测 → 画面变化时触发回调
// 来源：docs/05-用户故事.md US-05（持续场景监控）
// ============================================================

import { useCallback, useEffect, useRef, useState } from "react";
import { sampleFrame, compareFrames } from "../components/EdgeProcessor";

/** 画面变化显著阈值 */
const CHANGE_THRESHOLD = 0.85;
/** 采样间隔（ms） */
const SAMPLE_INTERVAL = 5000;

export interface ObservationOptions {
  /** 画面变化回调，携带当前帧的 DataURL */
  onChange?: (frameDataUrl: string) => void;
}

export function useObservationMode(options?: ObservationOptions) {
  const [isObserving, setIsObserving] = useState(false);
  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
  const prevFrameRef = useRef<Uint8ClampedArray | null>(null);
  const optionsRef = useRef(options);

  useEffect(() => {
    optionsRef.current = options;
  }, [options]);

  /**
   * 启动观察模式
   * @param video 摄像头 video 元素
   * @param captureFrame 从 video 捕获 DataURL 的函数
   */
  const startObserving = useCallback(
    (video: HTMLVideoElement | null, captureFrame: () => string | null) => {
      if (!video) return;

      // 立即采一帧作为基准
      prevFrameRef.current = sampleFrame(video);

      intervalRef.current = setInterval(() => {
        const current = sampleFrame(video);
        if (!current) return;

        if (prevFrameRef.current) {
          const { similarity } = compareFrames(prevFrameRef.current, current);

          if (similarity < CHANGE_THRESHOLD) {
            console.log(
              `[Observation] 画面变化 (similarity=${similarity.toFixed(2)})`,
            );
            const frameDataUrl = captureFrame();
            if (frameDataUrl) {
              optionsRef.current?.onChange?.(frameDataUrl);
            }
          }
        }

        prevFrameRef.current = current;
      }, SAMPLE_INTERVAL);

      setIsObserving(true);
    },
    [],
  );

  /** 停止观察模式 */
  const stopObserving = useCallback(() => {
    if (intervalRef.current) {
      clearInterval(intervalRef.current);
      intervalRef.current = null;
    }
    prevFrameRef.current = null;
    setIsObserving(false);
  }, []);

  // 组件卸载时清理
  useEffect(() => {
    return () => {
      if (intervalRef.current) {
        clearInterval(intervalRef.current);
      }
    };
  }, []);

  return { isObserving, startObserving, stopObserving };
}