imperial-command-center/electron/services/MotionDetector.ts

import { EventEmitter } from 'events';

interface MotionDetectorOptions {
  go2rtcUrl: string;
  cameraName: string;
  sensitivityThreshold: number; // % size change to trigger
  checkIntervalMs: number;
}

/**
 * Motion detection running in the main process (not throttled by browser).
 * Uses JPEG file size changes as a proxy for motion - more reliable than byte comparison.
 * When significant motion occurs, the JPEG compresses differently and size changes.
 */
export class MotionDetector extends EventEmitter {
  private options: MotionDetectorOptions;
  private intervalId: NodeJS.Timeout | null = null;
  private prevSize: number = 0;
  private baselineSize: number = 0;
  private sizeHistory: number[] = [];
  private isProcessing = false;
  private noMotionCount = 0;

  constructor(options: MotionDetectorOptions) {
    super();
    this.options = options;
  }

  start(): void {
    if (this.intervalId) return;
    console.log(`MotionDetector: Starting detection on ${this.options.cameraName}`);

    this.intervalId = setInterval(() => {
      this.checkMotion();
    }, this.options.checkIntervalMs);

    // Do initial checks to establish baseline
    this.checkMotion();
  }

  stop(): void {
    if (this.intervalId) {
      clearInterval(this.intervalId);
      this.intervalId = null;
    }
    this.prevSize = 0;
    this.baselineSize = 0;
    this.sizeHistory = [];
    console.log('MotionDetector: Stopped');
  }

  private async checkMotion(): Promise<void> {
    if (this.isProcessing) return;
    this.isProcessing = true;

    try {
      const frameData = await this.fetchFrame();
      if (!frameData) {
        this.isProcessing = false;
        return;
      }

      const currentSize = frameData.length;

      // Build up history for baseline (first 5 frames)
      if (this.sizeHistory.length < 5) {
        this.sizeHistory.push(currentSize);
        if (this.sizeHistory.length === 5) {
          // Calculate baseline as average of first 5 frames
          this.baselineSize = this.sizeHistory.reduce((a, b) => a + b, 0) / 5;
          console.log(`MotionDetector: Baseline established at ${this.baselineSize} bytes`);
        }
        this.prevSize = currentSize;
        this.isProcessing = false;
        return;
      }

      // Compare to previous frame AND baseline
      const prevDiff = Math.abs(currentSize - this.prevSize);
      const baselineDiff = Math.abs(currentSize - this.baselineSize);

      const prevChangePercent = (prevDiff / this.prevSize) * 100;
      const baselineChangePercent = (baselineDiff / this.baselineSize) * 100;

      // Motion detected if EITHER:
      // 1. Frame-to-frame change is significant (something just moved)
      // 2. Deviation from baseline is significant (scene has changed)
      const motionDetected = prevChangePercent > this.options.sensitivityThreshold ||
                            baselineChangePercent > (this.options.sensitivityThreshold * 2);

      if (motionDetected) {
        this.noMotionCount = 0;
        console.log(`MotionDetector: Motion detected (prev=${prevChangePercent.toFixed(1)}% baseline=${baselineChangePercent.toFixed(1)}%)`);
        this.emit('motion');
      } else {
        this.noMotionCount++;
        // Update baseline slowly when no motion (adapt to lighting changes)
        if (this.noMotionCount > 10) {
          this.baselineSize = this.baselineSize * 0.95 + currentSize * 0.05;
        }
      }

      this.prevSize = currentSize;
    } catch (error) {
      console.error('MotionDetector: Error checking motion:', error);
    } finally {
      this.isProcessing = false;
    }
  }

  private async fetchFrame(): Promise<Buffer | null> {
    // Try up to 2 times with a short delay
    for (let attempt = 0; attempt < 2; attempt++) {
      try {
        const url = `${this.options.go2rtcUrl}/api/frame.jpeg?src=${this.options.cameraName}&t=${Date.now()}`;

        const controller = new AbortController();
        const timeoutId = setTimeout(() => controller.abort(), 3000);

        const response = await fetch(url, { signal: controller.signal });
        clearTimeout(timeoutId);

        if (!response.ok) {
          continue;
        }

        const arrayBuffer = await response.arrayBuffer();
        return Buffer.from(arrayBuffer);
      } catch {
        if (attempt === 0) {
          await new Promise(r => setTimeout(r, 500));
        }
      }
    }
    return null;
  }
}