paint-ui/lib/worker-pool.ts

import type { FilterType, FilterParams } from '@/types/filter';

interface WorkerTask {
  type: FilterType;
  imageData: ImageData;
  params: FilterParams;
  resolve: (data: ImageData) => void;
  reject: (error: Error) => void;
}

/**
 * Worker Pool Manager
 * Manages a pool of Web Workers for parallel filter processing
 */
export class WorkerPool {
  private workers: Worker[] = [];
  private availableWorkers: Worker[] = [];
  private taskQueue: WorkerTask[] = [];
  private maxWorkers: number;

  constructor(maxWorkers: number = navigator.hardwareConcurrency || 4) {
    this.maxWorkers = Math.min(maxWorkers, 8); // Cap at 8 workers
  }

  /**
   * Initialize the worker pool
   */
  private initializeWorker(): Worker {
    const worker = new Worker(new URL('../workers/filter.worker.ts', import.meta.url));

    worker.onmessage = (e: MessageEvent) => {
      const { success, data, error } = e.data;

      // Find the task associated with this worker
      const taskIndex = this.taskQueue.findIndex((task) => {
        // This is a simple check - in production you'd want a better task tracking system
        return true;
      });

      if (taskIndex !== -1) {
        const task = this.taskQueue.splice(taskIndex, 1)[0];

        if (success) {
          // Create ImageData from the returned buffer
          const imageData = new ImageData(
            new Uint8ClampedArray(data),
            task.imageData.width,
            task.imageData.height
          );
          task.resolve(imageData);
        } else {
          task.reject(new Error(error || 'Worker processing failed'));
        }
      }

      // Mark worker as available and process next task
      this.availableWorkers.push(worker);
      this.processNextTask();
    };

    worker.onerror = (error) => {
      console.error('Worker error:', error);
      // Mark worker as available even on error
      this.availableWorkers.push(worker);
      this.processNextTask();
    };

    this.workers.push(worker);
    this.availableWorkers.push(worker);

    return worker;
  }

  /**
   * Process the next task in the queue
   */
  private processNextTask(): void {
    if (this.taskQueue.length === 0 || this.availableWorkers.length === 0) {
      return;
    }

    const worker = this.availableWorkers.pop()!;
    const task = this.taskQueue.shift()!;

    // Clone the image data for the worker
    const data = new Uint8ClampedArray(task.imageData.data);

    // Send task to worker (transfer ownership of the buffer for better performance)
    worker.postMessage(
      {
        type: task.type,
        data: data,
        width: task.imageData.width,
        height: task.imageData.height,
        params: task.params,
      },
      { transfer: [data.buffer] }
    );
  }

  /**
   * Execute a filter using the worker pool
   */
  async executeFilter(
    imageData: ImageData,
    type: FilterType,
    params: FilterParams
  ): Promise<ImageData> {
    return new Promise((resolve, reject) => {
      // Ensure we have at least one worker
      if (this.workers.length === 0) {
        this.initializeWorker();
      }

      // Add task to queue
      this.taskQueue.push({
        type,
        imageData,
        params,
        resolve,
        reject,
      });

      // Try to process immediately if workers are available
      this.processNextTask();

      // If no workers available but we can create more, do so
      if (
        this.availableWorkers.length === 0 &&
        this.workers.length < this.maxWorkers
      ) {
        this.initializeWorker();
        this.processNextTask();
      }
    });
  }

  /**
   * Terminate all workers and clear the pool
   */
  terminate(): void {
    this.workers.forEach((worker) => worker.terminate());
    this.workers = [];
    this.availableWorkers = [];
    this.taskQueue = [];
  }

  /**
   * Get the number of active workers
   */
  get activeWorkers(): number {
    return this.workers.length - this.availableWorkers.length;
  }

  /**
   * Get the number of queued tasks
   */
  get queuedTasks(): number {
    return this.taskQueue.length;
  }
}

// Singleton instance
let workerPool: WorkerPool | null = null;

/**
 * Get the global worker pool instance
 */
export function getWorkerPool(): WorkerPool {
  if (!workerPool) {
    workerPool = new WorkerPool();
  }
  return workerPool;
}

/**
 * Clean up the worker pool (call on app unmount)
 */
export function terminateWorkerPool(): void {
  if (workerPool) {
    workerPool.terminate();
    workerPool = null;
  }
}