src/lib/tools/requestQueue.ts

/**
 * tools/requestQueue.ts — Request queue for mobile
 *
 * Gestisce:
 * - Concorrenza limitata
 * - Timeout e retry
 * - Priority queue
 * - Abort support
 */

export interface QueuedRequest {
  id: string;
  priority: number; // 0-10, higher = more important
  fn: () => Promise<unknown>;
  timeout: number;
  retries: number;
  resolve: (value: unknown) => void;
  reject: (error: Error) => void;
  abortSignal?: AbortSignal;
}

export class RequestQueue {
  private queue: QueuedRequest[] = [];
  private running = 0;
  private maxConcurrent = 2; // iPhone-friendly
  private requestId = 0;

  constructor(maxConcurrent: number = 2) {
    this.maxConcurrent = maxConcurrent;
  }

  /**
   * Add request to queue
   */
  add<T>(
    fn: () => Promise<T>,
    options: {
      priority?: number;
      timeout?: number;
      retries?: number;
      abortSignal?: AbortSignal;
    } = {},
  ): Promise<T> {
    return new Promise((resolve, reject) => {
      const request: QueuedRequest = {
        id: `req_${++this.requestId}`,
        priority: options.priority ?? 5,
        fn,
        timeout: options.timeout ?? 30000,
        retries: options.retries ?? 1,
        resolve: resolve as (value: unknown) => void,
        reject,
        abortSignal: options.abortSignal,
      };

      this.queue.push(request);
      this.queue.sort((a, b) => b.priority - a.priority);
      this.process();
    });
  }

  /**
   * Process queue
   */
  private process(): void {
    while (
      this.running < this.maxConcurrent &&
      this.queue.length > 0
    ) {
      const request = this.queue.shift();
      if (!request) break;

      this.running++;
      this.executeRequest(request);
    }
  }

  /**
   * Execute single request with retry
   */
  private async executeRequest(
    request: QueuedRequest,
  ): Promise<void> {
    let lastError: Error | undefined;

    for (let attempt = 0; attempt <= request.retries; attempt++) {
      try {
        // Check abort signal
        if (request.abortSignal?.aborted) {
          throw new Error("Richiesta interrotta");
        }

        // Execute with timeout
        const result = await Promise.race([
          request.fn(),
          this.timeout(request.timeout),
        ]);

        request.resolve(result);
        this.running--;
        this.process();
        return;
      } catch (error) {
        lastError = error as Error;

        // Don't retry on abort
        if (
          lastError.message === "Richiesta interrotta"
        ) {
          break;
        }

        // Wait before retry
        if (attempt < request.retries) {
          await new Promise((resolve) =>
            setTimeout(resolve, 1000 * (attempt + 1)),
          );
        }
      }
    }

    request.reject(
      lastError || new Error("Errore sconosciuto"),
    );
    this.running--;
    this.process();
  }

  /**
   * Timeout promise
   */
  private timeout(ms: number): Promise<never> {
    return new Promise((_, reject) =>
      setTimeout(
        () => reject(new Error("Timeout della richiesta")),
        ms,
      ),
    );
  }

  /**
   * Get queue size
   */
  getSize(): number {
    return this.queue.length;
  }

  /**
   * Clear queue
   */
  clear(): void {
    for (const request of this.queue) {
      request.reject(new Error("Coda svuotata"));
    }
    this.queue = [];
  }

  /**
   * Set max concurrent
   */
  setMaxConcurrent(max: number): void {
    this.maxConcurrent = max;
    this.process();
  }
}

// Global queue instance
let globalQueue: RequestQueue | null = null;

export function getGlobalQueue(): RequestQueue {
  if (!globalQueue) {
    globalQueue = new RequestQueue(2);
  }
  return globalQueue;
}

export function setGlobalQueueConcurrency(
  max: number,
): void {
  getGlobalQueue().setMaxConcurrent(max);
}