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import { neverAbortedSignal } from './common/abort';import { defer } from './common/defer';import { EventEmitter } from './common/Event';import { ExecuteWrapper } from './common/Executor';import { BulkheadRejectedError } from './errors/BulkheadRejectedError';import { TaskCancelledError } from './errors/Errors';import { IDefaultPolicyContext, IPolicy } from './Policy';
interface IQueueItem<T> {  signal: AbortSignal;  fn(context: IDefaultPolicyContext): Promise<T> | T;  resolve(value: T): void;  reject(error: Error): void;}
export class BulkheadPolicy implements IPolicy {  public declare readonly _altReturn: never;
  private active = 0;  private readonly queue: Array<IQueueItem<unknown>> = [];  private readonly onRejectEmitter = new EventEmitter<void>();  private readonly executor = new ExecuteWrapper();
  /**   * @inheritdoc   */  public readonly onSuccess = this.executor.onSuccess;
  /**   * @inheritdoc   */  public readonly onFailure = this.executor.onFailure;
  /**   * Emitter that fires when an item is rejected from the bulkhead.   */  public readonly onReject = this.onRejectEmitter.addListener;
  /**   * Returns the number of available execution slots at this point in time.   */  public get executionSlots() {    return this.capacity - this.active;  }
  /**   * Returns the number of queue slots at this point in time.   */  public get queueSlots() {    return this.queueCapacity - this.queue.length;  }
  /**   * Bulkhead limits concurrent requests made.   */  constructor(private readonly capacity: number, private readonly queueCapacity: number) {}
  /**   * Executes the given function.   * @param fn Function to execute   * @throws a {@link BulkheadRejectedException} if the bulkhead limits are exceeeded   */  public async execute<T>(    fn: (context: IDefaultPolicyContext) => PromiseLike<T> | T,    signal = neverAbortedSignal,  ): Promise<T> {    if (signal.aborted) {      throw new TaskCancelledError();    }
    if (this.active < this.capacity) {      this.active++;      try {        return await fn({ signal });      } finally {        this.active--;        this.dequeue();      }    }
    if (this.queue.length < this.queueCapacity) {      const { resolve, reject, promise } = defer<T>();      this.queue.push({ signal, fn, resolve, reject });      return promise;    }
    this.onRejectEmitter.emit();    throw new BulkheadRejectedError(this.capacity, this.queueCapacity);  }
  private dequeue() {    const item = this.queue.shift();    if (!item) {      return;    }
    Promise.resolve()      .then(() => this.execute(item.fn, item.signal))      .then(item.resolve)      .catch(item.reject);  }}