react-native-epson-escposprinter/lib/module/Queue.js

A Turbo Module wrapper for the Epson ePOS Printer SDK.

"use strict";

// Polyfill for React Native
//
// RN 0.67 is too old for `??=` and bob only does "last 2 versions"
// https://callstack.github.io/react-native-builder-bob/build#commonjs
if (!Promise.withResolvers) {
  Promise.withResolvers = () => {
    let resolve;
    let reject;
    const promise = new Promise((res, rej) => {
      resolve = res;
      reject = rej;
    });
    return {
      promise,
      resolve: resolve,
      reject: reject
    };
  };
}

/**
 * A queue implementation that allows for adding and removing elements, with optional waiting when
 * popping elements from an empty queue.
 *
 * ```ts
 * import { assertEquals } from "@std/assert";
 * import { Queue } from "@core/asyncutil/queue";
 *
 * const queue = new Queue<number>();
 * queue.push(1);
 * queue.push(2);
 * queue.push(3);
 * assertEquals(await queue.pop(), 1);
 * assertEquals(await queue.pop(), 2);
 * assertEquals(await queue.pop(), 3);
 * ```
 */
export class Queue {
  #resolves = [];
  #items = [];

  /**
   * Gets the number of items in the queue.
   */
  get size() {
    return this.#items.length;
  }

  /**
   * Returns true if the queue is currently locked.
   */
  get locked() {
    return this.#resolves.length > 0;
  }

  /**
   * Adds an item to the end of the queue and notifies any waiting consumers.
   */
  push(value) {
    this.#items.push(value);
    this.#resolves.shift()?.();
  }

  /**
   * Removes the next item from the queue, optionally waiting if the queue is currently empty.
   *
   * @returns A promise that resolves to the next item in the queue.
   */
  async pop({
    signal
  } = {}) {
    // eslint-disable-next-line no-constant-condition
    while (true) {
      signal?.throwIfAborted();
      const value = this.#items.shift();
      if (value !== undefined) {
        return value;
      }
      const {
        promise,
        resolve,
        reject
      } = Promise.withResolvers();
      signal?.addEventListener("abort", () => reject(signal.reason), {
        once: true
      });
      this.#resolves.push(resolve);
      await promise;
    }
  }
}
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