queue.js

import { waitFor } from "./wait-for.js";

export class Queue {
  #writeQueue = new Array();
  #readQueue = new Array();
  #capacity = 10;

  constructor(capacity = 10) {
    this.#capacity = capacity;
  }

  async write(msg) {
    if (
      await waitFor({
        predicate: () => this.#writeQueue.length < this.#capacity,
        errorMsg: "Write timeout",
      })
    ) {
      this.#writeQueue.push(msg);
    }
  }

  async read() {
    // wait for writeQueue to fill up if readQueue is empty
    if (
      this.#readQueue.length == 0 &&
      (await waitFor({
        predicate: () => this.#writeQueue.length > 0,
        errorMsg: "Shift timeout",
      }))
    ) {
      // pop all elements from writeQueue and push them to readQueue
      while (this.#writeQueue.length > 0) {
        this.#readQueue.push(this.#writeQueue.pop());
      }
    }
    // return last element from readQueue if non-empty
    if (
      await waitFor({
        predicate: () => this.#readQueue.length > 0,
        errorMsg: "Read timeout",
      })
    ) {
      return this.#readQueue.pop();
    }
  }
}