@augment-vir/common/dist/augments/promise/promise-queue.js

A collection of augments, helpers types, functions, and classes for any JavaScript environment.

import { check } from '@augment-vir/assert';
import { DeferredPromise } from '@augment-vir/core';
import { defineTypedCustomEvent, ListenTarget } from 'typed-event-target';
/**
 * The event emitted from a {@link PromiseQueue} instance whenever the queue is updated (an item is
 * resolved or an item is added).
 *
 * @category Promise : Util
 * @category Package : @augment-vir/common
 * @package [`@augment-vir/common`](https://www.npmjs.com/package/@augment-vir/common)
 */
export class PromiseQueueUpdateEvent extends defineTypedCustomEvent()('promise-queue-update') {
}
/**
 * A queue that manages its items with promises.
 *
 * @category Promise
 * @category Package : @augment-vir/common
 * @package [`@augment-vir/common`](https://www.npmjs.com/package/@augment-vir/common)
 */
export class PromiseQueue extends ListenTarget {
    queue = [];
    currentlyAwaiting = undefined;
    /** The current size of the queue. */
    get size() {
        return this.queue.length;
    }
    /**
     * Add an item to the queue.
     *
     * @returns A promise that resolves at the same time as the added item.
     */
    add(item) {
        const newItem = {
            original: item,
            wrapper: new DeferredPromise(),
        };
        this.queue.push(newItem);
        this.dispatch(new PromiseQueueUpdateEvent({
            detail: {
                queueSize: this.size,
                addedItem: newItem,
            },
        }));
        this.triggerNextQueueItem();
        return newItem.wrapper.promise;
    }
    /** Handles a queue item finishing, whether it be a rejection or a resolution. */
    handleItemSettle({ rejection, resolution, }) {
        const item = this.currentlyAwaiting;
        if (!item) {
            throw new Error(`Cannot handle queue item settle without a currently awaited queue item.`);
        }
        this.queue.splice(0, 1);
        this.dispatch(new PromiseQueueUpdateEvent({
            detail: {
                queueSize: this.size,
                finishedItem: item,
            },
        }));
        if (rejection) {
            item.wrapper.reject(rejection);
        }
        else {
            item.wrapper.resolve(resolution);
        }
        this.currentlyAwaiting = undefined;
        this.triggerNextQueueItem();
        return item;
    }
    /**
     * Tries to trigger the next queue item, if there is one.
     *
     * @returns Whether a new queue item was triggered or not. `true` if it was, otherwise `false`.
     */
    triggerNextQueueItem() {
        if (this.currentlyAwaiting || !check.isLengthAtLeast(this.queue, 1)) {
            return false;
        }
        const item = this.queue[0];
        this.currentlyAwaiting = item;
        item.original()
            .then((result) => {
            this.handleItemSettle({ resolution: result });
        })
            .catch((error) => {
            this.handleItemSettle({ rejection: error });
        });
        return true;
    }
}