sflow/src/toLatest.ts

sflow is a powerful and highly-extensible library designed for processing and manipulating streams of data effortlessly. Inspired by the functional programming paradigm, it provides a rich set of utilities for transforming streams, including chunking, fil

/** 
 * Convert a readable stream to it's latest value
 * 
 * the return object is dynamic updated
 */
export function toLatests<T>(r: ReadableStream<T>): { latest: Promise<T>, next: Promise<T> } {
    let latest: T | undefined;
    let nextPromise = Promise.withResolvers<T>();
    r.pipeTo(
        new WritableStream<T>({
            write: (value) => {
                latest = value;
                nextPromise.resolve(value);
                nextPromise = Promise.withResolvers<T>();
            },
            close: () => {
                nextPromise.resolve(undefined);
            }
        })
    );
    return {
        get latest() {
            if (latest === undefined) {
                return nextPromise.promise;
            }
            return Promise.resolve(latest);
        },
        get next() {
            return nextPromise.promise;
        }
    };
}