thi-ng/umbrella

import { FIFOBuffer } from "./fifo.js";

/**
 * Returns a {@link SlidingBuffer} with given max. capacity.
 *
 * @remarks
 * With this implementation, writes are **always** possible, but not guaranteed
 * to happen: Whilst the buffer is at full capacity, new writes will first
 * expunge the oldest buffered value. Read behavior is the same as for
 * {@link fifo}.
 *
 * Also see {@link dropping} for alternative behavior.
 *
 * @param cap
 */
export const sliding = <T>(cap: number) => new SlidingBuffer<T>(cap);

export class SlidingBuffer<T> extends FIFOBuffer<T> {
    copy() {
        const buf = new SlidingBuffer<T>(1);
        buf.buf = this.buf.slice();
        buf.rpos = this.rpos;
        buf.wpos = this.wpos;
        buf.len = this.len;
        return buf;
    }

    writable() {
        return true;
    }

    write(x: T) {
        if (!super.writable()) {
            const { buf, rpos } = this;
            buf[rpos] = undefined;
            this.rpos = (rpos + 1) % buf.length;
            this.len--;
        }
        return super.write(x);
    }
}