thi-ng/umbrella

import type { IDeref, Maybe } from "@thi.ng/api";
import type { ClosableAsyncGenerator } from "./api.js";
import { source } from "./source.js";

export interface RAFOpts {
    /**
     * If true (default: false), passes the timestamps received
     * via `requestAnimationFrame()` as iterator values. If false, a simple
     * counter [0..∞) will be emitted.
     *
     * @defaultValue false
     */
    timestamp: boolean;
    /**
     * Only used if {@link RAFOpts.timestamp} is enabled. If given as
     * number, the value will be subtracted from all emitted timestamps. If this
     * option is set to true, the timestamps will be automatically zero-adjusted
     * such that the first emitted value will be zero. If undefined (default),
     * the browser supplied timestamps will be used as is.
     */
    t0: number | boolean;
}

export const raf = (
    opts?: Partial<RAFOpts>
): ClosableAsyncGenerator<number> & IDeref<Maybe<number>> => {
    let frame = 0;
    let t0 = opts?.t0 || 0;
    let isClosed = false;
    const gen = source<number>();
    gen.close = () => {
        isClosed = true;
        gen.write(undefined);
    };
    const update = (t: number) => {
        if (isClosed) return;
        if (opts?.timestamp) {
            if (t0 === true) t0 = t;
            if (t0) t -= t0;
        } else {
            t = frame++;
        }
        gen.write(t);
        requestAnimationFrame(update);
    };
    requestAnimationFrame(update);
    return gen;
};