thi-ng/umbrella

import { isNode } from "@thi.ng/checks/is-node";
import { isNumber } from "@thi.ng/checks/is-number";
import type { CommonOpts } from "./api.js";
import { __optsWithID } from "./idgen.js";
import { fromInterval } from "./interval.js";
import { stream } from "./stream.js";

export interface FromRAFOpts extends CommonOpts {
    /**
     * Browser only. If true (default: false), passes the timestamps received
     * via `requestAnimationFrame()` as stream values. If false, a simple
     * counter [0..∞) will be emitted.
     *
     * @defaultValue false
     */
    timestamp: boolean;
    /**
     * Only used if {@link FromRAFOpts.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;
}

/**
 * Yields {@link Stream} of a monotonically increasing counter (or timestamps),
 * triggered by a `requestAnimationFrame()` loop (only available in browser
 * environments).
 *
 * @remarks
 * In NodeJS, this function falls back to {@link fromInterval}, yielding a
 * similar (approx. 60Hz) stream (the {@link FromRAFOpts.timestamp} option will
 * be ignored).
 *
 * All subscribers to this stream will be processed during that same RAF loop
 * iteration.
 */
export const fromRAF = (opts: Partial<FromRAFOpts> = {}) =>
    isNode()
        ? fromInterval(16, opts)
        : stream<number>((stream) => {
                let i = 0;
                let isActive = true;
                let t0 = isNumber(opts.t0) ? opts.t0 : undefined;
                const loop: FrameRequestCallback = (time) => {
                    if (opts.timestamp && opts.t0) {
                        if (t0 === undefined) t0 = time;
                        time -= t0;
                    }
                    isActive && stream.next(opts.timestamp ? time : i++);
                    isActive && (id = requestAnimationFrame(loop));
                };
                let id = requestAnimationFrame(loop);
                return () => {
                    isActive = false;
                    cancelAnimationFrame(id);
                };
          }, __optsWithID("raf", opts));