// smooth scroll
// only for special usage of lrc maker

export default ((): void => {
    const duration = 468;

    const getNow = performance || Date;

    const ease = (k: number): number => {
        return 0.5 * (1 - Math.cos(Math.PI * k));
    };

    interface IContext {
        method: (x: number, y: number) => void;
        startTime: number;
        startX: number;
        startY: number;
        stopY: number;
    }

    const rafID = {
        current: 0,
    };

    const cancelScroll = (): void => {
        cancelAnimationFrame(rafID.current);
        cleanEventListener();
    };

    const listenerOptions = {
        passive: true,
        once: true,
    };

    const atachEventListener = (): void => {
        window.addEventListener("wheel", cancelScroll, listenerOptions);
        window.addEventListener("touchmove", cancelScroll, listenerOptions);
    };

    const cleanEventListener = (): void => {
        window.removeEventListener("wheel", cancelScroll);
        window.removeEventListener("touchmove", cancelScroll);
    };

    const step = (context: IContext): void => {
        const time = getNow.now();
        const { startTime, startX, startY, stopY } = context;
        const elapsed = (time - startTime) / duration;

        if (elapsed >= 1) {
            context.method(startX, stopY);
            cleanEventListener();
            return;
        }

        // apply easing to elapsed time
        const value = ease(elapsed);

        const currentY = startY + (stopY - startY) * value;

        context.method(startX, currentY);

        if (currentY !== stopY) {
            rafID.current = requestAnimationFrame(() => step(context));
        }
    };

    const scrollingElement = document.scrollingElement || document.documentElement;

    Element.prototype.scrollIntoView = function (): void {
        const { top, bottom } = this.getBoundingClientRect();

        const center = (top + bottom) / 2;

        const viewportHeight = window.visualViewport ? window.visualViewport.height : innerHeight;

        const startX = scrollingElement.scrollLeft;
        const startY = scrollingElement.scrollTop;
        const stopY = startY + center - viewportHeight / 2;

        cancelAnimationFrame(rafID.current);
        atachEventListener();

        step({
            method: (x: number, y: number) => window.scroll(x, y),
            startTime: getNow.now(),
            startX,
            startY,
            stopY,
        });
    };
})();