export class scroll_up {
    #button;

    constructor(button) {
        this.#button = button;
        this.#update();
        
        document.addEventListener("scroll", () => {
            this.#update()
        });

        this.#button.addEventListener("click", () => {
            this.scroll();
        });
    }

    scroll() {
        this.#position = 0; 
    }

    get #position() {
        return document.scrollingElement.scrollTop;
    }

    set #position(target) {
        document.scrollingElement.scrollTop = target;
    }

    get #visible() {
        return Number(this.#button.style.opacity) === 1;
    }

    set #visible(target) {
        this.#button.style.opacity = (target) ? "1" : "0";
    }

    get #margin() {
        return 20;
    }

    #update() {
        this.#visible = (this.#position > this.#margin);
    }
}