import { resolveElements } from "../utils/resolve-elements";
const thresholds = {
    any: 0,
    all: 1,
};
export function inView(elementOrSelector, onStart, { root, margin: rootMargin, amount = "any" } = {}) {
    /**
     * If this browser doesn't support IntersectionObserver, return a dummy stop function.
     * Default triggering of onStart is tricky - it could be used for starting/stopping
     * videos, lazy loading content etc. We could provide an option to enable a fallback, or
     * provide a fallback callback option.
     */
    if (typeof IntersectionObserver === "undefined") {
        return () => { };
    }
    const elements = resolveElements(elementOrSelector);
    const activeIntersections = new WeakMap();
    const onIntersectionChange = (entries) => {
        entries.forEach((entry) => {
            const onEnd = activeIntersections.get(entry.target);
            /**
             * If there's no change to the intersection, we don't need to
             * do anything here.
             */
            if (entry.isIntersecting === Boolean(onEnd))
                return;
            if (entry.isIntersecting) {
                const newOnEnd = onStart(entry);
                if (typeof newOnEnd === "function") {
                    activeIntersections.set(entry.target, newOnEnd);
                }
                else {
                    observer.unobserve(entry.target);
                }
            }
            else if (onEnd) {
                onEnd(entry);
                activeIntersections.delete(entry.target);
            }
        });
    };
    const observer = new IntersectionObserver(onIntersectionChange, {
        root,
        rootMargin,
        threshold: typeof amount === "number" ? amount : thresholds[amount],
    });
    elements.forEach((element) => observer.observe(element));
    return () => observer.disconnect();
}
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