import { __rest, __assign } from 'tslib';

/**
 * Map an IntersectionHandler callback to an element. We only ever make one handler for one
 * element, so even though these handlers might all be triggered by different
 * observers, we can keep them in the same map.
 */
var observerCallbacks = new WeakMap();
/**
 * Multiple observers can be created for multiple element/document roots. Each with
 * different settings. So here we store dictionaries of observers to each root,
 * using serialised settings (threshold/margin) as lookup keys.
 */
var observers = new WeakMap();
var fireObserverCallback = function (entry) {
    var _a;
    (_a = observerCallbacks.get(entry.target)) === null || _a === void 0 ? void 0 : _a(entry);
};
var fireAllObserverCallbacks = function (entries) {
    entries.forEach(fireObserverCallback);
};
function initIntersectionObserver(_a) {
    var root = _a.root, options = __rest(_a, ["root"]);
    var lookupRoot = root || document;
    /**
     * If we don't have an observer lookup map for this root, create one.
     */
    if (!observers.has(lookupRoot)) {
        observers.set(lookupRoot, {});
    }
    var rootObservers = observers.get(lookupRoot);
    var key = JSON.stringify(options);
    /**
     * If we don't have an observer for this combination of root and settings,
     * create one.
     */
    if (!rootObservers[key]) {
        rootObservers[key] = new IntersectionObserver(fireAllObserverCallbacks, __assign({ root: root }, options));
    }
    return rootObservers[key];
}
function observeIntersection(element, options, callback) {
    var rootInteresectionObserver = initIntersectionObserver(options);
    observerCallbacks.set(element, callback);
    rootInteresectionObserver.observe(element);
    return function () {
        observerCallbacks.delete(element);
        rootInteresectionObserver.unobserve(element);
    };
}

export { observeIntersection };