Move "core" folder out of "features" into "base"

src/base/hooks/useIntersectionObserver.tsx

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+import { RefObject, useLayoutEffect, useState } from 'react';
+
+export const useIntersectionObserver = (
+    ref: RefObject<HTMLElement | null> | HTMLElement | undefined | null,
+    callback: IntersectionObserverCallback,
+    {
+        ignoreInitialObserve = false,
+        root,
+        rootMargin,
+        threshold,
+    }: IntersectionObserverInit & { ignoreInitialObserve?: boolean } = {},
+): (() => void) => {
+    const [disconnect, setDisconnect] = useState<() => void>(() => {});
+
+    useLayoutEffect(() => {
+        const element = ref instanceof HTMLElement ? ref : ref?.current;
+
+        if (!element) {
+            return () => {};
+        }
+
+        // gets immediately observed once on initial render
+        let isInitialObserve = true;
+        const intersectionObserver = new IntersectionObserver(
+            (...args) => {
+                if (ignoreInitialObserve && isInitialObserve) {
+                    isInitialObserve = false;
+                    return;
+                }
+
+                callback(...args);
+            },
+            { root, rootMargin, threshold },
+        );
+        intersectionObserver.observe(element);
+
+        setDisconnect(() => () => intersectionObserver.disconnect());
+
+        return () => intersectionObserver.disconnect();
+    }, [ref, callback, ignoreInitialObserve, root, rootMargin, threshold]);
+
+    return disconnect;
+};