/*
 * Copyright 2022 Palantir Technologies, Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { useEffect, useRef } from "react";

/** React hook which tracks the previous state of a given value. */
export function usePrevious<T>(value: T) {
    // create a new reference
    const ref = useRef<T>();

    // store current value in ref
    useEffect(() => {
        ref.current = value;
    }, [value]);

    // return previous value (happens before update in useEffect above)
    return ref.current;
}