/**

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 *

 * @flow

 */

import {useSyncExternalStore} from 'use-sync-external-store/shim';

// Hook used for safely managing subscriptions in concurrent mode.

//

// In order to avoid removing and re-adding subscriptions each time this hook is called,

// the parameters passed to this hook should be memoized in some way–

// either by wrapping the entire params object with useMemo()

// or by wrapping the individual callbacks with useCallback().

export function useSubscription<Value>({

  // (Synchronously) returns the current value of our subscription.

  getCurrentValue,

  // This function is passed an event handler to attach to the subscription.

  // It should return an unsubscribe function that removes the handler.

  subscribe,

}: {

  getCurrentValue: () => Value,

  subscribe: (callback: Function) => () => void,

}): Value {

  return useSyncExternalStore(subscribe, getCurrentValue);

}