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An FSM that manages async non-blocking access to a Netty Channel

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/*
 * Copyright (c) 2024 Kevin Herron
 *
 * This program and the accompanying materials are made
 * available under the terms of the Eclipse Public License 2.0
 * which is available at https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 */

package com.digitalpetri.netty.fsm;

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

public interface Scheduler {

  /**
   * Schedule a command to run after a {@code delay}.
   *
   * @param command the commadn to run.
   * @param delay the time to delay.
   * @param unit the time unit of the delay.
   * @return a {@link Cancellable} that can be used to attempt cancellation if needed.
   */
  Cancellable schedule(Runnable command, long delay, TimeUnit unit);

  interface Cancellable {

    /**
     * Attempt to cancel a scheduled command.
     *
     * @return {@code true} if the command was canceled.
     */
    boolean cancel();

  }

  /**
   * Create a {@link Scheduler} from the provided {@link ScheduledExecutorService}.
   *
   * @param scheduledExecutor a {@link ScheduledExecutorService}.
   * @return a {@link Scheduler}.
   */
  static Scheduler fromScheduledExecutor(ScheduledExecutorService scheduledExecutor) {
    return (command, delay, unit) -> {
      ScheduledFuture future = scheduledExecutor.schedule(command, delay, unit);

      return () -> future.cancel(false);
    };
  }

}