/******************************************************************************
 * Copyright (c) 2016 TypeFox and others.
 * 
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 * 
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 ******************************************************************************/
package org.eclipse.lsp4j.jsonrpc;

import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executor;
import java.util.function.Function;

public final class CompletableFutures {
	private CompletableFutures() {}
	
	/**
	 * A utility method to create a {@link CompletableFuture} with cancellation support.
	 * 
	 * @param code a function that accepts a {@link CancelChecker} and returns the to be computed value
	 * @return a future
	 */
	public static <R> CompletableFuture<R> computeAsync(Function<CancelChecker, R> code) {
		CompletableFuture<CancelChecker> start = new CompletableFuture<>();
		CompletableFuture<R> result = start.thenApplyAsync(code);
		start.complete(new FutureCancelChecker(result));
		return result;
	}
	
	/**
	 * A utility method to create a {@link CompletableFuture} with cancellation support.
	 * 
	 * @param code a function that accepts a {@link CancelChecker} and returns the to be computed value
	 * @return a future
	 */
	public static <R> CompletableFuture<R> computeAsync(Executor executor, Function<CancelChecker, R> code) {
		CompletableFuture<CancelChecker> start = new CompletableFuture<>();
		CompletableFuture<R> result = start.thenApplyAsync(code, executor);
		start.complete(new FutureCancelChecker(result));
		return result;
	}
	
	public static class FutureCancelChecker implements CancelChecker {
		
		private final CompletableFuture<?> future;
		
		public FutureCancelChecker(CompletableFuture<?> future) {
			this.future = future;
		}

		@Override
		public void checkCanceled() {
			if (future.isCancelled()) 
				throw new CancellationException();
		}
		
		@Override
		public boolean isCanceled() {
			return future.isCancelled();
		}
		
	}
	
}