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/*
 * Copyright 2022 The Hekate Project
 *
 * The Hekate Project licenses this file to you 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.
 */

package io.hekate.messaging.operation;

/**
 * Callback for an {@link Aggregate} operation.
 *
 * @param  Base type of a messages.
 *
 * @see Aggregate#submit()
 * @see AggregateResult
 */
@FunctionalInterface
public interface AggregateCallback {
    /**
     * Called when the aggregation operation gets completed either successfully or with an error.
     *
     * 
     * If operation completes with a fatal error (f.e channel is closed) then {@code err} parameter will hold the error cause and
     * {@code result} parameter will be {@code null}. Otherwise {@code err} parameter will be {@code null} and {@code result} parameter
     * will hold the aggregation result.
     * 
     *
     * @param err Error ({@code null} if operation was successful).
     * @param result Aggregation result ({@code null} if operation failed).
     */
    void onComplete(Throwable err, AggregateResult result);
}