/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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 org.apache.fluss.utils;

import javax.annotation.concurrent.ThreadSafe;

import java.util.concurrent.ThreadLocalRandom;

/* This file is based on source code of Apache Kafka Project (https://kafka.apache.org/), licensed by the Apache
 * Software Foundation (ASF) under the Apache License, Version 2.0. See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership. */

/**
 * A utility class for computing exponential backoff values, commonly used for retry logic,
 * reconnection attempts, and timeout management.
 *
 * <p>The backoff interval increases exponentially with each attempt, following the formula:
 *
 * <pre>
 * Backoff(attempts) = random(1 - jitter, 1 + jitter) * initialInterval * multiplier^attempts
 * </pre>
 *
 * <p>If {@code maxInterval} is less than {@code initialInterval}, a constant backoff of {@code
 * maxInterval} will be applied. The jitter factor ensures randomness to avoid thundering herd
 * problems, but will never cause the result to exceed the configured maximum interval.
 *
 * <p>Instances of this class are thread-safe and can be shared across multiple threads.
 */
@ThreadSafe
public class ExponentialBackoff {
    private final long initialInterval;
    private final int multiplier;
    private final long maxInterval;
    private final double jitter;
    private final double expMax;

    public ExponentialBackoff(
            long initialInterval, int multiplier, long maxInterval, double jitter) {
        this.initialInterval = Math.min(maxInterval, initialInterval);
        this.multiplier = multiplier;
        this.maxInterval = maxInterval;
        this.jitter = jitter;
        this.expMax =
                maxInterval > initialInterval
                        ? Math.log(maxInterval / (double) Math.max(initialInterval, 1))
                                / Math.log(multiplier)
                        : 0;
    }

    public long backoff(long attempts) {
        if (expMax == 0) {
            return initialInterval;
        }
        double exp = Math.min(attempts, this.expMax);
        double term = initialInterval * Math.pow(multiplier, exp);
        double randomFactor =
                jitter < Double.MIN_NORMAL
                        ? 1.0
                        : ThreadLocalRandom.current().nextDouble(1 - jitter, 1 + jitter);
        long backoffValue = (long) (randomFactor * term);
        return Math.min(backoffValue, maxInterval);
    }

    @Override
    public String toString() {
        return "ExponentialBackoff{"
                + "multiplier="
                + multiplier
                + ", expMax="
                + expMax
                + ", initialInterval="
                + initialInterval
                + ", jitter="
                + jitter
                + '}';
    }
}
