/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.
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/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.action.bulk;

import org.opensearch.common.unit.TimeValue;
import org.opensearch.test.OpenSearchTestCase;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.concurrent.atomic.AtomicInteger;

import static org.opensearch.common.unit.TimeValue.timeValueMillis;

public class BackoffPolicyTests extends OpenSearchTestCase {
    public void testWrapBackoffPolicy() {
        TimeValue timeValue = timeValueMillis(between(0, Integer.MAX_VALUE));
        int maxNumberOfRetries = between(1, 1000);
        BackoffPolicy policy = BackoffPolicy.constantBackoff(timeValue, maxNumberOfRetries);
        AtomicInteger retries = new AtomicInteger();
        policy = BackoffPolicy.wrap(policy, retries::getAndIncrement);

        int expectedRetries = 0;
        {
            // Fetching the iterator doesn't call the callback
            Iterator<TimeValue> itr = policy.iterator();
            assertEquals(expectedRetries, retries.get());

            while (itr.hasNext()) {
                // hasNext doesn't trigger the callback
                assertEquals(expectedRetries, retries.get());
                // next does
                itr.next();
                expectedRetries += 1;
                assertEquals(expectedRetries, retries.get());
            }
            // next doesn't call the callback when there isn't a backoff available
            expectThrows(NoSuchElementException.class, () -> itr.next());
            assertEquals(expectedRetries, retries.get());
        }
        {
            // The second iterator also calls the callback
            Iterator<TimeValue> itr = policy.iterator();
            itr.next();
            expectedRetries += 1;
            assertEquals(expectedRetries, retries.get());
        }
    }

    public void testEqualJitterExponentialBackOffPolicy() {
        int baseDelay = 10;
        int maxDelay = 10000;
        BackoffPolicy policy = BackoffPolicy.exponentialEqualJitterBackoff(baseDelay, maxDelay);
        Iterator<TimeValue> iterator = policy.iterator();

        // Assert equal jitter
        int retriesTillMaxDelay = 10;
        for (int i = 0; i < retriesTillMaxDelay; i++) {
            TimeValue delay = iterator.next();
            assertTrue(delay.getMillis() >= baseDelay * (1L << i) / 2);
            assertTrue(delay.getMillis() <= baseDelay * (1L << i));
        }

        // Now policy should return max delay for next retries.
        int retriesAfterMaxDelay = randomInt(10);
        for (int i = 0; i < retriesAfterMaxDelay; i++) {
            TimeValue delay = iterator.next();
            assertTrue(delay.getMillis() >= maxDelay / 2);
            assertTrue(delay.getMillis() <= maxDelay);
        }
    }

    public void testExponentialBackOffPolicy() {
        long baseDelay = 10;
        int maxDelay = 10000;
        long currentDelay = baseDelay;
        BackoffPolicy policy = BackoffPolicy.exponentialFullJitterBackoff(baseDelay);
        Iterator<TimeValue> iterator = policy.iterator();

        // Assert equal jitter
        int numberOfRetries = randomInt(20);

        for (int i = 0; i < numberOfRetries; i++) {
            TimeValue delay = iterator.next();
            assertTrue(delay.getMillis() >= 0);
            assertTrue(delay.getMillis() <= currentDelay);
            currentDelay = currentDelay * 2;
        }
    }
}