/*
 * Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved.
 *
 * Licensed 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 com.hazelcast.client.spi.impl;

import com.hazelcast.core.HazelcastOverloadException;

import java.util.concurrent.atomic.AtomicLongArray;

import static com.hazelcast.nio.Bits.CACHE_LINE_LENGTH;
import static com.hazelcast.nio.Bits.LONG_SIZE_IN_BYTES;

public abstract class CallIdSequence {

    /**
     * Creates the next call-id.
     *
     * @return the generated callId.
     */
    public abstract long next();

    /**
     * Creates the call id without applying any backpressure
     *
     * @return the generated call id.
     */
    public abstract long forceNext();

    public abstract void complete();

    /**
     * A {@link com.hazelcast.spi.impl.operationservice.impl.CallIdSequence} that provided backpressure by taking
     * the number in flight operations into account when a call-id needs to be determined.
     *
     * It is possible to temporary exceed the capacity:
     * - due to system operations
     * - due to racy nature of checking if space is available and getting the next sequence.
     */
    public static final class CallIdSequenceFailFast extends CallIdSequence {

        private static final int INDEX_HEAD = 7;
        private static final int INDEX_TAIL = INDEX_HEAD + CACHE_LINE_LENGTH / LONG_SIZE_IN_BYTES;

        // instead of using two AtomicLongs, we use an array of width of 3 cache lines to prevent any false sharing
        private final AtomicLongArray longs = new AtomicLongArray(3 * CACHE_LINE_LENGTH / LONG_SIZE_IN_BYTES);

        private final int maxConcurrentInvocations;

        public CallIdSequenceFailFast(int maxConcurrentInvocations) {
            this.maxConcurrentInvocations = maxConcurrentInvocations;
        }

        @Override
        public long next() {
            if (!hasSpace()) {
                throw new HazelcastOverloadException("maxConcurrentInvocations: "
                        + maxConcurrentInvocations + " is reached");
            }

            return longs.incrementAndGet(INDEX_HEAD);
        }

        @Override
        public long forceNext() {
            return longs.incrementAndGet(INDEX_HEAD);
        }

        private boolean hasSpace() {
            return longs.get(INDEX_HEAD) - longs.get(INDEX_TAIL) < maxConcurrentInvocations;
        }

        @Override
        public void complete() {
            longs.incrementAndGet(INDEX_TAIL);
        }
    }
}