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This nifi-utils module should be a general purpose place to store widely and generally useful functions that any component might want to leverage. NO DEPENDENCIES should be added. This module is likely to be leveraged by every extension and should not bring along any other dependencies. The only dependency intended is the nifi-api and even this is expected to be already provided in any case where it would be used. The typical place this util would be found is within a nar and all nars already have nifi-api as a parent dependency. The nifi-api can be thought of as a NiFi Application Container level dependency.

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/*
 * 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.nifi.util.timebuffer;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.LongSupplier;

public class TimedBuffer {

    private final int numBins;
    private final EntitySum[] bins;
    private final EntityAccess entityAccess;
    private final TimeUnit binPrecision;
    private final LongSupplier currentTimeSupplier;

    public TimedBuffer(final TimeUnit binPrecision, final int numBins, final EntityAccess accessor) {
        this(binPrecision, numBins, accessor, System::currentTimeMillis);
    }

    @SuppressWarnings("unchecked")
    public TimedBuffer(final TimeUnit binPrecision, final int numBins, final EntityAccess accessor, final LongSupplier currentTimeSupplier) {
        this.binPrecision = binPrecision;
        this.numBins = numBins + 1;
        this.bins = new EntitySum[this.numBins];
        for (int i = 0; i < this.numBins; i++) {
            this.bins[i] = new EntitySum<>(binPrecision, numBins, accessor, currentTimeSupplier);
        }
        this.entityAccess = accessor;
        this.currentTimeSupplier = currentTimeSupplier;
    }

    public T add(final T entity) {
        final int binIdx = (int) (binPrecision.convert(currentTimeSupplier.getAsLong(), TimeUnit.MILLISECONDS) % numBins);
        final EntitySum sum = bins[binIdx];

        return sum.addOrReset(entity);
    }

    public T getAggregateValue(final long sinceEpochMillis) {
        final int startBinIdx = (int) (binPrecision.convert(sinceEpochMillis, TimeUnit.MILLISECONDS) % numBins);

        T total = null;
        for (int i = 0; i < numBins; i++) {
            int binIdx = (startBinIdx + i) % numBins;
            final EntitySum bin = bins[binIdx];

            if (!bin.isExpired()) {
                total = entityAccess.aggregate(total, bin.getValue());
            }
        }

        return total;
    }

    private static class EntitySum {

        private final EntityAccess entityAccess;
        private final AtomicReference ref = new AtomicReference<>();
        private final TimeUnit binPrecision;
        private final int numConfiguredBins;
        private final LongSupplier currentTimeSupplier;

        public EntitySum(final TimeUnit binPrecision, final int numConfiguredBins, final EntityAccess aggregator, final LongSupplier currentTimeSupplier) {
            this.binPrecision = binPrecision;
            this.entityAccess = aggregator;
            this.numConfiguredBins = numConfiguredBins;
            this.currentTimeSupplier = currentTimeSupplier;
        }

        private S add(final S event) {
            S newValue;
            S value;
            do {
                value = ref.get();
                newValue = entityAccess.aggregate(value, event);
            } while (!ref.compareAndSet(value, newValue));

            return newValue;
        }

        public S getValue() {
            return ref.get();
        }

        public boolean isExpired() {
            // entityAccess.getTimestamp(curValue) represents the time at which the current value
            // was last updated. If the last value is less than current time - 1 binPrecision, then it
            // means that we've rolled over and need to reset the value.
            final long maxExpectedTimePeriod = currentTimeSupplier.getAsLong() - TimeUnit.MILLISECONDS.convert(numConfiguredBins, binPrecision);

            final S curValue = ref.get();
            return (entityAccess.getTimestamp(curValue) < maxExpectedTimePeriod);
        }

        public S addOrReset(final S event) {
            // entityAccess.getTimestamp(curValue) represents the time at which the current value
            // was last updated. If the last value is less than current time - 1 binPrecision, then it
            // means that we've rolled over and need to reset the value.
            final long maxExpectedTimePeriod = currentTimeSupplier.getAsLong() - TimeUnit.MILLISECONDS.convert(1, binPrecision);

            final S curValue = ref.get();
            if (entityAccess.getTimestamp(curValue) < maxExpectedTimePeriod) {
                ref.compareAndSet(curValue, entityAccess.createNew());
            }
            return add(event);
        }
    }
}