Copyright 2019 Netflix, Inc.
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.
/**
 * Copyright 2019 Netflix, Inc.
 *
 * 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.netflix.concurrency.limits.limit.window;

import java.util.Arrays;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLongArray;

class ImmutablePercentileSampleWindow implements SampleWindow {
    private final long minRtt;
    private final int maxInFlight;
    private final boolean didDrop;
    private final AtomicLongArray observedRtts;
    private final int sampleCount;
    private final double percentile;

    ImmutablePercentileSampleWindow(double percentile, int windowSize) {
        this.minRtt = Long.MAX_VALUE;
        this.maxInFlight = 0;
        this.didDrop = false;
        this.observedRtts = new AtomicLongArray(windowSize);
        this.sampleCount = 0;
        this.percentile = percentile;
    }

    private ImmutablePercentileSampleWindow(
            long minRtt,
            int maxInFlight,
            boolean didDrop,
            AtomicLongArray observedRtts,
            int sampleCount,
            double percentile
    ) {
        this.minRtt = minRtt;
        this.maxInFlight = maxInFlight;
        this.didDrop = didDrop;
        this.observedRtts = observedRtts;
        this.sampleCount = sampleCount;
        this.percentile = percentile;
    }

    @Override
    public ImmutablePercentileSampleWindow addSample(long rtt, int inflight, boolean didDrop) {
        if (sampleCount >= observedRtts.length()) {
            return this;
        }
        observedRtts.set(sampleCount, rtt);
        return new ImmutablePercentileSampleWindow(
                Math.min(minRtt, rtt),
                Math.max(inflight, this.maxInFlight),
                this.didDrop || didDrop,
                observedRtts,
                sampleCount + 1,
                percentile
        );
    }

    @Override
    public long getCandidateRttNanos() {
        return minRtt;
    }

    @Override
    public long getTrackedRttNanos() {
        if (sampleCount == 0) {
            return 0;
        }
        long[] copyOfObservedRtts = new long[sampleCount];
        for (int i = 0; i < sampleCount; i++) {
            copyOfObservedRtts[i] = observedRtts.get(i);
        }
        Arrays.sort(copyOfObservedRtts);

        int rttIndex = (int) Math.round(sampleCount * percentile);
        int zeroBasedRttIndex = rttIndex - 1;
        return copyOfObservedRtts[zeroBasedRttIndex];
    }

    @Override
    public int getMaxInFlight() {
        return maxInFlight;
    }

    @Override
    public int getSampleCount() {
        return sampleCount;
    }

    @Override
    public boolean didDrop() {
        return didDrop;
    }

    @Override
    public String toString() {
        return "ImmutablePercentileSampleWindow ["
                + "minRtt=" + TimeUnit.NANOSECONDS.toMicros(minRtt) / 1000.0
                + ", p" + percentile + " rtt=" + TimeUnit.NANOSECONDS.toMicros(getTrackedRttNanos()) / 1000.0
                + ", maxInFlight=" + maxInFlight
                + ", sampleCount=" + sampleCount
                + ", didDrop=" + didDrop + "]";
    }
}