/*
 * Copyright (c) 2022-2023 nosqlbench
 *
 * 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 io.nosqlbench.nb.api.engine.metrics;

import com.codahale.metrics.Snapshot;
import org.HdrHistogram.Histogram;
import org.HdrHistogram.HistogramIterationValue;

import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import static java.nio.charset.StandardCharsets.UTF_8;

public final class DeltaHistogramSnapshot extends Snapshot {
    private final Histogram histogram;

    DeltaHistogramSnapshot(Histogram histogram) {
        this.histogram = histogram;
    }

    @Override
    public double getValue(double quantile) {
        return histogram.getValueAtPercentile(quantile * 100.0);
    }

    @Override
    public long[] getValues() {
        long[] vals = new long[(int) histogram.getTotalCount()];
        int i = 0;

        for (HistogramIterationValue value : histogram.recordedValues()) {
            long val = value.getValueIteratedTo();

            for (int j = 0; j < value.getCountAddedInThisIterationStep(); j++) {
                vals[i] = val;

                i++;
            }
        }

        if (i != vals.length) {
            throw new IllegalStateException(
                "Total count was " + histogram.getTotalCount() + " but iterating values produced " + vals.length);
        }

        return vals;
    }

    @Override
    public int size() {
        return (int) histogram.getTotalCount();
    }

    @Override
    public long getMax() {
        return histogram.getMaxValue();
    }

    @Override
    public double getMean() {
        return histogram.getMean();
    }

    @Override
    public long getMin() {
        return histogram.getMinValue();
    }

    @Override
    public double getStdDev() {
        return histogram.getStdDeviation();
    }

    @Override
    public void dump(OutputStream output) {
        try (PrintWriter p = new PrintWriter(new OutputStreamWriter(output, UTF_8))) {
            for (HistogramIterationValue value : histogram.recordedValues()) {
                for (int j = 0; j < value.getCountAddedInThisIterationStep(); j++) {
                    p.printf("%d%n", value.getValueIteratedTo());
                }
            }
        }
    }

    private String getPctlSummary(double... percentiles) {
        StringBuilder sb = new StringBuilder();
        for (double percentile : percentiles) {
            sb.append(String.format("%.3f",getValue(percentile))).append(",");
        }
        sb.setLength(sb.length()-1);
        return sb.toString();
    }

    @Override
    public String toString() {
        return
                String.format(" (count, mean, min, max) = (%d, %.3f, %d, %d)\n",
                getValues().length, getMean(), getMin(), getMax()) +
                "         p(25,50,75) = (" + getPctlSummary(0.25d, 0.5d, 0.75d) + ")\n" +
                " p(90,99,9.99,99.99) = (" + getPctlSummary(0.9d, 0.99d, 0.999, 0.9999d) + ")";
    }

    /**
     * Expose the wrapped histogram so that callers can reuse the encoded form when needed.
     */
    public Histogram getHistogram() {
        return histogram;
    }
}
