/**
 * Copyright (C) 2009-2013 FoundationDB, LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.foundationdb.util;

import java.sql.SQLException;

public abstract class MicroBenchmark
{
    public void beforeAction() throws Exception
    {}

    public void afterAction() throws Exception
    {}

    public abstract void action() throws Exception;

    public String name()
    {
        return getClass().getSimpleName();
    }

    public final double run() throws Exception
    {
        while (!converged()) {
            beforeAction();
            long start = System.nanoTime();
            action();
            long stop = System.nanoTime();
            afterAction();
            history[cycles++ % history.length] = stop - start;
        }
        return historyAverage;
    }

    public final void profile() throws Exception
    {
        while (true) {
            beforeAction();
            action();
            afterAction();
        }
    }

    protected MicroBenchmark(int historySize, double maxVariation)
    {
        this.maxVariation = maxVariation;
        this.history = new long[historySize];
    }

    private boolean converged()
    {
        boolean converged = false;
        if (cycles >= history.length) {
            long sum = 0;
            long min = Long.MAX_VALUE;
            long max = Long.MIN_VALUE;
            for (int i = 0; i < history.length; i++) {
                sum += history[i];
                min = Math.min(min, history[i]);
                max = Math.max(max, history[i]);
            }
            historyAverage = (double) sum / history.length;
            converged =
                min >= historyAverage * (1 - maxVariation) &&
                max <= historyAverage * (1 + maxVariation);
        }
        if (converged) {
            // In case this benchmark is rerun
            cycles = 0;
        }
        return converged;
    }

    private final double maxVariation;
    private long[] history;
    private double historyAverage;
    private int cycles = 0;
}