/**
 * Copyright (c) 2004-2011 QOS.ch
 * All rights reserved.
 *
 * Permission is hereby granted, free  of charge, to any person obtaining
 * a  copy  of this  software  and  associated  documentation files  (the
 * "Software"), to  deal in  the Software without  restriction, including
 * without limitation  the rights to  use, copy, modify,  merge, publish,
 * distribute,  sublicense, and/or sell  copies of  the Software,  and to
 * permit persons to whom the Software  is furnished to do so, subject to
 * the following conditions:
 *
 * The  above  copyright  notice  and  this permission  notice  shall  be
 * included in all copies or substantial portions of the Software.
 *
 * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
 * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
 * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */
package org.slf4j.helpers;

import junit.framework.AssertionFailedError;

/**
 * BogoPerf is used to check that the time required to perform a certain
 * operation does not deteriorate over time. BogoPerf adjusts to the CPU speed
 * and capabilities of the host.
 * 
 * @author Ceki Gülcü
 * 
 */
public class BogoPerf {

    private static long NANOS_IN_ONE_SECOND = 1000 * 1000 * 1000;
    private static int INITIAL_N = 1000;
    private static int LAST_N = 100;
    private static int SLACK_FACTOR = 3;

    static {
        // let the JIT warm up
        computeBogoIPS(INITIAL_N);
        double bogo_ips = computeBogoIPS(INITIAL_N);
        System.out.println("Host runs at " + bogo_ips + " BIPS");
    }

    /**
     * Compute bogoInstructions per second
     * <p>
     * on a 3.2 Ghz Pentium D CPU (around 2007), we obtain about 9'000 bogoIPS.
     * 
     * @param N
     *                number of bogoInstructions to average over in order to
     *                compute the result
     * @return bogo Instructions Per Second
     */
    private static double computeBogoIPS(int N) {
        long begin = System.nanoTime();

        for (int i = 0; i < N; i++) {
            bogoInstruction();
        }
        long end = System.nanoTime();

        // duration
        double D = end - begin;
        // average duration per instruction
        double avgDPIS = D / N;
        // System.out.println(D + " nanos for " + N + " instructions");
        // System.out.println(avgD + " nanos per instruction");

        double bogoIPS = NANOS_IN_ONE_SECOND / avgDPIS;
        // System.out.println(bogoIPS + " bogoIPS");

        return bogoIPS;
    }

    private static void bogoInstruction() {
        // use our own random number generator, independent of the host JDK
        MyRandom myRandom = new MyRandom(100);
        int len = 150;
        int[] intArray = new int[len];
        for (int i = 0; i < len; i++) {
            intArray[i] = myRandom.nextInt();
        }
        // use our own sort algorithm, independent of the host JDK
        BubbleSort.sort(intArray);
    }

    /**
     * Computed the BogoIPS for this host CPU.
     * 
     * @return
     */
    public static double currentBIPS() {
        return computeBogoIPS(LAST_N);
    }

    static double min(double a, double b) {
        return (a <= b) ? a : b;
    }

    /**
     * Assertion used for values that <b>decrease</b> with faster CPUs, typically
     * the time (duration) needed to perform a task.
     * 
     * @param currentDuration
     * @param referenceDuration
     * @param referenceBIPS
     * @throws AssertionFailedError
     */
    public static void assertDuration(double currentDuration, long referenceDuration, double referenceBIPS) throws AssertionFailedError {
        double ajustedDuration = adjustExpectedDuration(referenceDuration, referenceBIPS);
        if (currentDuration > ajustedDuration * SLACK_FACTOR) {
            throw new AssertionFailedError("current duration " + currentDuration + " exceeded expected " + ajustedDuration + " (adjusted reference), "
                            + referenceDuration + " (raw reference)");
        }
    }

    /**
     * Assertion used for values that <b>increase<b> with faster CPUs, typically
     * the number of operations accomplished per unit of time.
     * 
     * @param currentPerformance
     * @param referencePerformance
     * @param referenceBIPS
     * @throws AssertionFailedError
     */
    public static void assertPerformance(double currentPerformance, long referencePerformance, double referenceBIPS) throws AssertionFailedError {
        double ajustedPerf = adjustExpectedPerformance(referencePerformance, referenceBIPS);
        if (currentPerformance * SLACK_FACTOR < ajustedPerf) {
            throw new AssertionFailedError(currentPerformance + " below expected " + ajustedPerf + " (adjusted), " + referencePerformance + " (raw)");
        }
    }

    private static double adjustExpectedPerformance(long referenceDuration, double referenceBIPS) {
        double currentBIPS = currentBIPS();
        return referenceDuration * (currentBIPS / referenceBIPS);
    }

    private static double adjustExpectedDuration(long referenceDuration, double referenceBIPS) {
        double currentBIPS = currentBIPS();
        System.out.println("currentBIPS=" + currentBIPS + " BIPS");
        return referenceDuration * (referenceBIPS / currentBIPS);
    }
}