/*
 * Copyright (c) 2004-2008 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);
  }
}