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   */
  
  package testsuite.perf;
  
  import java.text.NumberFormat;
  import java.util.ArrayList;
  import java.util.List;
  
  import testsuite.BaseTestCase;
  
  /**
   * Base class for performance test cases. Handles statistics.
   */
  public abstract class BasePerfTest extends BaseTestCase {
      /**
       * Confidence interval lookup table, indexed by degrees of freedom at 95%.
       */
      private static final double[] T95 = { 12.706, 4.303, 3.182, 2.776, 2.571, 2.447, 2.365, 2.306, 2.262, 2.228, 2.201, 2.179, 2.160, 2.145, 2.131, 2.120,
              2.110, 2.101, 2.093, 2.086, 2.080, 2.074, 2.069, 2.064, 2.060, 2.056, 2.052, 2.048, 2.045, 2.042 };
  
      /**
       * Confidence interval lookup table, indexed by degrees of freedom at 99%.
       */
      private static final double[] T99 = { 63.657, 9.925, 5.841, 4.604, 4.032, 3.707, 3.499, 3.355, 3.250, 3.169, 3.106, 3.055, 3.012, 2.977, 2.947, 2.921,
              2.898, 2.878, 2.861, 2.845, 2.831, 2.819, 2.807, 2.797, 2.787, 2.779, 2.771, 2.763, 2.756, 2.750 };
  
      static NumberFormat numberFormatter = NumberFormat.getInstance();
  
      static {
          numberFormatter.setMaximumFractionDigits(4);
          numberFormatter.setMinimumFractionDigits(4);
      }
  
      /**
       * List of values for each iteration
       */
      private List<Double> testValuesList = new ArrayList<>();
  
      private double confidenceLevel = 95; // 95% by default
  
      private double confidenceValue = 0;
  
      private double intervalWidth = 0.1;
  
      private double meanValue = 0;
  
      private double squareSumValue = 0;
  
      private double sumValue = 0;
  
      private double variationValue = 0;
  
      /**
       * The number of iterations that we have performed
       */
      private int numIterations = 0;
  
      /**
       * Returns the meanValue.
       * 
       * @return double
       */
      public double getMeanValue() {
          return this.meanValue;
      }
  
      /**
       * Sub-classes should override this to perform the operation to be measured.
       * 
       * @throws Exception
       */
      protected abstract void doOneIteration() throws Exception;
  
      /**
       * Returns the current confidence level.
       * 
       * @return the current confidence level.
       */
      protected double getCurrentConfidence() {
          return (this.intervalWidth - this.confidenceValue) * 100;
      }
  
      /**
       * Returns the current margin of error.
       * 
       * @return the current margin of error.
       */
      protected double getMarginOfError() {
          return getConfidenceLookup() * (getStandardDeviationP() / Math.sqrt(this.numIterations));
      }
  
      /**
       * Returns the current STDDEV.
       * 
       * @return the current STDDEV
       */
      protected double getStandardDeviationP() {
          if (this.numIterations < 1) {
              return 0;
          }
  
          return Math.sqrt(((this.numIterations * this.squareSumValue) - (this.sumValue * this.sumValue)) / (this.numIterations * this.numIterations));
      }
  
      /**
       * Adds one test result to the statistics.
       * 
       * @param value
       *            a single result representing the value being measured in the test.
       */
      protected void addResult(double value) {
          this.numIterations++;
          this.testValuesList.add(new Double(value));
  
          this.sumValue += value;
          this.squareSumValue += (value * value);
          this.meanValue = this.sumValue / this.numIterations;
          this.variationValue = (this.squareSumValue / this.numIterations) - (this.meanValue * this.meanValue);
  
          // Can only have confidence when more than one test has been completed
          if (this.numIterations > 1) {
              this.confidenceValue = this.intervalWidth
                      - ((2.0 * getConfidenceLookup() * Math.sqrt(this.variationValue / (this.numIterations - 1.0))) / this.meanValue);
          }
      }
  
      /**
       * Calls doIteration() the <code>numIterations</code> times, displaying the mean, std, margin of error and confidence level.
       * 
       * @param num_iterations
       *            the number of iterations to perform ( < 30)
       * @throws Exception
       *             if an error occurs.
       */
      protected void doIterations(int num_iterations) throws Exception {
          for (int i = 0; i < num_iterations; i++) {
              doOneIteration();
          }
      }
  
      /**
       * Reports the current results to STDOUT, preceeded by <code>additionalMessage</code> if not null.
       * 
       * @param additionalMessage
       *            the additional message to print, or null if no message.
       */
      protected synchronized void reportResults(String additionalMessage) {
          StringBuilder messageBuf = new StringBuilder();
  
          if (additionalMessage != null) {
              messageBuf.append(additionalMessage);
              messageBuf.append(": ");
          }
  
          messageBuf.append(" mean: ");
          messageBuf.append(numberFormatter.format(this.meanValue));
          messageBuf.append(" stdevp: ");
          messageBuf.append(numberFormatter.format(getStandardDeviationP()));
          messageBuf.append(" m-o-e: ");
          messageBuf.append(numberFormatter.format(getMarginOfError()));
  
          System.out.println(messageBuf.toString());
      }
  
      private double getConfidenceLookup() {
          if (this.confidenceLevel == 95) {
              return T95[this.numIterations - 1];
          } else if (this.confidenceLevel == 99) {
              return T99[this.numIterations - 1];
          } else {
              throw new IllegalArgumentException("Confidence level must be 95 or 99");
          }
      }
  }
  