package com.twitter.search.common.encoding.features;

import com.google.common.base.Preconditions;

/**
 * A normalizer that normalizes the prediction score from a machine learning classifier, which
 * ranges within [0.0, 1.0], to an integer value by multiplying by (10 ^ precision), and returns
 * the rounded value. The lower the precision, the less amount of bits it takes to encode the score.
 * @see #precision
 *
 * This normalizer also could denormalize the normalized value from integer back to double using the
 * same precision.
 */
public class PredictionScoreNormalizer {

  private final int precision;
  private final double normalizingBase;

  public PredictionScoreNormalizer(int precision) {
    this.precision = precision;
    this.normalizingBase = Math.pow(10, this.precision);
  }

  /**
   * Returns the normalized int value for prediction score {@code score} by multiplying
   * by {@code normalizingBase}, and round the result.
   * @throws IllegalArgumentException when parameter {@code score} is not within [0.0, 1.0]
   */
  public int normalize(double score) {
    Preconditions.checkArgument(isScoreWithinRange(score));
    return (int) Math.round(score * this.normalizingBase);
  }

  /**
   * Converts the normalized int value back to a double score by dividing by {@code normalizingBase}
   * @throws IllegalStateException when the denormalized value is not within [0.0, 1.0]
   */
  public double denormalize(int normalizedScore) {
    double denormalizedValue = normalizedScore / this.normalizingBase;
    if (!isScoreWithinRange(denormalizedValue)) {
      throw new IllegalStateException(
          String.format("The denormalized value %s is not within [0.0, 1.0]", denormalizedValue)
      );
    }
    return denormalizedValue;
  }

  private static boolean isScoreWithinRange(double score) {
    return 0.0 <= score && score <= 1.0;
  }
}