/**
 * Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
 * 
 * Please see distribution for license.
 */
package com.opengamma.analytics.math.interpolation;

import org.apache.commons.lang.Validate;

import com.opengamma.analytics.math.interpolation.data.ArrayInterpolator1DDataBundle;
import com.opengamma.analytics.math.interpolation.data.Interpolator1DDataBundle;

/**
 * A one-dimensional step interpolator using the upper bound value.
 * <P>The interpolated value of the function
 * <i>x</i> with <i>x<sub>1</sub> <= x < x<sub>2</sub></i> is given by: <i>y = y<sub>1</sub></i>
 */
public class StepUpperInterpolator1D extends Interpolator1D {
  private static final long serialVersionUID = 1L;

  @Override
  public Double interpolate(final Interpolator1DDataBundle data, final Double x) {
    Validate.notNull(x, "value");
    Validate.notNull(data, "data bundle");
    // For x equal to a key
    Double exactValue = data.get(x);
    if (exactValue != null) {
      return exactValue;
    }
    // For intermediary values, return the higher key value.
    return data.get(data.higherKey(x));
  }

  @Override
  public double firstDerivative(final Interpolator1DDataBundle data, final Double x) {
    Validate.notNull(x, "value");
    Validate.notNull(data, "data bundle");
    return 0.;
  }

  @Override
  public Interpolator1DDataBundle getDataBundle(final double[] x, final double[] y) {
    return new ArrayInterpolator1DDataBundle(x, y);
  }

  @Override
  public Interpolator1DDataBundle getDataBundleFromSortedArrays(final double[] x, final double[] y) {
    return new ArrayInterpolator1DDataBundle(x, y, true);
  }

  @Override
  public double[] getNodeSensitivitiesForValue(Interpolator1DDataBundle data, Double value) {
    return getFiniteDifferenceSensitivities(data, value);
  }

}