/*
 * Units of Measurement Reference Implementation
 * Copyright (c) 2005-2016, Jean-Marie Dautelle, Werner Keil, V2COM.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of JSR-363 nor the names of its contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package tec.units.ri;

import java.util.ArrayList;
import java.util.List;

import javax.measure.UnitConverter;

/**
 * <p>
 * The base class for our {@link UnitConverter} implementations.
 * </p>
 *
 * @author <a href="mailto:units@catmedia.us">Werner Keil</a>
 * @version 0.8.1, $Date: 2016-01-17 $
 */
public abstract class AbstractConverter implements UnitConverter {

  /**
   * 
   */
  // private static final long serialVersionUID = 5790242858468427131L;

  /**
   * The ratio of the circumference of a circle to its diameter.
   **/
  protected static final double PI = 3.1415926535897932384626433832795;

  /**
   * Holds identity converter.
   */
  public static final AbstractConverter IDENTITY = new Identity();

  /**
   * Default constructor.
   */
  protected AbstractConverter() {
  }

  /**
   * Concatenates this physics converter with another unit converter. The resulting converter is equivalent to first converting by the specified
   * converter (right converter), and then converting by this converter (left converter).
   *
   * @param that
   *          the other converter.
   * @return the concatenation of this converter with that converter.
   */
  public AbstractConverter concatenate(AbstractConverter that) {
    return (that == IDENTITY) ? this : new Pair(this, that);
  }

  public boolean isIdentity() {
    return false;
  }

  @Override
  public abstract boolean equals(Object cvtr);

  @Override
  public abstract int hashCode();

  @Override
  public abstract AbstractConverter inverse();

  @Override
  public UnitConverter concatenate(UnitConverter converter) {
    return (converter == IDENTITY) ? this : new Pair(this, converter);
  }

  @Override
  public List<? extends UnitConverter> getConversionSteps() {
    final List<AbstractConverter> steps = new ArrayList<AbstractConverter>();
    steps.add(this);
    return steps;
  }

  /**
   * @throws IllegalArgumentException
   *           if the value is </code>null</code>.
   */
  public Number convert(Number value) {
    if (value != null) {
      return convert(value.doubleValue());
    } else {
      throw new IllegalArgumentException("Value cannot be null");
    }
  }

  public abstract double convert(double value);

  /**
   * This class represents the identity converter (singleton).
   */
  private static final class Identity extends AbstractConverter {

    @Override
    public boolean isIdentity() {
      return true;
    }

    @Override
    public Identity inverse() {
      return this;
    }

    @Override
    public double convert(double value) {
      return value;
    }

    @Override
    public UnitConverter concatenate(UnitConverter converter) {
      return converter;
    }

    @Override
    public boolean equals(Object cvtr) {
      return (cvtr instanceof Identity);
    }

    @Override
    public int hashCode() {
      return 0;
    }

    public boolean isLinear() {
      return true;
    }
  }

  /**
   * This class represents converters made up of two or more separate converters (in matrix notation <code>[pair] = [left] x [right]</code>).
   */
  public static final class Pair extends AbstractConverter {

    /**
     * Holds the first converter.
     */
    private final UnitConverter left;

    /**
     * Holds the second converter.
     */
    private final UnitConverter right;

    /**
     * Creates a compound converter resulting from the combined transformation of the specified converters.
     *
     * @param left
     *          the left converter.
     * @param right
     *          the right converter.
     * @throws IllegalArgumentException
     *           if either the left or right converter are </code>null</code>
     */
    public Pair(UnitConverter left, UnitConverter right) {
      this.left = left;
      this.right = right;
    }

    public boolean isLinear() {
      return left.isLinear() && right.isLinear();
    }

    @Override
    public boolean isIdentity() {
      return false;
    }

    @Override
    public List<UnitConverter> getConversionSteps() {
      final List<UnitConverter> steps = new ArrayList<UnitConverter>();
      List<? extends UnitConverter> leftCompound = left.getConversionSteps();
      List<? extends UnitConverter> rightCompound = right.getConversionSteps();
      steps.addAll(leftCompound);
      steps.addAll(rightCompound);
      return steps;
    }

    @Override
    public Pair inverse() {
      return new Pair(right.inverse(), left.inverse());
    }

    @Override
    public double convert(double value) {
      return left.convert(right.convert(value));
    }

    @Override
    public boolean equals(Object cvtr) {
      if (this == cvtr)
        return true;
      if (!(cvtr instanceof Pair))
        return false;
      Pair that = (Pair) cvtr;
      return (this.left.equals(that.left)) && (this.right.equals(that.right));
    }

    @Override
    public int hashCode() {
      return left.hashCode() + right.hashCode();
    }

    public UnitConverter getLeft() {
      return left;
    }

    public UnitConverter getRight() {
      return right;
    }
  }
}