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/*
 * Copyright (c) 1998-2018 University Corporation for Atmospheric Research/Unidata
 * See LICENSE for license information.
 */
package ucar.units;

import javax.annotation.concurrent.Immutable;
import java.io.Serializable;

/**
 * Provides support for a Base/exponent pair. Instances of this class are
 * immutable.
 * 
 * @author Steven R. Emmerson
 */
@Immutable
public final class Factor implements Serializable {
  private static final long serialVersionUID = 1L;

  /**
   * The Base entity.
   * 
   * @serial
   */
  private final Base _base;

  /**
   * The exponent.
   * 
   * @serial
   */
  private final int _exponent;

  /**
   * Constructs from a Base. The exponent is set to unity.
   * 
   * @param base
   *        The base entity.
   */
  public Factor(final Base base) {
    this(base, 1);
  }

  /**
   * Constructs from a Factor and an exponent.
   * 
   * @param factor
   *        The factor.
   * @param exponent
   *        The exponent.
   */
  public Factor(final Factor factor, final int exponent) {
    this(factor.getBase(), exponent);
  }

  /**
   * Constructs from a Base and an exponent.
   * 
   * @param base
   *        The base entity.
   * @param exponent
   *        The exponent.
   */
  public Factor(final Base base, final int exponent) {
    _base = base;
    _exponent = exponent;
  }

  /**
   * Returns the Base entity.
   * 
   * @return The Base entity.
   */
  public Base getBase() {
    return _base;
  }

  /**
   * Returns the identifier of the Base entity.
   * 
   * @return The identifier of the Base entity (symbol or name).
   */
  public String getID() {
    return getBase().getID();
  }

  /**
   * Returns the exponent of the Base entity.
   * 
   * @return The exponent of the Base entity.
   */
  public int getExponent() {
    return _exponent;
  }

  /**
   * Raises this Factor to a power.
   * 
   * @param power
   *        The power by which to raise this Factor.
   * @return The Factor resulting from raising this Factor to the given power.
   */
  public Factor pow(final int power) {
    return new Factor(getBase(), getExponent() * power);
  }

  /**
   * Returns the string representation of this Factor.
   * 
   * @return The string representation of this Factor.
   */
  @Override
  public final String toString() {
    return getExponent() == 0 ? "" : getExponent() == 1 ? getBase().toString() : getBase().toString() + getExponent();
  }

  /**
   * Indicates if this Factor is semantically identical to another object.
   * 
   * @param object
   *        The object.
   * @return true if and only if this Factor is semantically
   *         identical to object<
   *         /code>.
   */
  @Override
  public boolean equals(final Object object) {
    boolean equals;
    if (this == object) {
      equals = true;
    } else if (!(object instanceof Factor)) {
      equals = false;
    } else {
      final Factor that = (Factor) object;
      equals = getExponent() == that.getExponent() && (getExponent() == 0 || getBase().equals(that.getBase()));
    }
    return equals;
  }

  /**
   * Returns the hash code of this instance.
   * 
   * @return The hash code of this instance.
   */
  @Override
  public int hashCode() {
    return getExponent() == 0 ? getClass().hashCode() : getExponent() ^ getBase().hashCode();
  }

  /**
   * Indicates if this Factor is the reciprocal of another Factor.
   * 
   * @param that
   *        The other factor.
   * @return true if and only if this Factor is the reciprocal of
   *         that.
   */
  public boolean isReciprocalOf(final Factor that) {
    return getBase().equals(that.getBase()) && getExponent() == -that.getExponent();
  }

  /**
   * Indicates if this factor is dimensionless. A Factor is dimensionless if
   * and only if the exponent is zero or the Base entity is dimensionless.
   * 
   * @return true if and only if this Factor is dimensionless.
   */
  public boolean isDimensionless() {
    return getExponent() == 0 || getBase().isDimensionless();
  }
}