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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.util.SortedMap;
import java.util.TreeMap;

/**
 * Provides support for base units.
 * 
 * @author Steven R. Emmerson
 */
@Immutable
public class BaseUnit extends DerivedUnitImpl implements Base {
  private static final long serialVersionUID = 1L;

  /**
   * The identifier-to-unit map.
   * 
   * @serial
   */
  private static final SortedMap nameMap = new TreeMap<>();

  /**
   * The quantity-to-unit map.
   * 
   * @serial
   */
  private static final SortedMap quantityMap = new TreeMap<>();

  /**
   * The base quantity associated with this base unit.
   * 
   * @serial
   */
  private final BaseQuantity baseQuantity;

  /**
   * Constructs from identifiers and a base quantity.
   * 
   * @param id
   *        The identifiers for the base unit. 
   *        id.getSymbol()
   *        shall not return 
   *        null.
   * @param baseQuantity
   *        The base quantity of the base unit.
   * @throws NameException
   *         id.getSymbol() returned 
   *        null.
   */
  protected BaseUnit(final UnitName id, final BaseQuantity baseQuantity) throws NameException {
    super(id);
    if (id.getSymbol() == null) {
      throw new NameException("Base unit must have symbol");
    }
    setDimension(new UnitDimension(this));
    this.baseQuantity = baseQuantity;
  }

  /**
   * Factory method for creating a new BaseUnit or obtaining a
   * previously-created one.
   * 
   * @param id
   *        The identifier for the base unit. 
   *        id.getSymbol()
   *        shall not return 
   *        null.
   * @param baseQuantity
   *        The base quantity of the base unit.
   * @throws NameException
   *         id.getSymbol() returned 
   *        null.
   * @throws UnitExistsException
   *         Attempt to incompatibly redefine an existing base unit.
   */
  public static synchronized BaseUnit getOrCreate(final UnitName id, final BaseQuantity baseQuantity)
      throws NameException, UnitExistsException {
    BaseUnit baseUnit;
    final BaseUnit nameUnit = nameMap.get(id);
    final BaseUnit quantityUnit = quantityMap.get(baseQuantity);
    if (nameUnit != null || quantityUnit != null) {
      baseUnit = nameUnit != null ? nameUnit : quantityUnit;
      if ((nameUnit != null && !baseQuantity.equals(nameUnit.getBaseQuantity()))
          || (quantityUnit != null && !id.equals(quantityUnit.getUnitName()))) {
        throw new UnitExistsException("Attempt to incompatibly redefine base unit \"" + baseUnit + '"');
      }
    } else {
      baseUnit = new BaseUnit(id, baseQuantity);
      quantityMap.put(baseQuantity, baseUnit);
      nameMap.put(id, baseUnit);
    }
    return baseUnit;
  }

  /**
   * Returns the base quantity associated with this base unit.
   * 
   * @return The base quantity associated with this base unit.
   */
  public final BaseQuantity getBaseQuantity() {
    return baseQuantity;
  }

  /**
   * Returns the identifier for this base unit. This is identical to
   * getSymbol().
   * 
   * @return The identifier for this base unit.
   */
  public final String getID() {
    return getSymbol();
  }

  /**
   * Returns the string representation of this base unit. This is identical to
   * getID().
   * 
   * @return The string representation of this base unit.
   */
  @Override
  public final String toString() {
    return getID();
  }

  /**
   * Indicates if this base unit is dimensionless.
   * 
   * @return true if and only if this base unit is dimensionless
   *         (e.g. "radian").
   */
  @Override
  public boolean isDimensionless() {
    return baseQuantity.isDimensionless();
  }

}