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

import java.io.Serializable;
import java.util.HashMap;
import java.util.Iterator;

/**
 * @author Steven R. Emmerson
 */
public class UnitSystemImpl implements UnitSystem, Serializable {
  private static final long serialVersionUID = 1L;

  /**
   * The quantity-to-base-unit map.
   * 
   * @serial
   */
  private final HashMap quantityMap;

  /**
   * The base unit database;
   * 
   * @serial
   */
  private final UnitDB baseUnitDB;

  /**
   * The complete database;
   * 
   * @serial
   */
  private final UnitDBImpl acceptableUnitDB;

  /**
   * Constructs from a base unit database and a derived unit database.
   * 
   * @param baseUnitDB
   *        The base unit database. Shall only contain base units.
   * @param derivedUnitDB
   *        The derived unit database. Shall not contain any base units.
   * @throws UnitExistsException
   *         A unit with the same identifier exists in both databases.
   */
  protected UnitSystemImpl(final UnitDBImpl baseUnitDB, final UnitDBImpl derivedUnitDB) throws UnitExistsException {
    quantityMap = new HashMap<>(baseUnitDB.nameCount());
    for (final Iterator iter = baseUnitDB.getIterator(); iter.hasNext();) {
      final Unit unit = (Unit) iter.next();
      final BaseUnit baseUnit = (BaseUnit) unit;
      quantityMap.put(baseUnit.getBaseQuantity(), baseUnit);
    }
    this.baseUnitDB = baseUnitDB;
    acceptableUnitDB = new UnitDBImpl(baseUnitDB.nameCount() + derivedUnitDB.nameCount(),
        baseUnitDB.symbolCount() + derivedUnitDB.symbolCount());
    acceptableUnitDB.add(baseUnitDB);
    acceptableUnitDB.add(derivedUnitDB);
  }

  /**
   * Returns the base unit database.
   * 
   * @return The base unit database.
   */
  public final UnitDB getBaseUnitDB() {
    return baseUnitDB;
  }

  /**
   * Returns the complete unit database.
   * 
   * @return The complete unit database (both base units and derived units).
   */
  public final UnitDB getUnitDB() {
    return acceptableUnitDB;
  }

  /**
   * Returns the base unit corresponding to a base quantity.
   * 
   * @param quantity
   *        The base quantity.
   * @return The base unit corresponding to the base quantity in this system
   *         of units or 
   *        null if no such unit exists.
   */
  public final BaseUnit getBaseUnit(final BaseQuantity quantity) {
    return quantityMap.get(quantity);
  }
}