package org.djunits.unit;
   
   import java.io.Serializable;
   import java.util.HashMap;
   import java.util.HashSet;
   import java.util.Map;
   import java.util.Set;
   
   import org.djunits.locale.Localization;
  import org.djunits.unit.scale.Scale;
  import org.djunits.unit.scale.StandardScale;
  import org.djunits.unit.unitsystem.UnitSystem;
  
  /**
   * All units are internally <i>stored</i> relative to a standard unit with conversion factor. This means that e.g., a meter is
   * stored with conversion factor 1.0, whereas kilometer is stored with a conversion factor 1000.0. This means that if we want to
   * express a length meter in kilometers, we have to <i>divide</i> by the conversion factor.
   * <p>
   * Copyright (c) 2015-2018 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="http://djunits.org/docs/license.html">DJUNITS License</a>.
   * <p>
   * $LastChangedDate: 2018-01-28 03:17:44 +0100 (Sun, 28 Jan 2018) $, @version $Revision: 256 $, by $Author: averbraeck $,
   * initial version May 15, 2014 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @param <U> the unit for transformation reasons
   */
  public abstract class Unit<U extends Unit<U>> implements Serializable
  {
      /** */
      private static final long serialVersionUID = 20140607;
  
      /** The key to the locale file for the long name of the unit, or null when it is a user-defined unit. */
      private final String nameKey;
  
      /** The key to the locale file for the abbreviation of the unit, or null when it is a user-defined unit. */
      private final String abbreviationKey;
  
      /**
       * The long name of the unit in case it does not exist in the locale file, e.g. when defining a run-time unit. The name will
       * be null if the locale has to be used, i.e. for standard units.
       */
      private final String name;
  
      /**
       * The abbreviation of the unit in case it does not exist in the locale file, e.g. when defining a run-time unit. The
       * abbreviation will be null if the locale has to be used, i.e. for standard units.
       */
      private final String abbreviation;
  
      /** The unit system, e.g. SI or Imperial. */
      private final UnitSystem unitSystem;
  
      /** The scale to use to convert between this unit and the standard (e.g., SI) unit. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      protected Scale scale;
  
      /** SI unit information. */
      private SICoefficients siCoefficients;
  
      /** A static map of all defined coefficient strings, to avoid double creation and allow lookup. */
      private static final Map<String, SICoefficients> SI_COEFFICIENTS = new HashMap<String, SICoefficients>();
  
      /** A static map of all defined coefficient strings, mapped to the existing units. */
      private static final Map<String, Map<Class<Unit<?>>, Unit<?>>> SI_UNITS =
              new HashMap<String, Map<Class<Unit<?>>, Unit<?>>>();
  
      /** A static map of all defined units. */
      private static final Map<String, Set<Unit<?>>> UNITS = new HashMap<String, Set<Unit<?>>>();
  
      /** Localization information. */
      private static Localization localization = new Localization("localeunit");
  
      /** Has this class been initialized? */
      private static boolean initialized = false;
  
      /** Standard (SI) unit or not? */
      private boolean baseSIUnit;
  
      /** The array of the names of the standard units. */
      public static final String[] STANDARD_UNITS = new String[] { "AbsoluteTemperatureUnit", "AccelerationUnit",
              "AngleSolidUnit", "AngleUnit", "AreaUnit", "DensityUnit", "DimensionlessUnit", "DirectionUnit", "DurationUnit",
              "ElectricalChargeUnit", "ElectricalCurrentUnit", "ElectricalPotentialUnit", "ElectricalResistanceUnit",
              "EnergyUnit", "FlowMassUnit", "FlowVolumeUnit", "ForceUnit", "FrequencyUnit", "LengthUnit", "LinearDensityUnit",
              "MassUnit", "MoneyUnit", "MoneyPerAreaUnit", "MoneyPerEnergyUnit", "MoneyPerLengthUnit", "MoneyPerMassUnit",
              "MoneyPerDurationUnit", "MoneyPerVolumeUnit", "PositionUnit", "PowerUnit", "PressureUnit", "SpeedUnit",
              "TemperatureUnit", "TimeUnit", "TorqueUnit", "VolumeUnit" };
  
      /** the cached hashcode. */
      private final int cachedHashCode;
  
      /** Force all units to be loaded. */
      private static void initialize()
      {
          for (String className : STANDARD_UNITS)
          {
              try
              {
                  Class.forName("org.djunits.unit." + className);
              }
             catch (Exception exception)
             {
                 // TODO professional logging of errors
                 System.err.println("Could not load class org.djunits.unit." + className);
             }
         }
         initialized = true;
     }
 
     /**
      * Build a standard unit and create the fields for a unit. If the parameter standardUnit is true, it is a standard unit
      * where name is the nameKey, and abbreviation is the abbreviationKey; if false, this unit is a user-defined unit where the
      * localization files do not have an entry. If standardUnit is true, a UnitException is silently ignored; if standardUnit is
      * false a UnitException is thrown as a RunTimeException.
      * @param nameOrNameKey if standardUnit: the key to the locale file for the long name of the unit, otherwise the name itself
      * @param abbreviationOrAbbreviationKey if standardUnit: the key to the locale file for the abbreviation of the unit,
      *            otherwise the abbreviation itself
      * @param unitSystem the unit system, e.g. SI or Imperial
      * @param standardUnit indicates whether it is a standard unit with a definition in the locale, or a user-defined unit
      */
     protected Unit(final String nameOrNameKey, final String abbreviationOrAbbreviationKey, final UnitSystem unitSystem,
             final boolean standardUnit)
     {
         this.scale = StandardScale.SCALE;
         this.baseSIUnit = true;
         if (standardUnit)
         {
             this.nameKey = nameOrNameKey;
             this.abbreviationKey = abbreviationOrAbbreviationKey;
             this.name = null;
             this.abbreviation = null;
         }
         else
         {
             this.nameKey = null;
             this.abbreviationKey = null;
             this.name = nameOrNameKey;
             this.abbreviation = abbreviationOrAbbreviationKey;
         }
         this.unitSystem = unitSystem;
         this.cachedHashCode = generateHashCode();
         try
         {
             addUnit(this);
         }
         catch (UnitException ue)
         {
             if (!standardUnit)
             {
                 throw new RuntimeException(ue);
             }
         }
     }
 
     /**
      * Build a unit with a specific conversion scale to/from the standard unit. If the parameter standardUnit is true, it is a
      * standard unit where name is the nameKey, and abbreviation is the abbreviationKey; if false, this unit is a user-defined
      * unit where the localization files do not have an entry. If standardUnit is true, a UnitException is silently ignored; if
      * standardUnit is false a UnitException is thrown as a RunTimeException.
      * @param nameOrNameKey if standardUnit: the key to the locale file for the long name of the unit, otherwise the name itself
      * @param abbreviationOrAbbreviationKey if standardUnit: the key to the locale file for the abbreviation of the unit,
      *            otherwise the abbreviation itself
      * @param unitSystem the unit system, e.g. SI or Imperial
      * @param scale the conversion scale to use for this unit
      * @param standardUnit indicates whether it is a standard unit with a definition in the locale, or a user-defined unit
      */
     protected Unit(final String nameOrNameKey, final String abbreviationOrAbbreviationKey, final UnitSystem unitSystem,
             final Scale scale, final boolean standardUnit)
     {
         this(nameOrNameKey, abbreviationOrAbbreviationKey, unitSystem, standardUnit);
         this.scale = scale;
         this.baseSIUnit = scale.isBaseSIScale();
     }
 
     /**
      * Report if this unit support localization.
      * @return boolean; true if this unit supports localization; false if it does not
      */
     public final boolean isLocalizable()
     {
         return this.nameKey != null;
     }
 
     /**
      * Add a unit to the overview collection of existing units, and resolve the coefficients.
      * @param unit the unit to add. It will be stored in a set belonging to the simple class name String, e.g. "ForceUnit".
      * @throws UnitException when parsing or normalizing the SI coefficient string fails.
      */
     private void addUnit(final Unit<U> unit) throws UnitException
     {
         if (!UNITS.containsKey(unit.getClass().getSimpleName()))
         {
             UNITS.put(unit.getClass().getSimpleName(), new HashSet<Unit<?>>());
         }
         UNITS.get(unit.getClass().getSimpleName()).add(unit);
 
         // resolve the SI coefficients, and normalize string
         String siCoefficientsString = SICoefficients.normalize(getSICoefficientsString()).toString();
         if (SI_COEFFICIENTS.containsKey(siCoefficientsString))
         {
             this.siCoefficients = SI_COEFFICIENTS.get(siCoefficientsString);
         }
         else
         {
             this.siCoefficients = new SICoefficients(SICoefficients.parse(siCoefficientsString));
             SI_COEFFICIENTS.put(siCoefficientsString, this.siCoefficients);
         }
 
         // add the standard unit
         Map<Class<Unit<?>>, Unit<?>> unitMap = SI_UNITS.get(siCoefficientsString);
         if (unitMap == null)
         {
             unitMap = new HashMap<Class<Unit<?>>, Unit<?>>();
             SI_UNITS.put(siCoefficientsString, unitMap);
         }
         if (!unitMap.containsKey(unit.getClass()))
         {
             @SuppressWarnings("unchecked")
             Class<Unit<?>> clazz = (Class<Unit<?>>) unit.getClass();
             if (this.getStandardUnit() == null)
             {
                 unitMap.put(clazz, this);
             }
             else
             {
                 unitMap.put(clazz, this.getStandardUnit());
             }
         }
     }
 
     /**
      * Return a set of defined units for a given unit type.
      * @param <V> the unit type to use in this method.
      * @param unitClass the class for which the units are requested, e.g. ForceUnit.class
      * @return the set of defined units belonging to the provided class. The empty set will be returned in case the unit type
      *         does not have any units.
      */
     @SuppressWarnings("unchecked")
     public static <V extends Unit<V>> Set<V> getUnits(final Class<V> unitClass)
     {
         if (!initialized)
         {
             initialize();
         }
         Set<V> returnSet = new HashSet<V>();
         if (UNITS.containsKey(unitClass.getSimpleName()))
         {
             for (Unit<?> unit : UNITS.get(unitClass.getSimpleName()))
             {
                 returnSet.add((V) unit);
             }
         }
         return returnSet;
     }
 
     /**
      * Return a copy of the set of all defined units for this unit type.
      * @return the set of defined units belonging to this Unit class. The empty set will be returned in case the unit type does
      *         not have any units.
      */
     // TODO call static method from the instance method? The two are now too similar.
     @SuppressWarnings("unchecked")
     public final Set<Unit<U>> getAllUnitsOfThisType()
     {
         if (!initialized)
         {
             initialize();
         }
         Set<Unit<U>> returnSet = new HashSet<Unit<U>>();
         if (UNITS.containsKey(this.getClass().getSimpleName()))
         {
             for (Unit<?> unit : UNITS.get(this.getClass().getSimpleName()))
             {
                 returnSet.add((Unit<U>) unit);
             }
         }
         return returnSet;
     }
 
     /**
      * @return name, e.g. meters per second
      */
     public final String getName()
     {
         if (this.name != null)
         {
             return this.name;
         }
         return localization.getString(this.nameKey);
     }
 
     /**
      * This method returns the name key, or null in case the name is hard coded.
      * @return name key, e.g. DurationUnit.MetersPerSecond, or null for a user-defined unit
      */
     public final String getNameKey()
     {
         return this.nameKey;
     }
 
     /**
      * @return abbreviation, e.g., m/s
      */
     public final String getAbbreviation()
     {
         if (this.abbreviation != null)
         {
             return this.abbreviation;
         }
         return localization.getString(this.abbreviationKey);
     }
 
     /**
      * This method returns the abbreviation key, or null in case the abbreviation is hard coded.
      * @return abbreviation key, e.g. DurationUnit.m/s, or null for a user-defined unit
      */
     public final String getAbbreviationKey()
     {
         return this.abbreviationKey;
     }
 
     /**
      * @return the scale to transform between this unit and the reference (e.g., SI) unit.
      */
     @SuppressWarnings("checkstyle:designforextension")
     public Scale getScale()
     {
         return this.scale;
     }
 
     /**
      * @return unitSystem, e.g. SI or Imperial
      */
     public final UnitSystem getUnitSystem()
     {
         return this.unitSystem;
     }
 
     /**
      * @return the SI standard unit for this unit, or the de facto standard unit if SI is not available
      */
     public abstract U getStandardUnit();
 
     /**
      * @return the SI standard coefficients for this unit, e.g., kgm/s2 or m-2s2A or m^-2.s^2.A or m^-2s^2A (not necessarily
      *         normalized)
      */
     public abstract String getSICoefficientsString();
 
     /**
      * @return the SI coefficients
      */
     public final SICoefficients getSICoefficients()
     {
         return this.siCoefficients;
     }
 
     /**
      * Determine whether this unit is the standard unit.
      * @return boolean; whether this is the standard unit or not
      */
     public final boolean isBaseSIUnit()
     {
         return this.baseSIUnit;
     }
 
     /**
      * @param normalizedSICoefficientsString the normalized string (e.g., kg.m/s2) to look up
      * @return a set with the Units belonging to this string, or an empty set when it does not exist
      */
     public static Set<Unit<?>> lookupUnitWithSICoefficients(final String normalizedSICoefficientsString)
     {
         if (!initialized)
         {
             initialize();
         }
         if (SI_UNITS.containsKey(normalizedSICoefficientsString))
         {
             return new HashSet<Unit<?>>(SI_UNITS.get(normalizedSICoefficientsString).values());
         }
         return new HashSet<Unit<?>>();
     }
 
     /**
      * @param normalizedSICoefficientsString the normalized string (e.g., kg.m/s2) to look up
      * @return a set of Units belonging to this string, or a set with a new unit when it does not yet exist
      */
     // TODO call other static method? The two are now too similar.
     public static Set<Unit<?>> lookupOrCreateUnitWithSICoefficients(final String normalizedSICoefficientsString)
     {
         if (!initialized)
         {
             initialize();
         }
         if (SI_UNITS.containsKey(normalizedSICoefficientsString))
         {
             return new HashSet<Unit<?>>(SI_UNITS.get(normalizedSICoefficientsString).values());
         }
         SIUnit unit = new SIUnit("SIUnit." + normalizedSICoefficientsString);
         Set<Unit<?>> unitSet = new HashSet<Unit<?>>();
         unitSet.add(unit);
         return unitSet;
     }
 
     /**
      * @param normalizedSICoefficientsString the normalized string (e.g., kg.m/s2) to look up
      * @return the Unit belonging to this string, or a new unit when it does not yet exist
      */
     public static SIUnit lookupOrCreateSIUnitWithSICoefficients(final String normalizedSICoefficientsString)
     {
         if (!initialized)
         {
             initialize();
         }
         if (SI_UNITS.containsKey(normalizedSICoefficientsString)
                 && SI_UNITS.get(normalizedSICoefficientsString).containsKey(SIUnit.class))
         {
             return (SIUnit) SI_UNITS.get(normalizedSICoefficientsString).get(SIUnit.class);
         }
         SIUnit unit = new SIUnit("SIUnit." + normalizedSICoefficientsString, false);
         return unit;
     }
 
     /** {@inheritDoc} */
     @Override
     public final String toString()
     {
         return getAbbreviation();
     }
 
     /**
      * Generate a hashCode for caching.
      * @return a hashCode that is consistent with the equals() method.
      */
     public final int generateHashCode()
     {
         final int prime = 31;
         int result = 1;
         result = prime * result + ((this.abbreviation == null) ? 0 : this.abbreviation.hashCode());
         result = prime * result + ((this.abbreviationKey == null) ? 0 : this.abbreviationKey.hashCode());
         result = prime * result + ((this.name == null) ? 0 : this.name.hashCode());
         result = prime * result + ((this.nameKey == null) ? 0 : this.nameKey.hashCode());
         return result;
     }
 
     /** {@inheritDoc} */
     @SuppressWarnings("checkstyle:designforextension")
     @Override
     public int hashCode()
     {
         return this.cachedHashCode;
     }
 
     /** {@inheritDoc} */
     @SuppressWarnings({ "checkstyle:designforextension", "checkstyle:needbraces" })
     @Override
     public boolean equals(final Object obj)
     {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         Unit<?> other = (Unit<?>) obj;
         if (this.abbreviation == null)
         {
             if (other.abbreviation != null)
                 return false;
         }
         else if (!this.abbreviation.equals(other.abbreviation))
             return false;
         if (this.abbreviationKey == null)
         {
             if (other.abbreviationKey != null)
                 return false;
         }
         else if (!this.abbreviationKey.equals(other.abbreviationKey))
             return false;
         if (this.name == null)
         {
             if (other.name != null)
                 return false;
         }
         else if (!this.name.equals(other.name))
             return false;
         if (this.nameKey == null)
         {
             if (other.nameKey != null)
                 return false;
         }
         else if (!this.nameKey.equals(other.nameKey))
             return false;
         return true;
     }
 
 }