package org.djunits.unit;
   
   import java.util.Objects;
   
   import org.djunits.quantity.def.Quantity;
   import org.djunits.unit.scale.Scale;
   import org.djunits.unit.si.SIPrefix;
   import org.djunits.unit.si.SIPrefixes;
   import org.djunits.unit.system.UnitSystem;
  import org.djutils.exceptions.Throw;
  
  /**
   * The AbstractUnit is the parent class of all units, and encodes the common behavior of the units. 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, and 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>
   * The conversion to and from the base unit is left to a Scale. Many scales are linear (e.g., converting dm, cm, and mm to
   * meters), but there are also non-linear scales such as the percentage for an angle, where 90 degrees equals an infinite
   * percentage. Copyright (c) 2025-2026 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights
   * reserved. See for project information <a href="https://djunits.org" target="_blank">https://djunits.org</a>. The DJUNITS
   * project is distributed under a <a href="https://djunits.org/docs/license.html" target="_blank">three-clause BSD-style
   * license</a>.
   * @author Alexander Verbraeck
   * @param <U> the unit type
   * @param <Q> the quantity type belonging to this unit
   */
  public abstract class AbstractUnit<U extends UnitInterface<U, Q>, Q extends Quantity<Q, U>> implements UnitInterface<U, Q>
  {
      /** The textual abbreviation of the unit, which is also the id. */
      private final String textualAbbreviation;
  
      /** The symbolic representation of the unit, which is the default for display. */
      private final String displayAbbreviation;
  
      /** The full name of the unit. */
      private final String name;
  
      /** The scale to use to convert between this unit and the standard (e.g., SI, BASE) unit. */
      private final Scale scale;
  
      /** The unit system, e.g. SI or Imperial. */
      private final UnitSystem unitSystem;
  
      /** The SI-prefix, if any, to allow localization of the SI-prefix. */
      private SIPrefix siPrefix = null;
  
      /**
       * Create a new unit, where the textual abbreviation is the same as the display abbreviation.
       * @param textualAbbreviation the textual abbreviation of the unit, which also serves as the id
       * @param name the full name of the unit
       * @param scale the scale to use to convert between this unit and the standard (e.g., SI, BASE) unit
       * @param unitSystem unit system, e.g. SI or Imperial
       */
      public AbstractUnit(final String textualAbbreviation, final String name, final Scale scale, final UnitSystem unitSystem)
      {
          this(textualAbbreviation, textualAbbreviation, name, scale, unitSystem);
      }
  
      /**
       * Create a new unit, with textual abbreviation(s) and a display abbreviation.
       * @param textualAbbreviation the textual abbreviation of the unit, which also serves as the id
       * @param displayAbbreviation the display abbreviation of the unit
       * @param name the full name of the unit
       * @param scale the scale to use to convert between this unit and the standard (e.g., SI, BASE) unit
       * @param unitSystem unit system, e.g. SI or Imperial
       */
      public AbstractUnit(final String textualAbbreviation, final String displayAbbreviation, final String name,
              final Scale scale, final UnitSystem unitSystem)
      {
          // Check the validity
          String cName = Units.unitClassName(getClass());
          Throw.whenNull(textualAbbreviation, "Constructing unit %s: textualAbbreviation cannot be null", cName);
          Throw.whenNull(displayAbbreviation, "Constructing unit %s: displayAbbreviation cannot be null", cName);
          Throw.when(textualAbbreviation.length() == 0, UnitRuntimeException.class,
                  "Constructing unit %s: textualAbbreviation string cannot be empty", cName);
          Throw.whenNull(name, "Constructing unit %s.%s: name cannot be null", cName, textualAbbreviation);
          Throw.when(name.length() == 0, UnitRuntimeException.class, "Constructing unit %s.%s: name.length cannot be 0", cName,
                  textualAbbreviation);
          Throw.whenNull(scale, "Constructing unit %s.%s: scale cannot be null", cName, textualAbbreviation);
          Throw.whenNull(unitSystem, "Constructing unit %s.%s: unitSystem cannot be null", cName, textualAbbreviation);
  
          // Build the unit
          this.displayAbbreviation = displayAbbreviation;
          this.textualAbbreviation = textualAbbreviation;
          this.name = name;
          this.scale = scale;
          this.unitSystem = unitSystem;
  
          // Register the unit
          Units.register(this);
      }
  
      /**
       * Generate and register the units with all SI-prefixes.
       * @param kilo whether the base unit already has a "kilo" in its abbreviation/name, such as the kilogram
       * @param perUnit whether it is a "per unit" such as "per meter"
       * @return the unit for method chaining
       */
     @SuppressWarnings("unchecked")
     public U generateSiPrefixes(final boolean kilo, final boolean perUnit)
     {
         String cName = getClass().getSimpleName();
         Throw.when(!getScale().isBaseScale(), UnitRuntimeException.class,
                 "SI prefixes generation for unit %s only applicable to unit with base scale", cName);
         Throw.when(kilo && !perUnit && !getId().startsWith("k"), UnitRuntimeException.class,
                 "SI prefixes generated for kilo class for unit %s, but abbreviation %s does not start with a 'k'", cName,
                 getId());
         Throw.when(kilo && perUnit && !getId().startsWith("/k"), UnitRuntimeException.class,
                 "SI prefixes generated for per-kilo class for unit %s, but abbreviation %s does not start with '/k'", cName,
                 getId());
         Throw.when(kilo && !perUnit && !getStoredName().startsWith("kilo"), UnitRuntimeException.class,
                 "SI prefixes generated for kilo class for unit %s, but name %s does not start with 'kilo'", cName,
                 getStoredName());
         Throw.when(kilo && perUnit && !getStoredName().startsWith("per kilo"), UnitRuntimeException.class,
                 "SI prefixes generated for kilo class for unit %s, but name %s does not start with 'per kilo'", cName,
                 getStoredName());
         Throw.when(perUnit && !getId().startsWith("/"), UnitRuntimeException.class,
                 "SI prefixes generated for 'per' class for unit %s, but abbreviation %s does not start with '/'", cName,
                 getId());
         Throw.when(perUnit && !getStoredName().startsWith("per "), UnitRuntimeException.class,
                 "SI prefixes generated for 'per' class for unit %s, but name %s does not start with 'per '", cName,
                 getStoredName());
 
         if (!kilo)
         {
             if (!perUnit)
             {
                 for (SIPrefix sip : SIPrefixes.UNIT_PREFIXES.values())
                 {
                     U unit = deriveUnit(sip.getDefaultTextualPrefix() + getStoredTextualAbbreviation(),
                             sip.getDefaultDisplayPrefix() + getStoredDisplayAbbreviation(),
                             sip.getPrefixName() + getStoredName(), sip.getFactor(), getUnitSystem());
                     unit.setSiPrefix(sip);
                 }
             }
             else
             {
                 for (SIPrefix sip : SIPrefixes.PER_UNIT_PREFIXES.values())
                 {
                     U unit = deriveUnit(sip.getDefaultTextualPrefix() + getStoredTextualAbbreviation().substring(1),
                             sip.getDefaultDisplayPrefix() + getStoredDisplayAbbreviation().substring(1),
                             sip.getPrefixName() + getStoredName().substring(4), sip.getFactor(), getUnitSystem());
                     unit.setSiPrefix(sip);
                 }
             }
         }
         else
         {
             if (!perUnit)
             {
                 for (SIPrefix sip : SIPrefixes.KILO_PREFIXES.values())
                 {
                     U unit = deriveUnit(sip.getDefaultTextualPrefix() + getStoredTextualAbbreviation().substring(1),
                             sip.getDefaultDisplayPrefix() + getStoredDisplayAbbreviation().substring(1),
                             sip.getPrefixName() + getStoredName().substring(4), sip.getFactor(), getUnitSystem());
                     unit.setSiPrefix(sip);
                 }
             }
             else
             {
                 for (SIPrefix sip : SIPrefixes.PER_KILO_PREFIXES.values())
                 {
                     U unit = deriveUnit(sip.getDefaultTextualPrefix() + getStoredTextualAbbreviation().substring(2),
                             sip.getDefaultDisplayPrefix() + getStoredDisplayAbbreviation().substring(2),
                             sip.getPrefixName() + getStoredName().substring(8), sip.getFactor(), getUnitSystem());
                     unit.setSiPrefix(sip);
                 }
             }
         }
         return (U) this;
     }
 
     /**
      * Return a linearly scaled derived unit for this unit, where the textual abbreviation is the same as the display
      * abbreviation.
      * @param textualAbbreviation the textual abbreviation of the unit, which doubles as the id
      * @param name the full name of the unit
      * @param scaleFactor the (linear) scale factor to multiply with the current (linear) scale factor
      * @param unitSystem unit system, e.g. SI or Imperial
      * @return a derived unit for this unit
      */
     @SuppressWarnings("checkstyle:hiddenfield")
     public U deriveUnit(final String textualAbbreviation, final String name, final double scaleFactor,
             final UnitSystem unitSystem)
     {
         return deriveUnit(textualAbbreviation, textualAbbreviation, name, scaleFactor, unitSystem);
     }
 
     /**
      * Return a linearly scaled derived unit for this unit, with textual abbreviation(s) and a display abbreviation.
      * @param textualAbbreviation the textual abbreviation of the unit, which doubles as the id
      * @param displayAbbreviation the display abbreviation of the unit
      * @param name the full name of the unit
      * @param scaleFactor the (linear) scale factor to multiply with the current (linear) scale factor
      * @param unitSystem unit system, e.g. SI or Imperial
      * @return a derived unit for this unit
      */
     @SuppressWarnings("checkstyle:hiddenfield")
     public abstract U deriveUnit(String textualAbbreviation, String displayAbbreviation, String name, double scaleFactor,
             UnitSystem unitSystem);
 
     @Override
     public String getId()
     {
         return this.textualAbbreviation;
     }
 
     @Override
     public String getStoredTextualAbbreviation()
     {
         return this.textualAbbreviation;
     }
 
     @Override
     public String getTextualAbbreviation()
     {
         return Units.localizedUnitTextualAbbr(getClass(), getId());
     }
 
     @Override
     public String getStoredDisplayAbbreviation()
     {
         return this.displayAbbreviation;
     }
 
     @Override
     public String getDisplayAbbreviation()
     {
         return Units.localizedUnitDisplayAbbr(getClass(), getId());
     }
 
     @Override
     public String getStoredName()
     {
         return this.name;
     }
 
     @Override
     public String getName()
     {
         return Units.localizedUnitName(getClass(), getId());
     }
 
     @Override
     public Scale getScale()
     {
         return this.scale;
     }
 
     @Override
     public UnitSystem getUnitSystem()
     {
         return this.unitSystem;
     }
 
     @SuppressWarnings({"unchecked", "hiddenfield"})
     @Override
     public U setSiPrefix(final SIPrefix siPrefix)
     {
         this.siPrefix = siPrefix;
         return (U) this;
     }
 
     @Override
     public U setSiPrefix(final String prefix)
     {
         SIPrefix sip = SIPrefixes.getSiPrefix(prefix);
         return setSiPrefix(sip);
     }
 
     @Override
     public U setSiPrefixKilo(final String prefix)
     {
         SIPrefix sip = SIPrefixes.getSiPrefixKilo(prefix);
         return setSiPrefix(sip);
     }
 
     @Override
     public U setSiPrefixPer(final String prefix)
     {
         SIPrefix sip = SIPrefixes.getSiPrefixPer(prefix);
         return setSiPrefix(sip);
     }
 
     @Override
     public SIPrefix getSiPrefix()
     {
         return this.siPrefix;
     }
 
     @Override
     public int hashCode()
     {
         return Objects.hash(this.displayAbbreviation, this.name, this.scale, this.textualAbbreviation, this.unitSystem);
     }
 
     @Override
     @SuppressWarnings("checkstyle:needbraces")
     public boolean equals(final Object obj)
     {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         AbstractUnit<?, ?> other = (AbstractUnit<?, ?>) obj;
         return Objects.equals(this.displayAbbreviation, other.displayAbbreviation) && Objects.equals(this.name, other.name)
                 && Objects.equals(this.scale, other.scale)
                 && Objects.equals(this.textualAbbreviation, other.textualAbbreviation)
                 && Objects.equals(this.unitSystem, other.unitSystem);
     }
 
     @Override
     public String toString()
     {
         return this.displayAbbreviation;
     }
 }