package org.djunits.unit;
   
   import org.djunits.quantity.Dimensionless;
   import org.djunits.unit.scale.LinearScale;
   import org.djunits.unit.scale.Scale;
   import org.djunits.unit.si.SIUnit;
   import org.djunits.unit.system.UnitSystem;
   
   /**
   * Unitless encodes a unit without dimensions, e.g., to encode a constant.
   * <p>
   * 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
   */
  public class Unitless extends AbstractUnit<Unitless, Dimensionless>
  {
      /** The dimensions of the dimensionless quantity: 1 [rad, sr, kg, m, s, A, K, mol, cd]. */
      public static final SIUnit SI_UNIT = new SIUnit(new int[] {0, 0, 0, 0, 0, 0, 0, 0, 0});
  
      /** The SI or BASE unit. */
      public static final Unitless BASE = new Unitless(" ", " ", 1.0, UnitSystem.OTHER);
  
      /**
       * Create a new Dimensionless unit.
       * @param id the id or main abbreviation of the unit
       * @param name the full name of the unit
       * @param scaleFactorToBaseUnit the scale factor of the unit to convert it TO the base (SI) unit
       * @param unitSystem the unit system such as SI or IMPERIAL
       */
      public Unitless(final String id, final String name, final double scaleFactorToBaseUnit, final UnitSystem unitSystem)
      {
          super(id, name, new LinearScale(scaleFactorToBaseUnit), unitSystem);
      }
  
      /**
       * Return a 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 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 Unitless(final String textualAbbreviation, final String displayAbbreviation, final String name, final Scale scale,
              final UnitSystem unitSystem)
      {
          super(textualAbbreviation, displayAbbreviation, name, scale, unitSystem);
      }
  
      @Override
      public SIUnit siUnit()
      {
          return SI_UNIT;
      }
  
      @Override
      public Unitless getBaseUnit()
      {
          return BASE;
      }
  
      @Override
      public Dimensionless ofSi(final double si)
      {
          return Dimensionless.ofSi(si);
      }
  
      @Override
      public Unitless deriveUnit(final String textualAbbreviation, final String displayAbbreviation, final String name,
              final double scaleFactor, final UnitSystem unitSystem)
      {
          if (getScale() instanceof LinearScale ls)
          {
              return new Unitless(textualAbbreviation, displayAbbreviation, name,
                      new LinearScale(ls.getScaleFactorToBaseUnit() * scaleFactor), unitSystem);
          }
          throw new UnitRuntimeException("Only possible to derive a unit from a unit with a linear scale");
      }
  
  }