package org.djutils.data;
   
   import java.lang.reflect.InvocationTargetException;
   import java.lang.reflect.Method;
   import java.util.Objects;
   
   import org.djunits.value.Value;
   import org.djunits.value.base.Scalar;
   import org.djutils.base.Identifiable;
  import org.djutils.exceptions.Throw;
  import org.djutils.primitives.Primitive;
  
  /**
   * Column identifier and descriptor.
   * <p>
   * Copyright (c) 2020-2025 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://djutils.org/docs/current/djutils/licenses.html">DJUTILS License</a>.
   * </p>
   * @author <a href="https://github.com/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
   * @author <a href="https://dittlab.tudelft.nl">Wouter Schakel</a>
   * @param <T> value type
   */
  public class Column<T> implements Identifiable
  {
      /** Id. */
      private final String id;
  
      /** Description. */
      private final String description;
  
      /** Value type. */
      private final Class<T> valueType;
  
      /** Unit. */
      private final String unit;
  
      /**
       * Make a new column for a table with an id, description, type, and unit.
       * @param id id of the column
       * @param description description of the column
       * @param valueType value type of the column
       * @param unit unit, may be {@code null}
       */
      @SuppressWarnings("unchecked")
      public Column(final String id, final String description, final Class<T> valueType, final String unit)
      {
          Throw.whenNull(id, "id may not be null.");
          Throw.when(id.length() == 0, IllegalArgumentException.class, "id cannot be empty");
          Throw.whenNull(description, "description may not be null.");
          Throw.whenNull(valueType, "valueType may not be null.");
          this.id = id;
          this.description = description;
          this.valueType = valueType.isPrimitive() ? (Class<T>) Primitive.getWrapper(valueType) : valueType;
          Throw.when(Value.class.isAssignableFrom(valueType) && (unit == null || unit.length() == 0),
                  IllegalArgumentException.class, "For a DJUNITS value, unit cannot be null or the empty string");
          if (Scalar.class.isAssignableFrom(valueType))
          {
              try
              {
                  Method valueOfMethod = valueType.getDeclaredMethod("valueOf", String.class);
                  valueOfMethod.invoke(null, "1.0" + unit);
              }
              catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException | NoSuchMethodException
                      | SecurityException exception)
              {
                  throw new IllegalArgumentException(
                          "unit of the Column does not belong to Scalar of type " + valueType.getSimpleName());
              }
          }
          this.unit = unit;
      }
  
      /**
       * Make a new column for a table with an id, description, type. The unit is blank (null).
       * @param id id of the column
       * @param description description of the column
       * @param valueType value type of the column
       */
      public Column(final String id, final String description, final Class<T> valueType)
      {
          this(id, description, valueType, null);
      }
  
      @Override
      public String getId()
      {
          return this.id;
      }
  
      /**
       * Returns the column description.
       * @return column description
       */
      public String getDescription()
      {
          return this.description;
      }
  
     /**
      * Returns the type of the values in the column.
      * @return type of the values in the column
      */
     public Class<T> getValueType()
     {
         return this.valueType;
     }
 
     /**
      * Returns the unit of the column. Data is written an read using this unit.
      * @return unit of the column
      */
     public String getUnit()
     {
         return this.unit;
     }
 
     @Override
     public int hashCode()
     {
         return Objects.hash(this.id);
     }
 
     @Override
     public boolean equals(final Object obj)
     {
         if (this == obj)
         {
             return true;
         }
         if (obj == null)
         {
             return false;
         }
         if (getClass() != obj.getClass())
         {
             return false;
         }
         Column<?> other = (Column<?>) obj;
         return Objects.equals(this.id, other.id);
     }
 
     @Override
     public String toString()
     {
         return "Column [id=" + this.id + ", description=" + this.description + ", valueType=" + this.valueType
                 + (this.unit == null ? "]" : ", unit=" + this.unit + "]");
     }
 
 }