package org.lcsim.units.clhep;
   
   import java.lang.reflect.Field;
   import java.util.HashMap;
   import java.util.Map;
   import java.util.Set;
   import java.util.Map.Entry;
   
   /**
   * Statically accessible version of CLHEP units and 
   * physical constants.  Two methods are forwarded
   * from Map.
   * 
   * @see #get(String)
   * @see #entrySet()
   * 
   * The method 
   * 
   * @see #getInstance()
   * 
   * should be used to retrieve a static reference
   * to this class.
   *  
   * @author Jeremy McCormick <jeremym@slac.stanford.edu>
   *
   */
  public class Constants 
  {
      Map<String, Double> constantsMap = new HashMap<String, Double>();
      
      private static Constants instance = new Constants();
      
      public double get(String key)
      {
          return constantsMap.get(key);
      }
      
      public Set<Entry<String,Double>> entrySet()
      {
          return constantsMap.entrySet();
      }
      
      public static Constants getInstance()
      {
          return instance;
      }
      
      private Constants()
      {
          setupSystemOfUnits();
          setupPhysicalConstants();
      }
      
      private void setupSystemOfUnits()
      {
          SystemOfUnits units = new SystemOfUnits();      
          Class<SystemOfUnits> klass = SystemOfUnits.class;
          Field[] fields = klass.getFields();
          for (Field f : fields)
          {
              try {
                  constantsMap.put(f.getName(), f.getDouble(units));
              }
              catch ( IllegalAccessException x )
              {
                  throw new RuntimeException(x);
              }
          }
      }
      
      private void setupPhysicalConstants()
      {
          PhysicalConstants physc = new PhysicalConstants();
          Class<PhysicalConstants> klass = PhysicalConstants.class;
          Field[] fields = klass.getFields();
          for (Field f : fields)
          {
              try {
                  constantsMap.put(f.getName(), f.getDouble(physc));
              }
              catch ( IllegalAccessException x )
              {
                  throw new RuntimeException(x);
              }
          }
      }    
  }