package org.opentrafficsim.swing.gui;
   
   import java.awt.Color;
   import java.awt.event.FocusEvent;
   import java.awt.event.FocusListener;
   import java.beans.PropertyChangeEvent;
   import java.beans.PropertyChangeListener;
   
   import javax.swing.event.DocumentEvent;
  import javax.swing.event.DocumentListener;
  import javax.swing.text.JTextComponent;
  
  /**
   * Code taken from stack overflow. This class shows light gray text within a {@link JTextComponent} when it is empty, as a hint
   * as to what a user might type.
   * <p>
   * Copyright (c) 2024-2026 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author Wouter Schakel
   * @see <a href=
   *      "https://stackoverflow.com/questions/10506789/how-to-display-faint-gray-ghost-text-in-a-jtextfield">stackoverflow</a>
   */
  public class GhostText implements FocusListener, DocumentListener, PropertyChangeListener
  {
  
      /** Text component. */
      private final JTextComponent textComp;
  
      /** Whether its empty. */
      private boolean isEmpty;
  
      /** Ghost color. */
      private Color ghostColor;
  
      /** Regular color. */
      private Color foregroundColor;
  
      /** Ghost text. */
      private final String ghostText;
  
      /**
       * Constructor.
       * @param textComp text component to receive ghost text
       * @param ghostText ghost text
       */
      public GhostText(final JTextComponent textComp, final String ghostText)
      {
          this.textComp = textComp;
          this.ghostText = ghostText;
          this.ghostColor = Color.LIGHT_GRAY;
          textComp.addFocusListener(this);
          registerListeners();
          updateState();
          if (!this.textComp.hasFocus())
          {
              focusLost(null);
          }
      }
  
      /**
       * Delete ghost text.
       */
      public void delete()
      {
          unregisterListeners();
          this.textComp.removeFocusListener(this);
      }
  
      /**
       * Register listeners.
       */
      private void registerListeners()
      {
          this.textComp.getDocument().addDocumentListener(this);
          this.textComp.addPropertyChangeListener("foreground", this);
      }
  
      /**
       * Unregister listeners.
       */
      private void unregisterListeners()
      {
          this.textComp.getDocument().removeDocumentListener(this);
          this.textComp.removePropertyChangeListener("foreground", this);
      }
  
      /**
       * Get ghost color.
       * @return ghost color
       */
      public Color getGhostColor()
      {
          return this.ghostColor;
      }
  
      /**
       * Set ghost color.
       * @param ghostColor ghost color
      */
     public void setGhostColor(final Color ghostColor)
     {
         this.ghostColor = ghostColor;
     }
 
     /**
      * Update state.
      */
     private void updateState()
     {
         this.isEmpty = this.textComp.getText().length() == 0;
         this.foregroundColor = this.textComp.getForeground();
     }
 
     @Override
     public void focusGained(final FocusEvent e)
     {
         if (this.isEmpty)
         {
             unregisterListeners();
             try
             {
                 this.textComp.setText("");
                 this.textComp.setForeground(this.foregroundColor);
             }
             finally
             {
                 registerListeners();
             }
         }
     }
 
     @Override
     public void focusLost(final FocusEvent e)
     {
         if (this.isEmpty)
         {
             unregisterListeners();
             try
             {
                 this.textComp.setText(this.ghostText);
                 this.textComp.setForeground(this.ghostColor);
             }
             finally
             {
                 registerListeners();
             }
         }
     }
 
     @Override
     public void propertyChange(final PropertyChangeEvent evt)
     {
         updateState();
     }
 
     @Override
     public void changedUpdate(final DocumentEvent e)
     {
         updateState();
     }
 
     @Override
     public void insertUpdate(final DocumentEvent e)
     {
         updateState();
     }
 
     @Override
     public void removeUpdate(final DocumentEvent e)
     {
         updateState();
     }
 
 }