import java.io.File;
import java.util.*;
import javax.swing.*;
import javax.swing.filechooser.FileFilter;

/** A FileFilter that lets you specify which file extensions 
 *  will be displayed. Also includes a static getFileName 
 *  method that users can call to pop up a JFileChooser for 
 *  a set of file extensions.
 *  <P>
 *  Adapted from Sun SwingSet demo.
 *
 *  Taken from Core Web Programming from 
 *  Prentice Hall and Sun Microsystems Press,
 *  http://www.corewebprogramming.com/.
 *  &copy; 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted. 
 */

public class ExtensionFileFilter extends FileFilter {
  public static final int LOAD = 0;
  public static final int SAVE = 1;
  private String description;
  private boolean allowDirectories;
  private Hashtable extensionsTable = new Hashtable();
  private boolean allowAll = false;

  public ExtensionFileFilter(boolean allowDirectories) {
    this.allowDirectories = allowDirectories;
  }

  public ExtensionFileFilter() {
    this(true);
  }
  
  
  public static String getFileName(String initialDirectory,
                                   String description,
                                   String extension) {
    String[] extensions = new String[]{ extension };
    return(getFileName(initialDirectory, description, 
                       extensions, LOAD));
  }  

  public static String getFileName(String initialDirectory,
                                   String description,
                                   String extension,
                                   int mode) {
    String[] extensions = new String[]{ extension };
    return(getFileName(initialDirectory, description, 
                       extensions, mode));
  }

  public static String getFileName(String initialDirectory,
                                   String description,
                                   String[] extensions) {
    return(getFileName(initialDirectory, description, 
                       extensions, LOAD));
  }


  /** Pops up a JFileChooser that lists files with the 
   *  specified extensions. If the mode is SAVE, then the 
   *  dialog will have a Save button; otherwise, the dialog 
   *  will have an Open button. Returns a String corresponding
   *  to the file's pathname, or null if Cancel was selected.
   */

  public static String getFileName(String initialDirectory,
                                   String description,
                                   String[] extensions,
                                   int mode) {
    ExtensionFileFilter filter = new ExtensionFileFilter();
    filter.setDescription(description);
    for(int i=0; i<extensions.length; i++) {
      String extension = extensions[i];
      filter.addExtension(extension, true);
    }
    JFileChooser chooser =
      new JFileChooser(initialDirectory);
    chooser.setFileFilter(filter);
    int selectVal = (mode==SAVE) ? chooser.showSaveDialog(null)
                                 : chooser.showOpenDialog(null);
    if (selectVal == JFileChooser.APPROVE_OPTION) {
      String path = chooser.getSelectedFile().getAbsolutePath();
      return(path);
    } else {
      JOptionPane.showMessageDialog(null, "No file selected.");
      return(null);
    }
  }

  public void addExtension(String extension,
                           boolean caseInsensitive) {
    if (caseInsensitive) {
      extension = extension.toLowerCase();
    }
    if (!extensionsTable.containsKey(extension)) {
      extensionsTable.put(extension,
                          new Boolean(caseInsensitive));
      if (extension.equals("*") ||
          extension.equals("*.*") ||
          extension.equals(".*")) {
        allowAll = true;
      }
    }
  }

  public boolean accept(File file) {
    if (file.isDirectory()) {
      return(allowDirectories);
    }
    if (allowAll) {
      return(true);
    }
    String name = file.getName();
    int dotIndex = name.lastIndexOf('.');
    if ((dotIndex == -1) || (dotIndex == name.length() - 1)) {
      return(false);
    }
    String extension = name.substring(dotIndex + 1);
    if (extensionsTable.containsKey(extension)) {
      return(true);
    }
    Enumeration keys = extensionsTable.keys();
    while(keys.hasMoreElements()) {
      String possibleExtension = (String)keys.nextElement();
      Boolean caseFlag =
        (Boolean)extensionsTable.get(possibleExtension);
      if ((caseFlag != null) &&
          (caseFlag.equals(Boolean.FALSE)) &&
          (possibleExtension.equalsIgnoreCase(extension))) {
        return(true);
      }
    }
    return(false);
  }

  public void setDescription(String description) {
    this.description = description;
  }

  public String getDescription() {
    return(description);
  }
}