// This example is from _Java Examples in a Nutshell_. (http://www.oreilly.com)
// Copyright (c) 1997 by David Flanagan
// This example is provided WITHOUT ANY WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for non-commercial purposes.
// For any commercial use, see http://www.davidflanagan.com/javaexamples

import java.awt.*;
import java.awt.event.*;
import java.io.*;

/**
 * This class creates and displays a window containing a TextArea, 
 * in which the contents of a text file are displayed.
 **/
public class FileViewer extends CloseableFrame implements ActionListener {
  String directory;  // The default directory to display in the FileDialog
  TextArea textarea; // The area to display the file contents into 

  /** Convenience constructor: file viewer starts out blank */
  public FileViewer() { this(null, null); }
  /** Convenience constructor: display file from current directory */
  public FileViewer(String filename) { this(null, filename); }

  /**
   * The real constructor.  Create a FileViewer object to display the
   * specified file from the specified directory 
   **/
  public FileViewer(String directory, String filename) {
    super();  // Create the (closeable) frame
    
    // Create a TextArea to display the contents of the file in
    textarea = new TextArea("", 24, 80);
    textarea.setFont(new Font("MonoSpaced", Font.PLAIN, 12));
    textarea.setEditable(false);
    this.add("Center", textarea);
    
    // Create a bottom panel to hold a couple of buttons in
    Panel p = new Panel();
    p.setLayout(new FlowLayout(FlowLayout.RIGHT, 10, 5));
    this.add(p, "South");

    // Create the buttons and arrange to handle button clicks
    Font font = new Font("SansSerif", Font.BOLD, 14);
    Button openfile = new Button("Open File");
    Button close = new Button("Close");
    openfile.addActionListener(this);
    openfile.setActionCommand("open");
    openfile.setFont(font);
    close.addActionListener(this);
    close.setActionCommand("close");
    close.setFont(font);
    p.add(openfile);
    p.add(close);

    this.pack();

    // Figure out the directory, from filename or current dir, if necessary
    if (directory == null) {
      File f;
      if ((filename != null) && (f = new File(filename)).isAbsolute()) {
        directory = f.getParent();
        filename = f.getName();
      }
      else directory = System.getProperty("user.dir");
    }

    this.directory = directory;    // Remember the directory, for FileDialog
    setFile(directory, filename);  // Now load and display the file
  }
  
  /**
   * Load and display the specified file (if any) from the specified directory
   **/
  public void setFile(String directory, String filename) {
    if ((filename == null) || (filename.length() == 0)) return;
    File f;
    FileReader in = null;
    // Read and display the file contents.  Since we're reading text, we
    // use a FileReader instead of a FileInputStream.
    try {
      f = new File(directory, filename); // Create a file object
      in = new FileReader(f);            // Create a char stream to read  it
      int size = (int) f.length();       // Check file size
      char[] data = new char[size];      // Allocate an array big enough for it
      int chars_read = 0;                // How many chars read so far?
      while(chars_read < size)           // Loop until we've read it all
        chars_read += in.read(data, chars_read, size-chars_read);
      textarea.setText(new String(data));       // Display chars in TextArea
      this.setTitle("FileViewer: " + filename); // Set the window title
    }
    // Display messages if something goes wrong
    catch (IOException e) { 
      textarea.setText(e.getClass().getName() + ": " + e.getMessage());
      this.setTitle("FileViewer: " + filename + ": I/O Exception");
    }
    // Always be sure to close the input stream!
    finally { try { if (in != null) in.close(); } catch (IOException e) {} }
  }

  /**
   * Handle button clicks
   **/
  public void actionPerformed(ActionEvent e) {
    String cmd = e.getActionCommand();
    if (cmd.equals("open")) {          // If user clicked "Open" button
      // Create a file dialog box to prompt for a new file to display
      FileDialog f = new FileDialog(this, "Open File", FileDialog.LOAD);
      f.setDirectory(directory);       // Set the default directory
      f.show();                        // Display dialog and wait for response
      directory = f.getDirectory();    // Remember new default directory
      setFile(directory, f.getFile()); // Load and display selection
      f.dispose();                     // Get rid of the dialog box
    }
    else if (cmd.equals("close"))      // If user clicked "Close" button
      this.dispose();                  //    then close the window
  }
  
  /**
   * The FileViewer can be used by other classes, or it can be
   * used standalone with this main() method.
   **/
  static public void main(String[] args) throws IOException {
    // Create a FileViewer object
    Frame f = new FileViewer((args.length == 1)?args[0]:null);
    // Arrange to exit when the FileViewer window closes
    f.addWindowListener(new WindowAdapter() {
      public void windowClosed(WindowEvent e) { System.exit(0); }
    });
    // And pop the window up
    f.show();
  }
}