/*
 * Decrypt_Current.bsh - Decrypts the current buffer content. The physical file
 * content will not be modified until user saves the buffer. Buffer must be
 * encrypted with Encrypt_Current.bsh.
 *
 * Uses PBE with MD5 and DES algorithm. Macro will prompt the user for a 
 * password which will be used to decrypt the buffer content.
 *
 * David Mlejnek, mailto:davo@nadhlad.sk
 *
 */

import java.io.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.swing.border.*;

String TRANSFORMATION = "PBEWithMD5AndDES";
String ENCODING = buffer.getStringProperty(Buffer.ENCODING);
int BYTES_REPLACEMENT_OFFSET = 256;
int BYTES_REPLACEMENT_RADIX = 32;

void showDialog() {
  
  title = "Decrypt buffer";
  
  dialog = new JDialog(view, title, false);
  content = new JPanel(new BorderLayout());
  content.setBorder(new EmptyBorder(5, 5, 5, 5));
  dialog.setContentPane(content);
  
  pwPanel = new JPanel(new GridLayout(1, 2));
  pwLabel = new JLabel("Enter password: ");
  pwField = new JPasswordField();
  pwPanel.add(pwLabel);
  pwPanel.add(pwField);
  content.add(pwPanel, BorderLayout.CENTER);
  
  
  buttonPanel = new JPanel(new GridLayout(1, 2));
  buttonPanel.setBorder( new EmptyBorder(5, 0, 0, 0));
  
  okButton = new JButton("OK");
  cancelButton = new JButton("Cancel");
  
  buttonPanel.add(okButton);
  buttonPanel.add(cancelButton);
  
  content.add(buttonPanel, BorderLayout.SOUTH);
  
  okButton.addActionListener(this);
  cancelButton.addActionListener(this);
  
  dialog.getRootPane().setDefaultButton(okButton);
  
  actionPerformed(e) {
    
    this.dialog.dispose();
    
    cmd = e.getActionCommand();
    
    if(cmd.equals("OK")) {
      decryptBuffer(this.pwField.getPassword());
    }
    
    return;
  }

  dialog.pack();
  dialog.setLocationRelativeTo(view);
  dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
  dialog.setVisible(true);
  
}

void decryptBuffer(char[] passwd) {
  
  Cipher pbeCipher = createCipher(passwd, Cipher.DECRYPT_MODE);
  
  String content = textArea.getText();
  
  //Decode number representations to bytes
  byte[] dec = decodeBytes(content);
  if(dec == null) {
    return;
  }
  
  try {
    
    // Decrypt
    byte[] data = pbeCipher.doFinal(dec);
    
    // Decode using buffer encoding
    content = new String(data, ENCODING);
    
    
    textArea.setText(content);
    textArea.goToBufferStart(false);
  
  } catch(Exception e) {
    
    Macros.error(view, "Failed to decrypt buffer: Password invalid.");
    
  }
}

Cipher createCipher(char[] passwd, int opmode) {
  int iterationCount = 20;
  byte[] salt = {
      (byte)0xc7, (byte)0x73, (byte)0x21, (byte)0x8c,
      (byte)0x7e, (byte)0xc8, (byte)0xee, (byte)0x99
  };
  
  // Create PBE parameter set
  PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, iterationCount);
  PBEKeySpec pbeKeySpec = new PBEKeySpec(passwd);
  SecretKeyFactory keyFac = SecretKeyFactory.getInstance(TRANSFORMATION);
  SecretKey pbeKey = keyFac.generateSecret(pbeKeySpec);
  
  // Create PBE Cipher
  Cipher pbeCipher = Cipher.getInstance(TRANSFORMATION);
  pbeCipher.init(opmode, pbeKey, pbeParamSpec);
  
  return pbeCipher;
  
}

byte[] decodeBytes(String source) {
  
  String[] token = source.split("[\\s\\r\\n]+");
  byte[] data = new byte[token.length];
  
  for(int i=0; i<token.length; i++) {
    
    try {
      
      int n = Integer.parseInt(token[i], BYTES_REPLACEMENT_RADIX) - BYTES_REPLACEMENT_OFFSET;
      data[i] = (byte) n;
      
    } catch(NumberFormatException e) {
      Macros.error(view, "Failed to decrypt buffer: Invalid format.");
      return null;
    }
    
  }
  
  return data;
}


showDialog();