/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.pdfbox.examples.signature;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertStore;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CollectionCertStoreParameters;
import java.security.cert.X509Certificate;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.List;

import org.apache.pdfbox.exceptions.COSVisitorException;
import org.apache.pdfbox.exceptions.SignatureException;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.interactive.digitalsignature.PDSignature;
import org.apache.pdfbox.pdmodel.interactive.digitalsignature.SignatureInterface;
import org.apache.pdfbox.pdmodel.interactive.digitalsignature.SignatureOptions;
import org.apache.pdfbox.pdmodel.interactive.digitalsignature.visible.PDVisibleSigProperties;
import org.apache.pdfbox.pdmodel.interactive.digitalsignature.visible.PDVisibleSignDesigner;
import org.bouncycastle.cms.CMSSignedData;
import org.bouncycastle.cms.CMSSignedDataGenerator;
import org.bouncycastle.cms.CMSSignedGenerator;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

/**
 * <p>
 * This is an example for signing a pdf with bouncy castle.
 * </p>
 * <p>
 * And also you can create visible signature too
 * </p>
 * <p>
 * A keystore can be created with the java keytool (e.g. keytool -genkeypair -storepass 123456 -storetype pkcs12 -alias
 * test -validity 365 -v -keyalg RSA -keystore keystore.p12 )
 * </p>
 * 
 * @author Vakhtang koroghlishvili (Gogebashvili)
 */
public class CreateVisibleSignature implements SignatureInterface
{

  private static BouncyCastleProvider provider = new BouncyCastleProvider();

  private PrivateKey privKey;

  private Certificate[] cert;

  private SignatureOptions options = null;

  /**
   * Initialize the signature creator with a keystore (pkcs12) and pin that
   * should be used for the signature.
   * 
   * @param keystore
   *          is a pkcs12 keystore.
   * @param pin
   *          is the pin for the keystore / private key
   */
  public CreateVisibleSignature(KeyStore keystore, char[] pin)
  {
    try {
      /*
       * grabs the first alias from the keystore and get the private key. An
       * alternative method or constructor could be used for setting a specific
       * alias that should be used.
       */
      Enumeration<String> aliases = keystore.aliases();
      String alias = null;
      if (aliases.hasMoreElements()) {
        alias = aliases.nextElement();
      } else {
        throw new RuntimeException("Could not find alias");
      }
      privKey = (PrivateKey) keystore.getKey(alias, pin);
      cert = keystore.getCertificateChain(alias);
    } catch (KeyStoreException e) {
      e.printStackTrace();
    } catch (UnrecoverableKeyException e) {
      System.err.println("Could not extract private key.");
      e.printStackTrace();
    } catch (NoSuchAlgorithmException e) {
      System.err.println("Unknown algorithm.");
      e.printStackTrace();
    }
  }

  /**
   * Signs the given pdf file.
   * 
   * @param document is the pdf document
   * @param signatureProperties
   * @return the signed pdf document
   * @throws IOException
   * @throws COSVisitorException
   * @throws SignatureException
   */
  public File signPDF(File document, PDVisibleSigProperties signatureProperties) throws IOException,
      COSVisitorException, SignatureException
  {
    byte[] buffer = new byte[8 * 1024];
    if (document == null || !document.exists()) {
      new RuntimeException("Document for signing does not exist");
    }

    // creating output document and prepare the IO streams.
    String name = document.getName();
    String substring = name.substring(0, name.lastIndexOf("."));

    File outputDocument = new File(document.getParent(), substring + "_signed.pdf");
    FileInputStream fis = new FileInputStream(document);
    FileOutputStream fos = new FileOutputStream(outputDocument);

    int c;
    while ((c = fis.read(buffer)) != -1) {
      fos.write(buffer, 0, c);
    }
    fis.close();
    fis = new FileInputStream(outputDocument);

    // load document
    PDDocument doc = PDDocument.loadNonSeq(document, null);

    // create signature dictionary
    PDSignature signature = new PDSignature();
    signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE); // default filter
    // subfilter for basic and PAdES Part 2 signatures
    signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);
    signature.setName("signer name");
    signature.setLocation("signer location");
    signature.setReason("reason for signature");

    // the signing date, needed for valid signature
    signature.setSignDate(Calendar.getInstance());

    // register signature dictionary and sign interface

    if (signatureProperties != null && signatureProperties.isVisualSignEnabled()) {
      options = new SignatureOptions();
      options.setVisualSignature(signatureProperties);
      options.setPage(signatureProperties.getPage());
      // options.setPreferedSignatureSize(signatureProperties.getPreferredSize());
      doc.addSignature(signature, this, options);
    } else {
      doc.addSignature(signature, this);
    }

    // write incremental (only for signing purpose)
    doc.saveIncremental(fis, fos);
    if (options != null)
    {
        options.close();
    }

    return outputDocument;
  }

  /**
   * <p>
   * SignatureInterface implementation.
   * </p>
   * <p>
   * This method will be called from inside of the pdfbox and create the pkcs7 signature. The given InputStream contains
   * the bytes that are providen by the byte range.
   * </p>
   * <p>
   * This method is for internal use only.
   * </p>
   * <p>
   * Here the user should use his favorite cryptographic library and implement a pkcs7 signature creation.
   * </p>
   */
  public byte[] sign(InputStream content) throws SignatureException, IOException
  {
    CMSProcessableInputStream input = new CMSProcessableInputStream(content);
    CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
    // CertificateChain
    List<Certificate> certList = Arrays.asList(cert);

    CertStore certStore = null;
    try {
      certStore = CertStore.getInstance("Collection", new CollectionCertStoreParameters(certList), provider);
      gen.addSigner(privKey, (X509Certificate) certList.get(0), CMSSignedGenerator.DIGEST_SHA256);
      gen.addCertificatesAndCRLs(certStore);
      CMSSignedData signedData = gen.generate(input, false, provider);
      return signedData.getEncoded();
    } catch (Exception e) {
      // should be handled
      System.err.println("Error while creating pkcs7 signature.");
      e.printStackTrace();
    }
    throw new RuntimeException("Problem while preparing signature");
  }

  /**
   * Arguments are
   * [0] key store
   * [1] pin
   * [2] document that will be signed
   * [3] image of visible signature
   */
  public static void main(String[] args) throws KeyStoreException, NoSuchAlgorithmException, CertificateException,
      FileNotFoundException, IOException, COSVisitorException, SignatureException
  {

    if (args.length != 4) {
      usage();
      System.exit(1);
    } else {
      File ksFile = new File(args[0]);
      KeyStore keystore = KeyStore.getInstance("PKCS12", provider);
      char[] pin = args[1].toCharArray();
      keystore.load(new FileInputStream(ksFile), pin);

      File document = new File(args[2]);

      CreateVisibleSignature signing = new CreateVisibleSignature(keystore, pin.clone());

      FileInputStream image = new FileInputStream(args[3]);

      // page is 1-based here
      int page = 1;
      PDVisibleSignDesigner visibleSig = new PDVisibleSignDesigner(args[2], image, page);
      visibleSig.xAxis(0).yAxis(0).zoom(-50).signatureFieldName("signature");

      PDVisibleSigProperties signatureProperties = new PDVisibleSigProperties();

      signatureProperties.signerName("name").signerLocation("location").signatureReason("Security").preferredSize(0)
          .page(page).visualSignEnabled(true).setPdVisibleSignature(visibleSig).buildSignature();

      signing.signPDF(document, signatureProperties);
    }

  }

  /**
   * This will print the usage for this program.
   */
  private static void usage()
  {
    System.err.println("Usage: java " + CreateVisibleSignature.class.getName()
        + " <pkcs12-keystore-file> <pin> <input-pdf> <sign-image>");
  }
}
