package org.argeo.cms.security;
   
   import java.io.IOException;
   import java.math.BigInteger;
   import java.nio.MappedByteBuffer;
   import java.nio.channels.FileChannel;
   import java.nio.file.FileVisitResult;
   import java.nio.file.Files;
   import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.nio.file.SimpleFileVisitor;
  import java.nio.file.attribute.BasicFileAttributes;
  import java.security.MessageDigest;
  import java.util.Base64;
  import java.util.zip.Checksum;
  
  import org.argeo.cms.CmsException;
  
  /** Allows to fine tune how files are read. */
  public class ChecksumFactory {
  	private int regionSize = 10 * 1024 * 1024;
  
  	public byte[] digest(Path path, final String algo) {
  		try {
  			final MessageDigest md = MessageDigest.getInstance(algo);
  			if (Files.isDirectory(path)) {
  				long begin = System.currentTimeMillis();
  				Files.walkFileTree(path, new SimpleFileVisitor<Path>() {
  
  					@Override
  					public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
  						if (!Files.isDirectory(file)) {
  							byte[] digest = digest(file, algo);
  							md.update(digest);
  						}
  						return FileVisitResult.CONTINUE;
  					}
  
  				});
  				byte[] digest = md.digest();
  				long duration = System.currentTimeMillis() - begin;
  				System.out.println(printBase64Binary(digest) + " " + path + " (" + duration / 1000 + "s)");
  				return digest;
  			} else {
  				long begin = System.nanoTime();
  				long length = -1;
  				try (FileChannel channel = (FileChannel) Files.newByteChannel(path);) {
  					length = channel.size();
  					long cursor = 0;
  					while (cursor < length) {
  						long effectiveSize = Math.min(regionSize, length - cursor);
  						MappedByteBuffer mb = channel.map(FileChannel.MapMode.READ_ONLY, cursor, effectiveSize);
  						// md.update(mb);
  						byte[] buffer = new byte[1024];
  						while (mb.hasRemaining()) {
  							mb.get(buffer);
  							md.update(buffer);
  						}
  
  						// sub digest
  						// mb.flip();
  						// MessageDigest subMd =
  						// MessageDigest.getInstance(algo);
  						// subMd.update(mb);
  						// byte[] subDigest = subMd.digest();
  						// System.out.println(" -> " + cursor);
  						// System.out.println(IOUtils.encodeHexString(subDigest));
  						// System.out.println(new BigInteger(1,
  						// subDigest).toString(16));
  						// System.out.println(new BigInteger(1, subDigest)
  						// .toString(Character.MAX_RADIX));
  						// System.out.println(printBase64Binary(subDigest));
  
  						cursor = cursor + regionSize;
  					}
  					byte[] digest = md.digest();
  					long duration = System.nanoTime() - begin;
  					System.out.println(printBase64Binary(digest) + " " + path.getFileName() + " (" + duration / 1000000
  							+ "ms, " + (length / 1024) + "kB, " + (length / (duration / 1000000)) * 1000 / (1024 * 1024)
  							+ " MB/s)");
  					return digest;
  				}
  			}
  		} catch (Exception e) {
  			throw new CmsException("Cannot digest " + path, e);
  		}
  	}
  
  	/** Whether the file should be mapped. */
  	protected boolean mapFile(FileChannel fileChannel) throws IOException {
  		long size = fileChannel.size();
  		if (size > (regionSize / 10))
  			return true;
  		return false;
  	}
  
  	public long checksum(Path path, Checksum crc) {
  		final int bufferSize = 2 * 1024 * 1024;
  		long begin = System.currentTimeMillis();
 		try (FileChannel channel = (FileChannel) Files.newByteChannel(path);) {
 			byte[] bytes = new byte[bufferSize];
 			long length = channel.size();
 			long cursor = 0;
 			while (cursor < length) {
 				long effectiveSize = Math.min(regionSize, length - cursor);
 				MappedByteBuffer mb = channel.map(FileChannel.MapMode.READ_ONLY, cursor, effectiveSize);
 				int nGet;
 				while (mb.hasRemaining()) {
 					nGet = Math.min(mb.remaining(), bufferSize);
 					mb.get(bytes, 0, nGet);
 					crc.update(bytes, 0, nGet);
 				}
 				cursor = cursor + regionSize;
 			}
 			return crc.getValue();
 		} catch (Exception e) {
 			throw new CmsException("Cannot checksum " + path, e);
 		} finally {
 			long duration = System.currentTimeMillis() - begin;
 			System.out.println(duration / 1000 + "s");
 		}
 	}
 
 	public static void main(String... args) {
 		ChecksumFactory cf = new ChecksumFactory();
 		// Path path =
 		// Paths.get("/home/mbaudier/apache-maven-3.2.3-bin.tar.gz");
 		Path path;
 		if (args.length > 0) {
 			path = Paths.get(args[0]);
 		} else {
 			path = Paths.get("/home/mbaudier/Downloads/torrents/CentOS-7-x86_64-DVD-1503-01/"
 					+ "CentOS-7-x86_64-DVD-1503-01.iso");
 		}
 		// long adler = cf.checksum(path, new Adler32());
 		// System.out.format("Adler=%d%n", adler);
 		// long crc = cf.checksum(path, new CRC32());
 		// System.out.format("CRC=%d%n", crc);
 		String algo = "SHA1";
 		byte[] digest = cf.digest(path, algo);
 		System.out.println(algo + " " + printBase64Binary(digest));
 		System.out.println(algo + " " + new BigInteger(1, digest).toString(16));
 		// String sha1 = printBase64Binary(cf.digest(path, "SHA1"));
 		// System.out.format("SHA1=%s%n", sha1);
 	}
 
 	private static String printBase64Binary(byte[] arr) {
 		return Base64.getEncoder().encodeToString(arr);
 	}
 }