package net.github.dupsfinder;

import java.io.IOException;

import java.io.InputStream;

import java.nio.file.Files;

import java.nio.file.Path;

import java.security.DigestInputStream;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

/**

* Hashsum calculations utility class

*

* @author ava1ar

*/

public class Hashsum {

private static final int BUFFER_SIZE = 4096;

private Hashsum() {

// hidden constructor for the utility class

}

/**

* Calculated SHA-1 checksum form the file

*

* @param path path for file

* @return SHA-1 checksum of the file

* @throws HashsumCalculationException

*/

public static String getSha1sum(Path path) throws HashsumCalculationException {

return getSha1sum(path, 0);

}

/**

* Calculated SHA-1 checksum form the file

*

* @param path path for file

* @param maxBytes calculate checksum only for first maxBytes bytes

* @return SHA-1 checksum of the file

* @throws HashsumCalculationException

*/

public static String getSha1sum(Path path, int maxBytes) throws HashsumCalculationException {

return getHashSum(path, "SHA-1", maxBytes);

}

// calculate hashsum for path using algo

private static String getHashSum(Path path, String algo, int maxBytes) throws HashsumCalculationException {

if (!Files.isRegularFile(path)) {

throw new HashsumCalculationException("\"" + path + "\" is not a regular file!");

}

try (InputStream is = Files.newInputStream(path)) {

MessageDigest md = MessageDigest.getInstance(algo);

DigestInputStream dis = new DigestInputStream(is, md);

// if we want checksum for first maxBytes bytes only

if (maxBytes > 0) {

dis.read(new byte[maxBytes]);

// else read whole file

} else {

byte[] buffer = new byte[BUFFER_SIZE];

while (dis.read(buffer) != -1) {

// read complete file

}

}

// file checkum in byte array format

byte[] mdbytes = md.digest();

// convert the byte array to hex format

StringBuilder sb = new StringBuilder("");

for (int i = 0; i < mdbytes.length; i++) {

sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));

}

return sb.toString();

} catch (IOException | NoSuchAlgorithmException ex) {

throw new HashsumCalculationException(ex.getMessage());

}

}

}