/**
 * The contents of this file are subject to the license and copyright
 * detailed in the LICENSE and NOTICE files at the root of the source
 * tree and available online at
 *
 * http://www.dspace.org/license/
 */
package org.purl.sword.base;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import org.apache.logging.log4j.Logger;

/**
 * Utility class that holds Checksum related methods.
 *
 * @author Neil Taylor
 * @author Stuart Lewis
 */
public class ChecksumUtils {
    /**
     * Logger
     */
    private static Logger log = org.apache.logging.log4j.LogManager.getLogger(ChecksumUtils.class);

    /**
     * Default constructor
     */
    private ChecksumUtils() { }

    /**
     * Generate an MD5 hash for the file that is specified in the
     * filepath. The hash is returned as a String representation.
     *
     * @param filepath The path to the file to load.
     * @return A string hash of the file.
     * @throws NoSuchAlgorithmException If the MD5 algorithm is
     *                                  not supported by the installed virtual machine.
     * @throws IOException              If there is an error accessing the file.
     */
    public static String generateMD5(String filepath)
        throws NoSuchAlgorithmException, IOException {
        return generateMD5(new FileInputStream(filepath));
    }

    /**
     * Generate an MD5 hash for the file that is specified in the
     * filepath. The hash is returned as a String representation.
     *
     * @param md5Stream The InputStream to checksum.
     * @return A string hash of the file.
     * @throws NoSuchAlgorithmException If the MD5 algorithm is
     *                                  not supported by the installed virtual machine.
     * @throws IOException              If there is an error accessing the file.
     */
    public static String generateMD5(InputStream md5Stream)
        throws NoSuchAlgorithmException, IOException {
        String md5 = null;

        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.reset();

            byte[] bytes = new byte[1024];
            int count = 0;
            while ((count = md5Stream.read(bytes)) != -1) {
                md.update(bytes, 0, count);
            }

            byte[] md5Digest = md.digest();

            StringBuffer buffer = new StringBuffer();
            for (byte b : md5Digest) {
                // 0xFF is used to handle the issue of negative numbers in the bytes
                String hex = Integer.toHexString(b & 0xFF);
                if (hex.length() == 1) {
                    buffer.append("0");
                }
                buffer.append(hex);
            }

            md5 = buffer.toString();
        } catch (NoSuchAlgorithmException ex) {
            log.error("MD5 Algorithm Not found");
            throw ex;
        } finally {
            if (md5Stream != null) {
                md5Stream.close();
            }
        }

        return md5;
    }

    /**
     * Generate an MD5 hash for the file that is specified in the
     * filepath. The hash is returned as a String representation.
     *
     * @param bytes The byte array to checksum.
     * @return A string hash of the file.
     * @throws NoSuchAlgorithmException If the MD5 algorithm is
     *                                  not supported by the installed virtual machine.
     * @throws IOException              If there is an error accessing the file.
     */
    public static String generateMD5(byte[] bytes)
        throws NoSuchAlgorithmException, IOException {
        String md5 = null;

        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.reset();

            md.update(bytes);


            byte[] md5Digest = md.digest();

            StringBuffer buffer = new StringBuffer();
            for (byte b : md5Digest) {
                // 0xFF is used to handle the issue of negative numbers in the bytes
                String hex = Integer.toHexString(b & 0xFF);
                if (hex.length() == 1) {
                    buffer.append("0");
                }
                buffer.append(hex);
            }

            md5 = buffer.toString();
        } catch (NoSuchAlgorithmException ex) {
            log.error("MD5 Algorithm Not found");
            throw ex; // rethrow
        }

        return md5;
    }

    /**
     * Run a simple test to process the file.
     *
     * @param args the command line arguments given
     * @throws NoSuchAlgorithmException If there was an error generating the MD5.
     * @throws IOException              If there is an error accessing the file.
     */
    public static void main(String[] args)
        throws NoSuchAlgorithmException, IOException {
        System.out.println(ChecksumUtils.generateMD5(args[0]));
    }
}