package ru.redguy.tftpserver;

import java.io.FileInputStream;
import java.security.MessageDigest;


public class CheckSum {
    static String getChecksum(String fileName) {
        StringBuffer sb = new StringBuffer("");
        try {
            String datafile = fileName;
            //use SHA1 to calculate checksum
            MessageDigest md = MessageDigest.getInstance("SHA1");
            FileInputStream fis = new FileInputStream(datafile);
            byte[] dataBytes = new byte[1024];

            int nread = 0;

            while ((nread = fis.read(dataBytes)) != -1) {
                md.update(dataBytes, 0, nread);
            }
            fis.close();

            byte[] mdbytes = md.digest();

            // convert the byte to hex format
            for (int i = 0; i < mdbytes.length; i++) {
                sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
            }

        } catch (Exception e) {
            System.out.println("Generate Checksum Failed: " + e.getMessage());
        }

        return sb.toString();
    }
}