package org.openslx.imagemaster.util;

import java.security.MessageDigest;
import java.nio.charset.Charset;
import java.security.NoSuchAlgorithmException;

public class Hash
{
	// Cache of md5 digesters
	private static final ThreadLocal<MessageDigest> md5hash = new ThreadLocal<MessageDigest>() {
		@Override
		public MessageDigest initialValue()
		{
			try {
				return MessageDigest.getInstance( "MD5" );
			} catch ( NoSuchAlgorithmException e ) {
				e.printStackTrace();
				System.exit(1);
				return null;
			}
		}
	};
	// Cache of sha256 digesters
	private static final ThreadLocal<MessageDigest> sha256hash = new ThreadLocal<MessageDigest>() {
		@Override
		public MessageDigest initialValue()
		{
			try {
				return MessageDigest.getInstance( "SHA-256" );
			} catch ( NoSuchAlgorithmException e ) {
				e.printStackTrace();
				System.exit(1);
				return null;
			}
		}
	};
	// Cache of sha512 digesters
	private static final ThreadLocal<MessageDigest> sha512hash = new ThreadLocal<MessageDigest>() {
		@Override
		public MessageDigest initialValue()
		{
			try {
				return MessageDigest.getInstance( "SHA-512" );
			} catch ( NoSuchAlgorithmException e ) {
				e.printStackTrace();
				System.exit(1);
				return null;
			}
		}
	};
	// For converting to hex string
	private static final char[] HEX_CHARS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
	// Constant
	private static final Charset UTF8 = Charset.forName( "UTF-8" );

	// MD5
	
	public static String md5( final byte[] bytes )
	{
		return toHexString( md5hash.get().digest( bytes ) );
	}
	
	public static String md5( final String text )
	{
		return md5( text.getBytes( UTF8 ));
	}
	
	// SHA-256
	
	public static String sha256( final byte[] bytes )
	{
		return toHexString( sha256hash.get().digest( bytes ) );
	}
	
	public static String sha256( final String text )
	{
		return sha256( text.getBytes( UTF8 ));
	}
	
	// SHA-512
	
	public static MessageDigest getSha512Digest()
	{
		return sha512hash.get();
	}

	// Helper
	
	private static String toHexString( final byte[] bytes )
	{
		final char[] hexChars = new char[bytes.length * 2];
		for ( int j = 0; j < bytes.length; ++j ) {
			final int v = bytes[j] & 0xFF;
			hexChars[j * 2] = HEX_CHARS[v >>> 4];
			hexChars[j * 2 + 1] = HEX_CHARS[v & 0x0F];
		}
		return new String( hexChars );
	}

}