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/*
 * cron4j - A pure Java cron-like scheduler
 * 
 * Copyright (C) 2007-2010 Carlo Pelliccia (www.sauronsoftware.it)
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License version
 * 2.1, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License 2.1 for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License version 2.1 along with this program.
 * If not, see .
 */
package it.sauronsoftware.cron4j;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.UnknownHostException;
import java.util.Enumeration;

/**
 * A GUID generator.
 * 
 * @author Carlo Pelliccia
 * @since 2.0
 */
class GUIDGenerator {

	/**
	 * The machine descriptor, which is used to identified the underlying hardware machine.
	 */
	private static String MACHINE_DESCRIPTOR = getMachineDescriptor();
	
	/**
	 * Generates a GUID (48 chars).
	 * 
	 * @return The generated GUID.
	 */
	public static String generate() {
		StringBuffer id = new StringBuffer();
		encode(id, MACHINE_DESCRIPTOR);
		encode(id, Runtime.getRuntime());
		encode(id, Thread.currentThread());
		encode(id, System.currentTimeMillis());
		encode(id, getRandomInt());
		return id.toString();
	}

	/**
	 * Calculates a machine id, as an integer value.
	 * 
	 * @return The calculated machine id.
	 */
	private static String getMachineDescriptor() {
		StringBuffer descriptor = new StringBuffer();
		descriptor.append(System.getProperty("os.name"));
		descriptor.append("::");
		descriptor.append(System.getProperty("os.arch"));
		descriptor.append("::");
		descriptor.append(System.getProperty("os.version"));
		descriptor.append("::");
		descriptor.append(System.getProperty("user.name"));
		descriptor.append("::");
		StringBuffer b = buildNetworkInterfaceDescriptor();
		if (b != null) {
			descriptor.append(b);
		} else {
			// plain old InetAddress...
			InetAddress addr;
			try {
				addr = InetAddress.getLocalHost();
				descriptor.append(addr.getHostAddress());
			} catch (UnknownHostException e) {
				;
			}
		}
		return descriptor.toString();
	}

	/**
	 * Builds a descriptor fragment using the {@link NetworkInterface} class,
	 * available since Java 1.4.
	 * 
	 * @return A descriptor fragment, or null if the method fails.
	 */
	private static StringBuffer buildNetworkInterfaceDescriptor() {
		Enumeration e1;
		try {
			e1 = NetworkInterface.getNetworkInterfaces();
		} catch (Throwable t) {
			// not available
			return null;
		}
		StringBuffer b = new StringBuffer();
		while (e1.hasMoreElements()) {
			NetworkInterface ni = (NetworkInterface) e1.nextElement();
			StringBuffer b1 = getMACAddressDescriptor(ni);
			StringBuffer b2 = getInetAddressDescriptor(ni);
			StringBuffer b3 = new StringBuffer();
			if (b1 != null) {
				b3.append(b1);
			}
			if (b2 != null) {
				if (b3.length() > 0) {
					b3.append('=');
				}
				b3.append(b2);
			}
			if (b3.length() > 0) {
				if (b.length() > 0) {
					b.append(';');
				}
				b.append(b3);
			}
		}
		return b;
	}

	/**
	 * Builds a descriptor fragment using the machine MAC address.
	 * 
	 * @return A descriptor fragment, or null if the method fails.
	 */
	private static StringBuffer getMACAddressDescriptor(NetworkInterface ni) {
		byte[] haddr;
		try {
			haddr = ni.getHardwareAddress();
		} catch (Throwable t) {
			// not available.
			haddr = null;
		}
		StringBuffer b = new StringBuffer();
		if (haddr != null) {
			for (int i = 0; i < haddr.length; i++) {
				if (b.length() > 0) {
					b.append("-");
				}
				String hex = Integer.toHexString(0xff & haddr[i]);
				if (hex.length() == 1) {
					b.append('0');
				}
				b.append(hex);
			}
		}
		return b;
	}

	/**
	 * Builds a descriptor fragment using the machine inet address.
	 * 
	 * @return A descriptor fragment, or null if the method fails.
	 */
	private static StringBuffer getInetAddressDescriptor(NetworkInterface ni) {
		StringBuffer b = new StringBuffer();
		Enumeration e2 = ni.getInetAddresses();
		while (e2.hasMoreElements()) {
			InetAddress addr = (InetAddress) e2.nextElement();
			if (b.length() > 0) {
				b.append(',');
			}
			b.append(addr.getHostAddress());
		}
		return b;
	}

	/**
	 * Returns a random integer value.
	 * 
	 * @return A random integer value.
	 */
	private static int getRandomInt() {
		return (int) Math.round((Math.random() * Integer.MAX_VALUE));
	}

	/**
	 * Encodes an object and appends it to the buffer.
	 * 
	 * @param b
	 *            The buffer.
	 * @param obj
	 *            The object.
	 */
	private static void encode(StringBuffer b, Object obj) {
		encode(b, obj.hashCode());
	}

	/**
	 * Encodes an integer value and appends it to the buffer.
	 * 
	 * @param b
	 *            The buffer.
	 * @param value
	 *            The value.
	 */
	private static void encode(StringBuffer b, int value) {
		String hex = Integer.toHexString(value);
		int hexSize = hex.length();
		for (int i = 8; i > hexSize; i--) {
			b.append('0');
		}
		b.append(hex);
	}

	/**
	 * Encodes a long value and appends it to the buffer.
	 * 
	 * @param b
	 *            The buffer.
	 * @param value
	 *            The value.
	 */
	private static void encode(StringBuffer b, long value) {
		String hex = Long.toHexString(value);
		int hexSize = hex.length();
		for (int i = 16; i > hexSize; i--) {
			b.append('0');
		}
		b.append(hex);
	}

}