/*
 * Created on Dec 30, 2005
 * Created by Alon Rohter
 * Copyright (C) Azureus Software, Inc, All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 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 General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 */
package org.gudy.azureus2.core3.util;

import java.security.SecureRandom;
import java.util.Random;

import org.gudy.azureus2.core3.config.COConfigurationManager;

/**
 *	@author MjrTom
 *		2006/Jan/02:	added various methods, including some java.util.Random method aliases 
 */

public class 
RandomUtils 
{
	public static final Random RANDOM = new Random( System.currentTimeMillis() );
	
	public static final String INSTANCE_ID;
	
	static{
		byte[] bytes = new byte[3];
		
		RANDOM.nextBytes( bytes );
		
		INSTANCE_ID = Base32.encode( bytes ).toLowerCase();
	}
	
	public static final SecureRandom SECURE_RANDOM = new SecureRandom();
	
	/**
	 * Generate a random array of bytes.
	 * @param num_to_generate number of bytes to generate
	 * @return random byte array
	 */
	public static byte[] generateRandomBytes( int num_to_generate ) {
    byte[] id = new byte[ num_to_generate ];
    RANDOM.nextBytes( id );    
    return id;
  }
	
	
	/**
	 * Generate a random string of charactors.
	 * @param num_to_generate number of chars to generate
	 * @return random char string
	 */
	public static String generateRandomAlphanumerics( int num_to_generate ) {
		String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
		
		StringBuffer buff = new StringBuffer( num_to_generate );
		
    for( int i=0; i < num_to_generate; i++ ) {
    	int pos = (int)( RANDOM.nextDouble() * alphabet.length() );
    	buff.append( alphabet.charAt( pos ) );
    }
    
    return buff.toString();
  }
	
	
	public static final int LISTEN_PORT_MIN = 10000;
	public static final int LISTEN_PORT_MAX = 65535;
	
	
	/**
	 * Generate a random port number for binding a network IP listening socket to.
	 * NOTE: Will return a valid non-privileged port number >= LISTEN_PORT_MIN and <= LISTEN_PORT_MAX.
	 * @return random port number
	 */
	
	public static int 
	generateRandomNetworkListenPort() 
	{
		return( generateRandomNetworkListenPort( LISTEN_PORT_MIN, LISTEN_PORT_MAX ));
	}
	
	public static int 
	generateRandomNetworkListenPort(
		int		min_port,
		int		max_port ) 
	{
		if ( min_port > max_port ){
			int temp 	= min_port;
			min_port	= max_port;
			max_port	= temp;
		}
		
		if ( max_port > LISTEN_PORT_MAX ){
			
			max_port = LISTEN_PORT_MAX;
		}
		
		if ( max_port < 1 ){
			
			max_port = 1;
		}
		
		if ( min_port < 1 ){
			
			min_port = 1;
		}
		
		if ( min_port > max_port ){
			
			min_port = max_port;
		}
		
			// DON'T use NetworkManager methods to get the ports here else startup can hang
		
		int	existing_tcp	= COConfigurationManager.getIntParameter( "TCP.Listen.Port" );
		int existing_udp	= COConfigurationManager.getIntParameter( "UDP.Listen.Port" );
		int existing_udp2	= COConfigurationManager.getIntParameter( "UDP.NonData.Listen.Port" );
		
		int port = min_port;
		
		for ( int i=0;i<100;i++ ){
			int min 	= min_port;
			port 		= min + RANDOM.nextInt( max_port + 1 - min );
			
				// skip magnet ports
			
			if ( port >= 45100 && port <= 45110 ){
				
				continue;
			}
			
			if ( port != existing_tcp && port != existing_udp && port != existing_udp2){
				
				return port;
			}
		}
		
		return( port );
	}

	/**
	 * Generates a random +1 or -1
	 * @return +1 or -1
	 */
	public static int generateRandomPlusMinus1()
	{
		return RANDOM.nextBoolean() ? -1:1;
	}

	public static float nextFloat()
	{
		return RANDOM.nextFloat();
	}
	
    public static void nextBytes(byte[] bytes)
	{
    	RANDOM.nextBytes(bytes);
	}
    	
    public static void nextSecureBytes( byte[] bytes )
    {
    	SECURE_RANDOM.nextBytes( bytes );
    }
    
    public static byte[] nextSecureHash()
    {
    	byte[] hash = new byte[20];
    	
    	SECURE_RANDOM.nextBytes( hash );
    	
    	return( hash );
    }
    
    public static byte[] nextHash()
    {
    	byte[] hash = new byte[20];
    	
    	RANDOM.nextBytes( hash );
    	
    	return( hash );
    }
    
    public static int nextInt(int n)
	{
    	return RANDOM.nextInt(n);
	}
    	
    public static byte nextByte()
    {
        return (byte)RANDOM.nextInt();
    }
        
    public static int nextInt()
    {
        return RANDOM.nextInt();
    }
        
    public static int nextAbsoluteInt()
    {
    	return(( RANDOM.nextInt() << 1 ) >>> 1 );
    }
    
    public static long nextLong()
    {
        return RANDOM.nextLong();
    }
       
    public static long nextLong( long n )
    {
    	if ( n > Integer.MAX_VALUE ){
    		    		
    		while( true ){
    			
    			long rand 	= nextAbsoluteLong();
    			
    			long res	= rand % n;
    			
    				// deal with non-uniformity as rand not generally divisible by n
    			
    			if ( rand - res + (n-1) >= 0 ){
    				
    				return( res );
    			}
    		}
    	}
    	
        return((long)RANDOM.nextInt((int)n));
    }
       
    
    public static long nextAbsoluteLong()
    {
    	return(( RANDOM.nextLong() << 1 ) >>> 1 );
    }
    
    public static long nextSecureAbsoluteLong()
    {
    	while( true ){
    		
    		long val = Math.abs( SECURE_RANDOM.nextLong());
    		
    		if ( val >= 0 ){
    			
    			return( val );
    		}
    	}
    }
    
	/**
	 * @return random int between 0 and max-1. e.g. param of 10 returns 0->9
	 */
	public static int generateRandomIntUpto(int max)
	{
		return nextInt(max);
	}

	/**
	 * @return random int between min and max, e.g params of [5,7] returns 5,6 or 7
	 */
	public static int generateRandomIntBetween(int min, int max)
	{
		return min +generateRandomIntUpto(max + 1 - min);
	}
}
