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/**
 * Copyright (C) 2010-2018 Gordon Fraser, Andrea Arcuri and EvoSuite
 * contributors
 *
 * This file is part of EvoSuite.
 *
 * EvoSuite is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3.0 of the License, or
 * (at your option) any later version.
 *
 * EvoSuite 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 Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with EvoSuite. If not, see .
 */
package org.evosuite.runtime.vnet;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;


/**
 * Used to resolve host names
 * 
 * @author arcuri
 *
 */
public class DNS {

	/**
	 * The actual IP address does not really matter, as long
	 * as it is in the valid format
	 */
	private static final String MASK = "200.42.42.";

	/**
	 * Used to create unique new mappings
	 */
	private final AtomicInteger counter;
	
	
	/**
	 *  Key -> a host name to resolve
	 *  
	 *  Value -> the IP address for the given host
	 */
	private final Map resolved;
	
	
	public DNS(){
		counter = new AtomicInteger(0);
		resolved = new ConcurrentHashMap<>();
	}
	
	/**
	 * Get the IP address for the given host name (eg www.evosuite.org)
	 * 
	 * @param host
	 * @return {@code null} if the host was not resolved
	 */
	public synchronized String resolve(String host){
		
		//check if already resolved
		String addr = resolved.get(host);
		if(addr != null){
			return addr;
		}
		
		//check if IP numeric 
		if(EvoIPAddressUtil.textToNumericFormatV4(host) != null){
			return host;
		}
		
		if(counter.get() > 255){
			/*
			 * In theory, we could mock as many address resolutions
			 * as we want. But, if addresses are resolved in a loop
			 * based on an external string, we might end up in
			 * troubles. so just simulate a failure
			 */
			return null;
		}
		
		//need to create a new mapping
		
		addr = MASK + counter.getAndIncrement();
		resolved.put(host, addr);
		
		return addr;
	}
}