package Sequenic.T2.Seq;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.ObjectStreamException;
import java.util.Arrays;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Reduces the storage requirements for an array of Strings.
 * Intended to store collections of strings that are frequently used together.
 * E.g. the class names used in a TraceStep.
 * 
 * @author Jeiel Schalkwijk
 *
 */

public final class StringList implements Externalizable {
	
	private String[] arr;
	private int hashCode;
	
	public StringList() {}
	
	public String[] getStrings() {
		return arr;
	}
	
	/** Create a StringList containing the given strings.
	 * 
	 * @param strings
	 * @return
	 */
	public static StringList create(String... strings) {
		StringList res = new StringList();
		res.initialize(strings);
		return res;
	}
	
	private void initialize(String[] a) {
		arr = a;
		hashCode = Arrays.hashCode(arr);
	}
		
	@Override
	public int hashCode()
	{
		return hashCode;
	}
	
	@Override
	public boolean equals(Object obj)
	{
		if(obj instanceof StringList) {
			return Arrays.equals(arr, ((StringList) obj).arr);
		}
		return false;
	}

	@Override
	public void readExternal(ObjectInput in) throws IOException,
			ClassNotFoundException
	{
		initialize((String[])in.readObject());
	}

	@Override
	public void writeExternal(ObjectOutput out) throws IOException
	{
		//First intern each String, to avoid serializing duplicate String instances.
		for (int i = 0; i < arr.length; i++)
			arr[i] = arr[i].intern();
		//Then write the array of strings.
		out.writeObject(arr);
	}
	
	private static final ConcurrentHashMap<StringList, StringList> cache = 
		new ConcurrentHashMap<StringList, StringList>();

	/* By using a cache each unique StringList is serialized exactly once.
	 * References to duplicate (i.e. equivalent) StringList instances are replaced
	 * with a reference to the first instance that was serialized.
	 */
	private Object writeReplace() throws ObjectStreamException{
		final StringList list = cache.putIfAbsent(this, this);
		return list==null? this : list;
	}

}