package de.ugoe.cs.quest.usageprofiles;

import java.security.InvalidParameterException;
import java.util.LinkedList;
import java.util.List;

/**
 * <p>
 * Implements a round-trip buffered memory of a specified length that can be
 * used to remember the recent history. Every event that happend longer ago than
 * the length of the memory is forgotten, hence the memory is incomplete.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 * 
 * @param <T>
 *            Type which is memorized.
 */
public class IncompleteMemory<T> implements IMemory<T> {

	/**
	 * <p>
	 * Maximum length of the memory.
	 * </p>
	 */
	private int length;

	/**
	 * <p>
	 * Internal storage of the history.
	 * </p>
	 */
	private List<T> history;

	/**
	 * <p>
	 * Constructor. Creates a new IncompleteMemory.
	 * </p>
	 * 
	 * @param length
	 *            number of recent events that are remembered
	 * @throws InvalidParameterException
	 *             This exception is thrown if the length is smaller than 1
	 */
	public IncompleteMemory(int length) {
		if (length < 1) {
			throw new InvalidParameterException(
					"Length of IncompleteMemory must be at least 1.");
		}
		this.length = length;
		history = new LinkedList<T>();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see de.ugoe.cs.quest.usageprofiles.IMemory#add(java.lang.Object)
	 */
	@Override
	public void add(T state) {
		if (history.size() == length) {
			history.remove(0);
		}
		history.add(state);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see de.ugoe.cs.quest.usageprofiles.IMemory#getLast(int)
	 */
	@Override
	public List<T> getLast(int num) {
		if( num<1 ) {
			return new LinkedList<T>();
		} else {
		return new LinkedList<T>(history.subList(
				Math.max(0, history.size() - num),
				history.size())); // defensive copy
		}
	}

	/**
	 * <p>
	 * Returns the current length of the memory. This can be less than
	 * {@link #length}, if the overall history is less than {@link #length}.
	 * </p>
	 * 
	 * @return length of the current memory
	 */
	public int getLength() {
		return history.size();
	}
}