StateEntry.java

/*
 * Copyright: Almende B.V. (2014), Rotterdam, The Netherlands
 * License: The Apache Software License, Version 2.0
 */
package com.almende.eve.state;

import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.jodah.typetools.TypeResolver;

import com.almende.util.TypeUtil;
import com.almende.util.jackson.JOM;
import com.fasterxml.jackson.databind.JavaType;

/**
 * The Class StateEntry.
 * 
 * @author <a href="mailto:rick@almende.org">Rick van Krevelen</a>
 * @version $Revision: 911 $ $Author: a4g.almende $
 * @param <T>
 *            the type of value stored in this state entry {@link StateEntry}
 *            wraps agent state entry key and provides respective value
 *            type meta data
 * @date $Date: 2013-05-28 17:31:07 +0200 (Tue, 28 May 2013) $
 */
public abstract class StateEntry<T extends Serializable> {
	private static final Logger	LOG	= Logger.getLogger(StateEntry.class
											.getCanonicalName());
	private final String		key;
	private final JavaType		valueType;
	
	/**
	 * Constructs a {@link StateEntry} with specified {@code key} and.
	 * 
	 * @param key
	 *            the key {@code valueType} meta information
	 */
	public StateEntry(final String key) {
		this.key = key;
		this.valueType = JOM.getTypeFactory()
				.constructType(
						((ParameterizedType) TypeResolver.resolveGenericType(
								StateEntry.class, getClass()))
								.getActualTypeArguments()[0]);
	}
	
	/**
	 * Gets the key.
	 * 
	 * @return the {@link StateEntry} key's {@link String} value
	 */
	public String getKey() {
		return this.key;
	}
	
	/**
	 * Gets the value type.
	 * 
	 * @return the {@link StateEntry} value's type
	 */
	public Type getValueType() {
		return this.valueType;
	}
	
	/**
	 * Default value.
	 * 
	 * @return the value to persist/provide if none exists yet
	 */
	public T defaultValue() {
		return null;
	}
	
	/**
	 * Exists.
	 * 
	 * @param state
	 *            the {@link State} to search for this {@link StateEntry}
	 * @return {@code true} is specified {@code state} contains this
	 *         {@link StateEntry}'s key, {@code false} otherwise
	 * @see java.util.Map#containsKey(Object)
	 */
	public boolean exists(final State state) {
		return state.containsKey(getKey());
	}
	
	/**
	 * Gets the value.
	 * 
	 * @param state
	 *            the {@link State} from which to retrieve this
	 * @return the value retrieved from specified {@code state} or {@code null}
	 *         if none exists {@code StateEntry}'s value
	 * @see java.util.Map#get(Object)
	 */
	public T getValue(final State state) {
		try {
			return state.get(getKey(), valueType);
		} catch (final ClassCastException e) {
			LOG.log(Level.WARNING, "Problem casting agent's state value, key: "
					+ key, e);
			return null;
		}
	}
	
	/**
	 * Put value.
	 * 
	 * @param state
	 *            the {@link State} to update with specified {@code value}
	 * @param value
	 *            the new value for this {@link StateEntry} in specified
	 * @return the previous value or {@code null} if none existed {@code state}
	 * @see java.util.Map#put(Object, Object)
	 */
	public T putValue(final State state, final T value) {
		try {
			return TypeUtil.inject(state.put(getKey(), value), valueType);
		} catch (final ClassCastException e) {
			LOG.log(Level.WARNING,
					"Problem casting agent's previous state value, key: " + key,
					e);
			return null;
		}
	}
	
	/**
	 * Put value if unchanged.
	 * 
	 * @param state
	 *            the {@link State} to update with specified {@code value}
	 * @param newValue
	 *            the new value for this {@link StateEntry} in specified
	 * @param currentValue
	 *            the current/precondition value for this {@link StateEntry} in
	 *            specified {@code state}
	 * @return the previous value or {@code null} if none existed {@code state}
	 */
	public boolean putValueIfUnchanged(final State state, final T newValue,
			final T currentValue) {
		return state.putIfUnchanged(getKey(), newValue, currentValue);
	}
	
}