/*
 * Copyright 2004-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.webflow.conversation;

/**
 * A service for managing conversations. This interface is the entry point into the conversation subsystem.
 * 
 * @author Keith Donald
 * @author Erwin Vervaet
 */
public interface ConversationManager {

	/**
	 * Begin a new conversation.
	 * @param conversationParameters descriptive conversation parameters
	 * @return a service interface allowing access to the conversation context
	 * @throws ConversationException an exception occured
	 */
	public Conversation beginConversation(ConversationParameters conversationParameters) throws ConversationException;

	/**
	 * Get the conversation with the provided id.
	 * <p>
	 * Implementors should take care to manage conversation identity correctly. Although it is not strictly required to
	 * return the same (==) Conversation object every time this method is called with a particular conversation id in a
	 * single execution thread, callers will expect to recieve an object that allows them to manipulate the identified
	 * conversation. In other words, the following is legal ConversationManager client code:
	 * 
	 * <pre>
	 * 	ConversationManager manager = ...;
	 * 	ConversationId id = ...;
	 * 	Conversation conv = manager.getConversation(id);
	 *  conv.lock();
	 *  try {
	 *  	Conversation localReference = manager.getConversation(id);
	 *  	// no need to lock since conversation 'id' is already locked
	 *  	// even though possibly conv != localReference
	 *  	localReference.putAttribute("foo", "bar");
	 *  	Object foo = conv.getAttribute("foo");
	 * 	}
	 * 	finally {
	 * 		conv.unlock();
	 * 	}
	 * </pre>
	 * 
	 * @param id the conversation id
	 * @return the conversation
	 * @throws NoSuchConversationException the id provided was invalid
	 */
	public Conversation getConversation(ConversationId id) throws ConversationException;

	/**
	 * Parse the string-encoded conversationId into its object form. Essentially, the reverse of
	 * {@link ConversationId#toString()}.
	 * @param encodedId the encoded id
	 * @return the parsed conversation id
	 * @throws ConversationException an exception occured parsing the id
	 */
	public ConversationId parseConversationId(String encodedId) throws ConversationException;
}