/*
 * Copyright 2004-2007 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.execution;

import org.springframework.webflow.core.collection.AttributeMap;
import org.springframework.webflow.core.collection.MutableAttributeMap;
import org.springframework.webflow.definition.FlowDefinition;

/**
 * Provides contextual information about a flow execution. A flow execution is an runnable instance of a
 * {@link FlowDefinition}. It is the central Spring Web Flow construct for carrying out a conversation with a client.
 * This immutable interface provides access to runtime information about the conversation, such as it's
 * {@link #isActive() status} and {@link #getActiveSession() current state}.
 * <p>
 * An object implementing this interface is also traversable from a execution request context (see
 * {@link org.springframework.webflow.execution.RequestContext#getFlowExecutionContext()}).
 * <p>
 * This interface provides information that may span more than one request in a thread safe manner. The
 * {@link RequestContext} interface defines a <i>request specific</i> control interface for manipulating exactly one
 * flow execution locally from exactly one request.
 * 
 * @see FlowDefinition
 * @see FlowSession
 * @see RequestContext
 * 
 * @author Keith Donald
 * @author Erwin Vervaet
 */
public interface FlowExecutionContext {

	/**
	 * Returns the key assigned to this flow execution. The flow execution key is the flow execution's persistent
	 * identity.
	 * @return the flow execution key; may be <code>null</code> if a key has not yet been assigned.
	 */
	public FlowExecutionKey getKey();

	/**
	 * Returns the root flow definition associated with this executing flow.
	 * <p>
	 * A call to this method always returns the same flow definition -- the top-level "root" -- no matter what flow may
	 * actually be active (for example, if subflows have been spawned).
	 * @return the root flow definition
	 */
	public FlowDefinition getDefinition();

	/**
	 * Returns a flag indicating if this execution has been started. A flow execution that has started and is active is
	 * currently in progress. A flow execution that has started and is not active has ended.
	 * @see #isActive()
	 * @return true if started, false if not started
	 */
	public boolean hasStarted();

	/**
	 * Is the flow execution active?
	 * <p>
	 * All methods on an active flow execution context can be called successfully. If the flow execution is not active,
	 * a caller cannot access some methods such as {@link #getActiveSession()}.
	 * @return true if active, false if the flow execution has terminated
	 */
	public boolean isActive();

	/**
	 * Returns the active flow session of this flow execution. The active flow session is the currently executing
	 * session -- it may be the "root flow" session, or it may be a subflow session if this flow execution has spawned a
	 * subflow.
	 * @return the active flow session
	 * @throws IllegalStateException if this flow execution has not been started at all or if this execution has ended
	 * and is no longer actively executing
	 */
	public FlowSession getActiveSession() throws IllegalStateException;

	/**
	 * Returns a mutable map for data held in "flash scope". Attributes in this map are cleared out on the next event
	 * signaled against this flow execution. Flash attributes survive flow execution refresh operations.
	 * @return flash scope
	 */
	public MutableAttributeMap getFlashScope();

	/**
	 * Returns a mutable map for data held in "conversation scope". Conversation scope is a data structure that exists
	 * for the life of this flow execution and is accessible to all flow sessions.
	 * @return conversation scope
	 */
	public MutableAttributeMap getConversationScope();

	/**
	 * Returns runtime execution attributes that may influence the behavior of flow artifacts, such as states and
	 * actions.
	 * @return execution attributes
	 */
	public AttributeMap getAttributes();
}