jspwiki-main/src/main/java/org/apache/wiki/workflow/Decision.java

/* 
    Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
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    regarding copyright ownership.  The ASF licenses this file
    to you 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
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    specific language governing permissions and limitations
    under the License.  
 */
package org.apache.wiki.workflow;

import org.apache.wiki.api.exceptions.WikiException;
import org.apache.wiki.event.WorkflowEvent;

import java.security.Principal;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;


/**
 * <p>
 * AbstractStep subclass that asks an actor Principal to choose an Outcome on behalf of an owner (also a Principal). The actor
 * "makes the decision" by calling the {@link #decide(Outcome)} method. When this method is called, it will set the Decision's Outcome to
 * the one supplied. If the parent Workflow is in the {@link Workflow#WAITING} state, it will be re-started. Any checked WikiExceptions
 * thrown by the workflow after re-start will be re-thrown to callers.
 * </p>
 * <p>
 * When a Decision completes, its {@link #isCompleted()} method returns <code>true</code>. It also tells its parent WorkflowManager to
 * remove it from the list of pending tasks by calling {@link DecisionQueue#remove(Decision)}.
 * </p>
 * <p>
 * To enable actors to choose an appropriate Outcome, Decisions can store arbitrary key-value pairs called "facts." These facts can be
 * presented by the user interface to show details the actor needs to know about. Facts are added by calling classes to the Decision,
 * in order of expected presentation, by the {@link #addFact(Fact)} method. They can be retrieved, in order, via {@link #getFacts()}.
 * </p>
 *
 * @since 2.5
 */
public abstract class Decision extends AbstractStep {

    private static final long serialVersionUID = -6835601038263238062L;

    private Principal m_actor;

    private int m_id;

    private final Outcome m_defaultOutcome;

    private final List<Fact> m_facts;

    /**
     * Constructs a new Decision for a required "actor" Principal, having a default Outcome.
     *
     * @param workflow the parent Workflow object
     * @param messageKey the i18n message key that represents the message the actor will see
     * @param actor the Principal (<em>e.g.</em>, a WikiPrincipal, Role, GroupPrincipal) who is required to select an appropriate Outcome
     * @param defaultOutcome the Outcome that the user interface will recommend as the default choice
     */
    public Decision( final Workflow workflow, final String messageKey, final Principal actor, final Outcome defaultOutcome ) {
        super( workflow, messageKey );
        m_actor = actor;
        m_defaultOutcome = defaultOutcome;
        m_facts = new ArrayList<>();
        addSuccessor( defaultOutcome, null );
    }

    /**
     * Appends a Fact to the list of Facts associated with this Decision.
     * 
     * @param fact the new fact to add
     */
    public final void addFact( final Fact fact )
    {
        m_facts.add( fact );
    }

    /**
     * <p>
     * Sets this Decision's outcome, and restarts the parent Workflow if it is
     * in the {@link Workflow#WAITING} state and this Decision is its currently
     * active Step. Any checked WikiExceptions thrown by the workflow after
     * re-start will be re-thrown to callers.
     * </p>
     * <p>
     * This method cannot be invoked if the Decision is not the current Workflow
     * step; all other invocations will throw an IllegalStateException. If the
     * Outcome supplied to this method is one one of the Outcomes returned by
     * {@link #getAvailableOutcomes()}, an IllegalArgumentException will be
     * thrown.
     * </p>
     * 
     * @param outcome the Outcome of the Decision
     * @throws WikiException if the act of restarting the Workflow throws an exception
     */
    public void decide( final Outcome outcome ) throws WikiException {
        super.setOutcome( outcome );

        // If current workflow is waiting for input, restart it and remove Decision from DecisionQueue
        final Workflow w = getWorkflow();
        if( w.getCurrentState() == Workflow.WAITING && this.equals( w.getCurrentStep() ) ) {
            WorkflowEventEmitter.fireEvent( this, WorkflowEvent.DQ_REMOVAL );
            // Restart workflow
            w.restart();
        }
    }

    /**
     * Default implementation that always returns {@link Outcome#STEP_CONTINUE} if the current Outcome isn't a completion (which will be
     * true if the {@link #decide(Outcome)} method hasn't been executed yet. This method will also add the Decision to the associated
     * DecisionQueue.
     * 
     * @return the Outcome of the execution
     * @throws WikiException never
     */
    public Outcome execute() throws WikiException {
        if( getOutcome().isCompletion() ) {
            return getOutcome();
        }

        // Put decision in the DecisionQueue
        WorkflowEventEmitter.fireEvent( this, WorkflowEvent.DQ_ADDITION );

        // Indicate we are waiting for user input
        return Outcome.STEP_CONTINUE;
    }

    /**
     * {@inheritDoc}
     */
    public final Principal getActor() {
        return m_actor;
    }

    /**
     * Returns the default or suggested outcome, which must be one of those returned by {@link #getAvailableOutcomes()}. This method is
     * guaranteed to return a non-<code>null</code> Outcome.
     * 
     * @return the default outcome.
     */
    public Outcome getDefaultOutcome() {
        return m_defaultOutcome;
    }

    /**
     * Returns the Facts associated with this Decision, in the order in which they were added.
     * 
     * @return the list of Facts
     */
    public final List< Fact > getFacts() {
        return Collections.unmodifiableList( m_facts );
    }

    /**
     * Returns the unique identifier for this Decision. Normally, this ID is programmatically assigned when the Decision is added to the
     * DecisionQueue.
     * 
     * @return the identifier
     */
    public final int getId() {
        return m_id;
    }

    /**
     * Returns <code>true</code> if the Decision can be reassigned to another actor. This implementation always returns <code>true</code>.
     *
     * @return the result
     */
    public boolean isReassignable() {
        return true;
    }

    /**
     * Reassigns the Decision to a new actor (that is, provide an outcome). If the Decision is not reassignable, this method throws an
     * IllegalArgumentException.
     * 
     * @param actor the actor to reassign the Decision to
     */
    public final synchronized void reassign( final Principal actor ) {
        if( isReassignable() ) {
            m_actor = actor;
        } else {
            throw new IllegalArgumentException( "Decision cannot be reassigned." );
        }
    }

    /**
     * Sets the unique identfier for this Decision.
     * 
     * @param id the identifier
     */
    public final void setId( final int id ) {
        m_id = id;
    }

}