/*
 * Copyright 2005-2006 The Apache Software Foundation.
 *
 * 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.apache.servicemix.beanflow;

import org.apache.servicemix.beanflow.support.FieldIntrospector;
import org.apache.servicemix.beanflow.support.Introspector;

import java.util.Iterator;
import java.util.concurrent.CountDownLatch;

/**
 * A useful base class which allows simple bean activities to be written easily.
 * When this activity is started it will listen to all the state values which
 * can be found by the introspector (such as all the fields by default) calling
 * the {@link run} method when the state changes so that the activity can be
 * evaluted.
 * 
 * @version $Revision: $
 */
public abstract class AbstractActivity implements Runnable, Activity {

    private State<Transitions> state = new DefaultState<Transitions>(Transitions.Initialised);
    private Introspector introspector = new FieldIntrospector();
    private String failedReason;
    private Throwable failedException;

    /**
     * Starts the activity
     */
    public void start() {
        if (state.compareAndSet(Transitions.Initialised, Transitions.Starting)) {
            doStart();
            state.set(Transitions.Started);
        }
    }

    /**
     * Stops the activity
     */
    public void stop() {
        if (! state.isAny(Transitions.Stopped, Transitions.Failed)) {
            state.set(Transitions.Stopped);
            doStop();
        }
    }

    /**
     * Stops the activity with a failed state, giving the reason for the failure
     */
    public void fail(String reason) {
        this.failedReason = reason;
        state.set(Transitions.Failed);
        doStop();
    }

    /**
     * Stops the activity with a failed state with the given reason and
     * exception.
     */
    public void fail(String message, Throwable e) {
        fail(message);
        this.failedException = e;
    }

    /**
     * Returns the current running state of this activity
     */
    public State<Transitions> getState() {
        return state;
    }

    public boolean isStopped() {
        return state.isAny(Transitions.Stopped, Transitions.Failed);
    }

    public boolean isFailed() {
        return state.is(Transitions.Failed);
    }

    /**
     * Returns the reason for the failure
     */
    public String getFailedReason() {
        return failedReason;
    }

    /**
     * Returns the exception which caused the failure
     */
    public Throwable getFailedException() {
        return failedException;
    }

    /**
     * A helper method to add a task to fire when the activity is completed
     */
    public void onStop(final Runnable runnable) {
        getState().addRunnable(new Runnable() {

            public void run() {
                if (isStopped()) {
                    runnable.run();
                }
            }
        });
    }

    /**
     * A helper method to add a task to fire when the activity fails
     */
    public void onFailure(final Runnable runnable) {
        getState().addRunnable(new Runnable() {

            public void run() {
                if (isFailed()) {
                    runnable.run();
                }
            }
        });
    }

    /**
     * A helper method to block the calling thread until the activity completes
     */
    public void join() {
        while (!isStopped()) {
            final CountDownLatch latch = new CountDownLatch(1);
            onStop(new Runnable() {
                public void run() {
                    latch.countDown();
                }
            });
            try {
                latch.await();
            }
            catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }

    // Implementation methods
    // -------------------------------------------------------------------------
    protected void doStart() {
        addListeners(this);
    }

    protected void doStop() {
        removeListeners(this);
    }

    protected Introspector getIntrospector() {
        return introspector;
    }

    protected void setIntrospector(Introspector introspector) {
        this.introspector = introspector;
    }

    protected void addListeners(Runnable listener) {
        if (introspector != null) {
            Iterator<State> iter = introspector.iterator(this);
            while (iter.hasNext()) {
                iter.next().addRunnable(listener);
            }
        }
    }

    protected void removeListeners(Runnable listener) {
        if (introspector != null) {
            Iterator<State> iter = introspector.iterator(this);
            while (iter.hasNext()) {
                iter.next().removeRunnable(listener);
            }
        }
    }
}
