[utils] / system / general / src / main / java / org / wamblee / system / core / AbstractComponent.java

/*
 * Copyright 2005-2010 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.wamblee.system.core;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * Abstract subsystem class making it easy to implement new subsystems.
 * 
 */
public abstract class AbstractComponent<Type> implements Component<Type> {
    private static final Log LOG = LogFactory.getLog(AbstractComponent.class);

    private ThreadLocal<List<ProvidedInterface>> remaining;

    private String context;

    private String name;

    private List<ProvidedInterface> provided;

    private List<RequiredInterface> required;

    /**
     * Constructs the subsystem.
     * 
     * @param aName
     *            Name of the system.
     * @param aProvided
     *            Provided services.
     * @param aRequired
     *            Required services.
     */
    protected AbstractComponent(String aName,
        List<ProvidedInterface> aProvided, List<RequiredInterface> aRequired) {
        remaining = new ThreadLocal<List<ProvidedInterface>>();
        context = null;
        name = aName;
        provided = new ArrayList<ProvidedInterface>(aProvided);
        required = new ArrayList<RequiredInterface>(aRequired);
    }

    /**
     * Constructs the subsystem.
     * 
     * @param aName
     *            Name of the system.
     * @param aProvided
     *            Provided services.
     * @param aRequired
     *            Required services.
     */
    protected AbstractComponent(String aName, ProvidedInterface[] aProvided,
        RequiredInterface[] aRequired) {
        this(aName, Arrays.asList(aProvided), Arrays.asList(aRequired));
    }

    /**
     * Creates a new AbstractComponent object.
     * 
     */
    protected AbstractComponent(String aName) {
        this(aName, new ProvidedInterface[0], new RequiredInterface[0]);
    }

    public AbstractComponent<Type> addProvidedInterface(
        ProvidedInterface aProvided) {
        provided.add(aProvided);

        return this;
    }

    public AbstractComponent<Type> addRequiredInterface(
        RequiredInterface aRequired) {
        required.add(aRequired);

        return this;
    }

    @Override
    public final String getName() {
        return name;
    }

    @Override
    public void addContext(String aContext) {
        if (context == null) {
            context = aContext;
        } else {
            context = aContext + "." + context;
        }
    }

    @Override
    public String getContext() {
        return context;
    }

    @Override
    public String getQualifiedName() {
        if (context == null) {
            return getName();
        }

        return context + "." + getName();
    }

    @Override
    public final List<ProvidedInterface> getProvidedInterfaces() {
        return Collections.unmodifiableList(provided);
    }

    @Override
    public final List<RequiredInterface> getRequiredInterfaces() {
        return Collections.unmodifiableList(required);
    }

    @Override
    public final Type start(Scope aScope) {
        LOG.info("Initialization starting '" + getQualifiedName() + "'");

        List<ProvidedInterface> oldRemaining = remaining.get();
        remaining
            .set(new ArrayList<ProvidedInterface>(getProvidedInterfaces()));

        try {
            Type runtime = doStart(aScope);
            checkNotStartedInterfaces();
            LOG.info("Initialization finished '" + getQualifiedName() + "'");

            return runtime;
        } finally {
            remaining.set(oldRemaining);
        }
    }

    private void checkNotStartedInterfaces() {
        if (remaining.get().size() > 0) {
            StringBuffer notProvided = new StringBuffer();

            for (ProvidedInterface provided : remaining.get()) {
                notProvided.append("\nComponent " + getQualifiedName() +
                    " did not start interface " + provided);
            }

            throw new SystemAssemblyException(notProvided.toString());
        }
    }

    /**
     * Must be implemented for initializing the subsystem. The implementation
     * must call {@link #addInterface(ProvidedInterface, Object, Scope)} for
     * each service that is started.
     * 
     * 
     * @return Returns the runtime of the component.
     */
    protected abstract Type doStart(Scope aScope);

    /**
     * Implementations must call this method to indicate that a new service has
     * been started.
     * 
     * @param aDescriptor
     *            Provided interface.
     * @param aService
     *            Implementation of the interface.
     * @param aScope
     *            scope in which to publish the implementation.
     * 
     */
    protected final void addInterface(ProvidedInterface aDescriptor,
        Object aService, Scope aScope) {
        LOG.info("Interface '" + getQualifiedName() + "." +
            aDescriptor.getName() + "' started.");

        if (!remaining.get().remove(aDescriptor)) {
            throw new SystemAssemblyException("Component '" +
                getQualifiedName() + "' started an unexpected interface '" +
                aDescriptor +
                "' that was not registerd as a provided interface before");
        }

        aScope.publishInterface(aDescriptor, aService);
    }

    @Override
    public void stop(Type aRuntime) {
        LOG.info("Stopping initiated '" + getQualifiedName() + "'");
        doStop(aRuntime);
        LOG.info("Stopping completed '" + getQualifiedName() + "'");
    }

    protected abstract void doStop(Type aRuntime);

    @Override
    public String toString() {
        return getQualifiedName();
    }

    public ProvidedInterface findProvidedInterface(String aName) {
        for (ProvidedInterface provided : getProvidedInterfaces()) {
            if (provided.getName().equals(aName)) {
                return provided;
            }
        }

        return null;
    }

    public RequiredInterface findRequiredInterface(String aName) {
        for (RequiredInterface required : getRequiredInterfaces()) {
            if (required.getName().equals(aName)) {
                return required;
            }
        }

        return null;
    }
}