/*
 * OSGi and Gravity Service Binder tutorial.
 * Copyright (c) 2003  Richard S. Hall
 * http://oscar-osgi.sourceforge.net
**/

package tutorial.example6;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceEvent;

import tutorial.example5.service.SpellCheckService;

/**
 * This class implements a bundle that uses a spell check
 * service to check the spelling of a passage. This bundle
 * is essentially identical to Example 4, in that it monitors
 * the dynamic availability of the spell check service.
 * When starting this bundle, the thread calling the start()
 * method is used to read passages from standard input. You can
 * stop spell checking passages by entering an empty line, but
 * to start spell checking again you must stop and then restart
 * the bundle.
**/
public class Activator implements BundleActivator, ServiceListener
{
    // Bundle's context.
    private BundleContext m_context = null;
    // The service reference being used.
    private ServiceReference m_ref = null;
    // The service object being used.
    private SpellCheckService m_checker = null;

    /**
     * Implements BundleActivator.start(). Adds itself
     * as a listener for service events, then queries for all
     * available spell check services. If none are found it goes
     * into its normal "passage checking loop" and waits for a
     * spell check service to arrive. Once it has a spell check
     * service it reads passages from standard input and checks
     * their spelling using the spell check service.
     * (NOTE: It is very bad practice to use the calling thread
     * to perform a lengthy process like this; this is only done
     * for the purpose of the tutorial.)
     * @param context the framework context for the bundle.
    **/
    public void start(BundleContext context) throws Exception
    {
        m_context = context;

        // Listen for events pertaining to dictionary services.
        m_context.addServiceListener(this,
            "(objectClass=" + SpellCheckService.class.getName() + ")");

        // Query for a spell check service.
        m_ref = m_context.getServiceReference(SpellCheckService.class.getName());

        // If we found a spell check service, then get
        // a reference so we can use it.
        if (m_ref != null)
        {
            m_checker = (SpellCheckService) m_context.getService(m_ref);
        }

        try
        {
            System.out.println("Enter a blank line to exit.");
            String passage = "";
            BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

            // Loop endlessly.
            while (true)
            {
                // Ask the user to enter a passage.
                System.out.print("Enter passage: ");
                passage = in.readLine();

                // If the user entered a blank line, then
                // exit the loop.
                if (passage.length() == 0)
                {
                    break;
                }
                // If there is no spell checker, then say so.
                else if (m_checker == null)
                {
                    System.out.println("No spell checker available.");
                }
                // Otherwise check passage and print misspelled words.
                else
                {
                    String[] errors = m_checker.check(passage);

                    if (errors == null)
                    {
                        System.out.println("Passage is correct.");
                    }
                    else
                    {
                        System.out.println("Incorrect word(s):");
                        for (int i = 0; i < errors.length; i++)
                        {
                            System.out.println("    " + errors[i]);
                        }
                    }
                }
            }
        } catch (Exception ex) { }
    }

    /**
     * Implements BundleActivator.stop(). Does nothing since
     * the framework will automatically unget any used services.
     * @param context the framework context for the bundle.
    **/
    public void stop(BundleContext context)
    {
        // NOTE: The service is automatically released.
    }

    /**
     * Implements ServiceListener.serviceChanged(). Checks
     * to see if the service we are using is leaving or tries to get
     * a service if we need one.
     * @param event the fired service event.
    **/
    public void serviceChanged(ServiceEvent event)
    {
        String[] objectClass =
            (String[]) event.getServiceReference().getProperty("objectClass");

        // If a spell check service was registered, see if we
        // need one. If so, get a reference to it.
        if (event.getType() == ServiceEvent.REGISTERED)
        {
            if (m_ref == null)
            {
                // Get a reference to the service object.
                m_ref = event.getServiceReference();
                m_checker = (SpellCheckService) m_context.getService(m_ref);
            }
        }
        // If a spell check service was unregistered, see if it
        // was the one we were using. If so, unget the service
        // and try to query to get another one.
        else if (event.getType() == ServiceEvent.UNREGISTERING)
        {
            if (event.getServiceReference() == m_ref)
            {
                // Unget service object and null references.
                m_context.ungetService(m_ref);
                m_ref = null;
                m_checker = null;

                // Query to see if we can get another service.
                m_ref = m_context.getServiceReference(SpellCheckService.class.getName());
                if (m_ref != null)
                {
                    // Get a reference to the service object.
                    m_checker = (SpellCheckService) m_context.getService(m_ref);
                }
            }
        }
    }
}