/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * 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
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.felix.dependencymanager;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Dictionary;
import java.util.Properties;

import org.osgi.framework.BundleContext;
import org.osgi.framework.Constants;
import org.osgi.framework.ServiceRegistration;
import org.osgi.service.cm.ConfigurationException;
import org.osgi.service.cm.ManagedService;

/**
 * Configuration dependency that can track the availability of a (valid) configuration.
 * To use it, specify a PID for the configuration. The dependency is always required,
 * because if it is not, it does not make sense to use the dependency manager. In that
 * scenario, simply register your service as a <code>ManagedService(Factory)</code> and
 * handle everything yourself. Also, only managed services are supported, not factories.
 * There are a couple of things you need to be aware of when implementing the
 * <code>updated(Dictionary)</code> method:
 * <ul>
 * <li>Make sure it throws a <code>ConfigurationException</code> when you get a
 * configuration that is invalid. In this case, the dependency will not change:
 * if it was not available, it will still not be. If it was available, it will
 * remain available and implicitly assume you keep working with your old
 * configuration.</li>
 * <li>This method will be called before all required dependencies are available.
 * Make sure you do not depend on these to parse your settings.</li>
 * </ul>
 * 
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
 */
public class ConfigurationDependency implements Dependency, ManagedService, ServiceComponentDependency {
	private BundleContext m_context;
	private String m_pid;
	private ServiceRegistration m_registration;
	private volatile Service m_service;
	private Dictionary m_settings;
	private boolean m_propagate;
	private final Logger m_logger;
    private String m_callback;
	
	public ConfigurationDependency(BundleContext context, Logger logger) {
		m_context = context;
		m_logger = logger;
	}
	
	public synchronized boolean isAvailable() {
		return m_settings != null;
	}

	/**
	 * Will always return <code>true</code> as optional configuration dependencies
	 * do not make sense. You might as well just implement <code>ManagedService</code>
	 * yourself in those cases.
	 */
	public boolean isRequired() {
		return true;
	}
	
	/**
	 * Returns <code>true</code> when configuration properties should be propagated
	 * as service properties.
	 */
	public boolean isPropagated() {
		return m_propagate;
	}
	
	public Dictionary getConfiguration() {
		return m_settings;
	}
	
	public void start(Service service) {
		m_service = service;
		Properties props = new Properties();
		props.put(Constants.SERVICE_PID, m_pid);
		m_registration = m_context.registerService(ManagedService.class.getName(), this, props);
	}

	public void stop(Service service) {
		m_registration.unregister();
		m_service = null;
	}

        public Dependency setCallback(String callback) {
		m_callback = callback;
		return this;
	}

	public void updated(Dictionary settings) throws ConfigurationException {
		// if non-null settings come in, we have to instantiate the service and
		// apply these settings
		((ServiceImpl) m_service).initService();
		Object service = m_service.getService();
				
		Dictionary oldSettings = null; 
		synchronized (this) {
			oldSettings = m_settings;
		}
		
		if (oldSettings == null && settings == null) {
	       // CM has started but our configuration is not still present in the CM database: ignore
	       return;
		}
		
        if (service != null) {
          	String callback = (m_callback == null) ? "updated" : m_callback;
      	  	Method m;
			try {
			  	m = service.getClass().getDeclaredMethod(callback, new Class[] { Dictionary.class });
			  	m.setAccessible(true);
			  	// if exception is thrown here, what does that mean for the
			  	// state of this dependency? how smart do we want to be??
			  	// it's okay like this, if the new settings contain errors, we
			  	// remain in the state we were, assuming that any error causes
			  	// the "old" configuration to stay in effect.
			  	// CM will log any thrown exceptions.
			  	m.invoke(service, new Object[] { settings });
			} 
      	  	catch (InvocationTargetException e) {
                // The component has thrown an exception during it's callback invocation.
                if (e.getTargetException() instanceof ConfigurationException) {
                    // the callback threw an OSGi ConfigurationException: just re-throw it.
                    throw (ConfigurationException) e.getTargetException();
                }
                else {
                    // wrap the callback exception into a ConfigurationException.
                    throw new ConfigurationException(null, "Service " + m_service + " with " + this.toString() + " could not be updated", e.getTargetException());
                }
            }
            catch (Throwable t) {
                // wrap any other exception as a ConfigurationException.
                throw new ConfigurationException(null, "Service " + m_service + " with " + this.toString() + " could not be updated", t);
            }
        }
        else {
            m_logger.log(Logger.LOG_ERROR, "Service " + m_service + " with configuration dependency " + this + " could not be instantiated.");
            return;
        }

		// If these settings did not cause a configuration exception, we determine if they have 
		// caused the dependency state to change
		synchronized (this) {
			m_settings = settings;
		}

		if ((oldSettings == null) && (settings != null)) {
			m_service.dependencyAvailable(this);
		}
		if ((oldSettings != null) && (settings == null)) {
			m_service.dependencyUnavailable(this);
		}
		if ((oldSettings != null) && (settings != null)) {
			m_service.dependencyChanged(this);
		}
	}

	/**
	 * Sets the <code>service.pid</code> of the configuration you
	 * are depending on.
	 */
	public ConfigurationDependency setPid(String pid) {
		ensureNotActive();
		m_pid = pid;
		return this;
	}

	/**
	 * Sets propagation of the configuration properties to the service
	 * properties. Any additional service properties specified directly
	 * are merged with these.
	 */
	public ConfigurationDependency setPropagate(boolean propagate) {
		ensureNotActive();
		m_propagate = propagate;
		return this;
	}
	
	private void ensureNotActive() {
	  	if (m_service != null) {
	  	  throw new IllegalStateException("Cannot modify state while active.");
	  	}
    }
    
    public String toString() {
    	return "ConfigurationDependency[" + m_pid + "]";
    }

    public String getName() {
        return m_pid;
    }

    public int getState() {
        return (isAvailable() ? 1 : 0) + (isRequired() ? 2 : 0);
    }

    public String getType() {
        return "configuration";
    }
}