/*
 * Copyright 2007 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 java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

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

/**
 * Composite system consisting of multiple subsystems.
 * 
 * @author Erik Brakkee
 */
public class Container extends AbstractComponent {

	private static final Log LOG = LogFactory.getLog(Container.class);

	private Component[] _systems;

	public static RequiredInterface[] filterRequiredServices(
			ProvidedInterface aProvided,
			Collection<RequiredInterface> aDescriptors) {
		List<RequiredInterface> required = new ArrayList<RequiredInterface>();
		for (RequiredInterface descriptor : aDescriptors) {
			if (descriptor.implementedBy(aProvided)) {
				required.add(descriptor);
			}
		}
		return required.toArray(new RequiredInterface[0]);
	}

	public static ProvidedInterface[] filterProvidedServices(
			RequiredInterface aRequired, Collection<ProvidedInterface> aProvided) {
		List<ProvidedInterface> provided = new ArrayList<ProvidedInterface>();
		for (ProvidedInterface descriptor : aProvided) {
			if (aRequired.implementedBy(descriptor)) {
				provided.add(descriptor);
			}
		}
		return provided.toArray(new ProvidedInterface[0]);
	}

	/**
	 * Construcst the composite system.
	 * 
	 * @param aName
	 *            Name of the system.
	 * @param aRegistry
	 *            Service registry.
	 * @param aSystems
	 *            Subsystems.
	 * @param aProvided
	 *            Provided services of the system.
	 * @param aRequired
	 *            Required services by the system.
	 */
	public Container(String aName, Component[] aSystems,
			ProvidedInterface[] aProvided, RequiredInterface[] aRequired) {
		super(aName, aProvided, aRequired);
		_systems = aSystems;
		for (Component component : aSystems) {
			component.addContext(getQualifiedName());
		}
		validate();
	}

	/**
	 * Validates the subsystems together to check that there are no required
	 * services not in the required list and no services in the provided list
	 * that cannot be provided. Also logs a warning in case of superfluous
	 * requirements.
	 */
	private void validate() {
		List<ProvidedInterface> provided = new ArrayList<ProvidedInterface>();
		for (Component system : _systems) {
			provided.addAll(Arrays.asList(system.getProvidedInterfaces()));
		}

		List<RequiredInterface> required = new ArrayList<RequiredInterface>();
		for (Component system : _systems) {
			required.addAll(Arrays.asList(system.getRequiredInterfaces()));
		}

		validateProvidedInterfaces(provided);

		validateRequiredInterfaces(required);

		List<RequiredInterface> reallyRequired = validateRequiredProvidedMatch(
				provided, required);
		
		String missingRequired = "";
		for (RequiredInterface service : reallyRequired) {
			missingRequired += service + "\n";
		}
		if (missingRequired.length() > 0) {
			throw new SystemAssemblyException(getName()
					+ ": missing required services\n" + missingRequired);
		}
	}

	private List<RequiredInterface> validateRequiredProvidedMatch(
			List<ProvidedInterface> provided, List<RequiredInterface> required) {
		List<RequiredInterface> reallyRequired = new ArrayList<RequiredInterface>(
				required);
		// Compute all required interfaces that are not provided

		for (ProvidedInterface service : provided) {
			List<RequiredInterface> fulfilled = Arrays
					.asList(filterRequiredServices(service, reallyRequired));
			reallyRequired.removeAll(fulfilled);
		}
		// Now remove all optional interfaces from the list.
		for (Iterator<RequiredInterface> i = 
			reallyRequired.iterator(); i.hasNext(); ) { 
			RequiredInterface req = i.next();
			if ( req.isOptional() ) {
				i.remove(); 
			}
		}
		// Now the remaining interfaces should be covered by the required
		// list.
		reallyRequired.removeAll(Arrays.asList(getRequiredInterfaces()));
		return reallyRequired;
	}

	private void validateRequiredInterfaces(List<RequiredInterface> required) {
		for (RequiredInterface service : getRequiredInterfaces()) {
			// TODO required services by the subsystem could be 
			//      subclasses or implementations of the requirements
			//      of the contained systems. The code below assumes
			//      an exact match. 
			if (!(required.contains(service))) {
				info("Service '"
						+ service
						+ "' indicated as required is not actually required by any of the subsystems");
			}
			// Check for the case that the externally required service
			// is optional whereas the internally required service is 
			// mandatory. 
			if ( service.isOptional()) { 
				for (RequiredInterface intf: required) { 
					if ( intf.equals(service) && !intf.isOptional()) { 
						// TODO indicate which subsystem this is. 
						warn("Required service '" + service + "' indicated as optional is mandatory by one of its subsystems (" + getClients(intf) + ", " + intf + "), this can lead to problems when the system is started and the service is not there.");
					}
				}
			}
		}
	}

	private void validateProvidedInterfaces(List<ProvidedInterface> provided) {
		for (ProvidedInterface service : getProvidedInterfaces()) {
			// TODO provided interfaces by subsystems could be 
			//      provide subclasses or implementations of the 
			//      provided interfaces of the container.
			//      The code below assumes an exact match. 
			if (!(provided.contains(service))) {
				throw new SystemAssemblyException(getName() + ": Service '"
						+ service
						+ "' is not provided by any of the subsystems");
			}
		}
	}

	@Override
	protected void doStart() {
		LOG.info("Starting '" + getQualifiedName() + "'");
		List<ProvidedInterface> allProvided = new ArrayList<ProvidedInterface>();

		// all interfaces from the required list of this container are
		// provided to the components inside it.
		RequiredInterface[] required = getRequiredInterfaces();
		for (RequiredInterface intf : required) {
			ProvidedInterface provider = intf.getProvider();
			if (provider != null ) { 
				allProvided.add(provider);
			} else { 
				if ( !intf.isOptional()) { 
					throw new SystemAssemblyException(getQualifiedName()
							+ ": required interface '" + intf + "' is not provided");		
				}
			}
		}

		List<Component> started = new ArrayList<Component>();
		for (Component system : _systems) {
			try {
				// Check if all required services are already provided by
				// earlier
				// systems.

				for (RequiredInterface descriptor : system.getRequiredInterfaces()) {
					ProvidedInterface[] filtered = filterProvidedServices(
							descriptor, allProvided);
					if ( filtered.length == 1 ) { 
						descriptor.setProvider(filtered[0]);
					} else if ( filtered.length > 1 ) { 
						throw new SystemAssemblyException(
								"Service '"
										+ descriptor
										+ "' required by system '"
										+ system
										+ "' matches multiple services provided by other systems: "
										+ Arrays.asList(filtered));
					} else { 
						// filtered.length == 0
						if ( !descriptor.isOptional()) { 
							throw new SystemAssemblyException(
									"Service '"
											+ descriptor
											+ "' required by system '"
											+ system
											+ "' is not provided by systems that are started earlier");	
						}
					}
				}

				// Start the service.
				system.start();
				started.add(system);

				// add all provided services
				ProvidedInterface[] provided = system.getProvidedInterfaces();
				allProvided.addAll(Arrays.asList(provided));
			} catch (SystemAssemblyException e) { 
				throw e; 
			} catch (RuntimeException e) {
				LOG.error(getQualifiedName() + ": could not start '"
						+ system.getQualifiedName() + "'", e);
				// an exception occurred, stop the successfully started
				// systems
				for (int i = started.size() - 1; i >= 0; i--) {
					try {
						started.get(i).stop();
					} catch (Throwable t) {
						LOG.error(getQualifiedName() + ": error stopping "
								+ started.get(i).getQualifiedName());
					}
				}
				throw e; 
			}
		}

	}

	@Override
	protected void doStop() {
		for (int i = _systems.length - 1; i >= 0; i--) {
			_systems[i].stop();
		}
	}

	private void info(String aMsg) {
		LOG.info(getQualifiedName() + ": " + aMsg);
	}
	
	private void warn(String aMsg) {
		LOG.warn(getQualifiedName() + ": " + aMsg);
	}

	private List<Component> getClients(RequiredInterface aRequirement) {
		List<Component> clients = new ArrayList<Component>();
		for (Component component: _systems) { 
			for (RequiredInterface required: component.getRequiredInterfaces()) { 
				if ( required.equals(aRequirement) && required.isOptional() == aRequirement.isOptional()) { 
					clients.add(component);
				}
			}
		}
		return clients; 
	}
}