/*
 * 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.container;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.wamblee.general.Pair;
import org.wamblee.system.core.AbstractComponent;
import org.wamblee.system.core.Component;
import org.wamblee.system.core.DefaultScope;
import org.wamblee.system.core.ProvidedInterface;
import org.wamblee.system.core.RequiredInterface;
import org.wamblee.system.core.Scope;
import org.wamblee.system.core.SystemAssemblyException;
import org.wamblee.system.graph.component.ComponentGraph;

/**
 * Container consisting of multiple components.
 * 
 * @author Erik Brakkee
 */
public class Container extends AbstractComponent<Scope> {

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

    private List<Component> _components;
    private Set<String> _componentNames;
    private CompositeInterfaceRestriction _restriction;
    private boolean _sealed;

    /**
     * Constructs the container
     * 
     * @param aName
     *            Name of the container
     * @param aComponents
     *            Components.
     * @param aProvided
     *            Provided services of the container
     * @param aRequired
     *            Required services by the container.
     */
    public Container(String aName, Component[] aComponents,
            ProvidedInterface[] aProvided, RequiredInterface[] aRequired) {
        super(aName, aProvided, aRequired);
        _components = new ArrayList<Component>();

        _componentNames = new HashSet<String>();
        _restriction = new CompositeInterfaceRestriction();
        _sealed = false;
        for (Component component : aComponents) {
            addComponent(component);
        }
    }

    public Container(String aName) {
        this(aName, new Component[0], new ProvidedInterface[0],
                new RequiredInterface[0]);
    }

    public Container addComponent(Component aComponent) {
        checkSealed();
        if (aComponent.getContext() != null) {
            throw new SystemAssemblyException(
                    "Inconsistent hierarchy, component '"
                            + aComponent.getName()
                            + "' is already part of another hierarchy");
        }
        if (_componentNames.contains(aComponent.getName())) {
            throw new SystemAssemblyException("Duplicate component '"
                    + aComponent.getName() + "'");
        }
        _components.add(aComponent);
        _componentNames.add(aComponent.getName());
        aComponent.addContext(getQualifiedName());
        return this;
    }

    /**
     * Adds an interface restriction for explicitly configuring the relations
     * between components.
     * 
     * @param aRestriction
     *            Restriction to add.
     * @return Reference to this to allow call chaining.
     */
    public Container addRestriction(InterfaceRestriction aRestriction) {
        checkSealed();
        _restriction.add(aRestriction);
        return this;
    }

    @Override
    public Container addProvidedInterface(ProvidedInterface aProvided) {
        checkSealed();
        super.addProvidedInterface(aProvided);
        return this;
    }

    @Override
    public Container addRequiredInterface(RequiredInterface aRequired) {
        checkSealed();
        super.addRequiredInterface(aRequired);
        return this;
    }

    @Override
    public void addContext(String aContext) {
        super.addContext(aContext);
        for (Component component : _components) {
            component.addContext(aContext);
        }
    }

    /**
     * Validates the components 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.
     * 
     * @throws SystemAssemblyException
     *             in case of any validation problems.
     */
    public void validate() {
        doStartOptionalDryRun(null, true);
    }

    /**
     * Seal the container, meaning that no further components or interfaces may
     * be added.
     */
    public void seal() {
        _sealed = true;
    }

    /**
     * Checks if the container is sealed.
     * 
     * @return True iff the container is sealed.
     */
    public boolean isSealed() {
        return _sealed;
    }

    /**
     * Utility method to start with an empty external scope. This is useful for
     * top-level containers which are not part of another container.
     * 
     * @return Scope.
     */
    public Scope start() {
        Scope scope = new DefaultScope(getProvidedInterfaces());
        return super.start(scope);
    }

    @Override
    protected Scope doStart(Scope aExternalScope) {
        checkSealed();
        validate();
        Scope scope = new DefaultScope(getProvidedInterfaces(), aExternalScope);
        ComponentGraph graph = doStartOptionalDryRun(scope, false);
        exposeProvidedInterfaces(graph, aExternalScope, scope);
        seal();
        return scope;
    }

    private void exposeProvidedInterfaces(ComponentGraph aGraph, Scope aExternalScope,
            Scope aInternalScope) {
        for (Pair<ProvidedInterface,ProvidedInterface> mapping: 
            aGraph.findExternalProvidedInterfaceMapping()) { 
            Object svc = aInternalScope.getInterfaceImplementation(mapping.getSecond(), Object.class);
            addInterface(mapping.getFirst(), svc, aExternalScope);
        }
    }

    private ComponentGraph doStartOptionalDryRun(Scope aScope, boolean aDryRun) {
        ComponentGraph graph = createComponentGraph();
        graph.validate();
        if (!aDryRun) {
            graph.link();
        }

        LOG.info("Starting '" + getQualifiedName() + "'");

        List<Component> started = new ArrayList<Component>();
        for (Component component : _components) {
            try {
                // Start the service.
                if (!aDryRun) {
                    Object runtime = component.start(aScope);
                    aScope.addRuntime(component, runtime);
                    started.add(component);
                }
            } catch (SystemAssemblyException e) {
                throw e;
            } catch (RuntimeException e) {
                LOG.error(getQualifiedName() + ": could not start '"
                        + component.getQualifiedName() + "'", e);
                stopAlreadyStartedComponents(started, aScope);
                throw e;
            }
        }
        return graph;
    }

    private ComponentGraph createComponentGraph() {
        ComponentGraph graph = new ComponentGraph();
        for (RequiredInterface req : getRequiredInterfaces()) {
            graph.addRequiredInterface(this, req);
        }
        for (Component comp : _components) {
            graph.addComponent(comp);
        }
        for (ProvidedInterface prov: getProvidedInterfaces()) { 
            graph.addProvidedInterface(this, prov);
        }

        graph.addRestriction(_restriction);
        return graph;
    }

    private void stopAlreadyStartedComponents(List<Component> aStarted,
            Scope aScope) {
        // an exception occurred, stop the successfully started
        // components
        for (int i = aStarted.size() - 1; i >= 0; i--) {
            try {
                Component component = aStarted.get(i);
                aStarted.get(i).stop(aScope.getRuntime(component));
            } catch (Throwable t) {
                LOG.error(getQualifiedName() + ": error stopping "
                        + aStarted.get(i).getQualifiedName());
            }
        }
    }

    @Override
    protected void doStop(Scope aScope) {
        for (int i = _components.size() - 1; i >= 0; i--) {
            Component component = _components.get(i);
            Object runtime = aScope.getRuntime(component);
            component.stop(runtime);
        }
    }

    private void checkSealed() {
        if (_sealed) {
            throw new SystemAssemblyException("Container is sealed");
        }
    }
}