/*

* Copyright (c) 2009 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of the License "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description: 

*

*/

/**

 * 

 */

package com.nokia.sdt.component;

import com.nokia.sdt.uimodel.Messages;

import com.nokia.sdt.uimodel.UIModelPlugin;

import com.nokia.cpp.internal.api.utils.core.Check;

import com.nokia.cpp.internal.api.utils.core.Logging;

import org.eclipse.core.runtime.*;

import java.text.MessageFormat;

import java.util.HashMap;

import java.util.Map;

/**

 * The interface for the component system.

 * 

 * This maintains a collection of component providers. Each provider

 * represents a specific implementation of components and

 * can provide a unique set of IComponent instances.

 * 

 * @see IComponent

 * 

 * 

 */

public class ComponentSystem {

		/**

		 * Name of the component provider extension point

		 */

	public static final String PROVIDER_EXTENSION = "componentProvider"; //$NON-NLS-1$

	static private ComponentSystem instance;

        /**

         * Map of String -> IComponentProvider

         */

	private Map providers = new HashMap();

		/**

		 * Returns the singleton instance of the component system

		 */

	static public ComponentSystem getComponentSystem() {

		if (instance == null) {

			instance = new ComponentSystem();

		}

		return instance;

	}

	private ComponentSystem() {

	}

	/**

	 * Returns the requested component provider implementation, if loaded.

	 * @param id a string representing the provider

	 * @return provider or null if not yet loaded

	 * @throws CoreException

	 */

	public synchronized IComponentProvider findProvider(String id) throws CoreException {

		return (IComponentProvider) providers.get(id);

	}

	/**

	 * Returns the requested component provider implementation,

	 * loading its extension if necessary.

	 * @param id a string representing the provider

	 * @return provider or null if not found

	 * @throws CoreException

	 */

	public synchronized IComponentProvider getProvider(String id) throws CoreException {

			// check if already loaded this provider

		IComponentProvider result = (IComponentProvider) providers.get(id);

		if (result == null) {

	        result = loadExtensions(id);

	        providers.put(id, result);

		}

		return result;

	}

    /**

     * Set the component provider

     * <p>

     * For testing to set a provider without requiring a running workbench.

     * @param id a string representing the provider

     * @param provider the provider instance (must not be null)

     */

    public synchronized void setProvider(String id, IComponentProvider provider) {

        Check.checkArg(id);

        Check.checkArg(provider);

        providers.put(id, provider);

    }

    private IComponentProvider loadExtensions(String id) throws CoreException {

        IComponentProvider result = null;

        // Get implementors of the componentProvider extension point

        IExtensionRegistry er = Platform.getExtensionRegistry();

        if (er == null)

            return null;

        IExtensionPoint ep = er.getExtensionPoint(

                UIModelPlugin.PLUGIN_ID, PROVIDER_EXTENSION);

        IExtension matched = null;

        // Iterate over all providers looking for the requested one

        IExtension[] extensions = ep.getExtensions();

        for (int i = 0; i < extensions.length; i++) {

			IExtension extension = extensions[i];

			IConfigurationElement[] ces = extension.getConfigurationElements();

			if (ces != null && ces.length >= 1) {

				IConfigurationElement providerElement = ces[0];

				String name = providerElement.getAttribute("name"); //$NON-NLS-1$

				if (name != null && name.equals(id)) {

					if (providerElement.getAttribute("class") != null) { //$NON-NLS-1$

                        if (result != null) {

                            Logging.log(UIModelPlugin.getDefault(), 

                                    Logging.newStatus(UIModelPlugin.getDefault(),

                                            IStatus.ERROR,

                                            MessageFormat.format(Messages.getString("ComponentSystem.1"),

                                                    new Object[] { id, extension.getUniqueIdentifier(), matched.getUniqueIdentifier() })

                                            ));

                        } else {

                            result = (IComponentProvider) providerElement.createExecutableExtension("class"); //$NON-NLS-1$

                            matched = extension;

                        }

					}

				}

			}

        }

        return result;

    }

}