/*******************************************************************************
 * Copyright (c) 2007 Oracle Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Oracle - initial API and implementation
 *    
 ********************************************************************************/
package org.eclipse.jst.jsf.common.metadata.internal;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.eclipse.core.resources.IProject;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.jobs.Job;
import org.eclipse.jst.jsf.common.JSFCommonPlugin;
import org.eclipse.jst.jsf.common.metadata.Model;

/**
 * Singleton instance for each IProject used to manage all standard metdata models for that project.
 *
 * Manager is responsible for loading and caching MetaDataModels.  Models are keyed by URI.
 * 
 * The manager listens for project closing resource events so that the resources can be freed up.
 */
public final class MetaDataModelManager extends AbstractMetaDataModelManager {

	private static IMetaDataModelManager SHARED_INSTANCE;
	
	// used to lock all instance calls for getModel
	private static final Lock  GLOBAL_INSTANCE_LOCK = new ReentrantLock();
	private final ModelMap models; 
	
	
	/**
	 * @return instance that is project agnostic. 
	 */
	public synchronized static IMetaDataModelManager getSharedInstance(){
		if (SHARED_INSTANCE == null) {
			SHARED_INSTANCE = new MetaDataModelManager(null);
		}
		return SHARED_INSTANCE;
	}

	/**
	 * @param project
	 */
	MetaDataModelManager(final IProject project) {
//		this.project = project;
		models = new ModelMap();  
	}

    public Model getModel(
            final IMetaDataModelContext modelContext) 
    {
        boolean gotLock = false;
        try
        {
            final int maxTries = 6;
            int numTries = 0;
            final Job currentJob = Job.getJobManager().currentJob();
            while (numTries < maxTries &&
                    !(gotLock = GLOBAL_INSTANCE_LOCK.tryLock(5000, TimeUnit.MILLISECONDS)))
            {
                numTries++;
                if (currentJob != null)
                {
                    currentJob.yieldRule(null);
                }
            }

            if (!gotLock)
            {
                return null;
            }
            StandardModelFactory.debug(">START getModel: "+modelContext, StandardModelFactory.DEBUG_MD_GET); //$NON-NLS-1$

            MetaDataModel model = models.get(modelContext);
            if (model == null) {
                // long in = System.currentTimeMillis();
                model = loadMetadata(modelContext);
                //System.out.println("Time to load "+modelContext.getURI()+": "+
                // String.valueOf(System.currentTimeMillis() - in));
            } else if (model.needsRefresh()) {
                try {
                    model.reload();
                } catch (ModelNotSetException e) {
                    // simply load it - should not get here
                    model = loadMetadata(modelContext);
                }
            }
            
//            if (model != null && model.getRoot() != null)
//                ((Model) model.getRoot())
//                        .setCurrentModelContext(modelContext);

            StandardModelFactory.debug(">END getModel: "+modelContext, StandardModelFactory.DEBUG_MD_GET); //$NON-NLS-1$
            if (model != null && !model.isEmpty()){			
    			return (Model)model.getRoot();
    		}
    		return null;
        }
        catch (final InterruptedException e)
        {
            return null;
        }
        finally
        {
            if (gotLock)
            {
                GLOBAL_INSTANCE_LOCK.unlock();
            }
        }
    }

	private MetaDataModel loadMetadata(final IMetaDataModelContext context) {
//        if (!Thread.holdsLock(GLOBAL_INSTANCE_LOCK.)) {
//            JSFCommonPlugin
//                    .log(IStatus.ERROR,
//                            "Internal Error: loadMetadata must not be called if class lock not held"); //$NON-NLS-1$
//            return null;
//        }

        final IDomainLoadingStrategy strategy = DomainLoadingStrategyRegistry
                .getInstance().getLoadingStrategy(
                        context.getDomainId());
        ;
        if (strategy == null) {
            JSFCommonPlugin
                    .log(
                            IStatus.ERROR,
                            "Internal Error: Unable to locate metadata loading strategy for: " + context.toString()); //$NON-NLS-1$
            return null;
        }
        final MetaDataModel model = StandardModelFactory.getInstance().createModel(
                context, strategy);// new MetaDataModel(modelKey,
                                              // strategy);
        model.load();
        addModel(model);

        return model;
    }

    private void addModel(final MetaDataModel model) {
        if (model != null)
            models.put(model);
    }

    @Override
    public void dispose() {
    	super.dispose();
    	models.dispose();
    }

    @Override
    public void destroy() {
        // no persistent data to cleanup. just call dispose
        dispose();
    }

    /**
     * Map of models keyed by DOMAIN_ID:MODEL_ID from the context.   Project is not part of key.
     * 
     */
    private static class ModelMap 
    {
        final Map<String, MetaDataModel> map;
        private final AtomicBoolean _isDisposed = new AtomicBoolean(false);

        ModelMap() {
            map = new HashMap<String, MetaDataModel>();
        }

        /**
         * @param model
         *            adds model to the map using the given key descriptor
         */
        public void put(final MetaDataModel model) {
            assert !_isDisposed.get();
            final String key = calculateKey(model);
            synchronized (this) {
                map.put(key, model);
            }
        }

        /**
         * @param context
         * @return MetaDataModel for this context. May return null.
         */
        public MetaDataModel get(final IMetaDataModelContext context) {
            assert !_isDisposed.get();

            final String key = calculateKey(context);

            synchronized (this) 
            {
                return map.get(key);
            }
        }

        public void dispose() {
            if (_isDisposed.compareAndSet(false, true)) {
                synchronized(this)
                {
                    for (final Iterator<Map.Entry<String, MetaDataModel>> it = map.entrySet().iterator(); it.hasNext();) 
                    {
                        // System.out.println("kill mmModel: "+model.toString());
                        final Map.Entry<String, MetaDataModel> entry = it.next();
                        final MetaDataModel model = entry.getValue();

                        if (model != null)
                        {
                            model.cleanup();
                        }
                        it.remove();
                    }
                }
            }
        }

        private String calculateKey(final MetaDataModel model) {        	
            return calculateKey(model.getModelContext());
        }

        private String calculateKey(final IMetaDataModelContext context) {
        	final StringBuffer buf = new StringBuffer(context.getDomainId()).append(":").append(context.getModelIdentifier()); //$NON-NLS-1$; 
            return buf.toString();
        }
    }
}