/*
 * Copyright (C) 2005 Alfresco, Inc.
 *
 * Licensed under the Mozilla Public License version 1.1 
 * with a permitted attribution clause. You may obtain a
 * copy of the License at
 *
 *   http://www.alfresco.org/legal/license.txt
 *
 * 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.alfresco.repo.policy;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Queue;

import org.alfresco.error.AlfrescoRuntimeException;
import org.alfresco.repo.policy.Policy.Arg;
import org.alfresco.repo.rule.RuleTransactionListener;
import org.alfresco.repo.transaction.AlfrescoTransactionSupport;
import org.alfresco.repo.transaction.TransactionListener;
import org.alfresco.util.GUID;


/**
 * Transaction Behaviour Queue.
 * 
 * Responsible for keeping a record of behaviours to execute at the end of a transaction.
 */
public class TransactionBehaviourQueue implements TransactionListener
{
    /** Id used in equals and hash */
    private String id = GUID.generate();
    
    // Transaction Keys for Behaviour Execution state
    private static final String QUEUE_CONTEXT_KEY = TransactionBehaviourQueue.class.getName() + ".context";
    
    
    /**
     * Queue a behaviour for end-of-transaction execution
     *  
     * @param <P>
     * @param behaviour
     * @param definition
     * @param policyInterface
     * @param method
     * @param args
     */
    @SuppressWarnings("unchecked")
    public <P extends Policy> void queue(Behaviour behaviour, PolicyDefinition<P> definition, P policyInterface, Method method, Object[] args)
    {
        // Construct queue context, if required
        QueueContext queueContext = (QueueContext)AlfrescoTransactionSupport.getResource(QUEUE_CONTEXT_KEY);
        if (queueContext == null)
        {
            queueContext = new QueueContext();
            AlfrescoTransactionSupport.bindResource(QUEUE_CONTEXT_KEY, queueContext);
            AlfrescoTransactionSupport.bindListener(this);
        }
        
        // Determine if behaviour instance has already been queued
        Integer instanceKey = createInstanceKey(behaviour, definition.getArguments(), args);
        ExecutionContext executionContext = queueContext.index.get(instanceKey);
        if (executionContext == null)
        {
            // Create execution context for behaviour
            executionContext = new ExecutionContext<P>();
            executionContext.method = method;
            executionContext.args = args;
            executionContext.policyInterface = policyInterface;

            // Defer or execute now?
            if (!queueContext.committed)
            {
                // queue behaviour for deferred execution
                queueContext.queue.offer(executionContext);
            }
            else
            {
                // execute now
                execute(executionContext);
            }
            queueContext.index.put(instanceKey, executionContext);
        }
        else
        {
            // Update behaviour instance execution context, in particular, argument state that is marked END_TRANSACTION
            Arg[] argDefs = definition.getArguments();
            for (int i = 0; i < argDefs.length; i++)
            {
                if (argDefs[i].equals(Arg.END_VALUE))
                {
                    executionContext.args[i] = args[i];
                }
            }
        }
    }
    

    /* (non-Javadoc)
     * @see org.alfresco.repo.transaction.TransactionListener#flush()
     */
    public void flush()
    {
    }

    /* (non-Javadoc)
     * @see org.alfresco.repo.transaction.TransactionListener#beforeCommit(boolean)
     */
    @SuppressWarnings("unchecked")
    public void beforeCommit(boolean readOnly)
    {
        QueueContext queueContext = (QueueContext)AlfrescoTransactionSupport.getResource(QUEUE_CONTEXT_KEY);
        ExecutionContext context = queueContext.queue.poll();
        while (context != null)
        {
            execute(context);
            context = queueContext.queue.poll();
        }
        queueContext.committed = true;
    }

    /* (non-Javadoc)
     * @see org.alfresco.repo.transaction.TransactionListener#beforeCompletion()
     */
    public void beforeCompletion()
    {
    }

    /* (non-Javadoc)
     * @see org.alfresco.repo.transaction.TransactionListener#afterCommit()
     */
    public void afterCommit()
    {
    }

    /* (non-Javadoc)
     * @see org.alfresco.repo.transaction.TransactionListener#afterRollback()
     */
    public void afterRollback()
    {
    }

    /**
     * Create an instance key for the behaviour based on the "key" arguments passed in
     * 
     * @param argDefs  definitions of behaviour arguments
     * @param args  the argument values
     * @return  the key
     */
    private Integer createInstanceKey(Behaviour behaviour, Arg[] argDefs, Object[] args)
    {
        int key = behaviour.hashCode();
        for (int i = 0; i < argDefs.length; i++)
        {
            if (argDefs[i].equals(Arg.KEY))
            {
                key = (37 * key) + args[i].hashCode();
            }
        }
        return new Integer(key);
    }

    /**
     * Execute behaviour as described in execution context
     * 
     * @param context
     */
    private void execute(ExecutionContext context)
    {
        try
        {
            context.method.invoke(context.policyInterface, context.args);
        }
        catch (IllegalArgumentException e)
        {
            throw new AlfrescoRuntimeException("Failed to execute transaction-level behaviour " + context.method + " in transaction " + AlfrescoTransactionSupport.getTransactionId(), e);
        }
        catch (IllegalAccessException e)
        {
            throw new AlfrescoRuntimeException("Failed to execute transaction-level behaviour " + context.method + " in transaction " + AlfrescoTransactionSupport.getTransactionId(), e);
        }
        catch (InvocationTargetException e)
        {
            throw new AlfrescoRuntimeException("Failed to execute transaction-level behaviour " + context.method + " in transaction " + AlfrescoTransactionSupport.getTransactionId(), e.getTargetException());
        }
    }
    
    /**
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode()
    {
        return this.id.hashCode();
    }
    
    /**
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @Override
    public boolean equals(Object obj)
    {
        if (this == obj)
        {
            return true;
        }
        if (obj instanceof RuleTransactionListener)
        {
            TransactionBehaviourQueue that = (TransactionBehaviourQueue) obj;
            return (this.id.equals(that.id));
        }
        else
        {
            return false;
        }
    }
    
    /**
     * Behaviour execution Context
     * 
     * @param <P>
     */
    private class ExecutionContext<P extends Policy>
    {
        Method method;
        Object[] args;
        P policyInterface;
    }

    
    /**
     * Queue Context
     */
    private class QueueContext
    {
        // TODO: Tune sizes
        Queue<ExecutionContext> queue = new LinkedList<ExecutionContext>();
        Map<Integer, ExecutionContext> index = new HashMap<Integer, ExecutionContext>();
        boolean committed = false;
    }
        
}