/**
    * Copyright 2005-2014 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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.kuali.rice.krad.uif.lifecycle;
  
  import java.util.Deque;
  import java.util.IdentityHashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.Queue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.LinkedBlockingDeque;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.log4j.Logger;
  import org.kuali.rice.core.api.config.property.ConfigContext;
  import org.kuali.rice.core.api.exception.RiceRuntimeException;
  import org.kuali.rice.krad.service.KRADServiceLocatorWeb;
  import org.kuali.rice.krad.uif.freemarker.LifecycleRenderingContext;
  import org.kuali.rice.krad.uif.service.ViewHelperService;
  import org.kuali.rice.krad.uif.util.LifecycleElement;
  import org.kuali.rice.krad.uif.util.ProcessLogger;
  import org.kuali.rice.krad.uif.util.RecycleUtils;
  import org.kuali.rice.krad.uif.view.DefaultExpressionEvaluator;
  import org.kuali.rice.krad.uif.view.ExpressionEvaluator;
  import org.kuali.rice.krad.uif.view.ExpressionEvaluatorFactory;
  import org.kuali.rice.krad.util.GlobalVariables;
  import org.kuali.rice.krad.util.KRADConstants;
  
  /**
   * Static utility class for handling executor configuration and spreading {@link ViewLifecycle}
   * across multiple threads.
   * 
   * @author Kuali Rice Team (rice.collab@kuali.org)
   */
  public final class AsynchronousViewLifecycleProcessor extends ViewLifecycleProcessorBase {
  
      private static final Logger LOG = Logger.getLogger(AsynchronousViewLifecycleProcessor.class);
  
      private static final ThreadFactory LIFECYCLE_THREAD_FACTORY = new LifecycleThreadFactory();
  
      private static final ThreadPoolExecutor LIFECYCLE_EXECUTOR = new ThreadPoolExecutor(
              getMinThreads(), getMaxThreads(), getTimeout(), TimeUnit.MILLISECONDS,
              new LinkedBlockingDeque<Runnable>(), LIFECYCLE_THREAD_FACTORY);
  
      private static final Deque<AsynchronousLifecyclePhase> PENDING_PHASE_QUEUE =
              new LinkedList<AsynchronousLifecyclePhase>();
  
      private static final ThreadLocal<AsynchronousLifecyclePhase> ACTIVE_PHASE =
              new ThreadLocal<AsynchronousLifecyclePhase>();
      
      private static final Map<LifecycleElement, AsynchronousLifecyclePhase> BUSY_ELEMENTS =
              new IdentityHashMap<LifecycleElement, AsynchronousLifecyclePhase>();
  
      private static Integer minThreads;
      private static Integer maxThreads;
      private static Long timeout;
  
      private final Queue<LifecycleRenderingContext> renderingContextPool =
              ViewLifecycle.isRenderInLifecycle() ? new ConcurrentLinkedQueue<LifecycleRenderingContext>() : null;
      private final Queue<ExpressionEvaluator> expressionEvaluatorPool =
              new ConcurrentLinkedQueue<ExpressionEvaluator>();
  
      private Throwable error;
  
      /**
       * Gets the minimum number of lifecycle worker threads to maintain.
       * 
       * <p>
       * This value is controlled by the configuration parameter
       * &quot;krad.uif.lifecycle.asynchronous.minThreads&quot;.
       * </p>
       * 
       * @return minimum number of worker threads to maintain
       */
      public static int getMinThreads() {
          if (minThreads == null) {
              String propStr = ConfigContext.getCurrentContextConfig().getProperty(
                      KRADConstants.ConfigParameters.KRAD_VIEW_LIFECYCLE_MINTHREADS);
              minThreads = propStr == null ? 4 : Integer.parseInt(propStr);
          }
  
          return minThreads;
     }
 
     /**
      * Gets the maximum number of lifecycle worker threads to maintain.
      * 
      * <p>
      * This value is controlled by the configuration parameter
      * &quot;krad.uif.lifecycle.asynchronous.maxThreads&quot;.
      * </p>
      * 
      * @return maximum number of worker threads to maintain
      */
     public static int getMaxThreads() {
         if (maxThreads == null) {
             String propStr = ConfigContext.getCurrentContextConfig().getProperty(
                     KRADConstants.ConfigParameters.KRAD_VIEW_LIFECYCLE_MAXTHREADS);
             maxThreads = propStr == null ? 48 : Integer.parseInt(propStr);
         }
 
         return maxThreads;
     }
 
     /**
      * Gets the time, in milliseconds, to wait for a initial phase to process.
      * 
      * <p>
      * This value is controlled by the configuration parameter
      * &quot;krad.uif.lifecycle.asynchronous.timeout&quot;.
      * </p>
      * 
      * @return time in milliseconds to wait for the initial phase to process
      */
     public static long getTimeout() {
         if (timeout == null) {
             String propStr = ConfigContext.getCurrentContextConfig().getProperty(
                     KRADConstants.ConfigParameters.KRAD_VIEW_LIFECYCLE_TIMEOUT);
             timeout = propStr == null ? 30000 : Long.parseLong(propStr);
         }
 
         return timeout;
     }
 
     /**
      * Constructor.
      * 
      * @param lifecycle The lifecycle to process.
      */
     AsynchronousViewLifecycleProcessor(ViewLifecycle lifecycle) {
         super(lifecycle);
     }
 
     /**
      * Thread factory for lifecycle processing.
      * 
      * @author Kuali Rice Team (rice.collab@kuali.org)
      */
     private static class LifecycleThreadFactory implements ThreadFactory {
 
         private static final ThreadGroup GROUP = new ThreadGroup("krad-lifecycle-group");
 
         private int sequenceNumber = 0;
 
         @Override
         public Thread newThread(Runnable r) {
             return new Thread(GROUP, r, "krad-lifecycle("
                     + Integer.toString(++sequenceNumber) + ")");
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public ViewLifecyclePhase getActivePhase() {
         AsynchronousLifecyclePhase aphase = ACTIVE_PHASE.get();
 
         if (aphase == null) {
             throw new IllegalStateException("No phase worker is active on this thread");
         }
 
         ViewLifecyclePhase phase = aphase.phase;
         if (phase == null) {
             throw new IllegalStateException("No lifecycle phase is active on this thread");
         }
 
         return phase;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     void setActivePhase(ViewLifecyclePhase phase) {
         AsynchronousLifecyclePhase aphase = ACTIVE_PHASE.get();
 
         if (aphase == null) {
             throw new IllegalStateException("No phase worker is active on this thread");
         }
         
         if (phase == null) {
             // Ignore null setting, asychronous state is controlled by aphase.
             return;
         }
 
         if (aphase.phase != phase) {
             throw new IllegalStateException(
                     "Another lifecycle phase is already active on this thread "
                             + aphase.phase + ", setting " + phase);
         }
 
         aphase.phase = phase;
     };
 
     /**
      * {@inheritDoc}
      */
     @Override
     public LifecycleRenderingContext getRenderingContext() {
         if (!ViewLifecycle.isRenderInLifecycle()) {
             return null;
         }
 
         AsynchronousLifecyclePhase aphase = ACTIVE_PHASE.get();
 
         if (aphase == null) {
             throw new IllegalStateException("No phase worker is active on this thread");
         }
 
         // If a rendering context has already been assigned to this phase, return it.
         LifecycleRenderingContext renderContext = aphase.renderingContext;
         if (renderContext != null) {
             return renderContext;
         }
 
         // Get a reusable rendering context from a pool private to the current lifecycle. 
         renderContext = renderingContextPool.poll();
         if (renderContext == null) {
             // Create a new rendering context if a pooled instance is not available.
             ViewLifecycle lifecycle = getLifecycle();
             renderContext = new LifecycleRenderingContext(
                     lifecycle.model, lifecycle.request, lifecycle.response);
         }
 
         // Ensure that all view templates have been imported on the new/reused context
         List<String> viewTemplates = ViewLifecycle.getView().getViewTemplates();
         synchronized (viewTemplates) {
             for (String viewTemplate : viewTemplates) {
                 renderContext.importTemplate(viewTemplate);
             }
         }
 
         // Assign the rendering context to the current thread.
         aphase.renderingContext = renderContext;
         return renderContext;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public ExpressionEvaluator getExpressionEvaluator() {
         AsynchronousLifecyclePhase aphase = ACTIVE_PHASE.get();
 
         // If a rendering context has already been assigned to this phase, return it.
         ExpressionEvaluator expressionEvaluator = aphase == null ? null : aphase.expressionEvaluator;
         if (expressionEvaluator != null) {
             return expressionEvaluator;
         }
 
         // Get a reusable expression evaluator from a pool private to the current lifecycle. 
         expressionEvaluator = expressionEvaluatorPool.poll();
         if (expressionEvaluator == null) {
             // Create a new expression evaluator if a pooled instance is not available.
             ExpressionEvaluatorFactory expressionEvaluatorFactory;
             ViewHelperService helper = ViewLifecycle.getHelper();
             if (helper != null) {
                 expressionEvaluatorFactory = helper.getExpressionEvaluatorFactory();
             } else {
                 expressionEvaluatorFactory = KRADServiceLocatorWeb.getExpressionEvaluatorFactory();
             }
 
             if (expressionEvaluatorFactory == null) {
                 expressionEvaluator = new DefaultExpressionEvaluator();
             } else {
                 expressionEvaluator = expressionEvaluatorFactory.createExpressionEvaluator();
             }
 
             if (ViewLifecycle.isActive()) {
                 try {
                     expressionEvaluator.initializeEvaluationContext(ViewLifecycle.getModel());
                 } catch (IllegalStateException e) {
                     // Model is unavailable - may happen in unit test environments
                     LOG.warn("Model is not available", e);
                 }
             }
         }
 
         // Assign the rendering context to the current thread.
         if (aphase != null) {
             aphase.expressionEvaluator = expressionEvaluator;
         }
         
         return expressionEvaluator;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void pushPendingPhase(ViewLifecyclePhase phase) {
         AsynchronousLifecyclePhase aphase = getAsynchronousPhase(phase);
         if (phase.getStartViewStatus().equals(phase.getElement().getViewStatus())) {
             synchronized (BUSY_ELEMENTS) {
                 BUSY_ELEMENTS.put(phase.getElement(), aphase);
             }
         }
 
         synchronized (PENDING_PHASE_QUEUE) {
             PENDING_PHASE_QUEUE.push(aphase);
             PENDING_PHASE_QUEUE.notify();
         }
 
         spawnWorkers();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void offerPendingPhase(ViewLifecyclePhase phase) {
         AsynchronousLifecyclePhase aphase = getAsynchronousPhase(phase);
         if (phase.getStartViewStatus().equals(phase.getElement().getViewStatus())) {
             synchronized (BUSY_ELEMENTS) {
                 BUSY_ELEMENTS.put(phase.getElement(), aphase);
             }
         }
 
         synchronized (PENDING_PHASE_QUEUE) {
             PENDING_PHASE_QUEUE.offer(aphase);
             PENDING_PHASE_QUEUE.notify();
         }
 
         spawnWorkers();
     }
 
     /**
      * {@inheritDoc}
      * <p>This method should only be called a single time by the controlling thread in order to wait
      * for all pending phases to be performed, and should not be called by any worker threads.</p>
      */
     @Override
     public void performPhase(ViewLifecyclePhase initialPhase) {
         if (error != null) {
             throw new RiceRuntimeException("Error performing view lifecycle", error);
         }
 
         long now = System.currentTimeMillis();
         try {
             AsynchronousLifecyclePhase aphase = getAsynchronousPhase(initialPhase);
             aphase.initial = true;
 
             synchronized (PENDING_PHASE_QUEUE) {
                 PENDING_PHASE_QUEUE.offer(aphase);
                 PENDING_PHASE_QUEUE.notify();
             }
 
             spawnWorkers();
 
             while (System.currentTimeMillis() - now < getTimeout() &&
                     error == null && !initialPhase.isComplete()) {
                 synchronized (initialPhase) {
                     // Double-check lock
                     if (!initialPhase.isComplete()) {
                         LOG.info("Waiting for view lifecycle " + initialPhase);
                         initialPhase.wait(Math.min(5000L, getTimeout()));
                     }
                 }
             }
 
             if (error != null) {
                 throw new IllegalStateException("Error in lifecycle", error);
             }
 
             if (!initialPhase.isComplete()) {
                 error = new IllegalStateException("Time out waiting for lifecycle");
                 throw (IllegalStateException) error; 
             }
 
         } catch (InterruptedException e) {
             throw new IllegalStateException("Interrupted waiting for view lifecycle", e);
         }
     }
 
     /**
      * Gets a new context wrapper for processing a lifecycle phase using the same lifecycle and
      * thread context as the current thread.
      * 
      * @param phase The lifecycle phase.
      * @return context wrapper for processing the phase
      */
     private AsynchronousLifecyclePhase getAsynchronousPhase(ViewLifecyclePhase phase) {
         AsynchronousLifecyclePhase rv = RecycleUtils.getRecycledInstance(AsynchronousLifecyclePhase.class);
         if (rv == null) {
             rv = new AsynchronousLifecyclePhase();
         }
 
         rv.processor = this;
         rv.globalVariables = GlobalVariables.getCurrentGlobalVariables();
         rv.phase = phase;
 
         return rv;
     }
 
     /**
      * Recycles a phase context after processing.
      * 
      * @param aphase phase context previously acquired using
      *        {@link #getAsynchronousPhase(ViewLifecyclePhase)}
      */
     private static void recyclePhase(AsynchronousLifecyclePhase aphase) {
         if (aphase.initial) {
             return;
         }
 
         assert aphase.renderingContext == null;
         aphase.processor = null;
         aphase.phase = null;
         aphase.globalVariables = null;
         aphase.expressionEvaluator = null;
         RecycleUtils.recycle(aphase);
     }
 
     /**
      * Spawns new worker threads if needed.
      */
     private static void spawnWorkers() {
         int active = LIFECYCLE_EXECUTOR.getActiveCount();
         if (active < LIFECYCLE_EXECUTOR.getCorePoolSize() ||
                 (active * 16 < PENDING_PHASE_QUEUE.size() &&
                 active < LIFECYCLE_EXECUTOR.getMaximumPoolSize())) {
             LIFECYCLE_EXECUTOR.submit(new AsynchronousLifecycleWorker());
         }
     }
 
     /**
      * Private context wrapper for forwarding lifecycle state to worker threads.
      * 
      * @author Kuali Rice Team (rice.collab@kuali.org)
      */
     private static class AsynchronousLifecyclePhase {
         private boolean initial;
         private GlobalVariables globalVariables;
         private AsynchronousViewLifecycleProcessor processor;
         private ViewLifecyclePhase phase;
         private LifecycleRenderingContext renderingContext;
         private ExpressionEvaluator expressionEvaluator;
     }
 
     /**
      * Encapsulates lifecycle phase worker activity.
      * 
      * @author Kuali Rice Team (rice.collab@kuali.org)
      */
     private static class PhaseWorkerCall implements Callable<Void> {
 
         @Override
         public Void call() throws Exception {
             while (!PENDING_PHASE_QUEUE.isEmpty()) {
                 AsynchronousLifecyclePhase aphase;
                 synchronized (PENDING_PHASE_QUEUE) {
                     aphase = PENDING_PHASE_QUEUE.poll();
                 }
                 
                 if (aphase == null) {
                     continue;
                 }
 
                 AsynchronousViewLifecycleProcessor processor = aphase.processor;
                 ViewLifecyclePhase phase = aphase.phase;
 
                 if (processor.error != null) {
                     synchronized (phase) {
                         phase.notifyAll();
                     }
 
                     continue;
                 }
 
                 LifecycleElement element = phase.getElement();
                 AsynchronousLifecyclePhase busyPhase = BUSY_ELEMENTS.get(element);
                 if (busyPhase != null && busyPhase != aphase) {
                     // Another phase is already active on this component, requeue
                     synchronized (PENDING_PHASE_QUEUE) {
                         PENDING_PHASE_QUEUE.offer(aphase);
                     }
                     
                     continue;
                 }
 
                 try {
                     assert ACTIVE_PHASE.get() == null;
                     ACTIVE_PHASE.set(aphase);
                     ViewLifecycle.setProcessor(aphase.processor);
                     GlobalVariables.injectGlobalVariables(aphase.globalVariables);
 
                     phase.run();
 
                 } catch (Throwable t) {
                     processor.error = t;
 
                     ViewLifecyclePhase topPhase = phase;
                     while (topPhase.getPredecessor() != null) {
                         topPhase = topPhase.getPredecessor();
                     }
                     
                     synchronized (topPhase) {
                         topPhase.notifyAll();
                     }
                 } finally {
                     ACTIVE_PHASE.remove();
                     LifecycleRenderingContext renderingContext = aphase.renderingContext;
                     aphase.renderingContext = null;
                     if (renderingContext != null && aphase.processor != null) {
                         aphase.processor.renderingContextPool.offer(renderingContext);
                     }
 
                     ExpressionEvaluator expressionEvaluator = aphase.expressionEvaluator;
                     aphase.expressionEvaluator = null;
                     if (expressionEvaluator != null && aphase.processor != null) {
                         aphase.processor.expressionEvaluatorPool.offer(expressionEvaluator);
                     }
 
                     synchronized (BUSY_ELEMENTS) {
                         BUSY_ELEMENTS.remove(element);
                     }
                     GlobalVariables.popGlobalVariables();
                     ViewLifecycle.setProcessor(null);
                 }
 
                 recyclePhase(aphase);
             }
             return null;
         }
 
     }
 
     /**
      * Worker process to submit to the executor. Wraps {@link PhaseWorkerCall} in a process logger
      * for tracing activity.
      * 
      * @author Kuali Rice Team (rice.collab@kuali.org)
      */
     private static class AsynchronousLifecycleWorker implements Runnable {
 
         @Override
         public void run() {
             try {
                 PhaseWorkerCall call = new PhaseWorkerCall();
                 do {
                     if (PENDING_PHASE_QUEUE.isEmpty()) {
                         synchronized (PENDING_PHASE_QUEUE) {
                             PENDING_PHASE_QUEUE.wait(15000L);
                         }
                     } else if (ViewLifecycle.isTrace()) {
                         ProcessLogger.follow(
                                 "view-lifecycle", "KRAD lifecycle worker", call);
                     } else {
                         call.call();
                     }
                 } while (LIFECYCLE_EXECUTOR.getActiveCount() <= getMinThreads());
             } catch (Throwable t) {
                 LOG.fatal("Fatal error in View Lifecycle worker", t);
             }
         }
 
     }
 
 }