/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.juneau.rest.stats;

import java.lang.reflect.*;
import java.util.*;
import java.util.concurrent.atomic.*;

import org.apache.juneau.*;
import org.apache.juneau.cp.*;
import org.apache.juneau.internal.*;
import org.apache.juneau.marshaller.*;

/**
 * Method execution statistics.
 *
 * Keeps track of number of starts/finishes on tasks and keeps an average run time.
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/ExecutionStatistics">REST method execution statistics</a>
 * </ul>
 */
public class MethodExecStats {

   //-----------------------------------------------------------------------------------------------------------------
   // Static
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Static creator.
    *
    * @param beanStore The bean store to use for creating beans.
    * @return A new builder for this object.
    */
   public static Builder create(BeanStore beanStore) {
      return new Builder(beanStore);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Builder
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Builder class.
    */
   public static class Builder extends BeanBuilder<MethodExecStats> {

      Method method;
      ThrownStore thrownStore;

      /**
       * Constructor.
       *
       * @param beanStore The bean store to use for creating beans.
       */
      protected Builder(BeanStore beanStore) {
         super(MethodExecStats.class, beanStore);
      }

      @Override /* BeanBuilder */
      protected MethodExecStats buildDefault() {
         return new MethodExecStats(this);
      }

      //-------------------------------------------------------------------------------------------------------------
      // Properties
      //-------------------------------------------------------------------------------------------------------------

      /**
       * Specifies the Java method.
       *
       * @param value The new value for this setting.
       * @return This object.
       */
      public Builder method(Method value) {
         method = value;
         return this;
      }

      /**
       * Specifies the thrown store for tracking exceptions.
       *
       * @param value The new value for this setting.
       * @return This object.
       */
      public Builder thrownStore(ThrownStore value) {
         thrownStore = value;
         return this;
      }
      @Override /* Overridden from BeanBuilder */
      public Builder impl(Object value) {
         super.impl(value);
         return this;
      }

      @Override /* Overridden from BeanBuilder */
      public Builder type(Class<?> value) {
         super.type(value);
         return this;
      }
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Instance
   //-----------------------------------------------------------------------------------------------------------------

   private final long guid;
   private final Method method;
   private final ThrownStore thrownStore;

   private volatile int minTime = -1, maxTime;

   private AtomicInteger
      starts = new AtomicInteger(),
      finishes = new AtomicInteger(),
      errors = new AtomicInteger();

   private AtomicLong
      totalTime = new AtomicLong();

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   protected MethodExecStats(Builder builder) {
      this.guid = new Random().nextLong();
      this.method = builder.method;
      this.thrownStore = builder.thrownStore != null ? builder.thrownStore : new ThrownStore();
   }


   /**
    * Call when task is started.
    *
    * @return This object.
    */
   public MethodExecStats started() {
      starts.incrementAndGet();
      return this;
   }

   /**
    * Call when task is finished.
    *
    * @param nanoTime The execution time of the task in nanoseconds.
    * @return This object.
    */
   public MethodExecStats finished(long nanoTime) {
      finishes.incrementAndGet();
      int milliTime = (int)(nanoTime/1_000_000);
      totalTime.addAndGet(nanoTime);
      minTime = minTime == -1 ? milliTime : Math.min(minTime, milliTime);
      maxTime = Math.max(maxTime, milliTime);
      return this;
   }

   /**
    * Call when an error occurs.
    *
    * @param e The exception thrown.  Can be <jk>null</jk>.
    * @return This object.
    */
   public MethodExecStats error(Throwable e) {
      errors.incrementAndGet();
      thrownStore.add(e);
      return this;
   }

   /**
    * Returns a globally unique ID for this object.
    *
    * <p>
    * A random long generated during the creation of this object.
    * Allows this object to be differentiated from other similar objects in multi-node environments so that
    * statistics can be reliably stored in a centralized location.
    *
    * @return The globally unique ID for this object.
    */
   public long getGuid() {
      return guid;
   }

   /**
    * Returns the method name of these stats.
    *
    * @return The method name of these stats.
    */
   public Method getMethod() {
      return method;
   }

   /**
    * Returns the number of times the {@link #started()} method was called.
    *
    * @return The number of times the {@link #started()} method was called.
    */
   public int getRuns() {
      return starts.get();
   }

   /**
    * Returns the number currently running method invocations.
    *
    * @return The number of currently running method invocations.
    */
   public int getRunning() {
      return starts.get() - finishes.get();
   }

   /**
    * Returns the number of times the {@link #error(Throwable)} method was called.
    *
    * @return The number of times the {@link #error(Throwable)} method was called.
    */
   public int getErrors() {
      return errors.get();
   }

   /**
    * Returns the max execution time.
    *
    * @return The average execution time in milliseconds.
    */
   public int getMinTime() {
      return minTime == -1 ? 0 : minTime;
   }

   /**
    * Returns the max execution time.
    *
    * @return The average execution time in milliseconds.
    */
   public int getMaxTime() {
      return maxTime;
   }

   /**
    * Returns the average execution time.
    *
    * @return The average execution time in milliseconds.
    */
   public int getAvgTime() {
      int runs = finishes.get();
      return runs == 0 ? 0 : (int)(getTotalTime() / runs);
   }

   /**
    * Returns the total execution time.
    *
    * @return The total execution time in milliseconds.
    */
   public long getTotalTime() {
      return totalTime.get() / 1_000_000;
   }

   /**
    * Returns information on all stack traces of all exceptions encountered.
    *
    * @return Information on all stack traces of all exceptions encountered.
    */
   public ThrownStore getThrownStore() {
      return thrownStore;
   }

   @Override /* Object */
   public String toString() {
      return Json5.of(this);
   }
}