/*
 * 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.
 */
using System;
using System.Threading;
using Apache.NMS.Util;

namespace Apache.NMS.ActiveMQ.Util
{
    /// <summary>
    /// Utility class for Tracking Memory Usage with an imposed limit on the amount
    /// available.  Provides methods for objects to wait on more space to become
    /// available if the memory limit is reached.
    /// </summary>
    public class MemoryUsage
    {
        private readonly Atomic<bool> stopped = new Atomic<bool>(false);
        private long limit = 0;
        private long usage = 0;
        private readonly object mutex = new object();

        public MemoryUsage()
        {
        }

        public MemoryUsage( long limit )
        {
            this.limit = limit;
        }

        #region Property Accessors

        public long Limit
        {
            get { return limit; }
            set { limit = value; }
        }

        public long Usage
        {
            get { return usage; }
            set { usage = value; }
        }

        #endregion

        /// <summary>
        /// If no space is available then this method blocks until more becomes available.
        /// </summary>
        public void WaitForSpace()
        {
            TimeSpan indefiniteWait = TimeSpan.FromMilliseconds(Timeout.Infinite);
            this.WaitForSpace(indefiniteWait);
        }

        /// <summary>
        /// If no space is available then this method blocks until more becomes available
        /// or until the specified timeout expires.
        /// </summary>
        /// <param name="timeout">
        /// A <see cref="System.TimeSpan"/>
        /// </param>
        public void WaitForSpace( TimeSpan timeout )
        {
            lock(this.mutex)
            {
                while(this.IsFull() && !stopped.Value)
                {
					Tracer.Debug("MemoryUsage: Memory Limit Reached, waiting for more space.");
					
                    if(!Monitor.Wait(this.mutex, timeout))
                    {
                        return;
                    }
                }
            }
        }

        /// <summary>
        /// Attempts to increase the amount of Memory Used, if non is available to fill
        /// then this method blocks until more is freed.
        /// </summary>
        /// <param name="usage">
        /// A <see cref="System.Int64"/>
        /// </param>
        public void EnqueueUsage( long usage )
        {
            this.WaitForSpace();
            this.IncreaseUsage(usage);
        }

        /// <summary>
        /// Increase the level of Usage.
        /// </summary>
        /// <param name="value">
        /// A <see cref="System.Int64"/>
        /// </param>
        public void IncreaseUsage( long value )
        {
            if(value == 0)
            {
                return;
            }

            lock(this.mutex)
            {
                this.Usage += value;
				
				if(Tracer.IsDebugEnabled)
				{
					Tracer.DebugFormat("MemoryUsage: Increase Usage to: {0} bytes.", this.usage);
				}				
            }
        }

        /// <summary>
        /// Decrease the level of Usage.
        /// </summary>
        /// <param name="value">
        /// A <see cref="System.Int64"/>
        /// </param>
        public void DecreaseUsage(long value)
        {
            if(value == 0)
            {
                return;
            }

            lock(this.mutex)
            {
                if( value > this.Usage )
                {
                    this.Usage = 0;
                }
                else
                {
                    this.Usage -= value;
                }
				
				if(Tracer.IsDebugEnabled)
				{
					Tracer.DebugFormat("MemoryUsage: Decrease Usage to: {0} bytes.", this.usage);
				}
				
                Monitor.PulseAll(this.mutex);
            }
        }

        /// <summary>
        /// Checks if the Usage Windows has become full, is so returns true
        /// otherwise returns false.
        /// </summary>
        /// <returns>
        /// A <see cref="System.Boolean"/>
        /// </returns>
        public bool IsFull()
        {
            bool result = false;

            lock(this.mutex)
            {
                result = this.Usage >= this.Limit;
            }

            return result;
        }

        public void Stop()
        {
            this.stopped.Value = true;
            lock(this.mutex)
            {
                Monitor.PulseAll(this.mutex);
            }
        }
    }
}