//******************************************************************************************************
//  DeviceWrapper.cs - Gbtc
//
//  Copyright © 2014, Grid Protection Alliance.  All Rights Reserved.
//
//  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See
//  the NOTICE file distributed with this work for additional information regarding copyright ownership.
//  The GPA licenses this file to you under the MIT License (MIT), 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/MIT
//
//  Unless agreed to in writing, the subject software distributed under the License is distributed on an
//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the
//  License for the specific language governing permissions and limitations.
//
//  Code Modification History:
//  ----------------------------------------------------------------------------------------------------
//  02/24/2014 - Stephen C. Wills
//       Generated original version of source code.
//
//******************************************************************************************************

using System;
using System.Threading;

namespace GSF.TimeSeries.Statistics
{
    /// <summary>
    /// Helper class for calculating device statistics.
    /// </summary>
    /// <typeparam name="T">The type of the devices whose statistics are to be calculated.</typeparam>
    public class DeviceStatisticsHelper<T> where T : class, IDevice
    {
        #region [ Members ]

        // Fields
        private readonly T m_device;
        private int m_expectedMeasurementsPerSecond;

        private long m_lastUpdateTicks;
        private int m_measurementsInSecond;
        private double m_expectedMeasurements;

        #endregion

        #region [ Constructors ]

        /// <summary>
        /// Creates a new instance of the <see cref="DeviceStatisticsHelper{T}"/> class.
        /// </summary>
        /// <param name="device">The device whose statistics are to be calculated using this helper.</param>
        public DeviceStatisticsHelper(T device)
        {
            m_device = device;
            m_lastUpdateTicks = DateTime.UtcNow.Ticks;
        }

        #endregion

        #region [ Properties ]

        /// <summary>
        /// Gets the device whose statistics are being calculated using this helper.
        /// </summary>
        public T Device
        {
            get
            {
                return m_device;
            }
        }

        /// <summary>
        /// Gets or sets the number of measurements expected to be received from the device per second.
        /// </summary>
        public int ExpectedMeasurementsPerSecond
        {
            get
            {
                return m_expectedMeasurementsPerSecond;
            }
            set
            {
                m_expectedMeasurementsPerSecond = value;
            }
        }

        #endregion

        #region [ Methods ]

        /// <summary>
        /// Increases the count of the number of measurements received from the device.
        /// </summary>
        /// <param name="count">The number of measurements received from the device since the last time this method was called.</param>
        /// <remarks>
        /// Call this each time measurements have been received by the device in order
        /// to properly track the <see cref="IDevice.MeasurementsReceived"/> statistic.
        /// </remarks>
        public void AddToMeasurementsReceived(int count)
        {
            Interlocked.Add(ref m_measurementsInSecond, count);
        }

        /// <summary>
        /// Updates the statistics for the number of measurements received and the number
        /// of measurements expected in the <see cref="IDevice"/> wrapped by this helper.
        /// </summary>
        /// <remarks>
        /// Call this periodically, preferably on a slow timer (e.g., once per second),
        /// in order to update the <see cref="IDevice.MeasurementsReceived"/> and
        /// <see cref="IDevice.MeasurementsExpected"/> statistics.
        /// </remarks>
        public void Update()
        {
            Update(DateTime.UtcNow.Ticks);
        }

        /// <summary>
        /// Updates the statistics for the number of measurements received and the number
        /// of measurements expected in the <see cref="IDevice"/> wrapped by this helper.
        /// </summary>
        /// <param name="nowTicks">The current time, in ticks.</param>
        /// <remarks>
        /// Call this periodically, preferably on a slow timer (e.g., once per second),
        /// in order to update the <see cref="IDevice.MeasurementsReceived"/> and
        /// <see cref="IDevice.MeasurementsExpected"/> statistics. This method is preferred
        /// when tracking statistics for multiple <see cref="IDevice"/>s to reduce the number
        /// of calls to <see cref="DateTime.UtcNow"/>.
        /// </remarks>
        public void Update(long nowTicks)
        {
            int measurementsInSecond = Interlocked.Exchange(ref m_measurementsInSecond, 0);
            long expectedMeasurementsInSecond;
            double diff;

            if (m_lastUpdateTicks > 0L)
            {
                diff = (nowTicks - m_lastUpdateTicks) / (double)Ticks.PerSecond;
                m_expectedMeasurements += diff * m_expectedMeasurementsPerSecond;
                expectedMeasurementsInSecond = (long)m_expectedMeasurements;

                m_device.MeasurementsReceived += measurementsInSecond;
                m_device.MeasurementsExpected += expectedMeasurementsInSecond;

                m_expectedMeasurements -= expectedMeasurementsInSecond;
            }

            m_lastUpdateTicks = nowTicks;
        }

        /// <summary>
        /// Resets the member variables used to track
        /// statistics for the device wrapped by this helper.
        /// </summary>
        /// <remarks>
        /// Call this when the connection to a device has been
        /// reset to mark a starting point for statistics gathering.
        /// Since the <see cref="Update(long)"/> method keeps track
        /// of the time it was last called, it is necessary to call
        /// this method during long periods of downtime where Update
        /// was not being called in order to avoid momentary, unexpectedly
        /// large values to be calculated for measurements expected.
        /// </remarks>
        public void Reset()
        {
            Reset(DateTime.UtcNow.Ticks);
        }

        /// <summary>
        /// Resets the member variables used to track
        /// statistics for the device wrapped by this helper.
        /// </summary>
        /// <param name="nowTicks">The current time, in ticks.</param>
        /// <remarks>
        /// Call this when the connection to a device has been
        /// reset to mark a starting point for statistics gathering.
        /// Since the <see cref="Update(long)"/> method keeps track
        /// of the time it was last called, it is necessary to call
        /// this method during long periods of downtime where Update
        /// was not being called in order to avoid momentary, unexpectedly
        /// large values to be calculated for measurements expected.
        /// This method is preferred when tracking statistics for multiple
        /// <see cref="IDevice"/>s to reduce the number of calls to
        /// <see cref="DateTime.UtcNow"/>.
        /// </remarks>
        public void Reset(long nowTicks)
        {
            Interlocked.Exchange(ref m_measurementsInSecond, 0);
            m_expectedMeasurements = 0.0D;
            m_lastUpdateTicks = nowTicks;
        }

        #endregion
    }
}