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 * modification, are permitted provided that the following conditions are met:
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 *       notice, this list of conditions and the following disclaimer.
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 *       notice, this list of conditions and the following disclaimer in the
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 *       derived from this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
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 */

using System;
using System.Collections.Generic;
using System.Text;

namespace OpenSim.Framework.Monitoring
{
    /// <summary>
    /// Holds individual statistic details
    /// </summary>
    public class Stat
    {
        /// <summary>
        /// Category of this stat (e.g. cache, scene, etc).
        /// </summary>
        public string Category { get; private set; }

        /// <summary>
        /// Containing name for this stat.
        /// FIXME: In the case of a scene, this is currently the scene name (though this leaves
        /// us with a to-be-resolved problem of non-unique region names).
        /// </summary>
        /// <value>
        /// The container.
        /// </value>
        public string Container { get; private set; }

        public StatType StatType { get; private set; }

        public MeasuresOfInterest MeasuresOfInterest { get; private set; }

        /// <summary>
        /// Action used to update this stat when the value is requested if it's a pull type.
        /// </summary>
        public Action<Stat> PullAction { get; private set; }

        public StatVerbosity Verbosity { get; private set; }
        public string ShortName { get; private set; }
        public string Name { get; private set; }
        public string Description { get; private set; }
        public virtual string UnitName { get; private set; }

        public virtual double Value
        {
            get
            {
                // Asking for an update here means that the updater cannot access this value without infinite recursion.
                // XXX: A slightly messy but simple solution may be to flick a flag so we can tell if this is being
                // called by the pull action and just return the value.
                if (StatType == StatType.Pull)
                    PullAction(this);

                return m_value;
            }

            set
            {
                m_value = value;
            }
        }

        private double m_value;

        /// <summary>
        /// Historical samples for calculating measures of interest average.
        /// </summary>
        /// <remarks>
        /// Will be null if no measures of interest require samples.
        /// </remarks>
        private static Queue<double> m_samples;

        /// <summary>
        /// Maximum number of statistical samples.
        /// </summary>
        /// <remarks>
        /// At the moment this corresponds to 1 minute since the sampling rate is every 2.5 seconds as triggered from
        /// the main Watchdog.
        /// </remarks>
        private static int m_maxSamples = 24;

        public Stat(
            string shortName,
            string name,
            string description,
            string unitName,
            string category,
            string container,
            StatType type,
            Action<Stat> pullAction,
            StatVerbosity verbosity) 
                : this(
                    shortName, 
                    name, 
                    description, 
                    unitName, 
                    category, 
                    container, 
                    type, 
                    MeasuresOfInterest.None, 
                    pullAction, 
                    verbosity)
        {
        }

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name='shortName'>Short name for the stat.  Must not contain spaces.  e.g. "LongFrames"</param>
        /// <param name='name'>Human readable name for the stat.  e.g. "Long frames"</param>
        /// <param name='description'>Description of stat</param>
        /// <param name='unitName'>
        /// Unit name for the stat.  Should be preceeded by a space if the unit name isn't normally appeneded immediately to the value.
        /// e.g. " frames"
        /// </param>
        /// <param name='category'>Category under which this stat should appear, e.g. "scene".  Do not capitalize.</param>
        /// <param name='container'>Entity to which this stat relates.  e.g. scene name if this is a per scene stat.</param>
        /// <param name='type'>Push or pull</param>
        /// <param name='pullAction'>Pull stats need an action to update the stat on request.  Push stats should set null here.</param>
        /// <param name='moi'>Measures of interest</param>
        /// <param name='verbosity'>Verbosity of stat.  Controls whether it will appear in short stat display or only full display.</param>
        public Stat(
            string shortName,
            string name,
            string description,
            string unitName,
            string category,
            string container,
            StatType type,
            MeasuresOfInterest moi,
            Action<Stat> pullAction,
            StatVerbosity verbosity)
        {
            if (StatsManager.SubCommands.Contains(category))
                throw new Exception(
                    string.Format("Stat cannot be in category '{0}' since this is reserved for a subcommand", category));

            ShortName = shortName;
            Name = name;
            Description = description;
            UnitName = unitName;
            Category = category;
            Container = container;
            StatType = type;

            if (StatType == StatType.Push && pullAction != null)
                throw new Exception("A push stat cannot have a pull action");
            else
                PullAction = pullAction;

            MeasuresOfInterest = moi;

            if ((moi & MeasuresOfInterest.AverageChangeOverTime) == MeasuresOfInterest.AverageChangeOverTime)
                m_samples = new Queue<double>(m_maxSamples);

            Verbosity = verbosity;
        }

        /// <summary>
        /// Record a value in the sample set.
        /// </summary>
        /// <remarks>
        /// Do not call this if MeasuresOfInterest.None
        /// </remarks>
        public void RecordValue()
        {
            double newValue = Value;

            lock (m_samples)
            {
                if (m_samples.Count >= m_maxSamples)
                    m_samples.Dequeue();

                m_samples.Enqueue(newValue);
            }
        }

        public virtual string ToConsoleString()
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("{0}.{1}.{2} : {3}{4}", Category, Container, ShortName, Value, UnitName);

            AppendMeasuresOfInterest(sb);

            return sb.ToString();
        }

        protected void AppendMeasuresOfInterest(StringBuilder sb)
        {
            if ((MeasuresOfInterest & MeasuresOfInterest.AverageChangeOverTime) 
                == MeasuresOfInterest.AverageChangeOverTime)
            {
                double totalChange = 0;
                double? lastSample = null;

                lock (m_samples)
                {
                    foreach (double s in m_samples)
                    {
                        if (lastSample != null)
                            totalChange += s - (double)lastSample;

                        lastSample = s;
                    }
                }

                int divisor = m_samples.Count <= 1 ? 1 : m_samples.Count - 1;

                sb.AppendFormat(", {0:0.##}{1}/s", totalChange / divisor / (Watchdog.WATCHDOG_INTERVAL_MS / 1000), UnitName);
            }
        }
    }
}