#region File Description
//-----------------------------------------------------------------------------
// StatisticsValueStack.cs
//
// Microsoft XNA Community Game Platform
// Copyright (C) Microsoft Corporation. All rights reserved.
//-----------------------------------------------------------------------------
#endregion

#region Using Statements
using System;
using System.Collections.Generic;
#endregion

namespace RolePlayingGameData
{
    /// <summary>
    /// A collection of statistics that expire over time.
    /// </summary>
    public class StatisticsValueStack
    {
        #region Entry List


        /// <summary>
        /// One entry in the stack.
        /// </summary>
        private class StatisticsValueStackEntry
        {
            public StatisticsValue Statistics;
            public int RemainingDuration;
        }

        /// <summary>
        /// One entry in the stack.
        /// </summary>
        private List<StatisticsValueStackEntry> entries =
            new List<StatisticsValueStackEntry>();


        #endregion


        #region Totals


        /// <summary>
        /// The total of all unexpired statistics in the stack.
        /// </summary>
        private StatisticsValue totalStatistics = new StatisticsValue();

        /// <summary>
        /// The total of all unexpired statistics in the stack.
        /// </summary>
        public StatisticsValue TotalStatistics
        {
            get { return totalStatistics; }
        }


        /// <summary>
        /// Calculate the total of all unexpired entries.
        /// </summary>
        private void CalculateTotalStatistics()
        {
            totalStatistics = new StatisticsValue();
            foreach (StatisticsValueStackEntry entry in entries)
            {
                totalStatistics += entry.Statistics;
            }
        }


        #endregion


        /// <summary>
        /// Add a new statistics, with a given duration, to the stack.
        /// </summary>
        /// <remarks>Entries with durations of 0 or less never expire.</remarks>
        public void AddStatistics(StatisticsValue statistics, int duration)
        {
            if (duration < 0)
            {
                throw new ArgumentOutOfRangeException("duration");
            }

            StatisticsValueStackEntry entry = new StatisticsValueStackEntry();
            entry.Statistics = statistics;
            entry.RemainingDuration = duration;

            entries.Add(entry);

            CalculateTotalStatistics();
        }


        /// <summary>
        /// Advance the stack and remove expired entries.
        /// </summary>
        public void Advance()
        {
            // remove the entries at 1 - they are about to go to zero
            // -- values that are zero now, never expire
            entries.RemoveAll(delegate(StatisticsValueStackEntry entry)
            {
                return (entry.RemainingDuration == 1);
            });

            // decrement all of the remaining entries.
            foreach (StatisticsValueStackEntry entry in entries)
            {
                entry.RemainingDuration--;
            }

            // recalculate the total
            CalculateTotalStatistics();
        }
    }
}