LootTable

using System;
using System.Collections.Generic;
using System.Linq;

namespace NovaEngineFramework.Framework.Probability
{
    public class LootTable
    {
        private readonly List<string> _lootTable;
        private readonly Dictionary<string , uint> _cachedLoot;
        private readonly Random _rngInstance;
        private bool _isRebuildRequired;

        public LootTable()
        {
            _rngInstance = new Random();
            _cachedLoot = new Dictionary<string , uint>();
            _lootTable = new List<string>();
        }

        public LootTable( Random random )
        {
            this._rngInstance = random;
            _cachedLoot = new Dictionary<string , uint>();
            _lootTable = new List<string>();
        }

        public void AddLoot( uint probability , string name )
        {
            if( !_cachedLoot.ContainsKey( name ) )
            {
                this._cachedLoot.Add( name , probability );
                _isRebuildRequired = true;
            }
            else
            {
                throw new Exception( "Item: " + name + " Already Exists!" );
            }

        }

        public void DeleteLoot( string name )
        {
            if( _cachedLoot.ContainsKey( name ) )
            {
                this._cachedLoot.Remove( name );
                _isRebuildRequired = true;
            }
            else
            {
                throw new Exception( "Item: " + name + " Did not exist!" );
            }
        }

        public double CalculateProbability( string name )
        {
            if( _cachedLoot.ContainsKey( name ) )
            {
                double total = _cachedLoot.Values.Sum( n => ( int )n );
                double percent = _cachedLoot[ name ] / total;
                return Math.Round( percent * 100 , 2 );
            }
            throw new Exception( "Item: " + name + " Does not exist." );
        }

        public uint CheckRarity( string name )
        {
            if( _cachedLoot.ContainsKey( name ) )
            {
                return _cachedLoot[ name ];
            }
            throw new Exception( "Item: " + name + " Does not exist." );
        }

        public List<string> CheckLoot()
        {
            return this._cachedLoot.Keys.ToList();
        }

        public void EditLoot( string name , uint newProbability )
        {
            if( _cachedLoot.ContainsKey( name ) )
            {
                this._cachedLoot[ name ] = newProbability;
                _isRebuildRequired = true;
            }
            else
            {
                throw new Exception( "Item: " + name + " Does not exist." );
            }
        }

        public void ClearAllLoot()
        {
            this._cachedLoot.Clear();
            this._isRebuildRequired = true;
        }

        private void Build()
        {
            _lootTable.Clear();
            foreach( KeyValuePair<string , uint> pair in _cachedLoot )
            {
                for( int i = 0; i < pair.Value; i++ )
                {
                    _lootTable.Add( pair.Key );
                }
            }
            _isRebuildRequired = false;
        }

        public string NextRandomItem()
        {
            if( !_isRebuildRequired )
            {
                return _lootTable[ _rngInstance.Next( _lootTable.Count ) ];
            }
            this.Build(); // A rebuild is needed, let's go ahead and take care of it!
            return _lootTable[ _rngInstance.Next( _lootTable.Count ) ];
        }
    }
}