WeightedRandom.cs

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using System;
using System.Collections.Generic;
using System.Linq;
 
namespace Terraria.Utilities;
 
public class WeightedRandom<T>
{
    public readonly List<Tuple<T, double>> elements = new List<Tuple<T, double>>();
 
    public readonly UnifiedRandom random;
 
    public bool needsRefresh = true;
 
    private double _totalWeight;
 
    public WeightedRandom()
    {
        random = new UnifiedRandom();
    }
 
    public WeightedRandom(int seed)
    {
        random = new UnifiedRandom(seed);
    }
 
    public WeightedRandom(UnifiedRandom random)
    {
        this.random = random;
    }
 
    public WeightedRandom(params Tuple<T, double>[] theElements)
    {
        random = new UnifiedRandom();
        elements = theElements.ToList();
    }
 
    public WeightedRandom(int seed, params Tuple<T, double>[] theElements)
    {
        random = new UnifiedRandom(seed);
        elements = theElements.ToList();
    }
 
    public WeightedRandom(UnifiedRandom random, params Tuple<T, double>[] theElements)
    {
        this.random = random;
        elements = theElements.ToList();
    }
 
    public void Add(T element, double weight = 1.0)
    {
        elements.Add(new Tuple<T, double>(element, weight));
        needsRefresh = true;
    }
 
    public T Get()
    {
        if (needsRefresh)
        {
            CalculateTotalWeight();
        }
        double num = random.NextDouble();
        num *= _totalWeight;
        foreach (Tuple<T, double> element in elements)
        {
            if (num > element.Item2)
            {
                num -= element.Item2;
                continue;
            }
            return element.Item1;
        }
        return default(T);
    }
 
    public void CalculateTotalWeight()
    {
        _totalWeight = 0.0;
        foreach (Tuple<T, double> element in elements)
        {
            _totalWeight += element.Item2;
        }
        needsRefresh = false;
    }
 
    public void Clear()
    {
        elements.Clear();
    }
 
    public static implicit operator T(WeightedRandom<T> weightedRandom)
    {
        return weightedRandom.Get();
    }
}