private WeightedItem <T> ChooseRandomWeightedItem()
{
int lookupWeight = random.Next(1, totalWeight);
int currentWeight = 0;
WeightedItem <T> item = null;
foreach (WeightedItem <T> weightedItem in pool)
{
currentWeight += weightedItem.Weight;
if (currentWeight >= lookupWeight)
{
item = weightedItem;
break;
}
}
if (item == null)
{
throw new InvalidOperationException("The random lookup was greater than the total weight");
}
return(item);
}
private void Remove(WeightedItem <T> item)
{
if (item != null && pool.Remove(item))
{
totalWeight -= item.Weight;
}
}
/// <summary>
/// Take an item at random from the pool, keeping weights into consideration.
/// The item will be removed from the pool.
/// </summary>
/// <returns>An item of type T from the WeightedPool</returns>
/// <exception cref="InvalidOperationException">Thrown when the pool is empty</exception>
/// <exception cref="InvalidOperationException">Thrown when the random lookup is greater than the total weight. Could only happen if a bad implementation of IRandom were provided</exception>
public T Draw()
{
if (Count <= 0 || totalWeight <= 0)
{
throw new InvalidOperationException("Add items to the pool before attempting to draw one");
}
WeightedItem <T> item = ChooseRandomWeightedItem();
Remove(item);
return(item.Item);
}
/// <summary>
/// Choose an item at random from the pool, keeping weights into consideration.
/// The item itself will remain in the pool and a clone of the item selected will be returned.
/// </summary>
/// <returns>A clone of the item of type T from the WeightedPool</returns>
/// <exception cref="InvalidOperationException">Thrown when a clone function was not defined when the pool was constructed</exception>
/// <exception cref="InvalidOperationException">Thrown when the pool is empty</exception>
/// <exception cref="InvalidOperationException">Thrown when the random lookup is greater than the total weight. Could only happen if a bad implementation of IRandom were provided</exception>
public T Choose()
{
if (cloneFunc == null)
{
throw new InvalidOperationException("A clone function was not defined when this pool was constructed");
}
if (Count <= 0 || totalWeight <= 0)
{
throw new InvalidOperationException("Add items to the pool before attempting to choose one");
}
WeightedItem <T> item = ChooseRandomWeightedItem();
return(cloneFunc(item.Item));
}
/// <summary>
/// Add an item of type T to the WeightedPool with the given weight
/// </summary>
/// <param name="item">The item to add to the WeightedPool</param>
/// <param name="weight">
/// The chance that the item will be picked at random from the pool when weighted against all other items.
/// Higher weights mean it is more likely to be picked.
/// </param>
/// <exception cref="ArgumentNullException">Thrown when provided "item" argument is null</exception>
/// <exception cref="ArgumentException">Thrown when provided "weight" argument is not greater than 0</exception>
/// <exception cref="OverflowException">Thrown when adding the weight of the new item to the pool exceeds Int32.MaxValue</exception>
public void Add(T item, int weight)
{
if (item == null)
{
throw new ArgumentNullException(nameof(item), "Can not add null item to the pool");
}
if (weight <= 0)
{
throw new ArgumentException("Weight must be greater than 0", nameof(weight));
}
WeightedItem <T> weightedItem = new WeightedItem <T>(item, weight);
pool.Add(weightedItem);
if (int.MaxValue - weight < totalWeight)
{
throw new OverflowException("The weight of items in the pool would be over Int32.MaxValue");
}
totalWeight += weight;
}