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GamblingCoin/WeightedRandom.cs

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+namespace GamblingCoin;
+
+public class WeightedRandomExecutor<TEvent>
+{
+    private class WeightedAction
+    {
+        public Action<TEvent> Action { get; }
+        public double Weight { get; }
+
+        public WeightedAction(Action<TEvent> action, double weight)
+        {
+            if (weight <= 0)
+                throw new ArgumentOutOfRangeException(
+                    nameof(weight),
+                    "Weight must be positive."
+                );
+
+            Action = action ?? throw new ArgumentNullException(nameof(action));
+            Weight = weight;
+        }
+    }
+
+    private readonly List<WeightedAction> _actions = new();
+    private readonly Random _random = new();
+    private double _totalWeight;
+
+    /// <summary>
+    /// Adds a function to be potentially executed, along with its weight.
+    /// </summary>
+    /// <param name="action">The function to add. It must accept an argument of type TEvent.</param>
+    /// <param name="weight">The positive weight for this function. Higher weights mean higher probability.</param>
+    public WeightedRandomExecutor<TEvent> AddAction(Action<TEvent> action, double weight)
+    {
+        var weightedAction = new WeightedAction(action, weight);
+        _actions.Add(weightedAction);
+        _totalWeight += weight;
+        
+        return this;
+    }
+
+    /// <summary>
+    /// Executes one of the added functions randomly based on their weights.
+    /// The chosen function will be called with the provided 'ev' argument.
+    /// </summary>
+    /// <param name="ev">The event argument to pass to the chosen function.</param>
+    /// <exception cref="InvalidOperationException">Thrown if no actions have been added.</exception>
+    public void Execute(TEvent ev)
+    {
+        if (_actions.Count == 0)
+        {
+            throw new InvalidOperationException(
+                "No actions have been added to execute."
+            );
+        }
+
+        if (_totalWeight <= 0) // Should not happen if AddAction validates weight > 0
+        {
+            throw new InvalidOperationException(
+                "Total weight is zero or negative, cannot execute."
+            );
+        }
+
+        var randomNumber = _random.NextDouble() * _totalWeight;
+        double cumulativeWeight = 0;
+
+        foreach (var weightedAction in _actions)
+        {
+            cumulativeWeight += weightedAction.Weight;
+            if (!(randomNumber < cumulativeWeight)) continue;
+            weightedAction.Action(ev);
+            return; // Exit after executing one action
+        }
+
+        // Fallback in case of floating point inaccuracies,
+        // or if somehow randomNumber was exactly _totalWeight (NextDouble is < 1.0)
+        // This should ideally pick the last item if all weights were summed up.
+        if (_actions.Any())
+        {
+            _actions.Last().Action(ev);
+        }
+    }
+}