Added more sound effeects. Added audio manager.

AlientAttack.MonoGame/Audio/VariantSoundPool.cs

@@ -0,0 +1,48 @@
+using Microsoft.Xna.Framework.Audio;
+using System;
+
+namespace AlienAttack.MonoGame.Audio;
+
+public sealed class VariantSoundPool
+{
+    private readonly SoundPool[] _variantPools;
+    private readonly Random _rng;
+    private int _lastIndex = -1;
+
+    public VariantSoundPool(SoundEffect[] variants, int voicesPerVariant, Random rng)
+    {
+        if (variants == null || variants.Length == 0)
+            throw new ArgumentException("At least one variant is required.", nameof(variants));
+
+        ArgumentOutOfRangeException.ThrowIfLessThan(voicesPerVariant, 1);
+
+        _rng = rng ?? throw new ArgumentNullException(nameof(rng));
+
+        _variantPools = new SoundPool[variants.Length];
+
+        for (int i = 0; i < variants.Length; i++)
+            _variantPools[i] = new SoundPool(variants[i], voicesPerVariant);
+    }
+
+    public void Play(float volume = 1f, float pitch = 0f, float pan = 0f, bool avoidImmediateRepeat = true)
+    {
+        int idx = PickVariantIndex(avoidImmediateRepeat);
+        _variantPools[idx].Play(volume, pitch, pan);
+    }
+
+    private int PickVariantIndex(bool avoidImmediateRepeat)
+    {
+        if (_variantPools.Length == 1)
+            return 0;
+
+        int idx = _rng.Next(_variantPools.Length);
+        if (!avoidImmediateRepeat) { _lastIndex = idx; return idx; }
+
+        // Avoid playing the exact same sample twice in a row (nice polish)
+        if (idx == _lastIndex)
+            idx = (idx + 1 + _rng.Next(_variantPools.Length - 1)) % _variantPools.Length;
+
+        _lastIndex = idx;
+        return idx;
+    }
+}