implement smart bullet

tanks-backend/TanksServer/GameLogic/CollectPowerUp.cs

@@ -47,7 +47,7 @@ internal sealed class CollectPowerUp(
                     };
                     break;
                 default:
-                    throw new NotImplementedException();
+                    throw new UnreachableException();
             }
 
             tank.Owner.Scores.PowerUpsCollected++;

tanks-backend/TanksServer/GameLogic/GameRules.cs

@@ -25,4 +25,6 @@ internal sealed class GameRules
     public byte MagazineSize { get; set; } = 5;
 
     public int ReloadDelayMs { get; set; } = 3000;
+
+    public double SmartBulletInertia { get; set; } = 1;
 }

tanks-backend/TanksServer/GameLogic/MapEntityManager.cs

@@ -27,7 +27,8 @@ internal sealed class MapEntityManager(
             IsExplosive = type.HasFlag(MagazineType.Explosive),
             Timeout = DateTime.Now + _bulletTimeout,
             OwnerCollisionAfter = DateTime.Now + TimeSpan.FromSeconds(1),
-            Speed = speed
+            Speed = speed,
+            IsSmart = type.HasFlag(MagazineType.Smart)
         });
     }
 

tanks-backend/TanksServer/GameLogic/MoveBullets.cs

@@ -1,7 +1,12 @@
 namespace TanksServer.GameLogic;
 
-internal sealed class MoveBullets(MapEntityManager entityManager) : ITickStep
+internal sealed class MoveBullets(
+    MapEntityManager entityManager,
+    IOptions<GameRules> options
+) : ITickStep
 {
+    private readonly double _smartBulletInertia = options.Value.SmartBulletInertia;
+
     public ValueTask TickAsync(TimeSpan delta)
     {
         foreach (var bullet in entityManager.Bullets)
@@ -10,8 +15,15 @@ internal sealed class MoveBullets(MapEntityManager entityManager) : ITickStep
         return ValueTask.CompletedTask;
     }
 
-    private static void MoveBullet(Bullet bullet, TimeSpan delta)
+    private void MoveBullet(Bullet bullet, TimeSpan delta)
     {
+        if (bullet.IsSmart && TryGetSmartRotation(bullet.Position, bullet.Owner, out var wantedRotation))
+        {
+            var inertiaFactor = _smartBulletInertia * delta.TotalSeconds;
+            var difference = wantedRotation - bullet.Rotation;
+            bullet.Rotation += difference * inertiaFactor;
+        }
+
         var speed = bullet.Speed * delta.TotalSeconds;
         var angle = bullet.Rotation * 2 * Math.PI;
         bullet.Position = new FloatPosition(
@@ -19,4 +31,24 @@ internal sealed class MoveBullets(MapEntityManager entityManager) : ITickStep
             bullet.Position.Y - Math.Cos(angle) * speed
         );
     }
+
+    private bool TryGetSmartRotation(FloatPosition position, Player bulletOwner, out double rotation)
+    {
+        var nearestEnemy = entityManager.Tanks
+            .Where(t => t.Owner != bulletOwner)
+            .MinBy(t => position.Distance(t.Position));
+
+        if (nearestEnemy == null)
+        {
+            rotation = double.NaN;
+            return false;
+        }
+
+        var rotationRadians = Math.Atan2(
+            y: nearestEnemy.Position.Y - position.Y,
+            x: nearestEnemy.Position.X - position.X
+        ) + (Math.PI / 2);
+        rotation = rotationRadians / (2 * Math.PI);
+        return true;
+    }
 }

tanks-backend/TanksServer/GameLogic/SpawnPowerUp.cs

@@ -18,18 +18,17 @@ internal sealed class SpawnPowerUp(
             return ValueTask.CompletedTask;
 
 
-        var type = Random.Shared.Next(10) < 3
+        var type = Random.Shared.Next(4) == 0
             ? PowerUpType.MagazineSizeUpgrade
             : PowerUpType.MagazineTypeUpgrade;
 
         MagazineType? magazineType = type switch
         {
-            PowerUpType.MagazineTypeUpgrade => Random.Shared.Next(0, 4) switch
+            PowerUpType.MagazineTypeUpgrade => Random.Shared.Next(0, 3) switch
             {
                 0 => MagazineType.Fast,
                 1 => MagazineType.Explosive,
                 2 => MagazineType.Smart,
-                3 => MagazineType.Mine,
                 _ => throw new UnreachableException()
             },
             _ => null