Implement deterministic simulation spine

src/SideScrollerGame.Sim/Runtime/SimulationState.cs

@@ -0,0 +1,52 @@
+using System.Collections.Immutable;
+
+namespace SideScrollerGame.Sim.Runtime;
+
+public sealed class SimulationState
+{
+    public SimulationState(int tick, int seed, ulong randomState, ulong lastRandomValue, ImmutableArray<PlayerState> players)
+    {
+        Tick = tick;
+        Seed = seed;
+        RandomState = randomState;
+        LastRandomValue = lastRandomValue;
+        Players = players.IsDefault ? ImmutableArray<PlayerState>.Empty : players;
+    }
+
+    public SimulationState Clone()
+    {
+        var builder = ImmutableArray.CreateBuilder<PlayerState>(Players.Length);
+        foreach (var player in Players)
+            builder.Add(player.Clone());
+
+        return new(Tick, Seed, RandomState, LastRandomValue, builder.MoveToImmutable());
+    }
+
+    public PlayerState GetRequiredPlayer(PlayerId playerId)
+    {
+        foreach (var player in Players)
+        {
+            if (player.PlayerId == playerId)
+                return player;
+        }
+
+        throw new InvalidOperationException($"Unknown player id {playerId.Value}.");
+    }
+
+    public void AdvanceTick(int tick, ulong randomState, ulong lastRandomValue)
+    {
+        Tick = tick;
+        RandomState = randomState;
+        LastRandomValue = lastRandomValue;
+    }
+
+    public int Tick { get; private set; }
+
+    public int Seed { get; }
+
+    public ulong RandomState { get; private set; }
+
+    public ulong LastRandomValue { get; private set; }
+
+    public ImmutableArray<PlayerState> Players { get; }
+}