Changed project name

Ghost.SparseEntities/Systems/ISystem.cs

@@ -0,0 +1,27 @@
+namespace Ghost.SparseEntities.Systems;
+
+/// <summary>
+/// Attribute to declare that a system depends on one or more other systems.
+/// </summary>
+[AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class, AllowMultiple = false)]
+public class DependsOnAttribute : Attribute
+{
+    public Type[] Prerequisites
+    {
+        get;
+    }
+
+    public DependsOnAttribute(params Type[] prerequisites)
+    {
+        Prerequisites = prerequisites;
+    }
+}
+
+public interface ISystem
+{
+    public void OnCreate(in SystemState state);
+
+    public void OnUpdate(in SystemState state);
+
+    public void OnDestroy(in SystemState state);
+}

Ghost.SparseEntities/Systems/SystemDependencyBuilder.cs

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+using System.Reflection;
+
+namespace Ghost.SparseEntities.Systems;
+
+internal class SystemDependencyBuilder
+{
+    private readonly Dictionary<Type, List<Type>> _dependencies = new();
+    private readonly List<Type> _systemTypes;
+
+    public SystemDependencyBuilder(List<Type> allSystemTypes)
+    {
+        _systemTypes = allSystemTypes;
+    }
+
+    /// <summary>
+    /// Builds a dependency graph for all system types that implement the <see cref="ISystem"/> interface.
+    /// </summary>
+    /// <remarks>This method analyzes all system types and their dependencies, as defined by the <see
+    /// cref="DependsOnAttribute"/>. It validates that each system type is a concrete implementation of <see
+    /// cref="ISystem"/> and constructs a mapping of each system type to its direct dependencies.</remarks>
+    /// <exception cref="ArgumentException">Thrown if a type in <c>allSystemTypes</c> is not a concrete implementation of <see cref="ISystem"/>.</exception>
+    public void BuildDependencyGraph()
+    {
+        foreach (var systemType in _systemTypes)
+        {
+            if (!typeof(ISystem).IsAssignableFrom(systemType) || systemType.IsAbstract || systemType.IsInterface)
+            {
+                throw new ArgumentException($"{systemType.Name} is not a concrete ISystem type.");
+            }
+
+            var directDependencies = new List<Type>();
+            var dependsOnAttributes = systemType.GetCustomAttributes<DependsOnAttribute>(false);
+            foreach (var attr in dependsOnAttributes)
+            {
+                directDependencies.AddRange(attr.Prerequisites);
+            }
+
+            _dependencies[systemType] = directDependencies;
+        }
+    }
+
+    private void Visit(Type systemType, HashSet<Type> visited, HashSet<Type> permanentMark, List<Type> executionOrder)
+    {
+        if (permanentMark.Contains(systemType))
+        {
+            return;
+        }
+
+        if (visited.Contains(systemType))
+        {
+            throw new InvalidOperationException($"Circular dependency detected involving system: {systemType.Name}");
+        }
+
+        visited.Add(systemType); // Mark as currently visiting
+
+        if (_dependencies.TryGetValue(systemType, out var directDependencies))
+        {
+            foreach (var dependencyType in directDependencies)
+            {
+                // Ensure the dependency is a registered system type
+                if (!_systemTypes.Contains(dependencyType))
+                {
+                    throw new InvalidOperationException($"System {systemType.Name} depends on unregistered system {dependencyType.Name}.");
+                }
+
+                Visit(dependencyType, visited, permanentMark, executionOrder);
+            }
+        }
+
+        visited.Remove(systemType); // Done visiting this node in the current path
+        permanentMark.Add(systemType); // Mark as permanently processed
+        executionOrder.Add(systemType); // Add to the sorted list (this will be reversed later for correct order)
+    }
+
+    /// <summary>
+    /// Builds the topological order of systems.
+    /// </summary>
+    /// <returns>A list of system types in the order they should be executed.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if a circular dependency is detected.</exception>"
+    public List<Type> BuildExecutionOrder()
+    {
+        var executionOrder = new List<Type>(_systemTypes.Count);
+        var visited = new HashSet<Type>(); // Tracks visited nodes in the current DFS path (for cycle detection)
+        var permanentMark = new HashSet<Type>(); // Tracks nodes whose dependencies have been fully resolved
+
+        // Initialize dependencies for all registered systems, even those without explicit attributes
+        foreach (var sysType in _systemTypes)
+        {
+            if (!_dependencies.ContainsKey(sysType))
+            {
+                _dependencies[sysType] = new();
+            }
+        }
+
+        foreach (var systemType in _systemTypes)
+        {
+            if (!permanentMark.Contains(systemType))
+            {
+                Visit(systemType, visited, permanentMark, executionOrder);
+            }
+        }
+
+        return executionOrder;
+    }
+}

Ghost.SparseEntities/Systems/SystemState.cs

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+namespace Ghost.SparseEntities.Systems;
+
+public struct SystemState
+{
+    public World World
+    {
+        get;
+        init;
+    }
+}

Ghost.SparseEntities/Systems/SystemStorage.cs

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+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Ghost.SparseEntities.Systems;
+
+[SkipLocalsInit]
+public readonly struct SystemStorage
+{
+    private readonly List<Type> _systems = new();
+    private readonly List<ISystem> _executionList = new();
+
+    private readonly World _world;
+
+    internal ReadOnlySpan<Type> Systems => CollectionsMarshal.AsSpan(_systems);
+
+    internal SystemStorage(World world)
+    {
+        _world = world;
+    }
+
+    public readonly void AddSystem(Type systemType)
+    {
+        _systems.Add(systemType);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void AddSystem<T>()
+        where T : ISystem, new()
+    {
+        AddSystem(typeof(T));
+    }
+
+    public readonly void RemoveSystem(Type systemType)
+    {
+        _systems.Remove(systemType);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void RemoveSystem<T>()
+        where T : ISystem, new()
+    {
+        RemoveSystem(typeof(T));
+    }
+
+    internal void CreateSystems()
+    {
+        var builder = new SystemDependencyBuilder(_systems);
+        builder.BuildDependencyGraph();
+        var executionOrder = builder.BuildExecutionOrder();
+
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var systemType in executionOrder)
+        {
+            var system = (ISystem?)Activator.CreateInstance(systemType) ?? throw new InvalidOperationException($"Failed to create instance of system type {systemType.Name}.");
+
+            _executionList.Add(system);
+            system.OnCreate(in state);
+        }
+    }
+
+    internal void UpdateSystems()
+    {
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var system in _executionList)
+        {
+            system.OnUpdate(in state);
+        }
+    }
+
+    internal void Dispose()
+    {
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var system in _executionList)
+        {
+            system.OnDestroy(in state);
+        }
+
+        _systems.Clear();
+        _executionList.Clear();
+    }
+}