feat: added basic state machine system & Engine.Systems class library

Engine.Systems/StateMachine/StateMachine.cs

@@ -0,0 +1,49 @@
+using Syntriax.Engine.Core;
+
+namespace Syntriax.Engine.StateMachine;
+
+public class StateMachine : Behaviour
+{
+    public event OnStateChangedEventHandler? OnStateChanged = null;
+
+    private IState _state = new State();
+    public IState State
+    {
+        get => _state;
+        set
+        {
+            if (_state == value)
+                return;
+
+            IState previousState = _state;
+            previousState.OnStateTransitionReady -= OnStateTransitionReady;
+
+            _state = value;
+            previousState.TransitionFrom(value);
+            value.TransitionTo(_state);
+            OnStateChanged?.Invoke(this, previousState, value);
+
+            value.OnStateTransitionReady += OnStateTransitionReady;
+        }
+    }
+
+    private void OnStateTransitionReady(IState sender, IState toState)
+    {
+        State = toState;
+        while (State.GetNextState() is IState nextState)
+            State = nextState;
+    }
+
+    protected override void OnUpdate()
+    {
+        if (State is null)
+            return;
+
+        while (State.GetNextState() is IState nextState)
+            State = nextState;
+
+        State.Update();
+    }
+
+    public delegate void OnStateChangedEventHandler(StateMachine sender, IState previousState, IState newState);
+}