feat: more plugin work and intra-scope communication

addons/GodotDI/ValueProvider.cs

@@ -0,0 +1,46 @@
+using System;
+
+namespace GodotHostTest.GodotDI;
+
+/// <summary>
+///     An object that allows communication through scopes, by providing a couple getter/setter that can be injected in
+///     different scopes.
+/// </summary>
+/// <typeparam name="T">The type that's been passed through scopes.</typeparam>
+/// <seealso cref="BuilderExtensions.AddValueProvider" />
+public class ValueProvider<T>
+{
+    private bool _isSet;
+    private T? _value;
+
+    public ValueProvider()
+    {
+        Setter = new SetterImplementation(this);
+    }
+
+    public IValueSetter<T> Setter { get; }
+
+    public IValueGetter<T> Getter => !_isSet
+        ? throw new InvalidOperationException($"Value of type {typeof(T)} has not been set yet.")
+        : new GetterImplementation(_value!);
+
+    private class SetterImplementation(ValueProvider<T> valueProvider) : IValueSetter<T>
+    {
+        public void Set(T value)
+        {
+            if (valueProvider._isSet)
+                throw new InvalidOperationException($"A value (of type {typeof(T)}) cannot be set more than once.");
+
+            valueProvider._value = value;
+            valueProvider._isSet = true;
+        }
+    }
+
+    private class GetterImplementation(T value) : IValueGetter<T>
+    {
+        public T Get()
+        {
+            return value;
+        }
+    }
+}