godot-host-test/addons/AetherBind/ValueProvider.cs

using System;

namespace GodotHostTest.AetherBind;

/// <summary>
///     An object that allows communication through scopes (or inside the scope itself) by providing a couple getter/setter that can be injected in different scopes (or the same scope).
/// </summary>
/// <typeparam name="T">The type that's been passed through scopes.</typeparam>
/// <seealso cref="BuilderExtensions.AddValueProvider{TValueType,TScope}" />
/// <seealso cref="BuilderExtensions.AddValueProvider{TValueType,TSourceScope,TDestinationScope}" />
public class ValueProvider<T>
{
    private IValueGetter<T>? _getter;
    private bool _isSet;
    private T? _value;

    public ValueProvider()
    {
        Setter = new SetterImplementation(this);
    }

    public IValueSetter<T> Setter { get; }

    public IValueGetter<T> Getter
    {
        get
        {
            _getter ??= !_isSet
                ? throw new InvalidOperationException($"Value of type {typeof(T)} has not been set yet.")
                : new GetterImplementation(_value!);
            return _getter;
        }
    }

    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 Value => value;
    }
}