Dashboard/Dashboard.Common/Pal/DeviceContext.cs

using Dashboard.Collections;
using BindingFlags = System.Reflection.BindingFlags;

namespace Dashboard.Pal
{
    public abstract class DeviceContext : IContextBase<DeviceContext, IDeviceContextExtension>
    {
        private readonly TypeDictionary<IDeviceContextExtension> _extensions =
            new TypeDictionary<IDeviceContextExtension>(true);
        private readonly TypeDictionary<IDeviceContextExtension, Func<IDeviceContextExtension>> _preloadedExtensions =
            new TypeDictionary<IDeviceContextExtension, Func<IDeviceContextExtension>>(true);

        private readonly Dictionary<string, object> _attributes = new Dictionary<string, object>();


        public abstract string DriverName { get; }
        public abstract string DriverVendor { get; }
        public abstract Version DriverVersion { get; }

        public bool IsDisposed { get; private set; }

        /// <summary>
        /// Optional debugging object for your pleasure.
        /// </summary>
        public IContextDebugger? Debugger { get; set; }

        ~DeviceContext()
        {
            Dispose(false);
        }

        public virtual void Begin() { }

        // public abstract void Paint(object renderbuffer);

        public virtual void End() { }

        public bool IsExtensionAvailable<T>() where T : IDeviceContextExtension
        {
            return _extensions.Contains<T>() || _preloadedExtensions.Contains<T>();
        }

        public bool ExtensionPreload<T>(Func<IDeviceContextExtension> loader) where T : IDeviceContextExtension
        {
            return _preloadedExtensions.Add<T>(loader);
        }

        public bool ExtensionPreload<T>() where T : IDeviceContextExtension, new()
        {
            return _preloadedExtensions.Add<T>(() => new T());
        }

        public T ExtensionRequire<T>() where T : IDeviceContextExtension
        {
            T? extension = default;

            if (_extensions.TryGet(out extension))
                return extension;

            lock (_extensions)
            {
                if (_extensions.TryGet(out extension))
                    return extension;

                if (_preloadedExtensions.Remove<T>(out Func<IDeviceContextExtension>? loader))
                {
                    extension = (T)loader!();
                }
                else
                {
                    extension = Activator.CreateInstance<T>();
                }

                _extensions.Add(extension);
                extension.Require(this);
            }

            return extension;
        }

        public bool ExtensionLoad<T>(T instance) where T : IDeviceContextExtension
        {
            if (_extensions.Contains(instance))
                return false;

            _extensions.Add(instance);
            return true;
        }

        public void SetAttribute(string name, object? v)
        {
            if (v != null)
                _attributes[name] = v;
            else
                _attributes.Remove(name);
        }

        public void SetAttribute<T>(string name, T v) => SetAttribute(name, (object?)v);

        public object? GetAttribute(string name)
        {
            return _attributes.GetValueOrDefault(name);
        }

        public T? GetAttribute<T>(string name)
        {
            object? o = GetAttribute(name);
            if (o != null)
                return (T?)o;
            return default;
        }

        /// <summary>
        /// Implement your dispose in this function.
        /// </summary>
        /// <param name="isDisposing">True if disposing, false otherwise.</param>
        protected virtual void Dispose(bool isDisposing)
        {
            if (!isDisposing) return;

            foreach (IDeviceContextExtension extension in _extensions)
            {
                extension.Dispose();
            }

            GC.SuppressFinalize(this);
        }

        private void InvokeDispose(bool isDisposing)
        {
            if (IsDisposed) return;
                IsDisposed = true;

            Dispose(isDisposing);
        }

        public void Dispose() => InvokeDispose(true);
    }
}