Dashboard/Dashboard.Common/Pal/AppContext.cs

using Dashboard.Collections;
using Dashboard.Windowing;

namespace Dashboard.Pal
{
    public abstract class AppContext : IContextBase<AppContext, IAppContextExtension>
    {
        public abstract string DriverName { get; }
        public abstract string DriverVendor { get; }
        public abstract Version DriverVersion { get; }

        public virtual string AppTitle { get; set; } = "Dashboard Application";

        public bool IsInitialized { get; private set; } = false;
        public bool IsDisposed { get; private set; } = false;
        public IContextDebugger? Debugger { get; set; }

        private readonly TypeDictionary<IAppContextExtension> _extensions =
            new TypeDictionary<IAppContextExtension>(true);
        private readonly TypeDictionary<IAppContextExtension, Func<IAppContextExtension>> _preloadedExtensions =
            new TypeDictionary<IAppContextExtension, Func<IAppContextExtension>>(true);

        ~AppContext()
        {
            InvokeDispose(false);
        }

        public void Initialize()
        {
            if (IsInitialized)
                return;

            IsInitialized = true;

            InitializeInternal();
        }

        protected virtual void InitializeInternal()
        {
        }

        public virtual void RunEvents(bool wait)
        {
            if (!IsInitialized)
                Initialize();
        }

        public void Run() => Run(true, CancellationToken.None);

        public void Run(bool wait) => Run(wait, CancellationToken.None);

        public void Run(bool waitForEvents, CancellationToken token)
        {
            InitializeInternal();

            while (!token.IsCancellationRequested)
            {
                RunEvents(waitForEvents);
            }
        }

        #region Window API
            /// <summary>
            /// Creates a window. It could be a virtual window, or a physical window.
            /// </summary>
            /// <returns>A window.</returns>
            public abstract IWindow CreateWindow();

            /// <summary>
            /// Always creates a physical window.
            /// </summary>
            /// <returns>A physical window.</returns>
            public abstract IPhysicalWindow CreatePhysicalWindow();

            /// <summary>
            /// Create a physical window with a window manager.
            /// </summary>
            /// <returns>A physical window with the given window manager.</returns>
            public IPhysicalWindow CreatePhysicalWindow(IWindowManager wm)
            {
                IPhysicalWindow window = CreatePhysicalWindow();
                window.WindowManager = wm;
                return window;
            }
        #endregion

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

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

        public T ExtensionRequire<T>() where T : IAppContextExtension, new()
        {
            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<IAppContextExtension>? loader))
                {
                    extension = (T)loader!();
                }
                else
                {
                    extension = new T();
                }

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

            return extension;
        }

        protected virtual void Dispose(bool isDisposing)
        {
            if (!isDisposing) return;

            foreach (IAppContextExtension 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);
    }
}