AttachedShadowElementContext.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Numerics;

#if WINAPPSDK
using Microsoft.UI.Composition;
using Microsoft.UI.Xaml.Hosting;
#else
using Windows.UI.Composition;
using Windows.UI.Xaml.Hosting;
#endif

namespace CommunityToolkit.WinUI;

/// <summary>
/// Class which maintains the context of a <see cref="DropShadow"/> for a particular <see cref="UIElement"/> linked to the definition of that shadow provided by the <see cref="AttachedShadowBase"/> implementation being used.
/// </summary>
public sealed class AttachedShadowElementContext
{
    private bool _isConnected;

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

    internal long? VisibilityToken { get; set; }

    /// <summary>
    /// Gets a value indicating whether or not this <see cref="AttachedShadowElementContext"/> has been initialized.
    /// </summary>
    public bool IsInitialized { get; private set; }

    /// <summary>
    /// Gets the <see cref="AttachedShadowBase"/> that contains this <see cref="AttachedShadowElementContext"/>.
    /// </summary>
    public AttachedShadowBase Parent { get; private set; }

    /// <summary>
    /// Gets the <see cref="FrameworkElement"/> this instance is attached to
    /// </summary>
    public FrameworkElement Element { get; private set; }

    /// <summary>
    /// Gets the <see cref="Visual"/> for the <see cref="FrameworkElement"/> this instance is attached to.
    /// </summary>
    public Visual? ElementVisual { get; private set; }

    /// <summary>
    /// Gets the <see cref="Windows.UI.Composition.Compositor"/> for this instance.
    /// </summary>
    public Compositor? Compositor { get; private set; }

    /// <summary>
    /// Gets the <see cref="SpriteVisual"/> that contains the <see cref="DropShadow">shadow</see> for this instance
    /// </summary>
    public SpriteVisual? SpriteVisual { get; private set; }

    /// <summary>
    /// Gets the <see cref="DropShadow"/> that is rendered on this instance's <see cref="Element"/>
    /// </summary>
    public DropShadow? Shadow { get; private set; }

    /// <summary>
    /// Connects a <see cref="FrameworkElement"/> to its parent <see cref="AttachedShadowBase"/> definition.
    /// </summary>
    /// <param name="parent">The <see cref="AttachedShadowBase"/> that is using this context.</param>
    /// <param name="element">The <see cref="FrameworkElement"/> that a shadow is being attached to.</param>
    internal AttachedShadowElementContext(AttachedShadowBase parent, FrameworkElement element)
    {
        if (_isConnected)
        {
            throw new InvalidOperationException("This AttachedShadowElementContext has already been connected to an element");
        }

        _isConnected = true;
        Parent = parent ?? throw new ArgumentNullException(nameof(parent));
        Element = element ?? throw new ArgumentNullException(nameof(element));
        Element.Loaded += OnElementLoaded;
        Element.Unloaded += OnElementUnloaded;
        Initialize();
    }

    internal void DisconnectFromElement()
    {
        if (!_isConnected)
        {
            return;
        }

        Uninitialize();

        Element.Loaded -= OnElementLoaded;
        Element.Unloaded -= OnElementUnloaded;

        _isConnected = false;
    }

    /// <summary>
    /// Force early creation of this instance's resources, otherwise they will be created automatically when <see cref="Element"/> is loaded.
    /// </summary>
    public void CreateResources() => Initialize(true);

    private void Initialize(bool forceIfNotLoaded = false)
    {
        if (IsInitialized || !_isConnected || (!Element.IsLoaded && !forceIfNotLoaded))
        {
            return;
        }

        IsInitialized = true;

        ElementVisual = ElementCompositionPreview.GetElementVisual(Element);
        Compositor = ElementVisual.Compositor;

        Shadow = Compositor.CreateDropShadow();

        SpriteVisual = Compositor.CreateSpriteVisual();
        SpriteVisual.RelativeSizeAdjustment = Vector2.One;
        SpriteVisual.Shadow = Shadow;

        if (Parent.SupportsOnSizeChangedEvent == true)
        {
            Element.SizeChanged += OnElementSizeChanged;
        }

        Parent.OnElementContextInitialized(this);
    }

    private void Uninitialize()
    {
        if (!IsInitialized)
        {
            return;
        }

        IsInitialized = false;

        Parent.OnElementContextUninitialized(this);

        if (SpriteVisual != null)
        {
            SpriteVisual.Shadow = null;
            SpriteVisual.Dispose();
        }

        if (Shadow != null)
        {
            Shadow.Dispose();
        }

        if (Element != null)
        {
            ElementCompositionPreview.SetElementChildVisual(Element, null!);
            Element.SizeChanged -= OnElementSizeChanged;
        }

        SpriteVisual = null;
        Shadow = null;
        ElementVisual = null;
    }

    private void OnElementUnloaded(object sender, RoutedEventArgs e)
    {
        Uninitialize();
    }

    private void OnElementLoaded(object sender, RoutedEventArgs e)
    {
        Initialize();
    }

    private void OnElementSizeChanged(object sender, SizeChangedEventArgs e)
    {
        Parent.OnSizeChanged(this, e.NewSize, e.PreviousSize);
    }

    /// <summary>
    /// Adds a resource to this instance's resource dictionary with the specified key
    /// </summary>
    /// <typeparam name="T">The type of the resource being added.</typeparam>
    /// <param name="key">Key to use to lookup the resource later.</param>
    /// <param name="resource">Object to store within the resource dictionary.</param>
    /// <returns>The added resource</returns>
    public T AddResource<T>(string key, T resource)
        where T : notnull
    {
        if (_resources.ContainsKey(key))
        {
            _resources[key] = resource;
        }
        else
        {
            _resources.Add(key, resource);
        }

        return resource;
    }

    /// <summary>
    /// Retrieves a resource with the specified key and type if it exists
    /// </summary>
    /// <typeparam name="T">The type of the resource being retrieved.</typeparam>
    /// <param name="key">Key to use to lookup the resource.</param>
    /// <param name="resource">Object to retrieved from the resource dictionary or default value.</param>
    /// <returns>True if the resource exists, false otherwise</returns>
    public bool TryGetResource<T>(string key, out T? resource)
    {
        if (_resources.TryGetValue(key, out var objResource) && objResource is T tResource)
        {
            resource = tResource;
            return true;
        }

        resource = default;
        return false;
    }

    /// <summary>
    /// Retries a resource with the specified key and type
    /// </summary>
    /// <typeparam name="T">The type of the resource being retrieved.</typeparam>
    /// <param name="key">Key to use to lookup the resource.</param>
    /// <returns>The resource if available, otherwise default value.</returns>
    public T? GetResource<T>(string key)
    {
        if (TryGetResource(key, out T? resource))
        {
            return resource;
        }

        return default;
    }

    /// <summary>
    /// Removes an existing resource with the specified key and type
    /// </summary>
    /// <typeparam name="T">The type of the resource being removed.</typeparam>
    /// <param name="key">Key to use to lookup the resource.</param>
    /// <returns>The resource that was removed, if any</returns>
    public T? RemoveResource<T>(string key)
    {
        if (_resources.TryGetValue(key, out var objResource))
        {
            _resources.Remove(key);
            if (objResource is T resource)
            {
                return resource;
            }
        }

        return default;
    }

    /// <summary>
    /// Removes an existing resource with the specified key and type, and <see cref="IDisposable.Dispose">disposes</see> it
    /// </summary>
    /// <typeparam name="T">The type of the resource being removed.</typeparam>
    /// <param name="key">Key to use to lookup the resource.</param>
    /// <returns>The resource that was removed, if any</returns>
    public T? RemoveAndDisposeResource<T>(string key)
        where T : IDisposable
    {
        if (_resources.TryGetValue(key, out var objResource))
        {
            _resources.Remove(key);
            if (objResource is T resource)
            {
                resource.Dispose();
                return resource;
            }
        }

        return default;
    }

    /// <summary>
    /// Adds a resource to this instance's collection with the specified key
    /// </summary>
    /// <typeparam name="T">The type of the resource being added.</typeparam>
    /// <returns>The resource that was added</returns>
    public T AddResource<T>(TypedResourceKey<T> key, T resource)
        where T : notnull => AddResource(key.Key, resource);

    /// <summary>
    /// Retrieves a resource with the specified key and type if it exists
    /// </summary>
    /// <typeparam name="T">The type of the resource being retrieved.</typeparam>
    /// <returns>True if the resource exists, false otherwise</returns>
    public bool TryGetResource<T>(TypedResourceKey<T> key, out T? resource) => TryGetResource(key.Key, out resource);

    /// <summary>
    /// Retries a resource with the specified key and type
    /// </summary>
    /// <typeparam name="T">The type of the resource being retrieved.</typeparam>
    /// <returns>The resource if it exists or a default value.</returns>
    public T? GetResource<T>(TypedResourceKey<T> key) => GetResource<T>(key.Key);

    /// <summary>
    /// Removes an existing resource with the specified key and type
    /// </summary>
    /// <typeparam name="T">The type of the resource being removed.</typeparam>
    /// <returns>The resource that was removed, if any</returns>
    public T? RemoveResource<T>(TypedResourceKey<T> key) => RemoveResource<T>(key.Key);

    /// <summary>
    /// Removes an existing resource with the specified key and type, and <see cref="IDisposable.Dispose">disposes</see> it
    /// </summary>
    /// <typeparam name="T">The type of the resource being removed.</typeparam>
    /// <returns>The resource that was removed, if any</returns>
    public T? RemoveAndDisposeResource<T>(TypedResourceKey<T> key)
        where T : IDisposable => RemoveAndDisposeResource<T>(key.Key);

    /// <summary>
    /// Disposes of any resources that implement <see cref="IDisposable"/> and then clears all resources
    /// </summary>
    public void ClearAndDisposeResources()
    {
        foreach (var kvp in _resources)
        {
            (kvp.Value as IDisposable)?.Dispose();
        }

        _resources.Clear();
    }
}