4 files changed, 128 insertions, 0 deletions
diff --git a/Pages/Component/ErrorState.razor b/Pages/Component/ErrorState.razor
new file mode 100644
index 0000000..92baac6
--- /dev/null
+++ b/Pages/Component/ErrorState.razor
@@ -0,0 +1,23 @@
+@implements IDisposable
+@typeparam T
+
+@if(Parent.ComponentState == ComponentState.Error) {
+	@ChildContent
+}
+
+@code {
+	[Parameter]
+	public RenderFragment? ChildContent { get; set; }
+
+	[CascadingParameter]
+	public LoadableContent<T> Parent { get; set; }
+
+	protected override void OnInitialized() =>
+		Parent.OnStateChanged += OnStateChanged;
+
+	public void OnStateChanged(object? sender, EventArgs e) =>
+		InvokeAsync(StateHasChanged);
+
+	public void Dispose() =>
+		Parent.OnStateChanged -= OnStateChanged;
+}
diff --git a/Pages/Component/LoadableContent.razor b/Pages/Component/LoadableContent.razor
new file mode 100644
index 0000000..570317f
--- /dev/null
+++ b/Pages/Component/LoadableContent.razor
@@ -0,0 +1,59 @@
+@attribute [CascadingTypeParameter(nameof(T))]
+@typeparam T
+
+<CascadingValue Value=this>
+	@ChildContent
+</CascadingValue>
+
+@code {
+	[Parameter]
+	public RenderFragment? ChildContent { get; set; }
+
+	[Parameter]
+	public required Func<Task<T>> DataSource { private get; set; }
+
+	public T Data { get; private set; }
+
+	public ComponentState ComponentState { get; private set; } = ComponentState.Loading;
+
+	public event EventHandler? OnStateChanged;
+
+	private bool   reloadRequested = false;
+	private Task?  loadTask        = null;
+	private object loadLock        = new();
+
+	protected override void OnInitialized() => Load();
+
+	public void Load() {
+		lock(loadLock) {
+			reloadRequested = true;
+			if(loadTask is null || loadTask.IsCompleted) {
+				//loadTask = Task.Run(LoadInternalAsync);
+				loadTask = LoadInternalAsync();
+			}
+		}
+	}
+
+	private async Task LoadInternalAsync() {
+		while(true) {
+			lock(loadLock) {
+				if(!reloadRequested)
+					break;
+				reloadRequested = false;
+			}
+
+			//ComponentState = ComponentState.Loading;
+			//await InvokeAsync(() => OnStateChanged?.Invoke(this, EventArgs.Empty));
+			//await InvokeAsync(() => StateHasChanged());
+			try {
+				Data           = await DataSource.Invoke();
+				ComponentState = ComponentState.Loaded;
+			} catch {
+				ComponentState = ComponentState.Error;
+			}
+
+			await InvokeAsync(() => OnStateChanged?.Invoke(this, EventArgs.Empty));
+			await InvokeAsync(() => StateHasChanged());
+		}
+	}
+}
diff --git a/Pages/Component/LoadedState.razor b/Pages/Component/LoadedState.razor
new file mode 100644
index 0000000..fce18d8
--- /dev/null
+++ b/Pages/Component/LoadedState.razor
@@ -0,0 +1,23 @@
+@implements IDisposable
+@typeparam T
+
+@if(Parent.ComponentState == ComponentState.Loaded) {
+	@ChildContent
+}
+
+@code {
+	[Parameter]
+	public RenderFragment? ChildContent { get; set; }
+
+	[CascadingParameter]
+	public LoadableContent<T> Parent { get; set; }
+
+	protected override void OnInitialized() =>
+		Parent.OnStateChanged += OnStateChanged;
+
+	public void OnStateChanged(object? sender, EventArgs e) =>
+		InvokeAsync(StateHasChanged);
+
+	public void Dispose() =>
+		Parent.OnStateChanged -= OnStateChanged;
+}
diff --git a/Pages/Component/LoadingState.razor b/Pages/Component/LoadingState.razor
new file mode 100644
index 0000000..0a7cffc
--- /dev/null
+++ b/Pages/Component/LoadingState.razor
@@ -0,0 +1,23 @@
+@implements IDisposable
+@typeparam T
+
+@if(Parent.ComponentState == ComponentState.Loading) {
+	@ChildContent
+}
+
+@code {
+	[Parameter]
+	public RenderFragment? ChildContent { get; set; }
+
+	[CascadingParameter]
+	public LoadableContent<T> Parent { get; set; }
+
+	protected override void OnInitialized() =>
+		Parent.OnStateChanged += OnStateChanged;
+
+	public void OnStateChanged(object? sender, EventArgs e) =>
+		InvokeAsync(StateHasChanged);
+
+	public void Dispose() =>
+		Parent.OnStateChanged -= OnStateChanged;
+}