@implements IDisposable

@* In-page errors (b2b.next's WidmannErrorViewer): the validation messages of the cascading EditContext, then
   AdditionalError (one message) and AdditionalErrors (a list; never join a list into one string), one <li> each.
   Renders nothing when there is nothing to show. Messages are text, not markup: they can contain file names. *@
@if (HasContent)
{
	<DAlert Color="@(Severity is ErrorViewerSeverity.Warning ? DAlertColor.Warning : DAlertColor.Error)" Variant="DAlertVariant.Soft"
			class="@Cx("text-sm", ContainerClass)">
		<ul class="list-inside list-disc">
			@foreach (var message in Messages)
			{
				<li>@message</li>
			}
		</ul>
	</DAlert>
}

@code {
	[CascadingParameter] EditContext EditContext { get; set; }
	[Parameter] public string ContainerClass { get; set; }
	[Parameter] public ErrorViewerSeverity Severity { get; set; }
	[Parameter] public string AdditionalError { get; set; }
	[Parameter] public IEnumerable<string> AdditionalErrors { get; set; } = [];

	EditContext subscribedEditContext;

	IEnumerable<string> Messages =>
		(EditContext?.GetValidationMessages() ?? [])
		.Append(AdditionalError)
		.Concat(AdditionalErrors)
		.Where(message => !string.IsNullOrEmpty(message));

	bool HasContent => Messages.Any();

	static string Cx(params string[] classes) => DCx.Join(classes);

	protected override void OnParametersSet()
	{
		if (EditContext == subscribedEditContext)
			return;

		Unsubscribe();
		subscribedEditContext = EditContext;
		if (subscribedEditContext is not null)
			subscribedEditContext.OnValidationStateChanged += OnValidationStateChanged;
	}

	void OnValidationStateChanged(object sender, ValidationStateChangedEventArgs e) => _ = InvokeAsync(StateHasChanged);

	void Unsubscribe()
	{
		if (subscribedEditContext is not null)
			subscribedEditContext.OnValidationStateChanged -= OnValidationStateChanged;
	}

	public void Dispose() => Unsubscribe();
}