feat(centralui): DialogHost ShowAsync<T> custom-content + focus trap/restore + backdrop hook (T33a)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/DialogService.cs

@@ -1,3 +1,5 @@
+using Microsoft.AspNetCore.Components;
+
 namespace ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;
 
 /// <summary>
@@ -54,6 +56,41 @@ public class DialogService : IDialogService
         return Project(tcs.Task, static r => r as string);
     }
 
+    /// <inheritdoc />
+    public Task<TResult?> ShowAsync<TResult>(string title, RenderFragment<DialogContext<TResult>> body, string? size = null)
+    {
+        EnsureNoActiveDialog();
+        var tcs = new TaskCompletionSource<object?>(TaskCreationOptions.RunContinuationsAsynchronously);
+        _tcs = tcs;
+
+        // The context routes Close/Cancel back through the same boxed Resolve()
+        // path the host uses for confirm/prompt — Close boxes the typed value,
+        // Cancel passes null. Capturing Resolve (not a service reference) keeps
+        // the body's surface narrow and the resolution path uniform.
+        var context = new DialogContext<TResult>(Resolve);
+
+        // Materialise the caller's RenderFragment<DialogContext<TResult>> into a
+        // plain RenderFragment bound to this context, so DialogState stays
+        // generic-free and the host can render it without knowing TResult.
+        var content = body(context);
+
+        Current = new DialogState(
+            title,
+            DialogKind.Custom,
+            Body: string.Empty,
+            Danger: false,
+            PromptInitial: string.Empty,
+            Placeholder: null,
+            Content: content,
+            Size: size);
+        OnChange?.Invoke();
+
+        // Project the boxed result to TResult?: a Close value unboxes to the
+        // typed result; a Cancel (null) yields default(TResult?). The cast is
+        // safe because only Close (with a TResult) ever boxes a non-null value.
+        return Project(tcs.Task, static r => r is TResult typed ? typed : default);
+    }
+
     /// <summary>
     /// Awaits the host's result and projects it to the caller's type. The
     /// <c>await</c> here resumes on the caller's captured context (the renderer
@@ -66,11 +103,14 @@ public class DialogService : IDialogService
     }
 
     /// <summary>
-    /// Called by the host component when the user dismisses or confirms the
-    /// dialog. <paramref name="result"/> must be a <c>bool</c> for confirms
-    /// and a <c>string?</c> for prompts (null = cancel).
+    /// Called by the host component (or a custom dialog's
+    /// <see cref="DialogContext{TResult}"/>) when the user dismisses or confirms
+    /// the dialog. <paramref name="result"/> must be a <c>bool</c> for confirms,
+    /// a <c>string?</c> for prompts, or the boxed <c>TResult</c> (null = cancel)
+    /// for custom dialogs.
     /// </summary>
-    /// <param name="result">The user's response: a <c>bool</c> for confirms or a <c>string?</c> for prompts.</param>
+    /// <param name="result">The user's response: a <c>bool</c> for confirms, a
+    /// <c>string?</c> for prompts, or the boxed custom result (null = cancel).</param>
     internal void Resolve(object? result)
     {
         var tcs = _tcs;
@@ -92,24 +132,33 @@ public class DialogService : IDialogService
 
 /// <summary>
 /// Snapshot of a dialog's display state, exposed read-only on
-/// <see cref="DialogService.Current"/> for the host component to render.
+/// <see cref="DialogService.Current"/> for the host component to render. New
+/// fields are appended as optional positional parameters so existing
+/// confirm/prompt construct calls keep compiling unchanged.
 /// </summary>
 /// <param name="Title">Modal title text.</param>
-/// <param name="Kind">Discriminates between confirm and prompt rendering.</param>
-/// <param name="Body">For confirm: the message; for prompt: the input label.</param>
+/// <param name="Kind">Discriminates between confirm, prompt, and custom rendering.</param>
+/// <param name="Body">For confirm: the message; for prompt: the input label; ignored for custom.</param>
 /// <param name="Danger">When true, the confirm button uses danger styling.</param>
 /// <param name="PromptInitial">Initial value for prompt-kind dialogs.</param>
 /// <param name="Placeholder">Placeholder shown when the prompt input is empty.</param>
+/// <param name="Content">For <see cref="DialogKind.Custom"/>: the body fragment to
+/// render inside <c>.modal-body</c>; <c>null</c> for confirm/prompt.</param>
+/// <param name="Size">Optional Bootstrap modal-dialog size modifier class applied
+/// to the <c>modal-dialog</c> element (e.g. <c>modal-lg</c>); <c>null</c> = default.</param>
 public record DialogState(
     string Title,
     DialogKind Kind,
     string Body,
     bool Danger,
     string PromptInitial,
-    string? Placeholder);
+    string? Placeholder,
+    RenderFragment? Content = null,
+    string? Size = null);
 
 public enum DialogKind
 {
     Confirm,
-    Prompt
+    Prompt,
+    Custom
 }