# Skeleton

An animated grey placeholder that pulsates while real content is loading. Think of it as a rough pencil sketch of your UI — it shows the user where something will appear so the page feels responsive even before the data is ready.

---

## Quick example

```csharp
new Skeleton("h-4 w-3/4")   // a loading line of text
new Skeleton("h-10 w-full") // a loading input field
new Skeleton("rounded-full h-12 w-12")  // a loading avatar
```

---

## All the options

```csharp
public Skeleton(string classes = "")
```

| Parameter | What it does |
|---|---|
| `classes` | Tailwind classes that control the size and shape of the placeholder. |

There are no other parameters. The component itself is just an animated `<div>` — you shape it entirely through CSS classes.

---

## Real-world examples

### A card loading state (avatar + two text lines)

```html
<div class="flex items-center gap-4 p-6">
  $$AvatarSkeleton$$
  <div class="space-y-2 flex-1">
    $$Line1$$
    $$Line2$$
  </div>
</div>
```

```csharp
_avatarSkeleton = new Skeleton("rounded-full h-10 w-10");
_line1          = new Skeleton("h-4 w-1/2");
_line2          = new Skeleton("h-4 w-3/4");
```

### HTMX swap: show skeleton immediately, replace with real content

Render the skeleton into a slot. HTMX fires immediately on page load and swaps it with the real content:

```html
<div id="user-list"
     hx-get="/users"
     hx-trigger="load"
     hx-swap="outerHTML">
  $$UserListSkeleton$$
</div>
```

The skeleton appears instantly; the data loads in the background and replaces it.

### A full table loading state

```csharp
// Stack five skeleton rows to simulate a loading table
var rows = string.Concat(Enumerable.Range(0, 5).Select(_ =>
{
    var w = new System.Buffers.ArrayBufferWriter<byte>();
    new Skeleton("h-8 w-full mb-2").Render(new HtmxRenderContext(w));
    return System.Text.Encoding.UTF8.GetString(w.WrittenSpan);
}));
```

---

## How it works

Skeleton is a single `<div>` with `animate-pulse` (Tailwind's built-in pulsing animation) and `bg-muted`. You control the shape entirely through the `classes` parameter — use `h-*` and `w-*` for size, and `rounded-full` for circular shapes like avatars.
- `rounded-full` makes a circle — useful for avatar skeletons. Combine with equal `h-*` and `w-*` values.
- The `classes` parameter replaces the default empty string — provide complete size + spacing classes.
- For table skeletons, render a `Table` with each cell containing a Skeleton HTML string (pre-rendered to a string via `ArrayBufferWriter<byte>`).
- Do not use Skeleton for truly empty states (no data to show) — use an `Alert` or empty-state illustration instead.
- Do not use Skeleton for truly empty states (no data to show) — use an `Alert` or empty-state illustration instead.

---

## Complete page example

**`Templates/UserListPage.htmx`**
```html
<div class="max-w-3xl mx-auto py-10">
  <h1 class="text-2xl font-bold mb-6">Users</h1>
  <div id="user-list"
     hx-get="/users/data"
     hx-trigger="load"
     hx-swap="outerHTML">
  $$LoadingSkeleton$$
  </div>
</div>
```

**`Templates/UserListPage.htmx.cs`**
```csharp
namespace Htmx.ApiDemo.Templates;

public sealed class UserListPage : UserListPageBase
{
  private readonly byte[] _skeleton;

  public UserListPage()
  {
    // Build a table-shaped skeleton: 5 rows × 3 columns
    var row = new System.Text.StringBuilder();
    for (int i = 0; i < 5; i++)
    {
      row.Append("""<div class="flex gap-4 py-3 border-b">""");
      row.Append(SkeletonHtml("h-4 w-1/3"));
      row.Append(SkeletonHtml("h-4 w-1/4"));
      row.Append(SkeletonHtml("h-4 w-1/5"));
      row.Append("</div>");
    }
    _skeleton = row.ToString().ToUtf8Bytes();
  }

  private static string SkeletonHtml(string classes)
  {
    var buf = new System.Buffers.ArrayBufferWriter<byte>();
    new Components.Skeleton(classes).Render(new HtmxRenderContext(buf));
    return System.Text.Encoding.UTF8.GetString(buf.WrittenSpan);
  }

  protected override void RenderLoadingSkeleton(HtmxRenderContext ctx)
    => ctx.Writer.WriteUtf8(_skeleton);
}
```

**GET handlers**
```csharp
// Shell page — renders immediately with skeleton placeholder
[Handler]
[MapGet("/users")]
public static partial class GetUsersShellHandler
{
  public record Query();
  private static Task<IResult> HandleAsync(Query _, HttpContext ctx, CancellationToken ct)
    => ctx.WriteHtmxPage(new UserListPage(), title: "Users");
}

// Data endpoint — HTMX swaps this in place of the skeleton
[Handler]
[MapGet("/users/data")]
public static partial class GetUsersDataHandler
{
  public record Query();
  private static async Task<IResult> HandleAsync(
    Query _, HttpContext ctx, MongoDbService db, CancellationToken ct)
  {
    var users = await db.GetAllUsersAsync(ct);
    var table = new Components.Table(
      headers: new[] { "Name", "Email", "Role" },
      rows: users.Select(u => new[]
      {
        System.Net.WebUtility.HtmlEncode(u.DisplayName ?? ""),
        System.Net.WebUtility.HtmlEncode(u.Email),
        "user",
      }));
    var buf = new System.Buffers.ArrayBufferWriter<byte>();
    table.Render(new HtmxRenderContext(buf));
    return Results.Content(
      System.Text.Encoding.UTF8.GetString(buf.WrittenSpan), "text/html");
  }
}
```