# TreeView

A hierarchical tree structure with expandable branches and selectable items. Implements the full WAI-ARIA TreeView keyboard pattern including typeahead, expand-all-siblings (\*), and nested navigation.

## Anatomy

```svelte
<TreeView.Provider bind:expandedValue bind:selectedValue>
	<TreeView.Branch value="docs" depth={0}>
		<TreeView.BranchControl>
			<TreeView.BranchIndicator>▶</TreeView.BranchIndicator>
			<TreeView.Label>Documents</TreeView.Label>
		</TreeView.BranchControl>
		<TreeView.BranchContent>
			<TreeView.Item value="readme" depth={1}>README.md</TreeView.Item>
			<TreeView.Item value="license" depth={1}>LICENSE</TreeView.Item>

			<TreeView.Branch value="src" depth={1}>
				<TreeView.BranchControl>
					<TreeView.BranchIndicator>▶</TreeView.BranchIndicator>
					<TreeView.Label>src</TreeView.Label>
				</TreeView.BranchControl>
				<TreeView.BranchContent>
					<TreeView.Item value="index" depth={2}>index.ts</TreeView.Item>
				</TreeView.BranchContent>
			</TreeView.Branch>
		</TreeView.BranchContent>
	</TreeView.Branch>
</TreeView.Provider>
```

Branches can nest arbitrarily deep. Leaf items use `Item`, expandable folders use `Branch`.

## Parts

| Part                | Element | Description                                                                |
| ------------------- | ------- | -------------------------------------------------------------------------- |
| `Provider`          | `<div>` | Root container. `role="tree"`. Manages expand/select state, keyboard.      |
| `Branch`            | `<div>` | Expandable node. Contains BranchControl + BranchContent.                   |
| `BranchControl`     | `<div>` | Clickable row for a branch. `role="treeitem"`. Handles selection + expand. |
| `BranchContent`     | `<div>` | Children container. `role="group"`. Hidden when collapsed.                 |
| `BranchIndicator`   | `<div>` | Expand/collapse icon (e.g. arrow). Clicking toggles expand. Decorative.    |
| `BranchIndentGuide` | `<div>` | Visual indent line. Decorative (`aria-hidden`).                            |
| `Item`              | `<div>` | Leaf node. `role="treeitem"`. Selectable.                                  |
| `Label`             | `<div>` | Text label for branch or item.                                             |

## ARIA

| Part              | Attribute              | Value                                  |
| ----------------- | ---------------------- | -------------------------------------- |
| Provider          | `role`                 | `tree`                                 |
| Provider          | `aria-multiselectable` | `true` (when selectionMode='multiple') |
| Provider          | `aria-label`           | Configurable (default "Tree")          |
| BranchControl     | `role`                 | `treeitem`                             |
| BranchControl     | `aria-expanded`        | `true` \| `false`                      |
| BranchControl     | `aria-selected`        | `true` \| `false`                      |
| BranchControl     | `aria-level`           | Depth + 1 (1-based)                    |
| BranchControl     | `aria-disabled`        | `true` (when disabled)                 |
| BranchContent     | `role`                 | `group`                                |
| Item              | `role`                 | `treeitem`                             |
| Item              | `aria-selected`        | `true` \| `false`                      |
| Item              | `aria-level`           | Depth + 1 (1-based)                    |
| Item              | `aria-disabled`        | `true` (when disabled)                 |
| BranchIndicator   | `aria-hidden`          | `true`                                 |
| BranchIndentGuide | `aria-hidden`          | `true`                                 |

## Data Attributes

| Part              | Attribute                            | Values                  |
| ----------------- | ------------------------------------ | ----------------------- |
| Provider          | `data-tree-view`                     | Always present          |
| Branch            | `data-tree-view-branch`              | Always present          |
| Branch            | `data-value`                         | Branch value string     |
| Branch            | `data-state`                         | `open` \| `closed`      |
| Branch            | `data-selected`                      | Present when selected   |
| Branch            | `data-disabled`                      | Present when disabled   |
| Branch            | `data-depth`                         | Nesting depth (0-based) |
| BranchControl     | `data-tree-view-branch-control`      | Always present          |
| BranchControl     | `data-value`                         | Branch value            |
| BranchControl     | `data-state`                         | `open` \| `closed`      |
| BranchControl     | `data-selected`                      | Present when selected   |
| BranchControl     | `data-disabled`                      | Present when disabled   |
| BranchControl     | `data-depth`                         | Nesting depth           |
| BranchContent     | `data-tree-view-branch-content`      | Always present          |
| BranchContent     | `data-state`                         | `open` \| `closed`      |
| BranchContent     | `data-depth`                         | Nesting depth           |
| BranchIndicator   | `data-tree-view-branch-indicator`    | Always present          |
| BranchIndicator   | `data-state`                         | `open` \| `closed`      |
| BranchIndentGuide | `data-tree-view-branch-indent-guide` | Always present          |
| BranchIndentGuide | `data-depth`                         | Nesting depth           |
| Item              | `data-tree-view-item`                | Always present          |
| Item              | `data-value`                         | Item value string       |
| Item              | `data-selected`                      | Present when selected   |
| Item              | `data-disabled`                      | Present when disabled   |
| Item              | `data-depth`                         | Nesting depth           |

## CSS Variables

| Variable            | Part         | Description                                                                                       |
| ------------------- | ------------ | ------------------------------------------------------------------------------------------------- |
| `--soma-tree-depth` | Branch, Item | Nesting depth (0-based). Use for indentation: `padding-left: calc(var(--soma-tree-depth) * 1rem)` |

## Keyboard

| Key               | Action                                                           |
| ----------------- | ---------------------------------------------------------------- |
| `ArrowDown`       | Move focus to next visible item                                  |
| `ArrowUp`         | Move focus to previous visible item                              |
| `ArrowRight`      | Expand a collapsed branch, or move to first child if expanded    |
| `ArrowLeft`       | Collapse an expanded branch, or move to parent if leaf/collapsed |
| `Home`            | Move focus to first item                                         |
| `End`             | Move focus to last visible item                                  |
| `Enter` / `Space` | Select/deselect the focused item                                 |
| `*`               | Expand all siblings of the focused item                          |
| Character keys    | Typeahead — focus first matching item by text content            |

## Behavior

### Expand/collapse

Branches expand/collapse via:

- Arrow Right/Left keys
- Clicking the BranchIndicator
- Clicking BranchControl (when `expandOnClick` is true, default)
- `*` key to expand all siblings at the same level

### Selection

- `single` mode: one item selected at a time (clicking a new item deselects the previous)
- `multiple` mode: clicking toggles individual selection

### Typeahead

When `typeahead` is true (default), typing characters focuses the first visible item whose text starts with the typed string. Buffer clears after 500ms of inactivity.

### Depth tracking

Each Branch and Item receives a `depth` prop (0-based). This becomes:

- `aria-level` (1-based, as required by ARIA spec)
- `data-depth` attribute
- `--soma-tree-depth` CSS variable for indentation

## Usage

### Basic file tree

```svelte
<script>
	import { TreeView } from '$soma/components';

	let expanded = $state(['src']);
	let selected = $state<string[]>([]);
</script>

<TreeView.Provider bind:expandedValue={expanded} bind:selectedValue={selected}>
	<TreeView.Item value="readme" depth={0}>README.md</TreeView.Item>

	<TreeView.Branch value="src" depth={0}>
		<TreeView.BranchControl>
			<TreeView.BranchIndicator>▶</TreeView.BranchIndicator>
			src
		</TreeView.BranchControl>
		<TreeView.BranchContent>
			<TreeView.Item value="index" depth={1}>index.ts</TreeView.Item>
			<TreeView.Item value="app" depth={1}>App.svelte</TreeView.Item>
		</TreeView.BranchContent>
	</TreeView.Branch>
</TreeView.Provider>
```

### Multiple selection

```svelte
<TreeView.Provider selectionMode="multiple" bind:selectedValue>
	<!-- Multiple items can be selected -->
</TreeView.Provider>
```

### Indentation via CSS variable

```css
[data-tree-view-branch-control],
[data-tree-view-item] {
	padding-left: calc(var(--soma-tree-depth) * 1.5rem + 0.5rem);
}
```

## Comparison with reference libraries

| Feature                           | Ark UI                                                                                      | Radix Vue         | React Aria        | Soma                                                                                            |
| --------------------------------- | ------------------------------------------------------------------------------------------- | ----------------- | ----------------- | ----------------------------------------------------------------------------------------------- |
| Parts                             | Root, Branch, BranchControl, BranchContent, BranchIndicator, BranchIndentGuide, Item, Label | Root, Item (flat) | Tree, TreeItem    | Provider, Branch, BranchControl, BranchContent, BranchIndicator, BranchIndentGuide, Item, Label |
| Selection single/multiple         | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| `role="tree"` / `role="treeitem"` | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| `aria-expanded`                   | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| `aria-selected`                   | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| `aria-level`                      | Yes                                                                                         | Yes               | No (CSS var)      | Yes                                                                                             |
| `aria-setsize` / `aria-posinset`  | Yes                                                                                         | Yes               | Yes               | No (consumer can add)                                                                           |
| Arrow Up/Down navigate            | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| Arrow Right expand / first child  | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| Arrow Left collapse / parent      | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| Home/End                          | Yes                                                                                         | Yes               | Yes               | Yes                                                                                             |
| `*` expand all siblings           | Yes                                                                                         | No                | No                | Yes                                                                                             |
| Typeahead                         | Yes                                                                                         | No                | No                | Yes                                                                                             |
| `--depth` CSS variable            | Yes                                                                                         | data-indent       | --tree-item-level | Yes (`--soma-tree-depth`)                                                                       |
| `data-state` open/closed          | Yes                                                                                         | Yes               | No                | Yes                                                                                             |
| `data-selected`                   | Yes                                                                                         | Yes               | No                | Yes                                                                                             |
| `data-depth`                      | No                                                                                          | Yes (data-indent) | No                | Yes                                                                                             |
| `expandOnClick`                   | Yes                                                                                         | No                | No                | Yes                                                                                             |
| `dir` (RTL)                       | Yes                                                                                         | Yes               | No                | Yes                                                                                             |
| BranchIndentGuide                 | Yes                                                                                         | No                | No                | Yes                                                                                             |
| Inline renaming                   | Yes (F2)                                                                                    | No                | No                | No (future)                                                                                     |
| Async child loading               | Yes                                                                                         | No                | No                | No (future)                                                                                     |
| Drag & drop                       | No                                                                                          | No                | Yes               | No (future)                                                                                     |
| Checkbox mode                     | Yes                                                                                         | No                | No                | No (future)                                                                                     |