Initial version

README.md

@@ -1 +1,89 @@
-# tp-element
+# tp-tree-nav
+
+`tp-tree-nav` is a low-level, virtualized tree renderer for Lit. It is intentionally “dumb”: it only renders what it is given and emits events. Parents own all state (expanded/selected/custom), perform mutations, and pass updated data back in. This makes it a flexible foundation for building higher-level trees (e.g., VS Code–style explorer, Git ignore/selected indicators, custom icon trees).
+
+## Key ideas
+- **Multiple roots**: pass a `roots` array; each node may have `children`.
+- **Virtualized list**: uses `@lit-labs/virtualizer` to render a flat, indented list for large trees.
+- **Events only**: emits `node-click`, `node-context`, and `node-action` (for chevron toggle and context menu actions). Every event includes `originalEvent` so parents can cancel or coordinate.
+- **Opt-in actions**: provide `defaultActions` (array of action objects), and per-node `actions`; node actions override defaults on the same `action` key. Use `beforeContextMenu(node, actions)` to modify or block the menu.
+- **Custom render**: `renderNode(node, meta)` lets you override row rendering (e.g., icons per node type, state-based styling). Common states like `expanded`/`collapsed` are parent-managed via `node.states`.
+- **Helper methods (pure)**: `getNodesWithState`, `clearState`, `applyStateIf` return data; they don’t mutate internal state—parents update `roots`.
+- **Default icons**: `chevron`, `folder`, `file` are available via `tp-icon`; pass string keys or custom icons.
+
+## Usage example
+```js
+import './tp-tree-nav.js';
+
+const tree = document.querySelector('tp-tree-nav');
+
+const roots = [
+	{
+		label: 'Project A',
+		slug: 'project-a',
+		states: ['expanded'],
+		icon: 'folder',
+		children: [
+			{ label: 'main.js', slug: 'main-js', icon: 'file', states: [] },
+			{
+				label: 'src',
+				slug: 'src',
+				icon: 'folder',
+				states: ['expanded'],
+				children: [
+					{ label: 'index.js', slug: 'index-js', icon: 'file', states: [] },
+				],
+			},
+		],
+	},
+];
+
+tree.roots = roots;
+tree.defaultActions = [
+	{ label: 'Rename', action: 'rename', icon: 'pencil' },
+	{ label: 'Delete', action: 'delete', icon: 'delete' },
+];
+
+tree.beforeContextMenu = (node, actions) => {
+	// Example: hide delete on roots
+	if (node.slug === 'project-a') {
+		return actions.filter((a) => a.action !== 'delete');
+	}
+	return actions;
+};
+
+tree.renderNode = (node, { depth, states, path, hasChildren }) => {
+	const selected = states.includes('selected');
+	return html`
+		<div
+			class="row ${selected ? 'selected' : ''}"
+			style="--depth: ${depth}"
+			@click=${(e) => tree.dispatchEvent(new CustomEvent('node-click', { detail: { node, path, originalEvent: e }, bubbles: true, composed: true, cancelable: true }))}
+		>
+			<div class="indent"></div>
+			${hasChildren
+				? html`<tp-icon class="icon" .icon=${TpTreeNav.chevron}></tp-icon>`
+				: html`<span class="icon" aria-hidden="true"></span>`}
+			<tp-icon class="icon" .icon=${tree._resolveIcon(node.icon)}></tp-icon>
+			<div class="label">${node.label}</div>
+		</div>
+	`;
+};
+
+// Listen to actions (toggle, context menu items, etc.)
+tree.addEventListener('node-action', (e) => {
+	const { action, node, path } = e.detail;
+	if (action === 'toggle') {
+		// Parent mutates data: flip expanded state and reassign roots
+		const next = tree.applyStateIf('expanded', (n, p) => p.join('/') === path.join('/'));
+		tree.roots = next;
+	}
+});
+```
+
+## Building higher-level trees
+Wrap `tp-tree-nav` in a specialized component (e.g., file explorer) that:
+- Tracks expansion/selection state on nodes.
+- Supplies icons per node type via `renderNode` or `icon` strings.
+- Defines default/context actions relevant to the domain.
+- Handles action events to mutate the source data and pass updated `roots` back.