Wrap selected text with typed pairs (#119)

Adds modular selection-pair handling for the rich editor and source mode so typing (, {, [, ', " or ` around a selection wraps it instead of replacing it.

Reviewed-on: https://codeberg.org/ArkHost/HelixNotes/pulls/119

src/lib/editor/extensions/wrapSelectedText.ts

@@ -0,0 +1,30 @@
+import { Extension } from '@tiptap/core';
+import { Plugin, PluginKey, TextSelection } from '@tiptap/pm/state';
+import { getSelectionPair } from '../selectionPairs';
+
+// TipTap/ProseMirror behavior for wrapping a non-empty rich-editor selection
+// without flattening selected inline marks or content to plain text.
+export const WrapSelectedText = Extension.create({
+	name: 'wrapSelectedText',
+
+	addProseMirrorPlugins() {
+		return [
+			new Plugin({
+				key: new PluginKey('wrapSelectedText'),
+				props: {
+					// Intercept only supported single-character text input over a range.
+					// Everything else falls back to ProseMirror's normal input handling.
+					handleTextInput(view, from, to, text) {
+						const close = getSelectionPair(text);
+						if (!close || from === to) return false;
+
+						const tr = view.state.tr.insertText(close, to).insertText(text, from);
+						tr.setSelection(TextSelection.create(tr.doc, from + text.length, to + text.length));
+						view.dispatch(tr);
+						return true;
+					},
+				},
+			}),
+		];
+	},
+});

src/lib/editor/selectionPairs.ts

@@ -0,0 +1,15 @@
+// Shared source of truth for editor behaviors that wrap an active selection.
+// Keep this small: only characters users reasonably expect to form pairs.
+const selectionPairs: Record<string, string> = {
+	'(': ')',
+	'{': '}',
+	'[': ']',
+	"'": "'",
+	'"': '"',
+	'`': '`',
+};
+
+// Returns the closing character for a typed wrapper key, or null to pass through.
+export function getSelectionPair(key: string) {
+	return selectionPairs[key] ?? null;
+}

src/lib/editor/source/selectionPairs.ts

@@ -0,0 +1,14 @@
+import { getSelectionPair } from '../selectionPairs';
+
+// Pure source-mode helper: computes the wrapped textarea value and preserved
+// inner selection so Svelte event handlers stay as glue code.
+export function wrapTextareaSelection(value: string, start: number, end: number, key: string) {
+	const close = getSelectionPair(key);
+	if (!close || start === end) return null;
+
+	return {
+		value: value.slice(0, start) + key + value.slice(start, end) + close + value.slice(end),
+		selectionStart: start + key.length,
+		selectionEnd: end + key.length,
+	};
+}