fix(tui): align input word segmentation with editor (#5068)

packages/tui/src/word-navigation.ts

@@ -0,0 +1,117 @@
+import { getWordSegmenter, isWhitespaceChar, PUNCTUATION_REGEX } from "./utils.ts";
+
+const wordSegmenter = getWordSegmenter();
+
+/**
+ * Options for word navigation functions.
+ * When omitted, uses the default Intl.Segmenter word segmentation.
+ */
+export interface WordNavigationOptions {
+	/** Custom segmenter returning word segments for the given text. */
+	segment?: (text: string) => Iterable<Intl.SegmentData>;
+	/** Predicate identifying atomic segments that should be treated as single units (e.g. paste markers). */
+	isAtomicSegment?: (segment: string) => boolean;
+}
+
+/**
+ * Find the cursor position after moving one word backward from `cursor` in `text`.
+ * Skips trailing whitespace, then stops at the next word/punctuation boundary.
+ *
+ * Pure function - does not mutate any state.
+ */
+export function findWordBackward(text: string, cursor: number, options?: WordNavigationOptions): number {
+	if (cursor <= 0) return 0;
+
+	const textBeforeCursor = text.slice(0, cursor);
+	const segmentFn = options?.segment;
+	const isAtomic = options?.isAtomicSegment;
+	const segments = segmentFn ? [...segmentFn(textBeforeCursor)] : [...wordSegmenter.segment(textBeforeCursor)];
+	let newCursor = cursor;
+
+	// Skip trailing whitespace
+	while (
+		segments.length > 0 &&
+		!isAtomic?.(segments[segments.length - 1]?.segment || "") &&
+		isWhitespaceChar(segments[segments.length - 1]?.segment || "")
+	) {
+		newCursor -= segments.pop()?.segment.length || 0;
+	}
+
+	if (segments.length === 0) return newCursor;
+
+	const last = segments[segments.length - 1]!;
+
+	if (isAtomic?.(last.segment)) {
+		// Skip one atomic segment.
+		newCursor -= last.segment.length;
+	} else if (last.isWordLike) {
+		// Skip inside one word-like segment, preserving ASCII punctuation boundaries.
+		const segment = last.segment;
+		const matches = [...segment.matchAll(new RegExp(PUNCTUATION_REGEX, "g"))];
+		if (matches.length <= 0) {
+			newCursor -= segment.length;
+		} else {
+			const lastMatch = matches[matches.length - 1]!;
+			newCursor -= segment.length - (lastMatch.index + lastMatch[0].length);
+		}
+	} else {
+		// Skip non-word non-whitespace run (punctuation)
+		while (
+			segments.length > 0 &&
+			!isAtomic?.(segments[segments.length - 1]?.segment || "") &&
+			!segments[segments.length - 1]?.isWordLike &&
+			!isWhitespaceChar(segments[segments.length - 1]?.segment || "")
+		) {
+			newCursor -= segments.pop()?.segment.length || 0;
+		}
+	}
+
+	return newCursor;
+}
+
+/**
+ * Find the cursor position after moving one word forward from `cursor` in `text`.
+ * Skips leading whitespace, then stops at the next word/punctuation boundary.
+ *
+ * Pure function - does not mutate any state.
+ */
+export function findWordForward(text: string, cursor: number, options?: WordNavigationOptions): number {
+	if (cursor >= text.length) return text.length;
+
+	const textAfterCursor = text.slice(cursor);
+	const segmentFn = options?.segment;
+	const isAtomic = options?.isAtomicSegment;
+	const segments = segmentFn ? segmentFn(textAfterCursor) : wordSegmenter.segment(textAfterCursor);
+	const iterator = segments[Symbol.iterator]();
+	let next = iterator.next();
+	let newCursor = cursor;
+
+	// Skip leading whitespace
+	while (!next.done && !isAtomic?.(next.value.segment) && isWhitespaceChar(next.value.segment)) {
+		newCursor += next.value.segment.length;
+		next = iterator.next();
+	}
+
+	if (next.done) return newCursor;
+
+	if (isAtomic?.(next.value.segment)) {
+		// Skip one atomic segment.
+		newCursor += next.value.segment.length;
+	} else if (next.value.isWordLike) {
+		// Skip inside one word-like segment, preserving ASCII punctuation boundaries.
+		newCursor += PUNCTUATION_REGEX.exec(next.value.segment)?.index ?? next.value.segment.length;
+	} else {
+		// Skip non-word non-whitespace run (punctuation)
+		while (
+			!next.done &&
+			!isAtomic?.(next.value.segment) &&
+			!next.value.isWordLike &&
+			!isWhitespaceChar(next.value.segment)
+		) {
+			newCursor += next.value.segment.length;
+			next = iterator.next();
+		}
+	}
+
+	return newCursor;
+}