Function wordWrapLine

packages/pi-tui/src/components/editor.ts:115–218

(line: string, maxWidth: number, preSegmented?: Intl.SegmentData[])

 * @returns Array of chunks with text and position information
 */
export function wordWrapLine(line: string, maxWidth: number, preSegmented?: Intl.SegmentData[]): TextChunk[] {
	if (!line || maxWidth <= 0) {
		return [{ text: "", startIndex: 0, endIndex: 0 }];
	}

	const lineWidth = visibleWidth(line);
	if (lineWidth <= maxWidth) {
		return [{ text: line, startIndex: 0, endIndex: line.length }];
	}

	const chunks: TextChunk[] = [];
	const segments = preSegmented ?? [...graphemeSegmenter.segment(line)];

	let currentWidth = 0;
	let chunkStart = 0;

	// Wrap opportunity: the position after the last whitespace before a non-whitespace
	// grapheme, i.e. where a line break is allowed.
	let wrapOppIndex = -1;
	let wrapOppWidth = 0;

	for (let i = 0; i < segments.length; i++) {
		const seg = segments[i]!;
		const grapheme = seg.segment;
		const gWidth = visibleWidth(grapheme);
		const charIndex = seg.index;
		const isWs = !isPasteMarker(grapheme) && isWhitespaceChar(grapheme);

		// Overflow check before advancing.
		if (currentWidth + gWidth > maxWidth) {
			if (wrapOppIndex >= 0 && currentWidth - wrapOppWidth + gWidth <= maxWidth) {
				// Backtrack to last wrap opportunity (the remaining content
				// plus the current grapheme still fits within maxWidth).
				chunks.push({ text: line.slice(chunkStart, wrapOppIndex), startIndex: chunkStart, endIndex: wrapOppIndex });
				chunkStart = wrapOppIndex;
				currentWidth -= wrapOppWidth;
			} else if (chunkStart < charIndex) {
				// No viable wrap opportunity: force-break at current position.
				// This also handles the case where backtracking to a word
				// boundary wouldn't help because the remaining content plus
				// the current grapheme (e.g. a wide character) still exceeds
				// maxWidth.
				chunks.push({ text: line.slice(chunkStart, charIndex), startIndex: chunkStart, endIndex: charIndex });
				chunkStart = charIndex;
				currentWidth = 0;
			}
			wrapOppIndex = -1;
		}

		if (gWidth > maxWidth) {
			// Single atomic segment wider than maxWidth (e.g. paste marker
			// in a narrow terminal). Re-wrap it at grapheme granularity.

			// The segment remains logically atomic for cursor
			// movement / editing — the split is purely visual for word-wrap layout.
			const subSegments = [...graphemeSegmenter.segment(grapheme)];
			if (subSegments.length <= 1) {
				// An indivisible grapheme wider than maxWidth (e.g. a CJK