Function expandPanel

packages/core/src/widgets/splitPane.ts:304–342

(
  sizes: readonly number[],
  index: number,
  targetSize: number,
)

 * @returns Updated sizes with expanded panel
 */
export function expandPanel(
  sizes: readonly number[],
  index: number,
  targetSize: number,
): readonly number[] {
  if (index < 0 || index >= sizes.length) {
    return sizes;
  }

  const newSizes = [...sizes];
  const currentSize = sizes[index] ?? 0;
  const delta = targetSize - currentSize;

  if (delta <= 0) {
    return sizes;
  }

  let taken = 0;

  // Take space from adjacent panels
  if (index > 0) {
    const neighborSize = newSizes[index - 1] ?? 0;
    const take = Math.min(delta - taken, neighborSize);
    newSizes[index - 1] = neighborSize - take;
    taken += take;
  } else if (index < sizes.length - 1) {
    const neighborSize = newSizes[index + 1] ?? 0;
    const take = Math.min(delta - taken, neighborSize);
    newSizes[index + 1] = neighborSize - take;
    taken += take;
  }

  if (taken <= 0) {
    return sizes;
  }

  newSizes[index] = currentSize + taken;
  return Object.freeze(newSizes);
}

/**
 * Hit test to determine if a point is on a divider.