Function applyUpdate

packages/cli/src/transform.ts:305–350

* Apply a single update to an array of class strings. * Returns the modified array.

(classes: string[], update: ClassNameUpdate)

 * Returns the modified array.
 */
function applyUpdate(classes: string[], update: ClassNameUpdate): string[] {
  const newClass = buildClass(update);
  const result = [...classes];

  // 1. Check relatedPrefixes for shorthand splitting
  for (const relatedPrefix of update.relatedPrefixes ?? []) {
    const existingIdx = result.findIndex((c) =>
      classMatchesPrefix(c, relatedPrefix)
    );
    if (existingIdx === -1) continue;

    const existingCls = result[existingIdx];
    const split = SHORTHAND_SPLITS[relatedPrefix];
    if (!split) continue;

    const token = split.extractToken(existingCls);
    // Remove the shorthand class
    result.splice(existingIdx, 1);
    // Insert individual side classes, replacing the edited side with the new value
    const expansions: string[] = [];
    for (const side of split.sides) {
      if (side === update.tailwindPrefix) {
        expansions.push(newClass);
      } else {
        expansions.push(token === "DEFAULT" ? side : `${side}-${token}`);
      }
    }
    result.splice(existingIdx, 0, ...expansions);
    return result;
  }

  // 2. Find and replace existing class with same prefix
  const directIdx = result.findIndex((c) =>
    update.classPattern
      ? new RegExp(update.classPattern).test(c)
      : classMatchesPrefix(c, update.tailwindPrefix)
  );

  if (directIdx !== -1) {
    result[directIdx] = newClass;
  } else {
    result.push(newClass);
  }

  return result;
}

/**
 * Apply updates to a class string (space-separated list of classes).