Sparse Array Masking for Next.js Parallel Route Segment Routing

export function resolveParallelSlots(slotsArray, pathSegments) {
  const sparseMask = new Array(slotsArray.length);
  
  pathSegments.forEach((segment, idx) => {
    if (slotsArray.includes(segment)) {
      sparseMask[idx] = segment;
    }
  });
 
  const activeSlotIndex = sparseMask.findIndex(slot => slot !== undefined);
  
  switch (activeSlotIndex) {
    case -1:
      return 'default';
    case 0:
      return `@primary/${sparseMask[0]}`;
    default:
      return `@secondary/${sparseMask[activeSlotIndex]}`;
  }
}