import type { PageSummary } from '@/lib/pages'

/**
 * Reorder pages by moving sourceId beside targetId. Pinned and unpinned pages
 * are separate groups (the server sorts pinned first), so a cross-group drop
 * returns 'blocked' instead of silently landing at a different boundary.
 * `after` places the source after the target; otherwise it goes before it.
 */
export function reorderPages(
  pages: PageSummary[],
  sourceId: string,
  targetId: string,
  after = false,
): PageSummary[] | 'blocked' | null {
  const from = pages.findIndex((p) => p.id === sourceId)
  const to = pages.findIndex((p) => p.id === targetId)
  if (from < 0 || to < 0 || sourceId === targetId) return null
  if (pages[from].pinned !== pages[to].pinned) return 'blocked'
  const next = [...pages]
  const [moved] = next.splice(from, 1)
  let insertAt = to + (after ? 1 : 0)
  if (from < insertAt) insertAt--
  next.splice(insertAt, 0, moved)
  return next
}