// One visible breadcrumb trail per page (UI-SPEC L1): an app may place
// <SeoBreadcrumbs> in its layout while a layer's page renders one too; the
// first instance that renders in a request claims the page and later ones
// render nothing. The claim is kept per path, so a client navigation hands
// it out again (the layout instance, set up first, claims first). Pure, so
// `node --test` drives it; names start with `seo` (app/utils is
// auto-imported).

export interface SeoBreadcrumbClaim {
  path: string
  id: string
}

/**
 * Whether instance `id` owns the trail of `path`, and the claim to keep:
 * no claim or one for another path is taken over; the claim of this path
 * belongs to the instance that made it.
 */
export function seoClaimBreadcrumbs(state: SeoBreadcrumbClaim | null | undefined, path: string, id: string): { state: SeoBreadcrumbClaim; owns: boolean } {
  if (!state || state.path !== path) return { state: { path, id }, owns: true }
  return { state, owns: state.id === id }
}

/** Releases the claim of `id` (an instance that stops rendering its trail). */
export function seoReleaseBreadcrumbs(state: SeoBreadcrumbClaim | null | undefined, id: string): SeoBreadcrumbClaim | null {
  return state && state.id === id ? null : (state ?? null)
}