import { computed } from 'vue'
import { useRoute } from 'vue-router'
import type { ComputedRef } from 'vue'
import type { RouteLocationRaw } from 'vue-router'

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

/** A single breadcrumb item. `to` is absent for the current (last) item. */
export interface BreadcrumbItem {
  label: string
  to?: RouteLocationRaw
}

/**
 * Minimal shape we need from a matched route record.
 * Using a structural type keeps the pure helper testable without
 * requiring full RouteLocationMatched fixtures in unit tests.
 * RouteLocationMatched is structurally assignable to this interface so
 * route.matched (RouteLocationMatched[]) passes the type-checker.
 */
export interface BreadcrumbRouteRecord {
  meta?: Record<string, unknown> & {
    breadcrumb?: string
    title?: string
  }
  name?: string | symbol | null
  path?: string
}

// ---------------------------------------------------------------------------
// Pure helper — testable without a live router
// ---------------------------------------------------------------------------

/**
 * Convert an array of matched route records into breadcrumb items.
 *
 * Rules:
 * - Records without `meta.breadcrumb` OR `meta.title` are filtered out.
 * - Label = `meta.breadcrumb` if set, else `meta.title`.
 * - The last item is current — no `to` link.
 * - All preceding items carry a `to` pointing at their `path` (or `name`
 *   when path is absent).
 */
export function toBreadcrumbItems(matched: readonly BreadcrumbRouteRecord[]): BreadcrumbItem[] {
  const eligible = matched.filter(
    r => r.meta?.breadcrumb !== undefined || r.meta?.title !== undefined,
  )

  return eligible.map((record, index): BreadcrumbItem => {
    const label = (record.meta?.breadcrumb ?? record.meta?.title) as string
    const isLast = index === eligible.length - 1

    if (isLast)
      return { label }

    // Prefer path; fall back to name when path is absent/empty.
    // NOTE: a non-last record whose `path` is a param template (e.g. `/events/:id`)
    // would yield an unresolved-template `to` — acceptable in foundation scope because
    // param routes are normally the last (current, no-`to`) segment.
    // TODO TECH-WS-GUI-REDESIGN: resolve param paths if a non-leaf param route ever needs a crumb link
    const to: RouteLocationRaw
      = record.path
        ? record.path
        : { name: record.name as string }

    return { label, to }
  })
}

// ---------------------------------------------------------------------------
// Composable — thin wrapper around useRoute()
// ---------------------------------------------------------------------------

export interface UseBreadcrumbReturn {
  items: ComputedRef<BreadcrumbItem[]>
}

/**
 * Composable that derives breadcrumb items from the current route's
 * `matched` array. Reactive — updates automatically on navigation.
 *
 * Composables zone may NOT import from @/navigation — do not add
 * route-level nav helpers here.
 */
export function useBreadcrumb(): UseBreadcrumbReturn {
  const route = useRoute()

  const items = computed<BreadcrumbItem[]>(() =>
    toBreadcrumbItems(route.matched),
  )

  return { items }
}