import { computed } from 'vue'
import type { ComputedRef } from 'vue'
import type { V2NavGroup, V2NavItem } from '@/types/v2/nav'

// ---------------------------------------------------------------------------
// Local discriminated union for v1 nav entries (no `any`)
// ---------------------------------------------------------------------------

interface V1NavHeading {
  heading: string
}

interface V1NavLink {
  title: string
  to: { name: string }
  icon: { icon: string }
  count?: number
}

export type V1NavEntry = V1NavHeading | V1NavLink

function isHeading(entry: V1NavEntry): entry is V1NavHeading {
  return 'heading' in entry
}

// ---------------------------------------------------------------------------
// Pure adapter — exported so it can be unit-tested without mounting
// ---------------------------------------------------------------------------

/**
 * Folds a flat v1 nav array into V2NavGroup[].
 *
 * - A `{ heading }` entry closes the current group and opens a new one.
 * - Items before the first heading are placed in a leading group with label ''.
 * - A pure function with no side-effects.
 */
export function toV2NavGroups(items: readonly V1NavEntry[]): V2NavGroup[] {
  if (items.length === 0)
    return []

  const groups: V2NavGroup[] = []
  let current: V2NavGroup | null = null

  for (const entry of items) {
    if (isHeading(entry)) {
      // Close current group (if any) and start a new named group.
      if (current !== null)
        groups.push(current)

      current = { label: entry.heading, items: [] }
    }
    else {
      // Ensure there is a current group (leading ungrouped section).
      if (current === null)
        current = { label: '', items: [] }

      const navItem: V2NavItem = {
        id: entry.to.name, // v1 route names are already kebab-case; no normalisation needed
        label: entry.title,
        icon: entry.icon.icon,
        to: { name: entry.to.name },
        ...(entry.count !== undefined ? { count: entry.count } : {}),
      }

      current.items.push(navItem)
    }
  }

  // Flush the last open group.
  if (current !== null)
    groups.push(current)

  return groups
}

// ---------------------------------------------------------------------------
// Composable
// ---------------------------------------------------------------------------

/**
 * Wraps toV2NavGroups in a computed ref.
 *
 * Accepts the raw v1 nav items as a parameter so the composable (composables
 * boundary zone) does not need to import from @/navigation (navigation zone).
 * Call-sites in layouts/pages — which ARE allowed to import navigation —
 * pass orgNavItems directly:
 *
 *   import { orgNavItems } from '@/navigation/vertical'
 *   const { groups } = useV2Nav(orgNavItems)
 */
export function useV2Nav(items: readonly V1NavEntry[]): { groups: ComputedRef<V2NavGroup[]> } {
  const groups = computed(() => toV2NavGroups(items))

  return { groups }
}