import { useEffect, useState } from 'react'
import { api } from '../api/client.js'

// Which shard surfaces the current viewer may reach, from
// GET /public/shard/features. Admins configure this per feature (Admin → Shard
// Visibility), so the nav can't be a static list any more.
//
// This is PRESENTATION only. The gate is server-side: a disabled feature 404s
// and an out-of-rung one 403s whether or not the link is rendered. So while the
// answer is still in flight we return `null` and callers show their default set
// — better a link that briefly 403s than a nav that flickers in on every load.
//
// Cached module-level: the answer is per-viewer but stable for a session, and
// every consumer would otherwise refetch it on mount.
let cached = null
let inFlight = null

export function resetShardFeatures() {
  cached = null
  inFlight = null
}

export function useShardFeatures() {
  const [features, setFeatures] = useState(cached)

  useEffect(() => {
    if (cached) return undefined
    let alive = true
    inFlight =
      inFlight ||
      api.shard
        .features()
        .then((data) => {
          cached = { level: data.level, set: new Set(data.features || []) }
          return cached
        })
        .catch(() => {
          // A failed lookup must not blank the nav — fall back to "show
          // everything" and let the server do the gating.
          cached = null
          inFlight = null
          return null
        })
    inFlight.then((result) => {
      if (alive) setFeatures(result)
    })
    return () => {
      alive = false
    }
  }, [])

  return features
}

// Convenience: true when `name` is visible, or when we don't know yet.
export function canSee(features, name) {
  return !features || features.set.has(name)
}