import { notFound, redirect } from 'next/navigation'

/**
 * Minimal shape of a blog client's slug lookup. Matches both the shared
 * `@startsimpli/api/blog` client (`createBlogClient().fetchPostBySlug`) and the
 * legacy per-app `blog-api-server` modules, so callers can pass whichever they
 * already have without migrating their data layer first.
 */
export type ArticleSlugFetcher<TPost> = (slug: string) => Promise<TPost | null | undefined>

export interface ResolveArticleOptions {
  /**
   * List/index route a missing article falls back to, e.g. `/resources` or
   * `/articles`. Dead, stale, or mistyped article links land here.
   */
  indexPath: string
  /**
   * Behaviour when no post matches the slug.
   * - `'redirect'` (default): 307 to `indexPath` — the smart landing that keeps
   *   visitors (and crawlers following old links) inside the content instead of
   *   on a bare 404.
   * - `'notFound'`: trigger the nearest `not-found.tsx` (404 status). Use for
   *   routes where preserving the 404 signal matters more than the soft landing.
   */
  onMissing?: 'redirect' | 'notFound'
}

/**
 * Resolve a blog post by slug, applying the shared missing-article default.
 *
 * Every marketing-site article route (`/resources/[slug]`, `/articles/[slug]`,
 * `/guides/[guide]`, …) should call this instead of hand-rolling
 * `if (!post) notFound()` — so a non-existent or removed article URL
 * smart-redirects to its list page by default, consistently across every app
 * that shares the blog layer.
 *
 * Never returns a nullish value: it either returns the resolved post or throws
 * the redirect / not-found control-flow signal that Next.js expects. Call it at
 * the top level of a Server Component (do not wrap in try/catch, or the signal
 * will be swallowed).
 */
export async function resolveArticleOrFallback<TPost>(
  fetchPostBySlug: ArticleSlugFetcher<TPost>,
  slug: string,
  { indexPath, onMissing = 'redirect' }: ResolveArticleOptions,
): Promise<TPost> {
  const post = await fetchPostBySlug(slug)
  if (post) return post
  if (onMissing === 'notFound') notFound()
  redirect(indexPath)
}