/**
 * Short link client.
 *
 * - `createShortLink` runs in the browser and POSTs to `/api/share`, a Next.js
 *   route handler that proxies to the BFF. We can't call the BFF directly
 *   from the browser because `BFF_URL` is not exposed to the client bundle
 *   (no `NEXT_PUBLIC_` prefix). Same-origin proxy also avoids CORS.
 *
 * - `resolveShortLink` is only called from the `/share/[code]` server
 *   component, so it can use `bff()` directly with the server-side env var.
 */

import { bff } from "@/lib/bff";

// Module-scoped cache: a single user shouldn't generate a fresh code every
// time they re-click Share on the same selection. Keyed by the relative path
// (including ?hl=…), this returns the same promise for repeat calls.
const createCache = new Map<string, Promise<string | null>>();

type ResolveResponse = { url: string };

/**
 * Create a short code for a same-site relative path (`/books/bg/18/66?hl=…`).
 * Returns `null` on any failure — caller should fall back to the long URL.
 */
export function createShortLink(longPath: string): Promise<string | null> {
  const cached = createCache.get(longPath);
  if (cached) return cached;

  const promise = fetch("/api/share", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Accept: "application/json",
    },
    body: JSON.stringify({ url: longPath }),
  })
    .then(async (res) => {
      if (!res.ok) return null;
      const json = await res.json().catch(() => null);
      const code = json?.data?.code;
      return typeof code === "string" ? code : null;
    })
    .catch(() => null);

  createCache.set(longPath, promise);
  // If the request fails, evict so the next click can retry instead of
  // returning the cached null forever.
  promise.then((code) => {
    if (code === null) createCache.delete(longPath);
  });

  return promise;
}

/**
 * Resolve a short code to its full long path. Returns `null` when the code is
 * not found, expired, disabled, or the BFF is unreachable.
 */
export async function resolveShortLink(code: string): Promise<string | null> {
  try {
    const r = await bff<ResolveResponse>(`/share/${encodeURIComponent(code)}`, {
      revalidate: 0,
    });
    return r?.url ?? null;
  } catch {
    return null;
  }
}