import { HttpError } from "@/lib/errors";
import { readJson, route } from "@/lib/http";
import { categoryCounts, mutatePosts, readPosts } from "@/lib/store";
import { SLUG_RE } from "@/lib/validate";

export const dynamic = "force-dynamic";

export const GET = route(async () => {
  const { posts, revision } = await readPosts();
  return Response.json({ categories: categoryCounts(posts), revision });
});

/**
 * Body: { from, to, revision? }. Moves every post in `from` to `to`; if `to`
 * is already in use this is a merge. Categories are derived from posts, so a
 * category disappears once no post uses it.
 */
export const PATCH = route(async (req) => {
  const { from, to, revision: expected } = await readJson<{ from?: string; to?: string; revision?: string }>(req);
  const target = to?.trim() ?? "";
  if (!from) throw new HttpError(400, "from is required");
  if (!SLUG_RE.test(target)) throw new HttpError(400, "category must be lowercase kebab-case");

  const { result, revision } = await mutatePosts(expected, (posts) => {
    let changed = 0;
    for (const post of posts) {
      if (post.category !== from) continue;
      post.category = target;
      changed++;
    }
    if (!changed) throw new HttpError(404, `no posts in category "${from}"`);
    return changed;
  });
  return Response.json({ changed: result, revision });
});