/**
 * Checks which slugs a category may take. A category's feed lives at the URL
 * root (`/music`), so its slug must not shadow another top-level page. The
 * category service runs this check when a category is created or renamed, and
 * the migrations that reserve more words rename the categories that had one
 * with {@link renameReservedCategories}.
 *
 * Dump and playlist slugs reserve nothing: they live under their owner's
 * `dumps/` and `playlists/`, where nothing else is named by a user. A user
 * can't clash with a category either, since `@` is never in a slug.
 *
 * @module
 */

import type { DatabaseSync } from "node:sqlite";
import { FEED_TABS } from "../../shared/paths.ts";

/**
 * Lists the top-level path segments a category slug may not take: the feed
 * tabs (`/hot`), the SPA's own pages (`src/App.tsx`), and `api`, `ws`,
 * `assets` and `emojibase`, which the server answers before the SPA. Keep it
 * in step with the route table and the build's top-level folders.
 */
export const RESERVED_SLUGS: readonly string[] = [
  ...FEED_TABS,
  "search",
  "login",
  "register",
  "notifications",
  "reset-password",
  "unsubscribe",
  "settings",
  "manage",
  "community",
  "authorize",
  "federation",
  "api",
  "ws",
  "assets",
  "emojibase",
];

/** Checks whether `slug` is one of the {@link RESERVED_SLUGS}. */
export function isReservedSlug(slug: string): boolean {
  return RESERVED_SLUGS.includes(slug);
}

/**
 * Renames each category whose slug is now reserved, such as `hot`, to the
 * first of `<slug>-2`, `<slug>-3`… that is free, and logs it. Migration 0021
 * runs it for v4's words, 0022 for `community`, and 0024 for `authorize` and
 * `federation`.
 */
export function renameReservedCategories(db: DatabaseSync): void {
  const rows = db.prepare(`SELECT id, slug FROM categories;`).all() as {
    id: string;
    slug: string;
  }[];
  const taken = new Set(rows.map((r) => r.slug));
  for (const { id, slug } of rows) {
    if (!isReservedSlug(slug)) continue;
    let n = 2;
    while (taken.has(`${slug}-${n}`) || isReservedSlug(`${slug}-${n}`)) n++;
    const renamed = `${slug}-${n}`;
    taken.add(renamed);
    db.prepare(`UPDATE categories SET slug = ? WHERE id = ?;`).run(renamed, id);
    console.log(
      `[migrate] category "${slug}" is now "${renamed}": its slug is reserved`,
    );
  }
}