import type { MetadataRoute } from 'next';
import type { SitemapEntry } from '#web-runtime/types';
import type { PublicPathResolver } from './page-metadata';

/**
 * Turns the backend's page listing into sitemap entries.
 *
 * Pages that share a `groupKey` are the same page in different languages, so each entry links
 * to its siblings through `alternates.languages` — the sitemap equivalent of the `hreflang`
 * tags on the page itself, and the form Google prefers for multilingual sites.
 *
 * Kept free of `next/headers` and routing setup so it can be tested directly: the caller
 * supplies the path resolver and the absolute origin.
 */
export function buildSitemap(
  entries: SitemapEntry[],
  origin: URL,
  publicPath: PublicPathResolver
): MetadataRoute.Sitemap {
  const absolute = (locale: string, path: string) => new URL(publicPath(locale, path), origin).href;

  const byGroupKey = new Map<string, SitemapEntry[]>();
  for (const entry of entries) {
    if (!entry.groupKey) continue;

    const group = byGroupKey.get(entry.groupKey);
    if (group) group.push(entry);
    else byGroupKey.set(entry.groupKey, [entry]);
  }

  return entries.map((entry) => {
    const siblings = byGroupKey.get(entry.groupKey) ?? [];
    const lastModified = entry.updatedAt ?? entry.publishedAt;
    const item: MetadataRoute.Sitemap[number] = {
      url: absolute(entry.locale, entry.path)
    };

    if (lastModified) {
      item.lastModified = new Date(lastModified);
    }

    // A single-locale group has nothing to point at but itself; omit the noise.
    if (siblings.length > 1) {
      item.alternates = {
        languages: Object.fromEntries(
          siblings.map((sibling) => [sibling.locale, absolute(sibling.locale, sibling.path)])
        )
      };
    }

    return item;
  });
}