import type { MetadataRoute } from "next";
import { routing } from "@/i18n/routing";
import { getAllPosts } from "@/lib/posts";
import { siteConfig } from "@/lib/site-config";

/**
 * 动态生成 sitemap.xml。
 *
 * 覆盖：首页、关于页，以及全部已发布文章（草稿不会出现在这里）。
 * 每个条目都带上 hreflang alternate，帮助搜索引擎理解多语言对应关系。
 *
 * 内容来自数据库，因此 sitemap 也在请求时生成并缓存，
 * 而不是在构建期固化——否则构建之后新增的文章不会出现在 sitemap 中。
 *
 * 注意：Next.js 要求 sitemap 返回绝对 URL。
 */
export const revalidate = 60;

export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
	const posts = await getAllPosts();

	/** 为一条路径生成所有语言的 alternates */
	const buildAlternates = (path: string) => ({
		languages: Object.fromEntries(
			routing.locales.map((locale) => [
				locale,
				`${siteConfig.url}/${locale}${path}`,
			]),
		),
	});

	const staticEntries: MetadataRoute.Sitemap = routing.locales.flatMap(
		(locale) => [
			{
				url: `${siteConfig.url}/${locale}`,
				lastModified: new Date(),
				changeFrequency: "daily" as const,
				priority: 1,
				alternates: buildAlternates(""),
			},
			{
				url: `${siteConfig.url}/${locale}/about`,
				lastModified: new Date(),
				changeFrequency: "monthly" as const,
				priority: 0.6,
				alternates: buildAlternates("/about"),
			},
		],
	);

	const postEntries: MetadataRoute.Sitemap = routing.locales.flatMap((locale) =>
		posts.map((post) => ({
			url: `${siteConfig.url}/${locale}/posts/${post.slug}`,
			lastModified: new Date(`${post.date}T00:00:00Z`),
			changeFrequency: "weekly" as const,
			priority: 0.8,
			alternates: buildAlternates(`/posts/${post.slug}`),
		})),
	);

	return [...staticEntries, ...postEntries];
}