import type { Metadata } from "next";

/**
 * 公开站点 origin（访客浏览器地址栏），与 Go CORS 的 SITE_URL 同源。
 * 不使用 BACKEND_URL / NEXT_PUBLIC_API_URL（那是 Go API，可能是容器内网）。
 */

const TRACKING_KEYS = new Set([
  "gclid",
  "gbraid",
  "wbraid",
  "dclid",
  "fbclid",
  "msclkid",
  "twclid",
  "ttclid",
  "yclid",
  "_ga",
  "_gl",
  "mc_cid",
  "mc_eid",
]);

export type QueryValue = string | number | undefined | null;
export type QueryBag = Record<string, QueryValue>;
export type FeedSort = "latest" | "new" | "recommended";

function envOriginRaw(): string {
  return (process.env.SITE_URL || "").trim();
}

/** 解析为无尾斜杠的 http(s) origin；路径/账号/内部服务名视为非法 */
export function parseSiteOrigin(raw: string | undefined | null): string | null {
  const s = raw?.trim() ?? "";
  if (!s) return null;
  let u: URL;
  try {
    u = new URL(s);
  } catch {
    return null;
  }
  if (u.protocol !== "http:" && u.protocol !== "https:") return null;
  if (u.username || u.password) return null;
  const host = u.hostname.toLowerCase();
  if (!host || host === "api" || host.endsWith(".internal")) return null;
  const path = u.pathname.replace(/\/+$/, "");
  if (path !== "") return null;
  return `${u.protocol}//${u.host}`;
}

/**
 * 运行时公开 origin。
 * 开发态未配置时用 http://localhost:3000；生产态缺失或非法则返回 null（不回退 localhost）。
 */
export function resolveSiteOrigin(): string | null {
  const parsed = parseSiteOrigin(envOriginRaw());
  if (parsed) return parsed;
  if (process.env.NODE_ENV !== "production") return "http://localhost:3000";
  return null;
}

export function metadataBaseURL(): URL | undefined {
  const origin = resolveSiteOrigin();
  return origin ? new URL(`${origin}/`) : undefined;
}

export function isTrackingParam(key: string): boolean {
  const k = key.toLowerCase();
  return k.startsWith("utm_") || TRACKING_KEYS.has(k);
}

/** 路径规范化：保证以 / 开头，除首页外去掉尾斜杠 */
export function canonicalPath(pathname: string, query?: QueryBag): string {
  let path = pathname.trim() || "/";
  if (!path.startsWith("/")) path = `/${path}`;
  if (path.length > 1) path = path.replace(/\/+$/, "");
  const params = new URLSearchParams();
  if (query) {
    const keys = Object.keys(query).sort();
    for (const key of keys) {
      if (isTrackingParam(key)) continue;
      const raw = query[key];
      if (raw == null || raw === "") continue;
      params.set(key, String(raw));
    }
  }
  const qs = params.toString();
  return qs ? `${path}?${qs}` : path;
}

export function absoluteCanonical(pathname: string, query?: QueryBag): string | undefined {
  const origin = resolveSiteOrigin();
  if (!origin) return undefined;
  return `${origin}${canonicalPath(pathname, query)}`;
}

/** 写入 generateMetadata 的 alternates.canonical；origin 不可用时不加字段 */
export function canonicalFields(pathname: string, query?: QueryBag): Pick<Metadata, "alternates"> {
  const href = absoluteCanonical(pathname, query);
  if (!href) return {};
  return { alternates: { canonical: href } };
}

/** 页码：非法或 ≤1 视为首页（省略 page） */
export function canonicalPage(raw: string | undefined): number | undefined {
  const n = parseInt(raw || "1", 10);
  const page = Number.isFinite(n) ? Math.max(1, n) : 1;
  return page > 1 ? page : undefined;
}

/** 板块 id：≤0 或非法则省略 */
export function canonicalBoard(raw: string | undefined): number | undefined {
  const n = parseInt(raw || "0", 10);
  if (!Number.isFinite(n) || n <= 0) return undefined;
  return n;
}

export function defaultFeedSort(allowComments: boolean): FeedSort {
  return allowComments ? "latest" : "new";
}

/** 与首页 page.tsx 的排序解析一致 */
export function normalizeFeedSort(v: string | undefined, allowComments: boolean): FeedSort {
  if (v === "recommended") return "recommended";
  if (v === "new") return "new";
  if (!allowComments) return "new";
  if (v === "latest") return "latest";
  return "latest";
}

/**
 * 首页 query 归一化：保留 q / 非默认 sort / 有效 board / page>1；
 * 搜索时 board 不参与列表查询，故省略。
 */
export function homeCanonicalQuery(
  sp: { q?: string; page?: string; sort?: string; board?: string },
  allowComments: boolean
): QueryBag {
  const q = sp.q?.trim() || "";
  const bag: QueryBag = {};
  if (q) bag.q = q;
  const page = canonicalPage(sp.page);
  if (page) bag.page = page;
  const sort = normalizeFeedSort(sp.sort, allowComments);
  if (sort !== defaultFeedSort(allowComments)) bag.sort = sort;
  if (!q) {
    const board = canonicalBoard(sp.board);
    if (board) bag.board = board;
  }
  return bag;
}