import type { H3Event } from "h3";
import { createError, deleteCookie, getCookie, setCookie } from "h3";

/** 上游没有声明 session 过期时间时，本地登录态默认保留 3 天 */
const DEFAULT_AUTH_COOKIE_MAX_AGE = 60 * 60 * 24 * 3;

/** 本站保存 NewAPI session 的 httpOnly cookie 名称 */
export const NEWAPI_SESSION_COOKIE = "newapi_session";
/** 本站保存 NewAPI 用户 ID 的 httpOnly cookie 名称，用于服务端组装 New-Api-User */
export const NEWAPI_USER_ID_COOKIE = "newapi_user_id";

type CookieOptions = NonNullable<Parameters<typeof setCookie>[3]>;

export interface INewApiCookieMeta {
  /** 上游 session cookie 的 Max-Age，单位秒 */
  maxAge?: number;
  /** 上游 session cookie 的 Expires 过期时间 */
  expires?: Date;
}

/**
 * 从上游 Set-Cookie 响应头中提取指定 cookie 的值。
 *
 * 只返回 cookie value，不返回 Path/Expires 等属性，避免把元数据写进
 * 本站 newapi_session。
 */
export const extractCookieValueFromSetCookie = (
  headers: Headers,
  name: string
): string | null => {
  const setCookie = findSetCookie(headers, name);
  if (!setCookie) return null;

  const firstPart = setCookie.split(";")[0] ?? "";
  const equalsIndex = firstPart.indexOf("=");
  if (equalsIndex === -1) return null;

  return firstPart.slice(equalsIndex + 1).trim() || null;
};

/**
 * 从上游 Set-Cookie 中读取过期时间元数据。
 *
 * 本站 cookie 优先沿用上游 Max-Age/Expires；没有则在写入时默认 3 天。
 */
export const extractCookieMetaFromSetCookie = (
  headers: Headers,
  name: string
): INewApiCookieMeta | undefined => {
  const setCookie = findSetCookie(headers, name);
  if (!setCookie) return undefined;

  const meta: INewApiCookieMeta = {};
  for (const part of setCookie.split(";").slice(1)) {
    const [rawKey, ...rawValue] = part.trim().split("=");
    const key = rawKey?.toLowerCase();
    const value = rawValue.join("=");

    if (key === "max-age") {
      const maxAge = Number.parseInt(value, 10);
      if (Number.isFinite(maxAge)) meta.maxAge = maxAge;
    }

    if (key === "expires") {
      const expires = new Date(value);
      if (!Number.isNaN(expires.getTime())) meta.expires = expires;
    }
  }

  return meta.maxAge !== undefined || meta.expires ? meta : undefined;
};

/**
 * 写入本站认证 cookie。
 *
 * session 与 userId 都设置为 httpOnly，前端只通过 /api/auth/me 恢复状态，
 * 不直接接触 NewAPI session 明文。
 */
export const setNewApiAuthCookies = (
  event: H3Event,
  session: string,
  userId: number | string,
  upstreamCookieMeta?: INewApiCookieMeta
) => {
  const options = buildAuthCookieOptions(upstreamCookieMeta);

  setCookie(event, NEWAPI_SESSION_COOKIE, session, options);
  setCookie(event, NEWAPI_USER_ID_COOKIE, String(userId), options);
};

/** 清理本站保存的 NewAPI 登录态，登出和鉴权失败时都调用 */
export const clearNewApiAuthCookies = (event: H3Event) => {
  const options: CookieOptions = {
    path: "/",
    sameSite: "lax",
    secure: process.env.NODE_ENV === "production"
  };

  deleteCookie(event, NEWAPI_SESSION_COOKIE, options);
  deleteCookie(event, NEWAPI_USER_ID_COOKIE, options);
};

/** 从本项目 httpOnly cookie 中读取 NewAPI 用户 ID，缺失或非法时统一视为未登录 */
export const getNewApiUserIdFromCookie = (event: H3Event): number => {
  const userId = Number.parseInt(
    getCookie(event, NEWAPI_USER_ID_COOKIE) ?? "",
    10
  );

  if (!Number.isInteger(userId) || userId <= 0) {
    throw createError({
      statusCode: 401,
      statusMessage: "未登录"
    });
  }

  return userId;
};

/** 统一生成本站认证 cookie 选项，保证安全属性在两个 cookie 上一致 */
const buildAuthCookieOptions = (meta?: INewApiCookieMeta): CookieOptions => {
  const options: CookieOptions = {
    httpOnly: true,
    path: "/",
    sameSite: "lax",
    secure: process.env.NODE_ENV === "production"
  };

  if (typeof meta?.maxAge === "number") {
    options.maxAge = meta.maxAge;
  } else if (meta?.expires) {
    options.expires = meta.expires;
  } else {
    options.maxAge = DEFAULT_AUTH_COOKIE_MAX_AGE;
  }

  return options;
};

/** 在多个 Set-Cookie 值中找到指定名称的 cookie */
const findSetCookie = (headers: Headers, name: string): string | null => {
  const lowerName = name.toLowerCase();

  for (const setCookie of getSetCookieValues(headers)) {
    const firstPart = setCookie.split(";")[0] ?? "";
    const equalsIndex = firstPart.indexOf("=");
    if (equalsIndex === -1) continue;

    const cookieName = firstPart.slice(0, equalsIndex).trim().toLowerCase();
    if (cookieName === lowerName) return setCookie;
  }

  return null;
};

/**
 * 读取 Set-Cookie 头。
 *
 * Nuxt 服务端运行时优先使用 getSetCookie；没有该方法时读取合并后的
 * set-cookie 字符串再拆分。
 */
const getSetCookieValues = (headers: Headers): string[] => {
  const headersWithSetCookie = headers as Headers & {
    getSetCookie?: () => string[];
  };
  const values = headersWithSetCookie.getSetCookie?.();
  if (values?.length) return values;

  const headerValue = headers.get("set-cookie");
  return headerValue ? splitSetCookieHeader(headerValue) : [];
};

/**
 * 拆分被合并成一个字符串的 Set-Cookie。
 *
 * Expires 属性本身包含逗号，不能简单按逗号 split；这里只在后续片段
 * 看起来像新 cookie 名称时才切分。
 */
const splitSetCookieHeader = (headerValue: string): string[] => {
  const cookies: string[] = [];
  let start = 0;

  for (let index = 0; index < headerValue.length; index += 1) {
    if (headerValue[index] !== ",") continue;

    const rest = headerValue.slice(index + 1);
    if (/^\s*[^=;,\s]+=/.test(rest)) {
      cookies.push(headerValue.slice(start, index).trim());
      start = index + 1;
    }
  }

  cookies.push(headerValue.slice(start).trim());
  return cookies.filter(Boolean);
};