import { draftMode, cookies } from "next/headers";
import { fetchAPI } from "./api-client";
import type { WagtailPageSummary } from "@/types/wagtail";

/**
 * Wagtail 预览模式（wagtail_headless_preview + Next.js Draft Mode）。
 * 详见 documents/设计方案分析与完善版.md §2.16，后端实现见 apps/api/urls.py
 * 的 PagePreviewAPIViewSet（挂载在 /api/v2/page_preview/）。
 */

export const PREVIEW_CONTENT_TYPE_COOKIE = "wagtail_preview_content_type";
export const PREVIEW_TOKEN_COOKIE = "wagtail_preview_token";

/** content_type（`app_label.model`，小写）→ 对应前端路由的解析函数 */
const PREVIEW_PATH_RESOLVERS: Record<
  string,
  (page: WagtailPageSummary) => string
> = {
  "home.homepage": () => "/",
  "blog.blogpage": (page) => `/blog/${page.meta.slug}`,
  "products.productpage": (page) => `/products/${page.meta.slug}`,
  "cases.casestudypage": (page) => `/cases/${page.meta.slug}`,
  "solutions.solutionpage": (page) => `/solutions/${page.meta.slug}`,
};

/** 根据 content_type 解析预览内容应跳转到的前端路径，未知类型返回 null。 */
export function resolvePreviewPath(
  contentType: string,
  page: WagtailPageSummary,
): string | null {
  const resolver = PREVIEW_PATH_RESOLVERS[contentType];
  return resolver ? resolver(page) : null;
}

/**
 * 拉取草稿页面数据。`fields` 省略时仅返回 Wagtail API 默认字段（含 meta.slug/meta.type），
 * 用于 /preview 路由校验 token 是否有效。
 */
export async function fetchPreviewPage<T extends WagtailPageSummary>(
  contentType: string,
  token: string,
  fields?: string,
): Promise<T | null> {
  const query = new URLSearchParams({ content_type: contentType, token });
  if (fields) {
    query.set("fields", fields);
  }
  try {
    return await fetchAPI<T>(`/api/v2/page_preview/?${query.toString()}`, {
      revalidate: 0,
    });
  } catch {
    return null;
  }
}

/**
 * 在页面组件中调用：若 Draft Mode 已开启且 cookie 中记录的 content_type
 * 与当前页面类型一致，返回草稿数据；否则回退到 `fallback()`（正常已发布内容）。
 */
export async function getPreviewOrFallback<T extends WagtailPageSummary>(
  expectedContentType: string,
  fields: string,
  fallback: () => Promise<T | null>,
): Promise<T | null> {
  const { isEnabled } = await draftMode();
  if (!isEnabled) {
    return fallback();
  }

  const cookieStore = await cookies();
  const contentType = cookieStore.get(PREVIEW_CONTENT_TYPE_COOKIE)?.value;
  const token = cookieStore.get(PREVIEW_TOKEN_COOKIE)?.value;

  if (contentType !== expectedContentType || !token) {
    return fallback();
  }

  const preview = await fetchPreviewPage<T>(expectedContentType, token, fields);
  return preview ?? fallback();
}