import type { IdentityUser } from "@/modules/identity/contracts";
import {
  IdentityAuthorizationError,
  type IdentityServerSession,
} from "@/modules/identity/session";
import {
  authorizeAdminAccess,
  type AdminPermission,
  type AdminRole,
} from "./auth-policy";

export type AdminSession = {
  user: IdentityUser;
  roles: AdminRole[];
  permissions: AdminPermission[];
  requiresMfa: boolean;
  identitySession: {
    id: string;
    token: string;
    expiresAt: Date;
  };
};

export class AdminAuthorizationError extends Error {
  constructor(
    message: string,
    readonly status: 401 | 403 | 503,
  ) {
    super(message);
    this.name = "AdminAuthorizationError";
  }
}

export type AdminAuthorizationDependencies<IdentityConfig> = {
  readAuthProvider: () => string | undefined;
  readRequestHeaders: () => Headers | Promise<Headers>;
  readIdentityConfig: () => IdentityConfig;
  resolveIdentitySurface: (
    host: string | null,
    config: IdentityConfig,
  ) => "user" | "admin" | null;
  requireIdentitySession: (
    requestHeaders: Headers,
  ) => Promise<IdentityServerSession>;
  loadAdminSession: (
    user: IdentityUser,
    identitySession: AdminSession["identitySession"],
  ) => Promise<AdminSession>;
};

export async function authorizeAdminRequest<IdentityConfig>(
  permission: AdminPermission,
  requestHeaders: Headers | undefined,
  dependencies: AdminAuthorizationDependencies<IdentityConfig>,
): Promise<AdminSession> {
  try {
    if (dependencies.readAuthProvider()?.trim() !== "self-hosted") {
      throw new AdminAuthorizationError("后台身份服务未启用", 403);
    }

    const adminHeaders = requestHeaders
      ?? new Headers(await dependencies.readRequestHeaders());
    const identityConfig = dependencies.readIdentityConfig();
    if (
      dependencies.resolveIdentitySurface(
        adminHeaders.get("host"),
        identityConfig,
      ) !== "admin"
    ) {
      throw new AdminAuthorizationError("无权访问后台", 403);
    }

    const identitySession = await dependencies.requireIdentitySession(adminHeaders);
    const session = await dependencies.loadAdminSession(identitySession.user, {
      id: identitySession.sessionId,
      token: identitySession.sessionToken,
      expiresAt: identitySession.expiresAt,
    });
    const authorization = authorizeAdminAccess(
      identitySession.user,
      session.permissions,
      permission,
    );
    if (!authorization.allowed) {
      throw new AdminAuthorizationError("无权执行此操作", authorization.status);
    }
    return session;
  } catch (error) {
    if (error instanceof AdminAuthorizationError) throw error;
    if (error instanceof IdentityAuthorizationError) {
      throw new AdminAuthorizationError(
        error.status === 401 ? "请先登录" : "无权访问后台",
        error.status,
      );
    }
    throw new AdminAuthorizationError("后台服务暂时不可用", 503);
  }
}