import { isValidPreviewId, PREVIEW_ID_QUERY_PARAM } from '@akinon/next/utils/preview';
import {
  DEFAULT_PREVIEW_LINK_TTL_SECONDS,
  signPreviewToken
} from '@akinon/next/utils/preview-token';
import { NextRequest, NextResponse } from 'next/server';

/**
 * Mints a signed, expiring preview entry token for the theme editor.
 *
 * The editor is a static SPA on another origin and must never hold the
 * storefront's PREVIEW_SECRET. Instead it proves it is an editor user by
 * forwarding its Omnitron session token; this handler verifies that token
 * against Omnitron (`OMNITRON_URL`) and answers with a token the editor puts
 * on the link as `?preview=<token>`. The link opens exactly one preview and
 * stops working after PREVIEW_LINK_TTL_SECONDS (default 24h).
 *
 * CORS is open on purpose: the request carries no cookies, only the caller's
 * Omnitron token, and the response is worthless without one.
 */
const CORS_HEADERS = {
  'Access-Control-Allow-Origin': '*',
  'Access-Control-Allow-Methods': 'GET, OPTIONS',
  'Access-Control-Allow-Headers': 'Authorization, Content-Type',
  'Access-Control-Max-Age': '600',
  'Cache-Control': 'no-store'
};

const json = (body: Record<string, unknown>, status: number) =>
  NextResponse.json(body, { status, headers: CORS_HEADERS });

export async function OPTIONS() {
  return new NextResponse(null, { status: 204, headers: CORS_HEADERS });
}

/** Bounded wait for Omnitron — an unreachable host must fail fast, not hang the editor. */
const OMNITRON_TIMEOUT_MS = 8_000;

/** True when Omnitron accepts the token as a signed-in user. */
const isEditorUser = async (
  omnitronUrl: string,
  authorization: string
): Promise<boolean> => {
  try {
    const response = await fetch(
      `${omnitronUrl.replace(/\/+$/, '')}/api/v1/active_user/`,
      {
        headers: { Authorization: authorization, Accept: 'application/json' },
        cache: 'no-store',
        signal: AbortSignal.timeout(OMNITRON_TIMEOUT_MS)
      }
    );
    return response.status === 200;
  } catch {
    return false;
  }
};

export async function GET(request: NextRequest) {
  const secret = process.env.PREVIEW_SECRET;
  const omnitronUrl = process.env.OMNITRON_URL;
  if (!secret || !omnitronUrl) {
    return json(
      {
        error: 'preview-disabled',
        message:
          'Preview links are disabled: PREVIEW_SECRET and OMNITRON_URL must both be configured on the storefront.'
      },
      503
    );
  }

  const previewId =
    request.nextUrl.searchParams.get(PREVIEW_ID_QUERY_PARAM) ?? '';
  if (!isValidPreviewId(previewId)) {
    return json(
      { error: 'invalid-preview-id', message: 'A valid preview_id is required.' },
      400
    );
  }

  const authorization = request.headers.get('authorization') ?? '';
  if (!/^Token \S+$/i.test(authorization)) {
    return json(
      { error: 'unauthorized', message: 'An Omnitron token is required.' },
      401
    );
  }
  if (!(await isEditorUser(omnitronUrl, authorization))) {
    return json(
      {
        error: 'unauthorized',
        message: `Omnitron at ${omnitronUrl} did not accept the token (or did not answer).`
      },
      401
    );
  }

  const ttl =
    Number(process.env.PREVIEW_LINK_TTL_SECONDS) ||
    DEFAULT_PREVIEW_LINK_TTL_SECONDS;
  const expiresAt = Math.floor(Date.now() / 1000) + ttl;
  const token = await signPreviewToken({ previewId, expiresAt }, secret);

  return json(
    {
      token,
      previewId,
      expiresAt: new Date(expiresAt * 1000).toISOString(),
      // Ready to append to any page url of this storefront.
      query: `preview=${encodeURIComponent(token)}`
    },
    200
  );
}