import type { VercelRequest, VercelResponse } from '@vercel/node';

export type ApiHandler = (req: VercelRequest, res: VercelResponse) => Promise<void>;

function resolveCorsOrigin(req: VercelRequest): string {
  const requestOrigin = typeof req.headers.origin === 'string' ? req.headers.origin.trim() : '';
  const ALLOWED_ORIGINS = [
    'https://getcert.eu.cc',
    'https://verify.getcert.eu.cc',
    'https://getcert.vercel.app',
    'http://localhost:5173',
    'http://localhost:3000',
    'http://localhost:3001',
  ];

  if (
    requestOrigin &&
    (ALLOWED_ORIGINS.includes(requestOrigin) ||
      requestOrigin.endsWith('.getcert.eu.cc') ||
      requestOrigin.endsWith('.vercel.app'))
  ) {
    return requestOrigin;
  }

  const configured = (process.env.APP_ORIGIN || '').trim();
  if (configured && !configured.includes('hf.space')) {
    return configured;
  }

  return 'https://getcert.eu.cc';
}


export function applyCors(req: VercelRequest, res: VercelResponse): void {
  const origin = resolveCorsOrigin(req);
  res.setHeader('Vary', 'Origin');
  res.setHeader('Access-Control-Allow-Origin', origin);
  res.setHeader('Access-Control-Allow-Methods', 'GET,POST,OPTIONS');
  res.setHeader(
    'Access-Control-Allow-Headers',
    'Content-Type, Authorization, x-admin-review-secret, x-payment-review-secret'
  );
}

export function withCors(handler: ApiHandler): ApiHandler {
  return async (req, res) => {
    applyCors(req, res);

    if (req.method === 'OPTIONS') {
      res.status(200).end();
      return;
    }

    await handler(req, res);
  };
}

export function assertMethod(req: VercelRequest, res: VercelResponse, method: 'GET' | 'POST'): boolean {
  if (req.method === 'HEAD' && method === 'GET') {
    return true;
  }
  if (req.method !== method) {
    res.status(405).json({ success: false, error: `Method ${req.method} not allowed` });
    return false;
  }
  return true;
}

export function parseJsonBody<T>(req: VercelRequest): T {
  if (!req.body) {
    return {} as T;
  }

  if (typeof req.body === 'string') {
    return JSON.parse(req.body) as T;
  }

  return req.body as T;
}

export function ok(res: VercelResponse, payload: unknown): void {
  res.status(200).json({ success: true, data: payload });
}

export function fail(res: VercelResponse, status: number, error: string, details?: unknown): void {
  res.status(status).json({
    success: false,
    error,
    details: details ?? null,
  });
}