import type { CouponPreviewResponse } from '@/types/coupon';

function extractErrorMessage(payload: unknown): string {
  if (!payload || typeof payload !== 'object') {
    return 'coupon_error_generic';
  }

  const data = payload as Record<string, any>;

  if (data.message && typeof data.message === 'string') {
    return data.message;
  }

  if (data.errors) {
    const errors = data.errors as Record<string, string[]>;
    const firstKey = Object.keys(errors)[0];
    if (firstKey && Array.isArray(errors[firstKey]) && errors[firstKey][0]) {
      return errors[firstKey][0];
    }
  }

  return 'coupon_error_generic';
}

export async function previewCoupon(packageId: number, code: string): Promise<CouponPreviewResponse> {
  const response = await fetch('/api/v1/marketing/coupons/preview', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
    },
    body: JSON.stringify({
      package_id: packageId,
      code,
    }),
  });

  const payload = await response.json().catch(() => ({}));

  if (!response.ok) {
    throw new Error(extractErrorMessage(payload));
  }

  return payload as CouponPreviewResponse;
}