interface UspsToken {
  accessToken: string;
  expiresAt: number;
}

let cachedToken: UspsToken | null = null;

const USPS_BASE =
  process.env.USPS_ENV === 'production'
    ? 'https://apis.usps.com'
    : 'https://apis-tem.usps.com';

export function uspsConfigured(): boolean {
  return !!(process.env.USPS_CLIENT_ID && process.env.USPS_CLIENT_SECRET);
}

async function getToken(): Promise<string> {
  if (cachedToken && cachedToken.expiresAt > Date.now() + 60_000) {
    return cachedToken.accessToken;
  }
  const resp = await fetch(`${USPS_BASE}/oauth2/v3/token`, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      client_id: process.env.USPS_CLIENT_ID,
      client_secret: process.env.USPS_CLIENT_SECRET,
      grant_type: 'client_credentials',
      scope: 'addresses'
    })
  });
  const data = await resp.json();
  if (!resp.ok) throw new Error('USPS auth failed: ' + JSON.stringify(data));
  cachedToken = {
    accessToken: data.access_token,
    expiresAt: Date.now() + (parseInt(data.expires_in, 10) || 3000) * 1000
  };
  return cachedToken.accessToken;
}

export interface AddressInput {
  addressLine1: string;
  addressLine2?: string | null;
  city: string;
  state: string;
  postalCode: string;
}

export interface UspsValidationResult {
  validated: boolean;
  deliverable: boolean | null;
  standardized: Record<string, unknown> | null;
  reason?: string;
}

// Only validates domestic US addresses — USPS Addresses API has no international coverage.
export async function validateAddress(address: AddressInput): Promise<UspsValidationResult> {
  if (!uspsConfigured()) {
    return { validated: false, deliverable: null, standardized: null, reason: 'USPS not configured' };
  }
  try {
    const token = await getToken();
    const params = new URLSearchParams({
      streetAddress: address.addressLine1,
      city: address.city,
      state: address.state,
      ZIPCode: address.postalCode
    });
    if (address.addressLine2) params.set('secondaryAddress', address.addressLine2);

    const resp = await fetch(`${USPS_BASE}/addresses/v3/address?${params.toString()}`, {
      headers: { Authorization: `Bearer ${token}`, Accept: 'application/json' }
    });
    const data = await resp.json();
    if (!resp.ok) {
      return { validated: false, deliverable: null, standardized: null, reason: data.error?.message || 'USPS lookup failed' };
    }
    const deliverable = data.additionalInfo?.DPVConfirmation === 'Y';
    return { validated: true, deliverable, standardized: data };
  } catch (err) {
    return { validated: false, deliverable: null, standardized: null, reason: (err as Error).message };
  }
}