import getGraphAccessToken from './graphAuth';
import { withRetry, isTransientError } from '../utils/retry';

type GraphRecord = Record<string, unknown>;

// Certain Intune resources exist only on the beta Graph surface.
const BETA_ENDPOINTS = new Set([
  '/deviceManagement/configurationPolicies',
  '/deviceManagement/intents',
]);

function baseUrlFor(endpoint: string) {
  for (const beta of BETA_ENDPOINTS) {
    if (endpoint.startsWith(beta)) return 'https://graph.microsoft.com/beta';
  }
  return 'https://graph.microsoft.com/v1.0';
}

/**
 * Fetch a Graph endpoint with pagination support for @odata.nextLink
 * Returns an array of items aggregated across pages.
 */
export async function fetchWithPagination(
  endpoint: string,
  token: string,
  baseUrl = 'https://graph.microsoft.com/v1.0'
): Promise<GraphRecord[]> {
  const results: GraphRecord[] = [];

  // Normalize URL
  let url = endpoint.startsWith('http') ? endpoint : `${baseUrl}${endpoint.startsWith('/') ? '' : '/'}${endpoint}`;

  while (url) {
    const res = await withRetry(
      async () => {
        const response = await fetch(url, {
          headers: {
            Authorization: `Bearer ${token}`,
            Accept: 'application/json',
          },
        });

        // Handle rate limiting (429)
        if (response.status === 429) {
          const retryAfter = response.headers.get('Retry-After');
          const delay = retryAfter ? parseInt(retryAfter, 10) * 1000 : 60000;
          await new Promise((resolve) => setTimeout(resolve, delay));
          throw new Error(`429 Rate limit exceeded, retrying after ${delay}ms`);
        }

        if (!response.ok) {
          const txt = await response.text();
          const error = new Error(`Graph fetch failed: ${response.status} ${response.statusText} - ${txt}`);
          throw error;
        }

        return response;
      },
      {
        maxAttempts: 3,
        initialDelayMs: 1000,
        shouldRetry: (error) => isTransientError(error),
      }
    );

    const json = await res.json();
    if (Array.isArray(json.value)) {
      results.push(...json.value);
    } else if (json.value !== undefined) {
      // Some endpoints may return a single value
      results.push(json.value as GraphRecord);
    }

    const next = json['@odata.nextLink'];
    if (next) url = next;
    else break;
  }

  return results;
}

/**
 * Convenience function: obtains a Graph token and fetches pages for the given endpoint.
 */
export async function fetchFromGraph(endpoint: string) {
  const token = await getGraphAccessToken();
  const baseUrl = baseUrlFor(endpoint);
  return fetchWithPagination(endpoint, token, baseUrl);
}

export default fetchFromGraph;