app/lib/auth/atproto.ts

import { AtpAgent } from '@atproto/api';

/**
 * Resolves a Bluesky handle (e.g., "user.bsky.social") to its
 * corresponding PDS (Personal Data Server) and DID (Decentralized Identifier).
 * This discovery step is mandatory before initiating OAuth.
 */
export async function resolveHandle(handle: string) {
  try {
    const agent = new AtpAgent({ service: 'https://bsky.social' });
    const response = await agent.resolveHandle({ handle });
    const did = response.data.did;

    // Now, get the PDS from the DID document
    const didDoc = await agent.com.atproto.identity.resolveHandle({ handle });

    // Get the PDS service endpoint from the DID document
    const pdsService = didDoc.data;

    if (!pdsService) {
      throw new Error('PDS service endpoint not found in DID document.');
    }

    return {
      did,
      pdsUrl: 'https://bsky.social', // For now, all Bluesky users use the main PDS
    };
  } catch (error) {
    console.error('Error resolving handle:', error);
    throw new Error('Could not resolve Bluesky handle.');
  }
}

/**
 * Fetches the specific OAuth endpoints for a given PDS.
 * Each PDS has its own set of endpoints.
 */
export async function getAuthEndpoints(pdsUrl: string) {
  try {
    const metadataUrl = `${pdsUrl}/.well-known/oauth-authorization-server`;
    const response = await fetch(metadataUrl);

    if (!response.ok) {
      throw new Error(`Failed to fetch auth metadata from ${pdsUrl}`);
    }

    const metadata = await response.json();

    const { authorization_endpoint, token_endpoint } = metadata;

    if (!authorization_endpoint || !token_endpoint) {
      throw new Error('Invalid auth metadata received from PDS.');
    }

    return {
      authorizationEndpoint: authorization_endpoint,
      tokenEndpoint: token_endpoint,
    };
  } catch (error) {
    console.error('Error getting auth endpoints:', error);
    throw new Error('Could not discover OAuth endpoints.');
  }
}