import { contexts as credentialsContexts } from '@digitalbazaar/credentials-context';
import jsonld from 'jsonld';
import { DidDocumentResolver } from '../../resolvers/didDocumentResolver.js';
import { CredentialValidationOptions } from '../dto/validationOptions.dto.js';

/**
 * Bundled well-known contexts to avoid network round-trips.
 * Covers the three URL variants shipped by @digitalbazaar/credentials-context.
 */
const BUNDLED_CONTEXTS: Map<string, unknown> = new Map([
  ...credentialsContexts,
]);

/**
 * Creates a JSON-LD document loader for use with @digitalbazaar/vc
 * DataIntegrityProof verification.
 *
 * Resolution order:
 *   1. Bundled contexts (credentials/v1, credentials/v2, …) — no network
 *   2. DID URLs — resolved via the existing DidDocumentResolver
 *   3. All other URLs (e.g. custom credential contexts,
 *      https://w3id.org/security/…) — delegated to jsonld's node loader
 *      which fetches over HTTP (result is memoised by jsonld internally)
 */
export function createDocumentLoader(
  didDocumentResolver: DidDocumentResolver,
  opts?: CredentialValidationOptions,
) {
  const nodeLoader = jsonld.documentLoaders.node();

  return async (url: string) => {
    // 1. Serve bundled contexts without any network call
    const bundled = BUNDLED_CONTEXTS.get(url);
    if (bundled !== undefined) {
      return { contextUrl: null, documentUrl: url, document: bundled };
    }

    // 2. Resolve DID documents / verification-method objects
    if (url.startsWith('did:')) {
      const hashIndex = url.indexOf('#');
      const did = hashIndex !== -1 ? url.substring(0, hashIndex) : url;
      const fragment = hashIndex !== -1 ? url.substring(hashIndex + 1) : null;

      const didDocument = await didDocumentResolver.resolveDid(did, opts);

      if (fragment) {
        // Return just the specific verification-method object so that
        // EcdsaMultikey.from() receives the key material it needs.
        const vm = (didDocument.verificationMethod ?? []).find(
          (m) => m.id === url || m.id === `#${fragment}`,
        );
        if (!vm) {
          throw new Error(
            `Verification method "${url}" not found in DID document for "${did}".`,
          );
        }
        return { contextUrl: null, documentUrl: url, document: vm };
      }

      return { contextUrl: null, documentUrl: url, document: didDocument };
    }

    // 3. Fall back to the jsonld node loader for everything else
    //    (security contexts, custom credential contexts, …)
    return nodeLoader(url);
  };
}