export type AtprotoDidDocument = {
  "@context": string[];
  id: `did:${string}`;
  alsoKnownAs: string[];
  verificationMethod: AtprotoVerificationMethod[];
  service: AtprotoService[];
};

type AtprotoVerificationMethod = {
  id: string;
  type: "Multikey";
  controller: `did:${string}`;
  publicKeyMultibase: string;
};

type AtprotoService = {
  id: string;
  type: "AtprotoPersonalDataServer";
  serviceEndpoint: string;
};

export async function resolveDidDocument(
  did: string,
): Promise<AtprotoDidDocument> {
  const response = await fetch(getDidDocumentUrl(did));

  if (!response.ok) {
    throw new Error(`Failed to resolve DID: ${did}`);
  }

  return (await response.json()) as AtprotoDidDocument;
}

function getDidDocumentUrl(did: string): string {
  if (did.startsWith("did:plc:")) {
    return `https://plc.directory/${encodeURIComponent(did)}`;
  }

  if (did.startsWith("did:web:")) {
    const [, , identifier, ...pathParts] = did.split(":");

    if (!identifier) {
      throw new Error(`Invalid did:web identifier: ${did}`);
    }

    const hostname = decodeURIComponent(identifier);

    if (pathParts.length === 0) {
      return `https://${hostname}/.well-known/did.json`;
    }

    const path = pathParts.map(decodeURIComponent).join("/");
    return `https://${hostname}/${path}/did.json`;
  }

  throw new Error(`Unsupported DID method: ${did}`);
}