tinyat.ts

import { fromBase32, toBase32 } from "npm:@atcute/multibase";
import * as TID from "npm:@atcute/tid";
import { Did, Tid } from "npm:@atcute/lexicons";

interface RecordRef {
  did: Did;
  tid: Tid;
}

function encode({ did, tid }: RecordRef): string {
  const tidParsed = TID.parse(tid);
  let header = (BigInt(tidParsed.timestamp) << 10n) | BigInt(tidParsed.clockid);
  let didBytes: Uint8Array;
  if (did.startsWith("did:plc:")) {
    header |= 1n << 63n;
    didBytes = fromBase32(did.slice(8));
  } else {
    didBytes = new TextEncoder().encode(did.slice(4));
  }
  const buffer = new Uint8Array(8 + didBytes.length);
  const view = new DataView(buffer.buffer);
  view.setBigUint64(0, header, false);
  buffer.set(didBytes, 8);
  return toBase32(buffer);
}

function decode(encoded: string): RecordRef {
  const buffer = fromBase32(encoded);
  const view = new DataView(
    buffer.buffer,
    buffer.byteOffset,
    buffer.byteLength,
  );
  const header = view.getBigUint64(0, false);
  const isPlc = (header & (1n << 63n)) !== 0n;
  const timestamp = Number((header >> 10n) & ((1n << 53n) - 1n));
  const clockid = Number(header & 1023n);
  const tid = TID.create(timestamp, clockid);
  const payload = buffer.subarray(8);
  let did: Did;
  if (isPlc) {
    did = `did:plc:${toBase32(payload)}`;
  } else {
    did = `did:${new TextDecoder().decode(payload)}`;
  }
  return { did, tid };
}

const plcIn: RecordRef = {
  did: "did:plc:ttdrpj45ibqunmfhdsb4zdwq",
  tid: "3m3yeflczwk23",
};

// Expected: ted4uxcr7zaadhghc6tz2qdbi2ykohedzshna
const encodedPlc = encode(plcIn);
const decodedPlc = decode(encodedPlc);

console.log(`Encoded: ${encodedPlc}`);
console.log(
  `Match:   ${decodedPlc.did === plcIn.did && decodedPlc.tid === plcIn.tid}`,
);

const webIn: RecordRef = {
  did: "did:web:example.com",
  tid: "3m3yeflczwk23",
};

// Expected: ded4uxcr7zaac53fmi5gk6dbnvygyzjomnxw2
const encodedWeb = encode(webIn);
const decodedWeb = decode(encodedWeb);

console.log(`Encoded: ${encodedWeb}`);
console.log(
  `Match:   ${decodedWeb.did === webIn.did && decodedWeb.tid === webIn.tid}`,
);