const PREFIX = 'mhu1_';

export function encode(payload) {
  if (!payload || typeof payload !== 'object') {
    throw new Error('encode: payload must be an object');
  }
  const json = JSON.stringify(payload);
  const b64 = Buffer.from(json, 'utf8').toString('base64url');
  return PREFIX + b64;
}

export function decode(code) {
  if (typeof code !== 'string') {
    throw new Error('Invalid code: expected a string');
  }
  const trimmed = code.trim();
  if (!trimmed.startsWith(PREFIX)) {
    throw new Error('Invalid code: missing "mhu1_" prefix');
  }
  const b64 = trimmed.slice(PREFIX.length);
  if (!b64) {
    throw new Error('Invalid code: empty payload');
  }

  let json;
  try {
    json = Buffer.from(b64, 'base64url').toString('utf8');
  } catch {
    throw new Error('Invalid code: not valid base64url');
  }

  let payload;
  try {
    payload = JSON.parse(json);
  } catch {
    throw new Error('Invalid code: payload is not valid JSON');
  }

  if (!payload || typeof payload !== 'object') {
    throw new Error('Invalid code: payload is not an object');
  }
  if (payload.v !== 1) {
    throw new Error(`Invalid code: unsupported version (expected v=1, got ${payload.v})`);
  }
  const host = payload.h !== undefined ? payload.h : payload.host;
  const port = payload.p !== undefined ? payload.p : payload.port;
  const token = payload.t !== undefined ? payload.t : payload.token;
  const label = payload.n !== undefined ? payload.n : payload.label;
  const scheme = payload.s === 'wss' ? 'wss' : 'ws';
  if (host !== undefined && typeof host !== 'string') {
    throw new Error('Invalid code: "host" must be a string when present');
  }
  if (typeof port !== 'number' || !Number.isFinite(port)) {
    throw new Error('Invalid code: "port" must be a number');
  }
  if (typeof token !== 'string' || token.length === 0) {
    throw new Error('Invalid code: "token" must be a non-empty string');
  }
  if (label !== undefined && typeof label !== 'string') {
    throw new Error('Invalid code: "label" must be a string');
  }
  if (payload.fp !== undefined && typeof payload.fp !== 'string') {
    throw new Error('Invalid code: "fp" must be a string when present');
  }

  return { v: 1, host: host ? String(host) : undefined, port, token, label: label !== undefined ? String(label) : undefined, fp: payload.fp, scheme };
}