function bytesOf(value) {
  if (value == null) return null;
  if (typeof Buffer !== 'undefined' && Buffer.isBuffer(value)) {
    return value.length === 12 ? value : null;
  }
  if (value instanceof Uint8Array) {
    return value.byteLength === 12 ? Buffer.from(value) : null;
  }
  if (
    value &&
    value.type === 'Buffer' &&
    Array.isArray(value.data) &&
    value.data.length === 12
  ) {
    return Buffer.from(value.data);
  }
  if (typeof value !== 'object' || Array.isArray(value) || value instanceof Date) {
    return null;
  }

  const keys = Object.keys(value);
  if (keys.length !== 12) return null;

  const bytes = Buffer.alloc(12);
  for (let index = 0; index < 12; index += 1) {
    if (!Object.prototype.hasOwnProperty.call(value, index)) return null;
    const byte = Number(value[index]);
    if (!Number.isInteger(byte) || byte < 0 || byte > 255) return null;
    bytes[index] = byte;
  }
  return bytes;
}

const PURE_REF_KEYS = new Set(['_id', 'id', 'buffer', '$oid']);

function isPureRef(value) {
  if (value == null || typeof value !== 'object') return false;
  if (typeof value.toHexString === 'function') return true;
  if (Array.isArray(value) || value instanceof Date) return false;
  const keys = Object.keys(value);
  return keys.length > 0 && keys.every(key => PURE_REF_KEYS.has(key)) && refId(value) != null;
}

function isBinaryPayload(value) {
  if (value == null || typeof value !== 'object') return false;
  if (typeof Buffer !== 'undefined' && Buffer.isBuffer(value)) return true;
  if (value instanceof Uint8Array || value instanceof ArrayBuffer) return true;
  const name = value.constructor?.name;
  return name === 'Blob' || name === 'File';
}

// Object ids are always hex strings on the wire. File buffers are left alone.
export function stringifyIds(value) {
  if (value == null) return value;
  if (typeof value === 'string' || typeof value === 'number' || typeof value === 'boolean') {
    return value;
  }
  if (typeof value.toHexString === 'function') return value.toHexString();
  if (value instanceof Date || typeof value === 'function') return value;
  if (isBinaryPayload(value)) return value;
  if (Array.isArray(value)) return value.map(item => stringifyIds(item));
  if (typeof value === 'object') {
    if (isPureRef(value)) {
      const id = refId(value);
      if (typeof id === 'string') return id;
    }
    const copy = {};
    for (const [key, child] of Object.entries(value)) {
      copy[key] = stringifyIds(child);
    }
    return copy;
  }
  return value;
}

export function refId(value) {
  if (value == null || value === '') return null;
  if (typeof value === 'string') return value;
  if (typeof value === 'object' && typeof value.toHexString === 'function') {
    return value.toHexString();
  }
  if (typeof value !== 'object' || Array.isArray(value) || value instanceof Date) {
    return null;
  }
  if (typeof value.$oid === 'string') return refId(value.$oid);

  const keys = Object.keys(value);
  if (
    keys.length > 0 &&
    keys.every(key => key === 'buffer' || key === 'id' || key === 'type' || key === 'data')
  ) {
    const bytes = bytesOf(value.buffer) || bytesOf(value.id) || bytesOf(value);
    if (bytes) return bytes.toString('hex');
  }

  if (value._id != null) return refId(value._id);
  return null;
}