accountIndex.toU8a(true) -> AccountIndexSet (#299)

* accountIndex.toU8a(true) -> AccountIndexSet

* Fix length check

packages/types/src/AccountIndex.ts

@@ -2,6 +2,7 @@
 // This software may be modified and distributed under the terms
 // of the ISC license. See the LICENSE file for details.
 
+import BN from 'bn.js';
 import decodeAddress from '@polkadot/keyring/address/decode';
 import encodeAddress from '@polkadot/keyring/address/encode';
 import hexToU8a from '@polkadot/util/hex/toU8a';
@@ -11,6 +12,10 @@ import u8aConcat from '@polkadot/util/u8a/concat';
 
 import { AnyU8a } from './types';
 import U8a from './codec/U8a';
+import u8aToBn from '@polkadot/util/u8a/toBn';
+import bnToU8a from '@polkadot/util/bn/toU8a';
+
+const ENUMSET_SIZE = new BN(64);
 
 // A wrapper around an AccountIndex, which is a shortened, variable-length encoding
 // for an Account. We extends from U8a which is basically
@@ -85,9 +90,21 @@ export default class AccountIndex extends U8a {
     return this.toString();
   }
 
+  toBn (): BN {
+    if (this.raw.length === 1) {
+      return new BN(this.raw[0]);
+    }
+
+    return u8aToBn(this.raw, true);
+  }
+
   toU8a (isBare?: boolean): Uint8Array {
+    // HACK 15 Oct 2018 For isBare assume that we are dealing with an AccountIndex
+    // lookup (it is the only place where AccountIndex is used in such a manner to
+    // construct a query). This is needed to get enumSet(AccountIndex) queries to
+    // work in the way it was intended
     return isBare
-      ? this.raw
+      ? bnToU8a(this.toBn().div(ENUMSET_SIZE), 32, true)
       : u8aConcat(
         AccountIndex.writeLength(this.raw),
         this.raw