Derive controllers from stashes (#806)

* Derive controllers from stashes

* Fix combineLatest import

packages/api-derive/src/staking/controllers.ts

@@ -0,0 +1,35 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { Observable, combineLatest, of } from 'rxjs';
+import { switchMap } from 'rxjs/operators';
+import { ApiInterface$Rx } from '@polkadot/api/types';
+import { AccountId, Option } from '@polkadot/types';
+
+import { drr } from '../util/drr';
+
+function allBonds (api: ApiInterface$Rx, stashIds: Array<AccountId>) {
+  return combineLatest(
+    stashIds.map((id) =>
+      (api.query.staking.bonded(id) as Observable<Option<AccountId>>)
+    )
+  );
+}
+
+/**
+ * @description From the list of stash accounts, retrieve the list of controllers
+ */
+export function controllers (api: ApiInterface$Rx) {
+  return (): Observable<[Array<AccountId>, Array<Option<AccountId>>]> =>
+    (api.query.staking.validators() as any as Observable<[Array<AccountId>, any]>)
+      .pipe(
+        switchMap(([stashIds]) =>
+          combineLatest(
+            of(stashIds),
+            allBonds(api, stashIds)
+          )
+        ),
+        drr()
+      );
+}

packages/api-derive/src/staking/index.ts

@@ -2,4 +2,5 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
+export * from './controllers';
 export * from './intentionsBalances';