From 33c161f874cb067c6a4afcb0796878df92869644 Mon Sep 17 00:00:00 2001
From: Jaco Greeff <jacogr@gmail.com>
Date: Fri, 2 Oct 2020 13:48:25 +0200
Subject: [PATCH] Derive validators from stashes & nominations (#2672)

---
 packages/api-derive/src/staking/index.ts      |  1 +
 .../api-derive/src/staking/validatorsFrom.ts  | 35 +++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 packages/api-derive/src/staking/validatorsFrom.ts

diff --git a/packages/api-derive/src/staking/index.ts b/packages/api-derive/src/staking/index.ts
index 1d4ba6829a..1e490b8634 100644
--- a/packages/api-derive/src/staking/index.ts
+++ b/packages/api-derive/src/staking/index.ts
@@ -22,4 +22,5 @@ export * from './stakerRewards';
 export * from './stakerSlashes';
 export * from './stashes';
 export * from './validators';
+export * from './validatorsFrom';
 export * from './waitingInfo';
diff --git a/packages/api-derive/src/staking/validatorsFrom.ts b/packages/api-derive/src/staking/validatorsFrom.ts
new file mode 100644
index 0000000000..b7bbbd6f98
--- /dev/null
+++ b/packages/api-derive/src/staking/validatorsFrom.ts
@@ -0,0 +1,35 @@
+// Copyright 2017-2020 @polkadot/api-derive authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import { ApiInterfaceRx } from '@polkadot/api/types';
+import { AccountId, Nominations } from '@polkadot/types/interfaces';
+import { DeriveStakingQuery } from '../types';
+
+import { Observable } from 'rxjs';
+import { switchMap } from 'rxjs/operators';
+import { Option } from '@polkadot/types';
+
+import { memo } from '../util';
+
+/**
+ * @description From a list of stashIds, staking ledgers for those acting as validators and those being nominated
+ */
+export function validatorsFrom (instanceId: string, api: ApiInterfaceRx): (stashIds: (Uint8Array | string)[]) => Observable<DeriveStakingQuery[]> {
+  return memo(instanceId, (stashIds: (Uint8Array | string)[]): Observable<DeriveStakingQuery[]> =>
+    api.query.staking.nominators.multi<Option<Nominations>>(stashIds).pipe(
+      switchMap((optNoms) =>
+        api.derive.staking.queryMulti(
+          optNoms.reduce((validatorIds: AccountId[], optNom): AccountId[] => {
+            return optNom.unwrapOrDefault().targets.reduce((validatorIds: AccountId[], targetId): AccountId[] => {
+              if (!validatorIds.find((validatorId) => validatorId.eq(targetId))) {
+                validatorIds.push(targetId);
+              }
+
+              return validatorIds;
+            }, validatorIds);
+          }, [])
+        )
+      )
+    )
+  );
+}