feat(pool): add cumulative reward factor

schema.graphql

@@ -133,6 +133,8 @@ type Pool @entity {
   rewardCut: BigInt!
   "Transcoder's fee share during the earnings pool's round"
   feeShare: BigInt!
+  "Cumulative reward factor for delegator rewards calculation"
+  cumulativeRewardFactor: BigDecimal
 }
 
 """

src/mappings/bondingManager.ts

@@ -1,4 +1,4 @@
-import { store } from "@graphprotocol/graph-ts";
+import { store, Address } from "@graphprotocol/graph-ts";
 import {
   convertToDecimal,
   createOrLoadDelegator,
@@ -8,6 +8,7 @@ import {
   createOrLoadTranscoder,
   EMPTY_ADDRESS,
   getBlockNum,
+  integerFromString,
   makeEventId,
   makePoolId,
   makeUnbondingLockId,
@@ -500,6 +501,13 @@ export function reward(event: Reward): void {
   pool!.feeShare = transcoder.feeShare;
   pool!.rewardCut = transcoder.rewardCut;
 
+  let bondingManager = BondingManager.bind(event.address);
+  let earningsPool = bondingManager.getTranscoderEarningsPoolForRound(
+    Address.fromString(transcoder.id),
+    integerFromString(round.id)
+  );
+  pool!.cumulativeRewardFactor = convertToDecimal(earningsPool.cumulativeRewardFactor);
+
   transcoder.save();
   delegate.save();
   pool!.save();