feat: add oracle balance metric

__mocks__/@celo/contractkit/index.ts

@@ -84,6 +84,10 @@ export const newKit = () => ({
   web3: {
     eth: {
       getTransaction: async (_: string) => Promise.resolve(),
+      getBalance: jest.fn(async (_: string) => Promise.resolve('1000000000000000000')),
+    },
+    utils: {
+      fromWei: jest.fn((value: number) => value / 1e18),
     },
   },
 })

src/default_config.ts

@@ -1,19 +1,20 @@
-import BigNumber from 'bignumber.js'
-import Logger from 'bunyan'
-import {
-  BaseReporterConfigSubset,
-  BlockBasedReporterConfigSubset,
-  DataAggregatorConfigSubset,
-  OracleApplicationConfig,
-} from './app'
 import {
   AggregationMethod,
-  minutesToMs,
   OracleCurrencyPair,
   ReportStrategy,
-  secondsToMs,
   WalletType,
+  minutesToMs,
+  secondsToMs,
 } from './utils'
+import {
+  BaseReporterConfigSubset,
+  BlockBasedReporterConfigSubset,
+  DataAggregatorConfigSubset,
+  OracleApplicationConfig,
+} from './app'
+
+import BigNumber from 'bignumber.js'
+import Logger from 'bunyan'
 
 export const baseLogger = Logger.createLogger({
   name: 'oracle',

src/metric_collector.ts

@@ -57,6 +57,8 @@ export class MetricCollector {
 
   private lastBlockHeaderNumberGauge: Gauge<string>
 
+  private oracleBalanceValueGauge: Gauge<string>
+
   private potentialReportValueGauge: Gauge<string>
 
   private reportCountCounter: Counter<string>
@@ -113,6 +115,12 @@ export class MetricCollector {
       labelNames: ['type'],
     })
 
+    this.oracleBalanceValueGauge = new Gauge({
+      name: 'oracle_balance_value',
+      help: 'CELO balance of the oracle address',
+      labelNames: ['oracleAddress'],
+    })
+
     this.potentialReportValueGauge = new Gauge({
       name: 'oracle_potential_report_value',
       help:
@@ -330,6 +338,10 @@ export class MetricCollector {
     this.lastBlockHeaderNumberGauge.set({ type }, blockNumber)
   }
 
+  oracleBalanceValue(oracleAddress: string, balance: number) {
+    this.oracleBalanceValueGauge.set({ oracleAddress }, balance)
+  }
+
   websocketProviderSetup() {
     this.websocketProviderSetupCounter.inc()
   }

src/reporters/base.ts

@@ -513,6 +513,14 @@ export abstract class BaseReporter {
     })
   }
 
+  async setOracleBalanceMetric() {
+    const balance = await this.config.kit.web3.eth.getBalance(this.config.oracleAccount)
+    this.config.metricCollector!.oracleBalanceValue(
+      this.config.oracleAccount,
+      Number(this.config.kit.web3.utils.fromWei(balance))
+    )
+  }
+
   get lastReportedPrice(): BigNumber | undefined {
     return this._lastReportedPrice
   }

src/reporters/block_based_reporter.ts

@@ -226,6 +226,7 @@ export class BlockBasedReporter extends BaseReporter {
     if (shouldReport) {
       const trigger = heartbeat ? ReportTrigger.HEARTBEAT : ReportTrigger.PRICE_CHANGE
       await this.report(price, trigger)
+      await this.setOracleBalanceMetric()
     } else {
       this.logger.info(
         {

test/reporters/base.test.ts

@@ -440,6 +440,21 @@ describe('BaseReporter', () => {
       })
     })
 
+    describe('setOracleBalanceMetric()', () => {
+      it('should set the account balance metric', async () => {
+        const mockBalanceInWei = '1000000000000000000'
+        const mockBalance = 1
+        await reporter.setOracleBalanceMetric()
+
+        expect(reporter.config.kit.web3.eth.getBalance).toHaveBeenLastCalledWith(mockOracleAccount)
+        expect(reporter.config.kit.web3.utils.fromWei).toHaveBeenCalledWith(mockBalanceInWei)
+        expect(metricCollector!.oracleBalanceValue).toHaveBeenCalledWith(
+          mockOracleAccount,
+          mockBalance
+        )
+      })
+    })
+
     describe('expire()', () => {
       it('collects metrics', async () => {
         jest