From 0436bbe28f4f5beee435a7d1dda1f1689867c3ac Mon Sep 17 00:00:00 2001
From: Tyler Sorensen <tyler@makerdao.com>
Date: Thu, 21 May 2020 17:29:22 -0700
Subject: [PATCH] add getSystemSurplus function

---
 packages/dai-plugin-mcd/src/SystemDataService.js       | 10 ++++++++++
 packages/dai-plugin-mcd/test/SystemDataService.spec.js |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/packages/dai-plugin-mcd/src/SystemDataService.js b/packages/dai-plugin-mcd/src/SystemDataService.js
index 1cc1f76a6..4ce4cb418 100644
--- a/packages/dai-plugin-mcd/src/SystemDataService.js
+++ b/packages/dai-plugin-mcd/src/SystemDataService.js
@@ -1,6 +1,7 @@
 import { PublicService } from '@makerdao/services-core';
 import { RAD, RAY, ServiceRoles, SECONDS_PER_YEAR } from './constants';
 import BigNumber from 'bignumber.js';
+import { MDAI } from './index';
 
 export default class SystemDataService extends PublicService {
   constructor(name = ServiceRoles.SYSTEM_DATA) {
@@ -33,6 +34,15 @@ export default class SystemDataService extends PublicService {
     return live.eq(0);
   }
 
+  async getSystemSurplus() {
+    const vowAddr = this.get('smartContract').getContractAddress('MCD_VOW');
+    const [ dai, sin ] = await Promise.all([
+      this.vat.dai(vowAddr),
+      this.vat.sin(vowAddr)
+    ]);
+    return MDAI.rad(dai).minus(MDAI.rad(sin));
+  }
+
   // Helpers ----------------------------------------------
 
   get cat() {
diff --git a/packages/dai-plugin-mcd/test/SystemDataService.spec.js b/packages/dai-plugin-mcd/test/SystemDataService.spec.js
index 4d9ac5921..c47d4b618 100644
--- a/packages/dai-plugin-mcd/test/SystemDataService.spec.js
+++ b/packages/dai-plugin-mcd/test/SystemDataService.spec.js
@@ -1,5 +1,6 @@
 import { mcdMaker } from './helpers';
 import { ServiceRoles } from '../src/constants';
+import { MDAI } from '../src/index';
 
 let service;
 let maker;
@@ -23,3 +24,9 @@ test('get global settlement status', async () => {
   const cage = await service.isGlobalSettlementInvoked();
   expect(cage).toBe(false);
 });
+
+test('get system surplus', async () => {
+  const surplus = await service.getSystemSurplus();
+  console.log('surplus.toNumber', surplus.toNumber());
+  expect(surplus).toEqual(MDAI(0)); //TODO change to expect non-zero number
+});