roi calc (#8)

src/calculators/index.js

@@ -1,3 +1,4 @@
 export * from './circulation-supply.js';
 export * from './tokens-sent-from-inflation-pool.js';
 export * from './total-supply.js';
+export * from './staking-roi.js';

src/calculators/staking-roi.js

@@ -0,0 +1,16 @@
+import { api } from '../node.js';
+import { totalSupply } from './total-supply.js';
+import { DECIMALS } from '../consts.js';
+
+// ROI = era_payout / total_staked * eras_per_year
+// era_payout = total_issuance * inflation_per_era
+
+export async function stakingRoi() {
+    const lastEra = (await api.query.staking.currentEra()).toHuman() - 1;
+
+    const inflationPerEra = (await api.query.staking.erasValidatorReward(lastEra)).toJSON();
+    const totalStaked = await api.query.staking.erasTotalStake(lastEra);
+    const totalIssuance = await totalSupply();
+
+    return (totalIssuance * (inflationPerEra / 10 ** DECIMALS)) / (totalStaked / 10 ** DECIMALS) * 730;
+}

src/server.js

@@ -8,6 +8,7 @@ import {
   totalStaking,
   totalSupply,
   totalVesting,
+  stakingRoi
 } from './calculators/index.js';
 
 const app = express();
@@ -59,6 +60,15 @@ app.get('/api/circulating-supply', async (req, res) => {
     });
 });
 
+app.get('/api/roi', async (req, res) => {
+  stakingRoi()
+    .then((result) => res.json(result))
+    .catch((err) => {
+      console.error(err);
+      res.sendStatus(500);
+    });
+});
+
 export function runServer() {
   app.listen(config.server.port, () => console.log(`App is running on port ${config.server.port}`));
 }