feat: add in GhoDiscountRateStrategyService (#443)

* feat: add in typechain and setup base GhoDiscountRateService

* chore: add in type definition files

* chore: add in basic calculateDiscountRate function and unit test

* fix: skip unit test for now

* fix: allow to commit to repo and bypass jest coverage limit

* chore: write utility for calculating discount rate

* fix: write unit tests for all use cases for discount rates

* fix: write unit test for barrel file

* chore: jest config and export gho service

* fix: use zero values and mock return calls

* fix: test coverage and mocks

* chore: remove unnecessary coverage skips

jest.config.js

@@ -1,6 +1,6 @@
 module.exports = {
   preset: 'ts-jest',
-  collectCoverageFrom: ['packages/*/src/**/*.ts'],
+  collectCoverageFrom: ['packages/*/src/**(!typechain)/*.ts'],
   coverageDirectory: 'coverage',
   coverageReporters: ['lcov', 'text'],
   coverageThreshold: {
@@ -43,7 +43,6 @@ module.exports = {
     'packages/math-utils/src/formatters/reserve/index.ts', // TODO: remove
   ],
   modulePathIgnorePatterns: ['node_modules'],
-  preset: 'ts-jest',
   testEnvironment: 'node',
   verbose: true,
   watchPlugins: [

packages/contract-helpers/src/commons/BaseService.test.ts

@@ -197,7 +197,7 @@ describe('BaseService', () => {
       expect(gas?.gasLimit).toEqual('1');
       expect(gas?.gasPrice).toEqual('2');
     });
-    xit('Expects null when no gas limit', async () => {
+    it.skip('Expects null when no gas limit', async () => {
       const txCallback = async () => ({});
       const txs = [
         {

packages/contract-helpers/src/gho/GhoDiscountRateStrategyService.test.ts

@@ -0,0 +1,181 @@
+import { constants, BigNumber, BigNumberish, providers } from 'ethers';
+import { valueToWei } from '../commons/utils';
+import { GhoDiscountRateStrategyService } from './GhoDiscountRateStrategyService';
+import { GhoDiscountRateStrategy } from './typechain/GhoDiscountRateStrategy';
+import { GhoDiscountRateStrategy__factory } from './typechain/GhoDiscountRateStrategy__factory';
+
+jest.mock('../commons/gasStation', () => {
+  return {
+    __esModule: true,
+    estimateGasByNetwork: jest
+      .fn()
+      .mockImplementation(async () => Promise.resolve(BigNumber.from(1))),
+    estimateGas: jest.fn(async () => Promise.resolve(BigNumber.from(1))),
+  };
+});
+
+// Helper for contract call arguments
+const convertToBN = (n: string) => valueToWei(n, 18);
+
+describe('GhoDiscountRateStrategyService', () => {
+  const DISCOUNT_RATE_STRATEGY_ADDRESS = constants.AddressZero;
+  const correctProvider: providers.Provider = new providers.JsonRpcProvider();
+
+  // Mocking
+  jest
+    .spyOn(correctProvider, 'getGasPrice')
+    .mockImplementation(async () => Promise.resolve(BigNumber.from(1)));
+
+  afterEach(() => jest.clearAllMocks());
+
+  describe('Create new GhoDiscountRateStrategyService', () => {
+    it('Expects to be initialized correctly', () => {
+      const instance = new GhoDiscountRateStrategyService(
+        correctProvider,
+        DISCOUNT_RATE_STRATEGY_ADDRESS,
+      );
+      expect(instance).toBeInstanceOf(GhoDiscountRateStrategyService);
+    });
+  });
+
+  describe('calculateDiscountRate', () => {
+    it('should return zero discount if discount token balance does not meet minimum requirements to gain a discount', async () => {
+      // Create instance
+      const contract = new GhoDiscountRateStrategyService(
+        correctProvider,
+        DISCOUNT_RATE_STRATEGY_ADDRESS,
+      );
+
+      // Use case - borrowing 100 GHO owning 0 skAAVE
+      const ghoDebtTokenBalance: BigNumberish = convertToBN('100');
+      const stakedAaveBalance: BigNumberish = convertToBN('0');
+      const expected = BigNumber.from('0'); // 0%
+
+      // Mock it
+      const spy = jest
+        .spyOn(GhoDiscountRateStrategy__factory, 'connect')
+        .mockReturnValue({
+          calculateDiscountRate: async () => Promise.resolve(expected),
+        } as unknown as GhoDiscountRateStrategy);
+
+      // Call it
+      const result = await contract.calculateDiscountRate(
+        ghoDebtTokenBalance,
+        stakedAaveBalance,
+      );
+
+      // Assert it
+      expect(spy).toHaveBeenCalled();
+      expect(spy).toBeCalledTimes(1);
+      expect(result).toEqual(expected);
+    });
+
+    it('should return zero discount if GHO variable debt token balance does not meet minimum requirements to gain a discount', async () => {
+      // Create instance
+      const contract = new GhoDiscountRateStrategyService(
+        correctProvider,
+        DISCOUNT_RATE_STRATEGY_ADDRESS,
+      );
+
+      // Use case - borrowing 0 GHO owning 1 skAAVE
+      const ghoDebtTokenBalance: BigNumberish = convertToBN('0');
+      const stakedAaveBalance: BigNumberish = convertToBN('1');
+      const expected = BigNumber.from('0'); // 0%
+
+      // Mock it
+      const spy = jest
+        .spyOn(GhoDiscountRateStrategy__factory, 'connect')
+        .mockReturnValue({
+          calculateDiscountRate: async () => Promise.resolve(expected),
+        } as unknown as GhoDiscountRateStrategy);
+
+      // Call it
+      const result = await contract.calculateDiscountRate(
+        ghoDebtTokenBalance,
+        stakedAaveBalance,
+      );
+
+      // Assert it
+      expect(spy).toHaveBeenCalled();
+      expect(spy).toBeCalledTimes(1);
+      expect(result).toEqual(expected);
+    });
+
+    // Discounted balance = discount token * 100
+    it('should return the maximum discount rate of 20% if the calculated total discounted balance is greater or equal to the debt token balance', async () => {
+      // Create instance
+      const contract = new GhoDiscountRateStrategyService(
+        correctProvider,
+        DISCOUNT_RATE_STRATEGY_ADDRESS,
+      );
+
+      // Use case #1 - borrowing 100 GHO owning 1 stkAAVE
+      const ghoDebtTokenBalance: BigNumberish = convertToBN('100');
+      let stakedAaveBalance: BigNumberish = convertToBN('1');
+      const expected = BigNumber.from('2000'); // 20.00% discount
+
+      // Mock it
+      const spy = jest
+        .spyOn(GhoDiscountRateStrategy__factory, 'connect')
+        .mockReturnValue({
+          calculateDiscountRate: async () => Promise.resolve(expected),
+        } as unknown as GhoDiscountRateStrategy);
+
+      // Call it
+      let result = await contract.calculateDiscountRate(
+        ghoDebtTokenBalance,
+        stakedAaveBalance,
+      );
+
+      // Assert it
+      expect(spy).toHaveBeenCalled();
+      expect(spy).toBeCalledTimes(1);
+      expect(result).toEqual(expected);
+
+      // Use case #2 - borrowing 100 GHO owning 5 stkAAVE
+      stakedAaveBalance = convertToBN('5');
+
+      // Call it
+      result = await contract.calculateDiscountRate(
+        ghoDebtTokenBalance,
+        stakedAaveBalance,
+      );
+
+      // Assert it
+      expect(spy).toHaveBeenCalled();
+      expect(spy).toBeCalledTimes(1);
+      expect(result).toEqual(expected);
+    });
+
+    it('should return a sub-maximum discount if user borrows more GHO than can be discounted based off of the discount token balance', async () => {
+      // Create instance
+      const contract = new GhoDiscountRateStrategyService(
+        correctProvider,
+        DISCOUNT_RATE_STRATEGY_ADDRESS,
+      );
+
+      // Use case - borrowing 150 GHO owning 1 skAAVE
+      const ghoDebtTokenBalance: BigNumberish = convertToBN('150');
+      const stakedAaveBalance: BigNumberish = convertToBN('1');
+      const expected = BigNumber.from('1333'); // 13.33% discount
+
+      // Mock it
+      const spy = jest
+        .spyOn(GhoDiscountRateStrategy__factory, 'connect')
+        .mockReturnValue({
+          calculateDiscountRate: async () => Promise.resolve(expected),
+        } as unknown as GhoDiscountRateStrategy);
+
+      // Call it
+      const result = await contract.calculateDiscountRate(
+        ghoDebtTokenBalance,
+        stakedAaveBalance,
+      );
+
+      // Assert it
+      expect(spy).toHaveBeenCalled();
+      expect(spy).toBeCalledTimes(1);
+      expect(result).toEqual(expected);
+    });
+  });
+});

packages/contract-helpers/src/gho/GhoDiscountRateStrategyService.ts

@@ -0,0 +1,51 @@
+import { BigNumber, BigNumberish, providers } from 'ethers';
+import BaseService from '../commons/BaseService';
+import { GhoDiscountRateStrategy__factory } from './typechain/GhoDiscountRateStrategy__factory';
+import type { IGhoDiscountRateStrategy } from './typechain/IGhoDiscountRateStrategy';
+
+export interface GhoDiscountRateServiceInterface {
+  calculateDiscountRate: (
+    ghoDebtTokenBalance: BigNumberish,
+    skAaveBalance: BigNumberish,
+  ) => Promise<BigNumber>;
+}
+
+/**
+ * The service for interacting with the GhoDiscountRateStrategy.sol smart contract
+ * https://github.com/aave/gho/blob/main/src/contracts/facilitators/aave/interestStrategy/GhoDiscountRateStrategy.sol
+ */
+export class GhoDiscountRateStrategyService
+  extends BaseService<IGhoDiscountRateStrategy>
+  implements GhoDiscountRateServiceInterface
+{
+  readonly ghoDiscountRateStrategyAddress: string;
+
+  constructor(
+    provider: providers.Provider,
+    discountRateStrategyAddress: string,
+  ) {
+    super(provider, GhoDiscountRateStrategy__factory);
+    this.ghoDiscountRateStrategyAddress = discountRateStrategyAddress;
+  }
+
+  /**
+   * Calculates the discounted interest rate charged on the borrowed native GHO token from the Aave Protocol. Currently this is set to be 20% on 100 GHO borrowed per stkAAVE held. Additionally, a user's discount rate is
+   * updated anytime they send or receive the discount token (stkAAVE). Users are entitled to this discount for a given amount of time without needing to perform any additional actions (i.e. the discount lock period).
+   * @param ghoDebtTokenBalance - The balance for the user's GhoVariableDebtToken, i.e. the amount they currently have borrowed from the protocol
+   * @param stakedAaveBalance - The balance of the user's stkAAVE token balance
+   * @returns - The discounted interest rate charged on the borrowed native GHO token.
+   */
+  public async calculateDiscountRate(
+    ghoDebtTokenBalance: BigNumberish,
+    stakedAaveBalance: BigNumberish,
+  ) {
+    const contract = this.getContractInstance(
+      this.ghoDiscountRateStrategyAddress,
+    );
+    const result = await contract.calculateDiscountRate(
+      ghoDebtTokenBalance,
+      stakedAaveBalance,
+    );
+    return result;
+  }
+}

packages/contract-helpers/src/gho/index.test.ts

@@ -0,0 +1,7 @@
+import { GhoDiscountRateStrategyService } from './index';
+
+describe('gho contract helpers', () => {
+  it('exports out the GhoDiscountRateStrategyService', () => {
+    expect(GhoDiscountRateStrategyService).toBeTruthy();
+  });
+});

packages/contract-helpers/src/gho/index.ts

@@ -0,0 +1,3 @@
+import { GhoDiscountRateStrategyService } from './GhoDiscountRateStrategyService';
+
+export { GhoDiscountRateStrategyService };