StakedTokenV1 rate provider

.gitignore

@@ -25,4 +25,11 @@ cache/
 dist/
 
 # typechain artifacts
-typechain/
+typechain/
+
+# Mac
+.DS_Store
+contracts/.DS_Store
+
+# scripts
+scripts/

contracts/StakedTokenV1RateProvider.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./interfaces/IStakedTokenV1.sol";
+import "./interfaces/IRateProvider.sol";
+
+/**
+ * @title Coinbase Staked Token interface to return exchangeRate
+ * @notice Coinbase Staked token is an ERC20 token backed by staked cryptocurrency reserves
+ * `StakedTokenV1` inherits and extends centre's `FiatTokenV2_1`. It is issued to represent
+ * the corresponding staked wrapped asset. `StakedTokenV1` implements an additional
+ * `exchangeRate` parameter to improve composability. StakedTokenV1 is built on Coinbase's StakedTokenV1.
+ * https://github.com/coinbase/wrapped-tokens-os/blob/main/contracts/wrapped-tokens/staking/StakedTokenV1.sol.
+ * Coinbase controls the oracle's address and updates exchangeRate
+ * every 24 hours at 4pm UTC. This update cadende may change
+ * in the future.
+ */
+contract StakedTokenV1RateProvider is IRateProvider {
+    IStakedTokenV1 public immutable stakedTokenV1;
+
+    constructor(IStakedTokenV1 _stakedTokenV1) {
+        stakedTokenV1 = _stakedTokenV1;
+    }
+
+    /**
+     * @return value of StakedTokenV1 exchangeRate in terms of it's underlying scaled by 10**18
+     */
+    function getRate() public view override returns (uint256) {
+        return stakedTokenV1.exchangeRate();
+    }
+}

contracts/interfaces/IStakedTokenV1.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+/**
+ * @title Coinbase Staked Token interface to return exchangeRate
+ * @notice Coinbase Staked token is an ERC20 token backed by staked cryptocurrency reserves
+ * `StakedTokenV1` inherits and extends centre's `FiatTokenV2_1`. It is issued to represent
+ * the corresponding staked wrapped asset. `StakedTokenV1` implements an additional
+ * `exchangeRate` parameter to improve composability.
+ */
+interface IStakedTokenV1 {
+    /**
+     * @notice get exchange rate
+     * @return returns the current exchange rate scaled by by 10**18
+     */
+    function exchangeRate() external view returns (uint256);
+}

contracts/test/MockStakedTokenV1.sol

@@ -0,0 +1,18 @@
+//SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract MockStakedTokenV1 {
+    uint256 private _exchangeRate = 1; 
+
+    function exchangeRate() external view returns(uint256){
+        return _exchangeRate*1e18;
+    } 
+
+    // anyone can set the rate in this mock example
+    function setExchangeRate(uint256 newRate) external {
+        _exchangeRate = newRate;
+    }
+}
+
+

test/cbEthRateProvider.test.ts

@@ -0,0 +1,36 @@
+import { ethers } from 'hardhat';
+import { expect } from 'chai';
+import { Contract } from 'ethers';
+
+describe('StakedTokenV1RateProvider', function () {
+  let mockStakedTokenV1: Contract;
+  let stakedTokenV1RateProvider: Contract;
+  let tempAddress;
+
+  before('setup eoas', async () => {
+    console.log('Starting test from block:', await ethers.provider.getBlockNumber());
+  });
+
+  beforeEach('deploy mock & rate provider', async () => {
+    const MockStakedTokenV1 = await ethers.getContractFactory('MockStakedTokenV1');
+    mockStakedTokenV1 = await MockStakedTokenV1.deploy();
+    tempAddress = mockStakedTokenV1.address;
+    const StakedTokenV1RateProvider = await ethers.getContractFactory('StakedTokenV1RateProvider');
+    stakedTokenV1RateProvider = await StakedTokenV1RateProvider.deploy(tempAddress);
+  });
+
+  it('returns rate scaled correctly', async () => {
+    expect(await mockStakedTokenV1.exchangeRate()).to.equal(ethers.utils.parseUnits('1', 18));
+  });
+  it('can set rate', async () => {
+    await mockStakedTokenV1.setExchangeRate(2);
+    expect(await mockStakedTokenV1.exchangeRate()).to.equal(ethers.utils.parseUnits('2', 18));
+  });
+  it('gets rate from rateProvider', async () => {
+    expect(await stakedTokenV1RateProvider.getRate()).to.equal(ethers.utils.parseUnits('1', 18));
+  });
+  it('gets correct rate from rateProvider after underlying rate update', async () => {
+    await mockStakedTokenV1.setExchangeRate(2);
+    expect(await stakedTokenV1RateProvider.getRate()).to.equal(ethers.utils.parseUnits('2', 18));
+  });
+});

test/cbEthRateProviderMainnetFork.test.ts

@@ -0,0 +1,29 @@
+import { ethers } from 'hardhat';
+import { expect } from 'chai';
+import { BigNumber, Contract } from 'ethers';
+
+describe('Coinbase Eth rate provider - mainnet fork', function () {
+  let stakedTokenV1RateProvider: Contract;
+  // mainnet coinbase staked ether
+  const stakedTokenV1Address = '0xBe9895146f7AF43049ca1c1AE358B0541Ea49704';
+
+  before('setup eoas', async () => {
+    console.log('Starting test from block:', await ethers.provider.getBlockNumber());
+  });
+
+  beforeEach('deploy rate provider', async () => {
+    const StakedTokenV1RateProvider = await ethers.getContractFactory('StakedTokenV1RateProvider');
+    stakedTokenV1RateProvider = await StakedTokenV1RateProvider.deploy(stakedTokenV1Address);
+  });
+  it('checks if proxy = asset in rate provider', async () => {
+    expect(await stakedTokenV1RateProvider.stakedTokenV1()).to.equal(stakedTokenV1Address);
+  });
+  it('greater than 18 decimals scale - scaled', async () => {
+    const currentRate = await stakedTokenV1RateProvider.getRate();
+    expect(currentRate.gt(BigNumber.from(10).pow(18))).to.be.true;
+  });
+  it('is lower than 19 decimals - scaled', async () => {
+    const currentRate = await stakedTokenV1RateProvider.getRate();
+    expect(currentRate.lt(BigNumber.from(10).pow(19))).to.be.true;
+  });
+});