Added daily limit for reserve spending

packages/protocol/contracts/common/test/MockGoldToken.sol

@@ -7,6 +7,7 @@ pragma solidity ^0.5.3;
 contract MockGoldToken {
   uint8 public constant decimals = 18;
   uint256 public totalSupply;
+  mapping(address => uint256) balances;
 
   function setTotalSupply(uint256 value) external {
     totalSupply = value;
@@ -19,4 +20,13 @@ contract MockGoldToken {
   function transferFrom(address, address, uint256) external pure returns (bool) {
     return true;
   }
+
+  function setBalanceOf(address a, uint256 value) external {
+    balances[a] = value;
+  }
+
+  function balanceOf(address a) external view returns (uint256) {
+    return balances[a];
+  }
+
 }

packages/protocol/contracts/stability/Reserve.sol

@@ -37,6 +37,10 @@ contract Reserve is IReserve, Ownable, Initializable, UsingRegistry, ReentrancyG
   bytes32[] public assetAllocationSymbols;
   uint256[] public assetAllocationWeights;
 
+  uint256 private lastSpendingDay;
+  FixidityLib.Fraction public spendingRatio;
+  uint256 private spendingLimit;
+
   event TobinTaxStalenessThresholdSet(uint256 value);
   event TokenAdded(address token);
   event TokenRemoved(address token, uint256 index);
@@ -65,6 +69,7 @@ contract Reserve is IReserve, Ownable, Initializable, UsingRegistry, ReentrancyG
     _transferOwnership(msg.sender);
     setRegistry(registryAddress);
     setTobinTaxStalenessThreshold(_tobinTaxStalenessThreshold);
+    spendingRatio = FixidityLib.fixed1();
   }
 
   /**
@@ -77,6 +82,22 @@ contract Reserve is IReserve, Ownable, Initializable, UsingRegistry, ReentrancyG
     emit TobinTaxStalenessThresholdSet(value);
   }
 
+  /**
+   * @notice Set the ratio of reserve that is spendable per day.
+   * @param ratio Spending ratio as unwrapped Fraction.
+   */
+  function setDailySpendingRatio(uint256 ratio) public onlyOwner {
+    spendingRatio = FixidityLib.wrap(ratio);
+  }
+
+  /**
+   * @notice Get daily spending ratio.
+   * @return Spending ratio as unwrapped Fraction.
+   */
+  function getDailySpendingRatio() public view onlyOwner returns (uint256) {
+    return spendingRatio.unwrap();
+  }
+
   /**
    * @notice Sets target allocations for Celo Gold and a diversified basket of non-Celo assets.
    * @param symbols The symbol of each asset in the Reserve portfolio.
@@ -204,6 +225,14 @@ contract Reserve is IReserve, Ownable, Initializable, UsingRegistry, ReentrancyG
    */
   function transferGold(address to, uint256 value) external returns (bool) {
     require(isSpender[msg.sender], "sender not allowed to transfer Reserve funds");
+    uint256 currentDay = now / 1 days;
+    if (currentDay > lastSpendingDay) {
+      uint256 balance = getGoldToken().balanceOf(address(this));
+      lastSpendingDay = currentDay;
+      spendingLimit = spendingRatio.multiply(FixidityLib.newFixed(balance)).fromFixed();
+    }
+    require(spendingLimit >= value, "Exceeding spending limit");
+    spendingLimit = spendingLimit.sub(value);
     require(getGoldToken().transfer(to, value), "transfer of gold token failed");
     return true;
   }

packages/protocol/test/stability/reserve.ts

@@ -5,6 +5,7 @@ import {
   assertSameAddress,
   timeTravel,
 } from '@celo/protocol/lib/test-utils'
+import { toFixed } from '@celo/utils/lib/fixidity'
 import BigNumber from 'bignumber.js'
 import BN = require('bn.js')
 import {
@@ -67,6 +68,16 @@ contract('Reserve', (accounts: string[]) => {
     })
   })
 
+  describe('#setDailySpendingRatio()', async () => {
+    it('should allow owner to set the ratio', async () => {
+      await reserve.setDailySpendingRatio(123)
+      assert.equal(123, (await reserve.getDailySpendingRatio()).toNumber())
+    })
+    it('should not allow other users to set the ratio', async () => {
+      await assertRevert(reserve.setDailySpendingRatio(123, { from: nonOwner }))
+    })
+  })
+
   describe('#setRegistry()', () => {
     it('should allow owner to set registry', async () => {
       await reserve.setRegistry(anAddress)
@@ -152,20 +163,34 @@ contract('Reserve', (accounts: string[]) => {
   })
 
   describe('#transferGold()', () => {
-    const aValue = 10
+    const aValue = 10000
     beforeEach(async () => {
-      await web3.eth.sendTransaction({
-        from: accounts[0],
-        to: reserve.address,
-        value: aValue,
-      })
+      await mockGoldToken.setBalanceOf(reserve.address, aValue)
       await reserve.addSpender(spender)
     })
 
     it('should allow a spender to call transferGold', async () => {
       await reserve.transferGold(nonOwner, aValue, { from: spender })
     })
 
+    it('should not allow a spender to transfer more than daily ratio', async () => {
+      await reserve.setDailySpendingRatio(toFixed(0.2))
+      await assertRevert(reserve.transferGold(nonOwner, aValue / 2, { from: spender }))
+    })
+
+    it('daily spending accumulates', async () => {
+      await reserve.setDailySpendingRatio(toFixed(0.15))
+      await reserve.transferGold(nonOwner, aValue * 0.1, { from: spender })
+      await assertRevert(reserve.transferGold(nonOwner, aValue * 0.1, { from: spender }))
+    })
+
+    it('daily spending limit should be reset after 24 hours', async () => {
+      await reserve.setDailySpendingRatio(toFixed(0.15))
+      await reserve.transferGold(nonOwner, aValue * 0.1, { from: spender })
+      await timeTravel(3600 * 24, web3)
+      await reserve.transferGold(nonOwner, aValue * 0.1, { from: spender })
+    })
+
     it('should not allow a removed spender to call transferGold', async () => {
       await reserve.removeSpender(spender)
       await assertRevert(reserve.transferGold(nonOwner, aValue, { from: spender }))
@@ -414,7 +439,7 @@ contract('Reserve', (accounts: string[]) => {
     })
   })
 
-  describe.only('#setAssetAllocations', () => {
+  describe('#setAssetAllocations', () => {
     const newAssetAllocationSymbols = [
       web3.utils.padRight(web3.utils.utf8ToHex('cGLD'), 64),
       web3.utils.padRight(web3.utils.utf8ToHex('BTC'), 64),