payFee function

contracts/staking/contracts/src/core/MixinFees.sol

@@ -0,0 +1,57 @@
+/*
+
+  Copyright 2018 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity ^0.5.5;
+
+import "../interfaces/IVault.sol";
+import "../libs/LibZrxToken.sol";
+import "@0x/contracts-utils/contracts/src/SafeMath.sol";
+import "../immutable/MixinStorage.sol";
+import "../immutable/MixinConstants.sol";
+import "../interfaces/IStakingEvents.sol";
+import "./MixinStakeBalances.sol";
+import "./MixinEpoch.sol";
+import "./MixinPools.sol";
+
+
+contract MixinFees is
+    SafeMath,
+    IStakingEvents,
+    MixinConstants,
+    MixinStorage,
+    MixinEpoch,
+    MixinStakeBalances,
+    MixinPools
+{
+
+    function _payFee(address makerAddress, uint256 amount)
+        internal
+    {
+        bytes32 poolId = _getMakerPoolId(makerAddress);
+        uint256 _feesCollectedThisEpoch = feesCollectedThisEpochByPoolId[poolId];
+        feesCollectedThisEpochByPoolId[poolId] = _safeAdd(_feesCollectedThisEpoch, amount);
+        if (_feesCollectedThisEpoch == 0) {
+            activePoolIdsThisEpoch.append(poolId);
+        }
+    }
+
+    function _payRebates()
+    {
+        
+    }
+}

contracts/staking/contracts/src/core/MixinStake.sol

@@ -176,7 +176,7 @@ contract MixinStake is
         delegatedStakeByPoolId[poolId] = _safeSub(delegatedStakeByPoolId[poolId], amount);
     }
 
-    // Epoch | lockedAt  | total | pending |  | timelock() | withdraw() | available()
+    // Epoch | lockedAt  | total | pending | deactivated | timelock() | withdraw() | available()
     // 0     | 0         | 0     | 0       | 0       |            |            | 0
     // 1     | 1         | 5     | 0       | 0       | +5         |            | 0
     // 2     | 1         | 5     | 0       | 0       |            |            | 0

contracts/staking/contracts/src/immutable/MixinStorage.sol

@@ -74,6 +74,12 @@ contract MixinStorage is
     // current epoch start time
     uint64 currentTimelockPeriodStartEpoch = INITIAL_EPOCH;
 
+    // fees collected this epoch
+    mapping (bytes32 => uint256) feesCollectedThisEpochByPoolId;
+
+    // 
+    bytes32[] activePoolIdsThisEpoch;
+
     // ZRX vault
     IVault zrxVault;