Update BEP153's design

assets/bep-153/SampleStakingContract.sol

@@ -177,22 +177,15 @@ contract Sample {
   address public constant STAKING_CONTRACT_ADDR = 0x0000000000000000000000000000000000002001;
 
   // data struct
-  struct UserInfo {
-    uint256 amount; // total BNB delegated
-    uint256 rewardDebt; // reward debt
-    //   pending reward = (user.amount * pool.rewardPerShare) - user.rewardDebt
-    //
-    // Whenever a user deposits or withdraws BNBs to a pool. Here's what happens:
-    //   1. The pool's `rewardPerShare` (and `lastRewardBlock`) gets updated.
-    //   2. User receives the pending reward sent to his/her address.
-    //   3. User's `amount` gets updated.
-    //   4. User's `rewardDebt` gets updated.
+  struct PoolInfo {
+    uint256 rewardPerShare;
+    uint256 lastRewardBlock;
+    uint256 lastTotalReward;
   }
 
-  struct PoolInfo {
-    uint256 rewardPerShare; // Accumulated reward per share
-    uint256 lastRewardBlock; // Last block number that reward distribution occurs
-    uint256 lastTotalReward; // Last total reward at lastRewardBlock
+  struct UserInfo {
+    uint256 amount;
+    uint256 rewardDebt;
   }
 
   // global variables
@@ -218,7 +211,7 @@ contract Sample {
   }
 
   modifier noReentrant() {
-    require(!locked, "No re-entrance");
+    require(!locked, "No re-entrancy");
     locked = true;
     _;
     locked = false;
@@ -250,15 +243,15 @@ contract Sample {
   /*********************** Design for user **************************/
   // This function will not submit delegation request to the staking system contract.
   // The real delegation process should be finished by the operator periodically or in other desirable way.
-  function delegate(uint256 amount) external payable {
-    require(msg.value > oracleRelayerFee, "received BNB amount should be no less than the oracleRelayerFee");
+  function delegate() external payable noReentrant {
+    uint256 amount = msg.value;
 
     // claim reward first
     UserInfo storage user = userInfo[msg.sender];
     _updatePool();
     if (user.amount > 0) {
       uint256 pendingReward = user.amount.mul(poolInfo.rewardPerShare).sub(user.rewardDebt);
-      msg.sender.transfer(pendingReward);
+      payable(msg.sender).transfer(pendingReward);
       emit rewardClaimed(msg.sender, pendingReward);
     }
     user.amount = user.amount.add(amount);
@@ -276,7 +269,7 @@ contract Sample {
     require(address(this).balance >= amount, "insufficient balance, please try again later");
     _updatePool();
     uint256 pendingReward = user.amount.mul(poolInfo.rewardPerShare).sub(user.rewardDebt);
-    msg.sender.transfer(amount.add(pendingReward));
+    payable(msg.sender).transfer(amount.add(pendingReward));
     user.amount  = user.amount.sub(amount);
     user.rewardDebt = user.amount.mul(poolInfo.rewardPerShare);
 
@@ -292,7 +285,7 @@ contract Sample {
     }
     _updatePool();
     uint256 pendingReward = user.amount.mul(poolInfo.rewardPerShare).sub(user.rewardDebt);
-    msg.sender.transfer(pendingReward);
+    payable(msg.sender).transfer(pendingReward);
     user.rewardDebt = user.amount.mul(poolInfo.rewardPerShare);
     emit rewardClaimed(msg.sender, pendingReward);
   }