Fixes based on Slither for re-entrancy and code readability

contracts/Migrations.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: MIT
-pragma solidity >=0.4.22 <0.8.0;
+pragma solidity >=0.4.22 <=0.8.0;
 
 contract Migrations {
   address public owner = msg.sender;

contracts/StarfleetStake.sol

@@ -1,4 +1,4 @@
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity >=0.6.0 <=0.8.0;
 
 import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
 import "openzeppelin-solidity/contracts/math/SafeMath.sol";
@@ -18,10 +18,10 @@ contract StarfleetStake is Ownable {
   // Time periods
 
   // Official start time of the staking period
-  uint256 public t_zero;
-  uint256 public BOARDING_PERIOD_LENGTH = 30 days;
-  uint256 public LOCK_PERIOD_LENGTH = 180 days;
-  uint256 public BRIDGE_PERIOD_LENGTH = 180 days;
+  uint256 public tZero;
+  uint256 public constant BOARDING_PERIOD_LENGTH = 30 days;
+  uint256 public constant LOCK_PERIOD_LENGTH = 180 days;
+  uint256 public constant BRIDGE_PERIOD_LENGTH = 180 days;
   bool public min_threshold_reached = false;
 
   // list of participants
@@ -42,9 +42,9 @@ contract StarfleetStake is Ownable {
   constructor(uint256 startTime,address tokenAddress)  public {
 
     if(startTime!=0){
-      t_zero = startTime;
+      tZero = startTime;
     }else{
-      t_zero = now;  
+      tZero = now;  
     }
 
     if (tokenAddress!=address(0x0)){
@@ -60,8 +60,8 @@ contract StarfleetStake is Ownable {
 // Functional requirement FR1
  function depositTokens(uint256 amount) public {
 
-  require(now >= t_zero);
-  require(now < t_zero + BOARDING_PERIOD_LENGTH);
+  require(now >= tZero);
+  require(now < tZero + BOARDING_PERIOD_LENGTH);
   require(token.balanceOf(address(this)) + amount <= MAX_THRESHOLD, "Sender cannot deposit amounts that would cross the MAX_THRESHOLD");
   require(token.allowance(msg.sender, address(this)) >= amount, "Sender allowance must be equal to or higher than chosen amount");
   require(token.balanceOf(msg.sender) >= amount, "Sender balance must be equal to or higher than chosen amount!");
@@ -98,31 +98,33 @@ function isMinimumReached() public view returns(bool){
 // Functional requirement FR2
 function withdrawTokens() public {
 
-  require(now >= t_zero);
+  require(now >= tZero);
   require(!min_threshold_reached);
   require(stake[msg.sender] > 0);
-
-  token.transfer(msg.sender, stake[msg.sender]);
-  emit TokenWithdrawn(msg.sender, stake[msg.sender]); 
+  uint256 amount = stake[msg.sender];
   stake[msg.sender] = 0;
+  token.transfer(msg.sender, amount);
+  emit TokenWithdrawn(msg.sender, amount); 
+
 
 }
 
 // Functional requirement FR6
 function fallbackWithdrawTokens() public {
 
-  require(now > t_zero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
+  require(now > tZero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
   require(StarTRAC_snapshot[msg.sender] > 0);
-
-  token.transfer(msg.sender, StarTRAC_snapshot[msg.sender]);
-  emit TokenFallbackWithdrawn(msg.sender, StarTRAC_snapshot[msg.sender]);
+  uint256 amount = StarTRAC_snapshot[msg.sender];
   StarTRAC_snapshot[msg.sender] = 0;
+  token.transfer(msg.sender, amount);
+  emit TokenFallbackWithdrawn(msg.sender, StarTRAC_snapshot[msg.sender]);
+
 
 }
 
 // Functional requirement FR5
 function accountStarTRAC(address[] memory contributors, uint256[] memory amounts) onlyOwner public {
-  require(now > t_zero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
+  require(now > tZero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
   require(contributors.length == amounts.length);
   for (uint i = 0; i < contributors.length; i++) {
     StarTRAC_snapshot[contributors[i]] = amounts[i];
@@ -139,7 +141,7 @@ function getStarTRACamount(address contributor) public view returns(uint256){
 function transferTokens(address custodian) onlyOwner public {
 
   require(custodian != address(0x0));
-  require(now >= t_zero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH && now < t_zero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
+  require(now >= tZero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH && now < tZero + BOARDING_PERIOD_LENGTH + LOCK_PERIOD_LENGTH + BRIDGE_PERIOD_LENGTH);
 
   uint256 balanceTransferred= token.balanceOf(address(this));
   token.transfer(custodian, token.balanceOf(address(this)));

contracts/TracToken.sol

@@ -1,10 +1,10 @@
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity >=0.6.0 <=0.8.0;
 
 import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
 
 contract TestTraceToken is ERC20 {
 
-	uint public INITIAL_SUPPLY = 5e26;
+	uint public constant INITIAL_SUPPLY = 5e26;
 	// for contract testing purposes, not to be confused with TRAC
 	constructor() public ERC20('Test-Trace token', 'T-TRAC') {
 		_mint(msg.sender, INITIAL_SUPPLY);