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contracts/Lottery.sol

@@ -1,26 +1,37 @@
 pragma solidity >=0.4.22;
 
 contract Lottery {
-    string internal constant ENTER_MESSAGE = "The player needs to stake at least 0.1 ether";
-    string internal constant RESTRICTED_MESSAGE = "Only manager can do";
+    string internal constant INSUFFICIENT_FUND_MESSAGE = "Insufficient Fund";
+    string internal constant RESTRICTED_MESSAGE = "Unauthorized Access";
 
-    address public manager;
-    address payable[] public players;
+    address public manager;  // The adress of the owner of this contract
+    address payable[] public players;  // The players of current session
 
     constructor() public {
         manager = msg.sender;
     }
 
+    /**
+     * @dev The player enters into the current lottery session by
+     *      paying at least 0.1 token.
+     */
     function enter() public payable {
-        require(msg.value > .1 ether, ENTER_MESSAGE);
+        require(msg.value > .1 ether, INSUFFICIENT_FUND_MESSAGE);
 
         players.push(msg.sender);
     }
 
+    /**
+     * @dev Random number used for picking the winner.
+     */
     function random() private view returns (uint) {
         return uint(keccak256(abi.encodePacked(now, msg.sender, this)));
     }
 
+    /**
+     * @dev Randomly select one of the players in current session as winner
+     *      and send all the token in smart contract balance to it.
+     */
     function pickWinner() public payable restricted {
         uint index = random() % players.length;
         players[index].transfer(address(this).balance);
@@ -32,6 +43,9 @@ contract Lottery {
         _;
     }
 
+    /**
+     * @dev Returns a list of all players in the current session.
+     */
     function getPlayers() public view returns (address payable[] memory) {
         return players;
     }