diff --git a/contracts/Puzzle.sol b/contracts/Puzzle.sol
index b3ce15d8a..370e85079 100644
--- a/contracts/Puzzle.sol
+++ b/contracts/Puzzle.sol
@@ -1,37 +1,97 @@
 pragma solidity >=0.4.22; 
+
 contract Puzzle {
     string internal constant INSUFFICIENT_FUND_MESSAGE = "Insufficient Fund";
     string internal constant RESTRICTED_MESSAGE = "Unauthorized Access";
+    string internal constant INCORRECT_SESSION = "Player requesting payout for unknown session";
+    string internal constant INCORRECT_LEVEL = "Player requesting payout for earlier level";
+    uint amount;
+    uint sessionID;
+    uint progress;
+    string seq;
+    uint constant thresholdLevel = 4;
+    mapping(address => uint) playerLevel;
+    mapping(address => uint) playerSession;
+    mapping(address => uint) playerStake;
     address public manager;  // The adress of the owner of this contract
-    mapping(address => uint8) public level_map;
+    address payable[] public players;   // The players of current session
 
-    constructor() public payable {
+    constructor() public {
         manager = msg.sender;
     }
-
+    
+    /**
+     * @dev random number generator
+     *     
+     */
+    function random() private returns (uint) {
+        sessionID = uint(keccak256(abi.encodePacked(now, msg.sender, this)));
+        return sessionID;   
+    }
+    
     /**
      * @dev The player enters into the current game session by
      *      paying at least 2 token.
      */
-    function play() public payable {
+    function play() public payable returns (uint) {
         require(msg.value >= 2 ether, INSUFFICIENT_FUND_MESSAGE);
+        sessionID = random();
+        playerLevel[msg.sender] = 0;
+        playerSession[msg.sender] = sessionID;
+        playerStake[msg.sender] = msg.value;
+        players.push(msg.sender);
+        return sessionID;
     }
 
+    /**
+     * @dev returns the current best level the player has crossed   
+     */
+    function setLevel(address player, uint level) public{
+         playerLevel[player] = level;
+    }
+    
     /**
      * @dev pay the player if they have crossed their last best level.
      */
-    function payout(address payable player, uint8 new_level) public payable restricted {
-        uint8 cur_level = level_map[player];
-        if (new_level >= cur_level) {
-            player.transfer(2 * (new_level - cur_level + 1) * 1 ether);
-            level_map[player] = new_level;
-        } else {
-            delete level_map[player];
-        }
+    function payout(address payable player, uint level, uint session, string memory /*sequence*/) public payable restricted {
+            require(playerSession[player] == session, INCORRECT_SESSION );
+            require(level > playerLevel[player], INCORRECT_LEVEL);
+            progress = level - playerLevel[player]; //if a later transaction for a higher level comes earlier.
+            setLevel(player,level);
+            amount = progress*(playerStake[player]/thresholdLevel);
+            player.transfer(amount);
     }
 
     modifier restricted() {
         require(msg.sender == manager, RESTRICTED_MESSAGE);
         _;
     }
+    
+    /**
+     * @dev Resets the current session of one player
+     */
+    function resetPlayer(address player) public restricted {
+            delete playerLevel[player];
+            delete playerSession[player];
+            delete playerStake[player]; 
+    }
+    
+    /**
+     * @dev Resets the current session by deleting all the players
+     */
+    function reset() public restricted {
+        uint arrayLength = players.length;
+        for(uint i=0; i< arrayLength; i++) {
+            address player = players[i];
+            resetPlayer(player);
+        }
+        players.length = 0;
+    }
+    
+    /**
+     * @dev Returns a list of all players in the current session.
+     */
+    function getPlayers() public view returns (address payable[] memory) {
+        return players;
+    }
 }