add prediction market

contract/NBAPrediction.sol

@@ -0,0 +1,96 @@
+pragma solidity 0.5.10;
+
+interface ERC20Interface {
+    function totalSupply() external view returns (uint);
+    function balanceOf(address tokenOwner) external view returns (uint balance);
+    function allowance(address tokenOwner, address spender) external view returns (uint remaining);
+    function transfer(address to, uint tokens) external returns (bool success);
+    function approve(address spender, uint tokens) external returns (bool success);
+    function transferFrom(address from, address to, uint tokens) external returns (bool success);
+}
+
+interface QueryInterface {
+  enum QueryStatus { INVALID, OK, NOT_AVAILABLE, DISAGREEMENT }
+
+  function query(bytes calldata input)
+    external payable returns (bytes32 output, uint256 updatedAt, QueryStatus status);
+
+  function queryPrice() external view returns (uint256);
+}
+
+
+contract NBAPrediction {
+
+    bool public hasResolved = false;
+    bool public isHomeWin = false;
+
+    uint256 public predictionEndTime;
+    uint256 public homeTeamTotalWeight;
+    uint256 public awayTeamTotalWeight;
+    bytes public eventKey;
+
+    ERC20Interface public token;
+    QueryInterface public oracle;
+
+    //           who => betting amount
+    mapping (address => uint256) bettingOnHomeTeam;
+    mapping (address => uint256) bettingOnAwayTeam;
+
+    constructor(
+        bytes memory _eventKey,
+        uint256 _predictionEndTime,
+        ERC20Interface _token,
+        QueryInterface _oracle
+    ) public {
+        eventKey = _eventKey;
+        predictionEndTime = _predictionEndTime;
+        token = _token;
+        oracle = _oracle;
+    }
+
+    function bet(uint256 betAmount, bool isHome) public {
+        require(now < predictionEndTime);
+        require(betAmount > 0);
+        require(bettingOnHomeTeam[msg.sender] == 0);
+        require(bettingOnAwayTeam[msg.sender] == 0);
+
+        require(token.transferFrom(msg.sender, address(this), betAmount));
+
+        if (isHome) {
+            bettingOnHomeTeam[msg.sender] = betAmount;
+            homeTeamTotalWeight += betAmount;
+        } else {
+            bettingOnAwayTeam[msg.sender] = betAmount;
+            awayTeamTotalWeight += betAmount;
+        }
+    }
+
+    function resolve() public payable {
+        require(now >= predictionEndTime);
+        require(!hasResolved);
+
+        (bytes32 rawData,, QueryInterface.QueryStatus status) = oracle.query.value(oracle.queryPrice())(eventKey);
+        require(status == QueryInterface.QueryStatus.OK);
+
+        uint8 homeScore = uint8(rawData[0]);
+        uint8 awayScore = uint8(rawData[1]);
+
+        isHomeWin = homeScore > awayScore;
+
+        hasResolved = true;
+    }
+
+    function withdraw() public {
+        require(hasResolved);
+        require(bettingOnHomeTeam[msg.sender] > 0 || bettingOnAwayTeam[msg.sender] > 0);
+        if (bettingOnHomeTeam[msg.sender] > 0 && isHomeWin) {
+            uint256 withdrawAmount = (bettingOnHomeTeam[msg.sender]*(homeTeamTotalWeight+awayTeamTotalWeight))/homeTeamTotalWeight;
+            require(token.transfer(msg.sender,withdrawAmount));
+        } else if (bettingOnAwayTeam[msg.sender] > 0 && !isHomeWin) {
+            uint256 withdrawAmount = (bettingOnAwayTeam[msg.sender]*(homeTeamTotalWeight+awayTeamTotalWeight))/awayTeamTotalWeight;
+            require(token.transfer(msg.sender,withdrawAmount));
+        }
+        bettingOnHomeTeam[msg.sender] = 0;
+        bettingOnAwayTeam[msg.sender] = 0;
+    }
+}