first commit

contracts/Draw.sol

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+pragma solidity ^0.6.6;
+import "@chainlink/contracts/src/v0.6/VRFConsumerBase.sol";
+
+contract Draw is VRFConsumerBase {
+    enum requestStatus {started, returned} 
+    bytes32 internal keyHash;
+    uint256 internal fee;
+    uint256 internal seed;
+
+	struct Twitter {
+		uint256 numParticipants;
+		uint256[] participants;
+		bytes32 requestId;
+	}
+
+	struct DrawRequest {
+		uint256 twitterId;
+		requestStatus status;
+		uint256 seed;
+		uint256 randomNumber;
+		uint256 originalRandomNumber;
+	}
+
+    mapping(uint256 => Twitter) drawTweet; 
+    mapping(bytes32 => DrawRequest) drawRequest; 
+    address public owner;
+
+	 /**
+     * Constructor inherits VRFConsumerBase
+     * 
+     * Network: Rinkeby
+     * Chainlink VRF Coordinator address: 0xb3dCcb4Cf7a26f6cf6B120Cf5A73875B7BBc655B
+     * LINK token address:                0x01BE23585060835E02B77ef475b0Cc51aA1e0709
+     * Key Hash: 0x2ed0feb3e7fd2022120aa84fab1945545a9f2ffc9076fd6156fa96eaff4c1311
+     */
+    constructor() 
+        VRFConsumerBase(
+			 0xb3dCcb4Cf7a26f6cf6B120Cf5A73875B7BBc655B, // VRF Coordinator
+            0x01BE23585060835E02B77ef475b0Cc51aA1e0709  // LINK Token
+        ) public
+    {
+		owner = msg.sender;
+        keyHash = 0x2ed0feb3e7fd2022120aa84fab1945545a9f2ffc9076fd6156fa96eaff4c1311;
+        fee = 0.1 * 10 ** 18; // 0.1 LINK
+        seed = 0;
+    }
+
+    /** 
+     * Requests randomness from a user-provided seed
+     */
+    function takeDraw(uint256 twitterId, uint256[] memory participants, uint256 num_participants, uint256 seed) external {
+		require(msg.sender == owner, 'should be owner');
+	  	require(LINK.balanceOf(address(this)) > fee, "Not enough LINK - fill contract with faucet");
+	  	require(num_participants > 0, "num_participants should be bigger than 0");
+	  	require(num_participants <= 2000, "num_participants should be lesser than 2000");
+		require(drawTweet[twitterId].numParticipants == 0, "tweet should not be drawn twice");
+
+		drawTweet[twitterId].numParticipants = num_participants; 
+        bytes32 requestId = requestRandomness(keyHash, fee, seed);
+		drawTweet[twitterId].requestId = requestId; 
+		drawRequest[requestId].twitterId = twitterId;
+		drawRequest[requestId].seed = seed;
+		for(uint i=0; i<num_participants; i++){
+			drawTweet[twitterId].participants.push(participants[i]);
+		}
+    }
+
+
+    function getParticipantByPosition(uint256 twitterId, uint256 position) public view returns (uint256) {
+		return drawTweet[twitterId].participants[position];
+    }
+
+
+	function getRandomNumberByTwitterId(uint256 twitterId) public view returns (uint256 randomness) {
+		bytes32 request_id = drawTweet[twitterId].requestId;
+		require(drawRequest[request_id].status == requestStatus.returned);
+		return drawRequest[request_id].randomNumber;
+	}
+
+	function getWinnerByTwitterId(uint256 twitterId) public view returns (uint256 winner) {
+		bytes32 requestId = drawTweet[twitterId].requestId;
+		require(drawRequest[requestId].status == requestStatus.returned);
+		return drawTweet[twitterId].participants[drawRequest[requestId].randomNumber];
+	}
+
+	function getRandomRequestInfo(uint256 twitterId) public view returns (requestStatus status, 
+			uint256 seed, uint256 randomNumber, uint256 originalRandomNumber
+	) {
+		bytes32 requestId = drawTweet[twitterId].requestId;
+		status = drawRequest[requestId].status;
+		seed = drawRequest[requestId].seed;
+		randomNumber = drawRequest[requestId].randomNumber;
+		originalRandomNumber = drawRequest[requestId].originalRandomNumber;
+	}
+
+    /**
+     * Callback function used by VRF Coordinator
+     */
+    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override{
+        require(msg.sender == vrfCoordinator, "Fulfilment only permitted by Coordinator");
+		drawRequest[requestId].originalRandomNumber = randomness; 
+		drawRequest[requestId].randomNumber = randomness % drawTweet[drawRequest[requestId].twitterId].numParticipants;
+		drawRequest[requestId].status = requestStatus.returned;
+    }
+}

contracts/Migrations.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity >=0.4.22 <0.8.0;
+
+contract Migrations {
+  address public owner = msg.sender;
+  uint public last_completed_migration;
+
+  modifier restricted() {
+    require(
+      msg.sender == owner,
+      "This function is restricted to the contract's owner"
+    );
+    _;
+  }
+
+  function setCompleted(uint completed) public restricted {
+    last_completed_migration = completed;
+  }
+}

migrations/1_initial_migration.js

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+const Migrations = artifacts.require("Migrations");
+
+module.exports = function (deployer) {
+  deployer.deploy(Migrations);
+};