Voting contract init

packages/concordia-contracts/contracts/Forum.sol

@@ -1,5 +1,5 @@
 //SPDX-License-Identifier: MIT
-pragma solidity 0.7.1;
+pragma solidity 0.7.4;
 
 contract Forum {
 
@@ -145,6 +145,11 @@ contract Forum {
         return topics[topicID].postIDs;
     }
 
+    function getTopicAuthor(uint topicID) public view returns (address) {
+        require(topicID<numTopics); // Topic should exist
+        return topics[topicID].author;
+    }
+
     function getPost(uint postID) public view returns (address, string memory, uint, uint) {
         require(postID<numPosts);
         return (

packages/concordia-contracts/contracts/Migrations.sol

@@ -1,10 +1,11 @@
-pragma solidity 0.7.1;
+//SPDX-License-Identifier: MIT
+pragma solidity 0.7.4;
 
 contract Migrations {
     address public owner;
     uint public last_completed_migration;
 
-    constructor() public {
+    constructor() {
         owner = msg.sender;
     }
 

packages/concordia-contracts/contracts/Voting.sol

@@ -0,0 +1,90 @@
+//SPDX-License-Identifier: MIT
+pragma solidity 0.7.4;
+
+import "./Forum.sol";
+
+contract Voting {
+    Forum public forum;
+
+    constructor(Forum addr) {
+        forum = Forum(addr);
+    }
+
+    struct Poll {
+        uint topicID;
+        uint numOptions;
+        string dataHash;
+        mapping (address => uint) voters;
+        uint[] voteCounts;  // First element will hold total count
+        uint timestamp;
+    }
+
+    mapping (uint => Poll) polls;
+
+    event PollCreated(uint topicID);
+    event UserVoted(address userAddress);
+
+    function createPoll(uint topicID, uint numOptions, string memory dataHash) public returns (uint) {
+        require(forum.hasUserSignedUp(msg.sender));  // Only registered users can create polls
+        require(topicID<forum.getNumberOfTopics()); // Only allow poll creation if topic exists
+        require (forum.getTopicAuthor(topicID) == msg.sender); // Only allow poll creation from the author of the topic
+        require(polls[topicID].timestamp == 0); // Only allow poll creation if it doesn't exist yet
+
+        Poll storage poll = polls[topicID];
+        poll.topicID = topicID;
+        poll.numOptions = numOptions;
+        poll.dataHash = dataHash;
+        poll.voteCounts = new uint[](numOptions+1);
+        poll.timestamp = block.timestamp;
+
+        emit PollCreated(topicID);
+        return topicID;
+    }
+
+    // Verify that poll exists
+    function isPollExistent(uint topicID) public view returns (bool) {
+        if (polls[topicID].timestamp != 0)
+            return true;
+        return false;
+    }
+
+    function hasVoted(uint topicID, address voter) public view returns (bool) {
+        require(isPollExistent(topicID));
+        if (polls[topicID].voters[voter] != 0)
+            return true;
+        return false;
+    }
+
+    function getPollInfo(uint topicID) public view returns (uint, string memory, uint, uint) {
+        require(isPollExistent(topicID));
+        return (
+        polls[topicID].numOptions,
+        polls[topicID].dataHash,
+        polls[topicID].timestamp,
+        polls[topicID].voteCounts[0]
+        );
+    }
+
+    // Gets vote count for a specific option (option 0 will return total count)
+    function getVoteCount(uint topicID, uint option) public view returns (uint) {
+        require(isPollExistent(topicID)); // Verify that poll exists
+        return (polls[topicID].voteCounts[option]);
+    }
+
+    function vote(uint topicID, uint option) public {
+        require(isPollExistent(topicID));
+        Poll storage poll = polls[topicID];
+        require(option > 0 && option <= poll.numOptions); // Verify that this option exists
+        address voter = msg.sender;
+        uint currentVote = poll.voters[voter];
+        if(currentVote == option)
+            return;
+        if(currentVote == 0)   // Voter hadn't voted before
+            poll.voteCounts[0]++;
+        else
+            poll.voteCounts[currentVote]--;
+        poll.voteCounts[option]++;
+        poll.voters[voter] = option;
+        emit UserVoted(voter);
+    }
+}

packages/concordia-contracts/migrations/2_deploy_contracts.js

@@ -1,6 +1,7 @@
 const Forum = artifacts.require('Forum');
+const Voting = artifacts.require('Voting');
 
 // eslint-disable-next-line func-names
 module.exports = function (deployer) {
-  deployer.deploy(Forum);
+  deployer.deploy(Forum).then((forum) => deployer.deploy(Voting, forum.address));
 };

packages/concordia-contracts/truffle-config.js

@@ -8,7 +8,7 @@ module.exports = {
   // to customize your Truffle configuration!
   compilers: {
     solc: {
-      version: '0.7.1',
+      version: '0.7.4',
     },
   },
   contracts_build_directory: path.join(__dirname, 'build/'),