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@apogiatzis
Created May 3, 2022 23:05
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// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
/**
* @title Ballot
* @dev Implements voting process along with vote delegation
*/
contract Ballot {
struct Voter {
uint weight; // weight is accumulated by delegation
bool voted; // if true, that person already voted
address delegate; // person delegated to
uint vote; // index of the voted proposal
}
struct Proposal {
// If you can limit the length to a certain number of bytes,
// always use one of bytes1 to bytes32 because they are much cheaper
bytes32 name; // short name (up to 32 bytes)
uint voteCount; // number of accumulated votes
}
// Voting starts as soon as contract is deployed
// Therefore the timestmap of block can be used as startTime
uint256 public startTime = block.timestamp;
address public chairperson;
mapping(address => Voter) public voters;
Proposal[] public proposals;
// Modifier voteEnded checks if the voting period is over
modifier voteEnded() {
require(
block.timestamp <= (startTime + 5 minutes),
"Ballot has ended!"
);
_;
}
/**
* @dev Create a new ballot to choose one of 'proposalNames'.
* @param proposalNames names of proposals
*/
constructor(bytes32[] memory proposalNames) {
chairperson = msg.sender;
voters[chairperson].weight = 1;
for (uint i = 0; i < proposalNames.length; i++) {
// 'Proposal({...})' creates a temporary
// Proposal object and 'proposals.push(...)'
// appends it to the end of 'proposals'.
proposals.push(Proposal({
name: proposalNames[i],
voteCount: 0
}));
}
}
/**
* @dev Give 'voter' the right to vote on this ballot. May only be called by 'chairperson'.
* @param voter address of voter
*/
function giveRightToVote(address voter) public {
require(
msg.sender == chairperson,
"Only chairperson can give right to vote."
);
require(
!voters[voter].voted,
"The voter already voted."
);
require(voters[voter].weight == 0);
voters[voter].weight = 1;
}
/**
* @dev Delegate your vote to the voter 'to'.
* @param to address to which vote is delegated
*/
function delegate(address to) public {
Voter storage sender = voters[msg.sender];
require(!sender.voted, "You already voted.");
require(to != msg.sender, "Self-delegation is disallowed.");
while (voters[to].delegate != address(0)) {
to = voters[to].delegate;
// We found a loop in the delegation, not allowed.
require(to != msg.sender, "Found loop in delegation.");
}
sender.voted = true;
sender.delegate = to;
Voter storage delegate_ = voters[to];
if (delegate_.voted) {
// If the delegate already voted,
// directly add to the number of votes
proposals[delegate_.vote].voteCount += sender.weight;
} else {
// If the delegate did not vote yet,
// add to her weight.
delegate_.weight += sender.weight;
}
}
/**
* @dev Give your vote (including votes delegated to you) to proposal 'proposals[proposal].name'.
* @param proposal index of proposal in the proposals array
*/
function vote(uint proposal) public voteEnded {
Voter storage sender = voters[msg.sender];
require(sender.weight != 0, "Has no right to vote");
require(!sender.voted, "Already voted.");
sender.voted = true;
sender.vote = proposal;
// If 'proposal' is out of the range of the array,
// this will throw automatically and revert all
// changes.
proposals[proposal].voteCount += sender.weight;
}
/**
* @dev Computes the winning proposal taking all previous votes into account.
* @return winningProposal_ index of winning proposal in the proposals array
*/
function winningProposal() public view
returns (uint winningProposal_)
{
uint winningVoteCount = 0;
for (uint p = 0; p < proposals.length; p++) {
if (proposals[p].voteCount > winningVoteCount) {
winningVoteCount = proposals[p].voteCount;
winningProposal_ = p;
}
}
}
/**
* @dev Calls winningProposal() function to get the index of the winner contained in the proposals array and then
* @return winnerName_ the name of the winner
*/
function winnerName() public view
returns (bytes32 winnerName_)
{
winnerName_ = proposals[winningProposal()].name;
}
}
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