Voting Contract

abi.json

[
			{
				"inputs": [
					{
						"internalType": "address",
						"name": "chairperson_",
						"type": "address"
					}
				],
				"stateMutability": "nonpayable",
				"type": "constructor"
			},
			{
				"inputs": [],
				"name": "candidateRegis",
				"outputs": [],
				"stateMutability": "nonpayable",
				"type": "function"
			},
			{
				"inputs": [
					{
						"internalType": "address",
						"name": "",
						"type": "address"
					}
				],
				"name": "candidates",
				"outputs": [
					{
						"internalType": "bool",
						"name": "isRegistered",
						"type": "bool"
					},
					{
						"internalType": "uint256",
						"name": "voteCount",
						"type": "uint256"
					}
				],
				"stateMutability": "view",
				"type": "function"
			},
			{
				"inputs": [],
				"name": "chairperson",
				"outputs": [
					{
						"internalType": "address",
						"name": "",
						"type": "address"
					}
				],
				"stateMutability": "view",
				"type": "function"
			},
			{
				"inputs": [],
				"name": "endVoting",
				"outputs": [],
				"stateMutability": "nonpayable",
				"type": "function"
			},
			{
				"inputs": [],
				"name": "getWinner",
				"outputs": [
					{
						"internalType": "address",
						"name": "",
						"type": "address"
					}
				],
				"stateMutability": "view",
				"type": "function"
			},
			{
				"inputs": [],
				"name": "startVoting",
				"outputs": [],
				"stateMutability": "nonpayable",
				"type": "function"
			},
			{
				"inputs": [],
				"name": "state",
				"outputs": [
					{
						"internalType": "uint256",
						"name": "",
						"type": "uint256"
					}
				],
				"stateMutability": "view",
				"type": "function"
			},
			{
				"inputs": [
					{
						"internalType": "address",
						"name": "candidate",
						"type": "address"
					}
				],
				"name": "vote",
				"outputs": [],
				"stateMutability": "nonpayable",
				"type": "function"
			},
			{
				"inputs": [
					{
						"internalType": "address",
						"name": "",
						"type": "address"
					}
				],
				"name": "voters",
				"outputs": [
					{
						"internalType": "bool",
						"name": "voted",
						"type": "bool"
					}
				],
				"stateMutability": "view",
				"type": "function"
			}
		]

voting_contract.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

// Modified from Ballot contract https://docs.soliditylang.org/en/v0.8.9/solidity-by-example.html 

contract VotingContract {
   
    struct Voter {
        bool voted;  // if true, that person already voted
    }

    struct Candidate {
        bool isRegistered; // if true, that person is a candidate
        uint voteCount;
        
    }

    address public chairperson;

    mapping(address => Voter) public voters;
    
    mapping(address => Candidate) public candidates;
    
    uint public state; // 0: setup, 1: voting, 2: voting end
    
    address private topCandidate;
    

    constructor(address chairperson_) {
        chairperson = chairperson_;
    }
    
    function candidateRegis() public {
        require(state == 0, "Registration is now closed.");
        require(msg.sender != chairperson, "Chairperson cannot be a candidate.");
        require(
            !voters[msg.sender].voted,
            "Voter cannot be a candidate."
        );
        candidates[msg.sender].isRegistered = true;
    }
    
    function startVoting() public {
        require(
            msg.sender == chairperson,
            "Only chairperson can start voting."
        );
        require(state == 0, "Unable to start voting.");
        state = 1;
    }
    
    function endVoting() public {
        require(
            msg.sender == chairperson,
            "Only chairperson can end voting."
        );
        require(state == 1, "Voting is not open or already closed.");
        state = 2;
    }
    
    function vote(address candidate) public {
        Voter storage sender = voters[msg.sender];
        require(state == 1, "Voting is not open or already closed.");
        require(msg.sender != chairperson, "Chairperson cannot give a vote.");
        require(
            !candidates[msg.sender].isRegistered,
            "Candidate cannot vote."
        );
        require(!sender.voted, "Already voted.");
        sender.voted = true;
        candidates[candidate].voteCount++;
        if (candidates[candidate].voteCount > candidates[topCandidate].voteCount) {
            topCandidate = candidate;
        }
    }
    
     function getWinner() public view
            returns (address)
    {
        require(state == 2, "Winner is not announced yet.");
        return topCandidate;
    }
}