Dapp from zero to Programmer

Players choose a number from 1-10
Bet value is 1 ETH
If total slots exceed, prize will be distributed
Won players will receive totalbet/(number of player who bet winner number)

Init project

npm install -g truffle
mkdir betting-app
cd betting-app
truffle init

Write contract & test & deploy on Remix IDE

deployed contract address: 0x10760d4227c8c87161a3ef93e2c4c3b6b04b95e1

Install metamask

https://metamask.io/

Create contract file

create Betting.sol inside contracts folder and open it.

Constructor & Destructor

pragma solidity ^0.4.23

contract Betting {
  address owner;

  constructor () public {
    owner = msg.sender;
  }

  function kill() public {
    require(msg.sender == owner);
    selfdestruct(owner);
  }
}

Declare variables

uint public lastWinnerNumber;
uint public betValue = 1 ether;
uint public totalBet;
uint public numberOfBets;
uint public totalPlayers = 3;
address[] players;

mapping(uint => address[]) public numberToPlayers;
mapping(address => uint) public playerToNumber;

Check a bet is valid or not

modifier validBet(uint betNumber) {
    require(playerToNumber[msg.sender] == 0);
    require(msg.value >= betValue);
    require(numberOfBets < 10);
    require(betNumber >= 1 && betNumber <= 10);
    _;
}

bet function

function bet(uint betNumber) public payable validBet(betNumber) {
    if (msg.value > betValue) {
        msg.sender.transfer(msg.value - betValue);
    }
    playerToNumber[msg.sender] = betNumber;
    players.push(msg.sender);
    numberToPlayers[betNumber].push(msg.sender);
    numberOfBets += 1;
    totalBet += msg.value;
    if(numberOfBets >= totalPlayers) {
        distributePrizes();
    }
}

Right after total players exceeds, we will find a winnerNumber and distribute prizes to the lucky one

function distributePrizes() internal {
    uint winnerNumber = generateRandomNumber();
    address[] memory winners = numberToPlayers[winnerNumber];
    if (winners.length > 0) {
        uint winnerEtherAmount = totalBet / winners.length;
        for (uint i = 0; i < numberToPlayers[winnerNumber].length; i++) {
            numberToPlayers[winnerNumber][i].transfer(winnerEtherAmount);
        }
    }
    lastWinnerNumber = winnerNumber;
    reset();
}

At the end of a game, we reset all data

function reset() internal {
    for (uint i = 1; i <= 10; i++) {
        numberToPlayers[i].length = 0;
    }

    for (uint j = 0; j < players.length; j++) {
        playerToNumber[players[j]] = 0;
    }

    players.length = 0;
    totalBet = 0;
    numberOfBets = 0;
}

Test it on Remix IDE

Write front-ent

src/
  css/
    boostrap.min.css
    index.css
  images/
    logo.png
  js/
    app.js
    boostrap.min.js
    web3.min.js
  index.html

Run front-end

install lite-server

npm init -y
npm install lite-server

config bs-config.json

{
    "server": {
      "baseDir": ["./src"]
    }
}

config package.json

"scripts": {
    "dev": "lite-server",

run app

npm run dev

Deploy to IPFS (optional)

run ipfs daemon

ipfs daemon

get peers

ipfs swarm peers

share your content

ipfs add -r src/

your can see some thing like bellow

added QmYUaCPwvJWiueRXFSTTv8vdedWWzRhRdn8RMw35e7k67u src/css/bootstrap.min.css
added QmdeMuRDxvEcva1wUW6yQzqS3JDJqnXtSNpB48rPuCEp4J src/css/index.css
added QmWYhkEbjC1ZsxeEUNQ5bfLYyNJuuc1SDZJ1MfSvfV1Dzx src/index.html
added QmTcHzbH9poCjJPrkoC1MQx4M444Uu47Yk2awsbiR3znpD src/js/app.js
added QmNXRFREw7waGtKW9uBUze3PkR9E12HeeAQSkZQSiFUJqo src/js/bootstrap.min.js
added QmdTtsVM7KtvycQ68f9M43N4EQKvbd58q8aeAhP2fMz4Di src/js/web3.min.js
added Qmah2JkYdcqytu794cY8NxVhtUXckYgiDJJPWKct6ywVJN src/cssadded QmUtKod7sQRbZYr2kKBnT4egn1xT6C6KxHTCue7zYx1zJX src/js
added QmXGoRSnAqs155hNHXNdD2q7UTBZm3UoSH9jUKTDKf6oxy src

publish your site

ipfs name publish QmXGoRSnAqs155hNHXNdD2q7UTBZm3UoSH9jUKTDKf6oxy

wait for a minutes, your site will be ready:

Published to Qmaig4moutzi6ZUTrVUTDUDi6rMYX7tKSHuFjaDCEiZ34M: /ipfs/QmXGoRSnAqs155hNHXNdD2q7UTBZm3UoSH9jUKTDKf6oxy

go to http://gateway.ipfs.io/ipns/QmXGoRSnAqs155hNHXNdD2q7UTBZm3UoSH9jUKTDKf6oxy and check your site

dotrungkien/betting-app