Provably fair algorithm of selecting the winner based on bitcoin hash

draw-winner-selection-algo.js

// bitcoin_hash is the hash (in hex) of the latest Bitcoin block
// arrPoints is array of points of all addresses ordered by address [{address: "...", points: 1234}, ...]
// rows1 is array of balances of all addresses ordered by address [{address: "...", balance: 1234}, ...]
// sum is the sum of all points

// 1. winner by points
let hash = crypto.createHash('sha256').update(bitcoin_hash).digest('hex');
let number = new BigNumber(hash, 16);
let random = (number.div(new BigNumber(2).pow(256))).times(sum);

let sum2 = new BigNumber(0);
let winner_address;
for (let i = 0; i < arrPoints.length; i++) {
	sum2 = sum2.add(arrPoints[i].points);
	if (random.lte(sum2)) {
		winner_address = arrPoints[i].address;
		break;
	}
}

// 2. winner by balances
let bal_hash = crypto.createHash('sha256').update(hash).digest('hex');
let bal_number = new BigNumber(bal_hash, 16);
let bal_random = (bal_number.div(new BigNumber(2).pow(256))).times(sum_balances);

let bal_sum2 = 0;
let balance_winner_address;
for (let i = 0; i < rows1.length; i++) {
	bal_sum2 += rows1[i].balance;
	if (bal_random.lte(bal_sum2)) {
		balance_winner_address = rows1[i].address;
		break;
	}
}