Community-Focused Giveaway Tool

  const Encrypt = (hash, serverSeed) => {
    return CryptoJS.HmacSHA256(serverSeed, hash).toString();
  }

  const Calculate = (hash, lastDigits) => {
    let d = new BigNumber(hash, 16).toFixed();
    let digits = lastDigits;
    if (digits < 8) digits = 8;
    else if (digits > 16) digits = 16;
    return d.slice(-digits);
  }

  const LotterySingle = (
    clientSeedJoinUid,
    serverSeed,
    lastDigits
    ) => {
    let hash = Encrypt(clientSeedJoinUid, serverSeed);
    return Calculate(hash, lastDigits);
  }

  const instantDrawWinner = (
    probabilityValue,
    clientSeedJoinUid,
    serverSeed,
    lastDigits = 8) => {
    let res = new Decimal(LotterySingle(clientSeedJoinUid, serverSeed, lastDigits));
    let lastDigitsMaxNumber = new Decimal(10).pow(lastDigits);
    const probabilityRes = lastDigitsMaxNumber.mul(probabilityValue);
    if (res.greaterThanOrEqualTo(probabilityRes)) return false;
    return true;
  }

  const notInstantDrawWinner = (
    ethBlockHash,
    serverSeed,
    min = 0,
    max,
    winnerNum
  ) => {
    const hash = Encrypt(ethBlockHash, serverSeed);
    return CalculateWinnersV2(hash, min, max, winnerNum);
  }

  class LCG {
    constructor(seed) {
      this.modulus = 2 << 30;
      this.multiplier = 1103515245;
      this.increment = 12345;
      this.seed = seed;
    }
    IntN = function (min, max) {
      this.seed = new BigNumber(this.multiplier, 10)
        .multipliedBy(this.seed)
        .plus(this.increment)
        .mod(this.modulus);
      return +this.seed.toNumber() % (max - min) + min;
    }
  }


  const CalculateWinnersV2 = (
    hash,
    min,
    max,
    winnerNum) => {
    let res = [];
    if (max < winnerNum) {
      for (let i = min; i < max - 1; i++) {
        res.push(i);
      }
      return res;
    }
    const sourceArr = Array.from(new Array((max)).keys())
    let d = new BigNumber(hash, 16).toFixed();
    let digit10NumberString = d.slice(0, 10);
    let di = parseInt(digit10NumberString);
    let lcg = new LCG(di);

    for (let i = 0; i < winnerNum; i++) {
      let ri = lcg.IntN(i, sourceArr.length);
      [sourceArr[i], sourceArr[ri]] = [sourceArr[ri], sourceArr[i]]
    }

    return sourceArr.slice(0, winnerNum);
  }