coinflip.js

import * as web3 from "@solana/web3.js";
import crypto from "crypto";

const MIN_OFFSET = 5;

const httpsRPC =
  "";
const wssRPC =
  "";

let currentBet = 0;
let solanaConnection;

// Returns true(heads)/false(tail)
async function coinflip() {
  const betId = currentBet + 1;

  const privateSeed = crypto.randomBytes(32);
  const privateHash = crypto
    .createHash("sha256")
    .update(privateSeed)
    .digest("hex");

  const targetOffset = MIN_OFFSET + Math.floor(Math.random() * 10);
  const currentSlot = await solanaConnection.getSlot("confirmed");
  const targetSlot = currentSlot + targetOffset;
  console.log("Waiting for", targetSlot);

  const actualSlot = await new Promise((resolve, reject) => {
    const sub = solanaConnection.onSlotChange((slot) => {
      console.log("Found", slot.slot);
      if (slot.slot >= targetSlot) {
        solanaConnection.removeSlotChangeListener(sub);
        resolve(slot.slot);
      }
    });
  });
  console.log("Found targetSlot", actualSlot, "waiting for block...");

  let block;
  while (true) {
    await new Promise((resolve) => setTimeout(resolve, 10 * 1000));
    try {
      block = await solanaConnection.getBlock(actualSlot);
      break;
    } catch (err) {
      if (!err.toString().includes("Block not available")) {
        console.log(err);
      }
    }
  }

  const publicSeed = `${privateSeed}.${block.blockhash}.${betId}`;
  const publicSeedHash = crypto
    .createHash("sha256")
    .update(publicSeed)
    .digest("hex");

  const hex = publicSeedHash.slice(0, 2);
  const flip = parseInt(hex, 16);
  return (flip % 2) + 1 === 1;
}

solanaConnection = new web3.Connection(httpsRPC, {
  wsEndpoint: wssRPC,
});

coinflip().then((c) => console.log(c));
coinflip().then((c) => console.log(c));
coinflip().then((c) => console.log(c));