Prove. Commit. Verify.

import { sha256 } from '@noble/hashes/sha256';

// alpha = sha256(slotHash(32B) || utf8(spinId)) — the public VRF input.
export function vrfAlphaHex(slotHashHex: string, spinId: number): string {
  const slot = Buffer.from(slotHashHex.replace(/^0x/, ''), 'hex');
  const id = new TextEncoder().encode(String(spinId));
  const msg = new Uint8Array(slot.length + id.length);
  msg.set(slot, 0); msg.set(id, slot.length);
  return Buffer.from(sha256(msg)).toString('hex');
}

// The published roll IS the VRF output beta[0:32].
export function rollFromBeta(betaHex: string): string {
  return '0x' + betaHex.replace(/^0x/, '').slice(0, 64);
}

// Same [0,1) map + chance compare as the worker.
export function isWin(rollHex: string, chanceBps: number): boolean {
  const n = BigInt(rollHex);
  const unit = Number((n * 1_000_000_000_000n) / 2n ** 256n) / 1e12;
  return unit < chanceBps / 10_000;
}

// Verify the ECVRF proof itself in-browser (no server, no CC dependency):
//   import { verifyVRF, hexToBytes } from '@collectorcrypt/ecvrf';
//   verifyVRF(hexToBytes(operatorKey), hexToBytes(alpha), hexToBytes(proof)) === true
// Cross-check operatorKey is the on-chain frozen one at
// https://vrf.collectorcrypt.com/#/verify.