import { createHmac } from 'crypto';
import Decimal from 'decimal.js';

const UINT32_MAX = 0x100000000; // 2^32

/**
 * Generates an infinite deterministic stream of cryptographically secure
 * 32-bit unsigned integers derived from HMAC-SHA256.
 *
 * @param key - Secret cryptographic key (server seed). Must remain private until revealed.
 * @param message - Public input string (e.g., client seed, nonce, or domain label).
 *
 * @remarks
 * - Uses HMAC-SHA256 as a pseudorandom function (PRF) to produce a reproducible
 *   and verifiable sequence of numbers.
 * - `step` ensures each 32-bit block is derived from a unique input.
 * - Output is split into 32-bit chunks, suitable for unbiased integer or bit-level
 *   extraction.
 * - Bits are consumed starting from the Most Significant Bit (MSB) to preserve
 *   full numeric precision and maximum entropy.
 * - Fully deterministic: anyone with the same key and message can verify the results.
 */
function* getUint32Stream(key: string, message: string): Iterator<number> {
  let step = 0;

  while (true) {
    const hmac = createHmac('sha256', key);
    hmac.update(`${message}:${step}`);
    const hash = hmac.digest(); // 32 bytes (256 bits)

    for (let i = 0; i < hash.length; i += 4) {
      yield (
        (hash[i] << 24) |
        (hash[i + 1] << 16) |
        (hash[i + 2] << 8) |
        hash[i + 3]
      ) >>> 0; // force unsigned 32-bit
    }

    step++;
  }
}

/**
 * Converts a 32-bit random number into an unbiased integer within [0, range).
 *
 * @param uint32StreamFactory - Function that returns a stream of 32-bit integers.
 * @param range - The desired upper bound (exclusive) for the output.
 *
 * @remarks
 * - Uses rejection sampling to avoid modulo bias.
 * - Every integer within the range is equally likely.
 * - Critical for fair gameplay and provably fair verification.
 */
function getUnbiasedInt(uint32StreamFactory: () => Iterator<number>, range: number) {
  if (!Number.isInteger(range) || range <= 0) {
    throw new Error('Invalid range');
  }

  const maxAcceptable = UINT32_MAX - (UINT32_MAX % range);
  const stream = uint32StreamFactory();
  let next = stream.next();

  while (!next.done) {
    const value = next.value;
    if (value < maxAcceptable) {
      return value % range;
    }
    next = stream.next();
  }

  throw new Error('Failed to generate unbiased value: entropy stream exhausted');
}

function determineResult(options: {
  serverSeed: string;
  clientSeed: string;
  nonce: number;
  bet: number;
  over: boolean;
}) {
  const uint32Generator = getUint32Stream(options.serverSeed, `${options.clientSeed}:${options.nonce}:dice`);
  const diceRange = 10_000;

  const rollValue = getUnbiasedInt(
    () => uint32Generator,
    diceRange
  );

  const convertedBetValue = Decimal(options.bet).mul(100);

  const isWinResult = options.over
    ? convertedBetValue.lessThanOrEqualTo(rollValue)
    : convertedBetValue.greaterThan(rollValue);

  return { 
    isWinResult,
    betValue: options.bet,
    rollValue: Decimal(rollValue).dividedBy(100)
  };
}

// console.log(
//   determineResult({
//     clientSeed: 'player_input_client_seed',
//     serverSeed: 'player_input_server_seed',
//     nonce: 0,
//     bet: 50,
//     over: true
//   })
// )