import { createHmac } from 'crypto';

const UINT32_MAX = 0x100000000; // 2^32

/**
 * Generates an infinite deterministic stream of cryptographically secure
 * 32-bit unsigned integers derived from HMAC-SHA512.
 *
 * @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-SHA512 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.
 *   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('sha512', key);
    hmac.update(`${message}:${step}`);
    const hash = hmac.digest(); // 64 bytes (512 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 getUnbiasedIntFromStream(
  stream: Iterator<number>,
  range: number
) {
  if (!Number.isInteger(range) || range <= 0) {
    throw new Error('Invalid range');
  }

  const maxAcceptable = UINT32_MAX - (UINT32_MAX % range);

  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');
}

/**
 * Lazily draws items from a list **without replacement** using a provably fair RNG.
 *
 * @param uint32StreamFactory - Function that returns a stream of 32-bit integers.
 * @param data - The full list of items to draw from (e.g., cards in a shoe).
 *
 * @remarks
 * This function implements a **partial Fisher-Yates shuffle** (a.k.a. Knuth shuffle),
 * but performed lazily — meaning we only shuffle as much as needed for each draw.
 */
export function createLazyDrawWithoutReplacement<T>(
  uint32StreamFactory: () => Iterator<number>,
  data: readonly T[]
) {
  const records = [...data];
  const stream = uint32StreamFactory();

  let drawnCount = 0;

  function drawOne(): T {
    const remaining = records.length - drawnCount;

    if (remaining <= 0) {
      throw new Error('No items remaining');
    }

    const swapIndex = getUnbiasedIntFromStream(stream, remaining);
    const targetIndex = remaining - 1;

    [records[targetIndex], records[swapIndex]] = [records[swapIndex]!, records[targetIndex]!];

    drawnCount++;

    return records[targetIndex]!;
  }

  return {
    drawMany(count: number) {
      if (!Number.isInteger(count) || count < 0) {
        throw new Error('Invalid count');
      }

      if (count > records.length - drawnCount) {
        throw new Error('Not enough items remaining');
      }

      return Array.from({ length: count }, () => drawOne());
    }
  };
}

export const CardRank = ['A', '2', '3', '4', '5', '6', '7', '8', '9', 'T', 'J', 'Q', 'K'] as const;
export const CardSuit = ['c', 'd', 'h', 's'] as const;

function getShoe(
  options: {
    nonce: number,
    clientSeed: string,
    serverSeed: string
  }) {
  const baseDeck = CardSuit.flatMap(suit =>
    CardRank.map(rank => [rank, suit])
  )

  const deckCount = 8;

  const decks = Array.from({ length: deckCount }, () => [...baseDeck]).flat();

  const uint32Generator = getUint32Stream(options.serverSeed, `${options.clientSeed}:${options.nonce}:war`);
  const shoeDrawer = createLazyDrawWithoutReplacement(() => uint32Generator, decks);

  return shoeDrawer.drawMany(26);
}

console.log(
  getShoe({
    clientSeed: 'war-test',
    serverSeed: 'war-test',
    nonce: 0,
  })
);