#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <openssl/sha.h>

std::string sha256(const std::string& input) {
    unsigned char hash[SHA256_DIGEST_LENGTH];
    SHA256_CTX sha256;
    SHA256_Init(&sha256);
    SHA256_Update(&sha256, input.c_str(), input.length());
    SHA256_Final(hash, &sha256);

    std::stringstream ss;
    for (int i = 0; i < SHA256_DIGEST_LENGTH; i++) {
        ss << std::hex << std::setw(2) << std::setfill('0') << (int)hash[i];
    }

    return ss.str();
}

bool isValidProof(const std::string& hash, int difficulty) {
    for (int i = 0; i < difficulty; i++) {
        if (hash[i] != '0') {
            return false;
        }
    }
    return true;
}

std::string calculateProofOfWork(const std::string& previousHash, int difficulty) {
    int nonce = 0;
    std::string hash;
    std::string data = previousHash + std::to_string(nonce);

    do {
        hash = sha256(data);
        nonce++;
        data = previousHash + std::to_string(nonce);
    } while (!isValidProof(hash, difficulty));

    return hash;
}

int main() {
    std::string previousHash = "00000000000000000000000000000000";
    int difficulty = 4; // Number of leading zeros required for Proof of Work

    std::string proofOfWork = calculateProofOfWork(previousHash, difficulty);

    std::cout << "Proof of Work found: " << proofOfWork << std::endl;

    return 0;
}