#include <iostream>
#include <string>
#include <vector>
#include <openssl/sha.h>

using namespace std;

/*
 FLASKIO Math Engine (PoI Validator)
 - Deterministic
 - Session-bound
 - Replay-safe
*/

string sha256(const string& input) {
    unsigned char hash[SHA256_DIGEST_LENGTH];
    SHA256((unsigned char*)input.c_str(), input.size(), hash);

    char output[65];
    for (int i = 0; i < SHA256_DIGEST_LENGTH; i++) {
        sprintf(output + (i * 2), "%02x", hash[i]);
    }
    output[64] = 0;
    return string(output);
}

// Simulates deterministic 800-question verification
bool verify_flaskio_block(
    const string& wallet,
    const string& session_nonce,
    const string& user_solution
) {
    if (user_solution.empty()) return false;
    if (user_solution.length() < 128) return false;

    // Deterministic seed (Ledger can recompute this)
    string seed = sha256(wallet + session_nonce);

    // Simulate 300 math + 500 logic checks
    int score = 0;
    for (int i = 0; i < 800; i++) {
        string q = sha256(seed + to_string(i));
        if (user_solution.find(q.substr(0, 4)) != string::npos) {
            score++;
        }
    }

    return score >= 800; // Must solve all
}

int main(int argc, char* argv[]) {
    // Docker healthcheck
    if (argc == 1) {
        cout << "FLASKIO_ENGINE_READY" << endl;
        return 0;
    }

    if (argc < 4) {
        cerr << "Usage: ./flaskio_engine [wallet] [session_nonce] [solution]" << endl;
        return 1;
    }

    string wallet = argv[1];
    string session_nonce = argv[2];
    string solution = argv[3];

    if (!verify_flaskio_block(wallet, session_nonce, solution)) {
        cout << "INVALID" << endl;
        return 1;
    }

    // Proof hash (submitted to Ledger)
    string proof = sha256(wallet + session_nonce + solution);

    cout << "VALID" << endl;
    cout << proof << endl;

    return 0;
}