/*
 *  Copyright (C) 2004-2023 Savoir-faire Linux Inc.
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program. If not, see <https://www.gnu.org/licenses/>.
 */
#include "diffie-hellman.h"
#include "fileutils.h"

#include <chrono>
#include <ciso646>
#include <filesystem>

namespace dhtnet {
namespace tls {

DhParams::DhParams(const std::vector<uint8_t>& data)
{
    gnutls_dh_params_t new_params_;
    int ret = gnutls_dh_params_init(&new_params_);
    if (ret)
        throw std::runtime_error(std::string("Error initializing DH params: ")
                                 + gnutls_strerror(ret));
    params_.reset(new_params_);
    const gnutls_datum_t dat {(uint8_t*) data.data(), (unsigned) data.size()};
    if (int ret_pem = gnutls_dh_params_import_pkcs3(params_.get(), &dat, GNUTLS_X509_FMT_PEM))
        if (int ret_der = gnutls_dh_params_import_pkcs3(params_.get(), &dat, GNUTLS_X509_FMT_DER))
            throw std::runtime_error(std::string("Error importing DH params: ")
                                     + gnutls_strerror(ret_pem) + " " + gnutls_strerror(ret_der));
}

DhParams&
DhParams::operator=(const DhParams& other)
{
    if (not params_) {
        // We need a valid DH params pointer for the copy
        gnutls_dh_params_t new_params_;
        auto err = gnutls_dh_params_init(&new_params_);
        if (err != GNUTLS_E_SUCCESS)
            throw std::runtime_error(std::string("Error initializing DH params: ")
                                     + gnutls_strerror(err));
        params_.reset(new_params_);
    }

    auto err = gnutls_dh_params_cpy(params_.get(), other.get());
    if (err != GNUTLS_E_SUCCESS)
        throw std::runtime_error(std::string("Error copying DH params: ") + gnutls_strerror(err));

    return *this;
}

std::vector<uint8_t>
DhParams::serialize() const
{
    if (!params_) {
        // JAMI_WARN("serialize() called on an empty DhParams");
        return {};
    }
    gnutls_datum_t out;
    if (gnutls_dh_params_export2_pkcs3(params_.get(), GNUTLS_X509_FMT_PEM, &out))
        return {};
    std::vector<uint8_t> ret {out.data, out.data + out.size};
    gnutls_free(out.data);
    return ret;
}

DhParams
DhParams::generate()
{
    using clock = std::chrono::high_resolution_clock;

    auto bits = gnutls_sec_param_to_pk_bits(GNUTLS_PK_DH,
                                            /* GNUTLS_SEC_PARAM_HIGH */ GNUTLS_SEC_PARAM_HIGH);
    // JAMI_DBG("Generating DH params with %u bits", bits);
    auto start = clock::now();

    gnutls_dh_params_t new_params_;
    int ret = gnutls_dh_params_init(&new_params_);
    if (ret != GNUTLS_E_SUCCESS) {
        // JAMI_ERR("Error initializing DH params: %s", gnutls_strerror(ret));
        return {};
    }
    DhParams params {new_params_};

    ret = gnutls_dh_params_generate2(params.get(), bits);
    if (ret != GNUTLS_E_SUCCESS) {
        // JAMI_ERR("Error generating DH params: %s", gnutls_strerror(ret));
        return {};
    }

    std::chrono::duration<double> time_span = clock::now() - start;
    // JAMI_DBG("Generated DH params with %u bits in %lfs", bits, time_span.count());
    return params;
}

DhParams
DhParams::loadDhParams(const std::filesystem::path& path)
{
    std::lock_guard<std::mutex> l(fileutils::getFileLock(path));
    try {
        // writeTime throw exception if file doesn't exist
        auto writeTime = std::filesystem::last_write_time(path);
        auto duration = decltype(writeTime)::clock::now() - writeTime;
        if (duration >= std::chrono::hours(24 * 3)) // file is valid only 3 days
            throw std::runtime_error("file too old");

        // JAMI_DBG("Loading DhParams from file '%s'", path.c_str());
        return {fileutils::loadFile(path)};
    } catch (const std::exception& e) {
        // JAMI_DBG("Failed to load DhParams file '%s': %s", path.c_str(), e.what());
        if (auto params = tls::DhParams::generate()) {
            try {
                fileutils::saveFile(path, params.serialize(), 0600);
                // JAMI_DBG("Saved DhParams to file '%s'", path.c_str());
            } catch (const std::exception& ex) {
                // JAMI_WARN("Failed to save DhParams in file '%s': %s", path.c_str(), ex.what());
            }
            return params;
        }
        // JAMI_ERR("Can't generate DH params.");
        return {};
    }
}

} // namespace tls
} // namespace dhtnet