// SPDX-License-Identifier: LGPL-2.1-or-later
/****************************************************************************
 *                                                                          *
 *   Copyright (c) 2025 Kindred Systems <development@kindred-systems.com>   *
 *                                                                          *
 *   This file is part of FreeCAD.                                          *
 *                                                                          *
 *   FreeCAD is free software: you can redistribute it and/or modify it     *
 *   under the terms of the GNU Lesser General Public License as            *
 *   published by the Free Software Foundation, either version 2.1 of the   *
 *   License, or (at your option) any later version.                        *
 *                                                                          *
 *   FreeCAD 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       *
 *   Lesser General Public License for more details.                        *
 *                                                                          *
 *   You should have received a copy of the GNU Lesser General Public       *
 *   License along with FreeCAD. If not, see                                *
 *   <https://www.gnu.org/licenses/>.                                       *
 *                                                                          *
 ***************************************************************************/

#include "SolverRegistry.h"

#include <Base/Console.h>

#include <cstdlib>
#include <cstring>
#include <filesystem>
#include <sstream>

#ifdef _WIN32
# define WIN32_LEAN_AND_MEAN
# include <windows.h>
#else
# include <dlfcn.h>
#endif

namespace fs = std::filesystem;

namespace
{

// Platform extension for shared libraries.
#ifdef _WIN32
constexpr const char* PLUGIN_EXT = ".dll";
constexpr char PATH_SEP = ';';
#elif defined(__APPLE__)
constexpr const char* PLUGIN_EXT = ".dylib";
constexpr char PATH_SEP = ':';
#else
constexpr const char* PLUGIN_EXT = ".so";
constexpr char PATH_SEP = ':';
#endif

// Dynamic library loading wrappers.
void* open_library(const char* path)
{
#ifdef _WIN32
    return static_cast<void*>(LoadLibraryA(path));
#else
    return dlopen(path, RTLD_LAZY);
#endif
}

void* get_symbol(void* handle, const char* symbol)
{
#ifdef _WIN32
    return reinterpret_cast<void*>(
        GetProcAddress(static_cast<HMODULE>(handle), symbol));
#else
    return dlsym(handle, symbol);
#endif
}

std::string load_error()
{
#ifdef _WIN32
    DWORD err = GetLastError();
    char* msg = nullptr;
    FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                   nullptr, err, 0, reinterpret_cast<char*>(&msg), 0, nullptr);
    std::string result = msg ? msg : "unknown error";
    LocalFree(msg);
    return result;
#else
    const char* err = dlerror();
    return err ? err : "unknown error";
#endif
}

/// Parse major version from a version string like "1.0" or "2.1.3".
/// Returns -1 on failure.
int parse_major_version(const char* version_str)
{
    if (!version_str) {
        return -1;
    }
    char* end = nullptr;
    long major = std::strtol(version_str, &end, 10);
    if (end == version_str || major < 0) {
        return -1;
    }
    return static_cast<int>(major);
}

}  // anonymous namespace


namespace KCSolve
{

// Plugin C entry point types.
using ApiVersionFn = const char* (*)();
using CreateFn = IKCSolver* (*)();


// ── Singleton ──────────────────────────────────────────────────────

SolverRegistry& SolverRegistry::instance()
{
    static SolverRegistry reg;
    return reg;
}

SolverRegistry::SolverRegistry() = default;

SolverRegistry::~SolverRegistry()
{
    for (void* handle : handles_) {
        close_handle(handle);
    }
}

void SolverRegistry::close_handle(void* handle)
{
    if (!handle) {
        return;
    }
#ifdef _WIN32
    FreeLibrary(static_cast<HMODULE>(handle));
#else
    dlclose(handle);
#endif
}


// ── Registration ───────────────────────────────────────────────────

bool SolverRegistry::register_solver(const std::string& name, CreateSolverFn factory)
{
    std::lock_guard<std::mutex> lock(mutex_);
    auto [it, inserted] = factories_.emplace(name, std::move(factory));
    if (!inserted) {
        Base::Console().warning("KCSolve: solver '%s' already registered, skipping\n",
                                name.c_str());
        return false;
    }
    if (default_name_.empty()) {
        default_name_ = name;
    }
    Base::Console().log("KCSolve: registered solver '%s'\n", name.c_str());
    return true;
}


// ── Lookup ─────────────────────────────────────────────────────────

std::unique_ptr<IKCSolver> SolverRegistry::get(const std::string& name) const
{
    std::lock_guard<std::mutex> lock(mutex_);
    const std::string& key = name.empty() ? default_name_ : name;
    if (key.empty()) {
        return nullptr;
    }
    auto it = factories_.find(key);
    if (it == factories_.end()) {
        return nullptr;
    }
    return it->second();
}

std::vector<std::string> SolverRegistry::available() const
{
    std::lock_guard<std::mutex> lock(mutex_);
    std::vector<std::string> names;
    names.reserve(factories_.size());
    for (const auto& [name, _] : factories_) {
        names.push_back(name);
    }
    return names;
}

std::vector<BaseJointKind> SolverRegistry::joints_for(const std::string& name) const
{
    auto solver = get(name);
    if (!solver) {
        return {};
    }
    return solver->supported_joints();
}

bool SolverRegistry::set_default(const std::string& name)
{
    std::lock_guard<std::mutex> lock(mutex_);
    if (factories_.find(name) == factories_.end()) {
        return false;
    }
    default_name_ = name;
    return true;
}

std::string SolverRegistry::get_default() const
{
    std::lock_guard<std::mutex> lock(mutex_);
    return default_name_;
}


// ── Plugin scanning ────────────────────────────────────────────────

void SolverRegistry::scan(const std::string& directory)
{
    std::error_code ec;
    if (!fs::is_directory(directory, ec)) {
        // Non-existent directories are not an error — just skip.
        return;
    }

    Base::Console().log("KCSolve: scanning '%s' for plugins\n", directory.c_str());

    for (const auto& entry : fs::directory_iterator(directory, ec)) {
        if (ec) {
            Base::Console().warning("KCSolve: error iterating '%s': %s\n",
                                    directory.c_str(), ec.message().c_str());
            break;
        }

        if (!entry.is_regular_file(ec)) {
            continue;
        }

        const auto& path = entry.path();
        if (path.extension() != PLUGIN_EXT) {
            continue;
        }

        const std::string path_str = path.string();

        // Load the shared library.
        void* handle = open_library(path_str.c_str());
        if (!handle) {
            Base::Console().warning("KCSolve: failed to load '%s': %s\n",
                                    path_str.c_str(), load_error().c_str());
            continue;
        }

        // Check API version.
        auto version_fn = reinterpret_cast<ApiVersionFn>(
            get_symbol(handle, "kcsolve_api_version"));
        if (!version_fn) {
            // Not a KCSolve plugin — silently skip.
            close_handle(handle);
            continue;
        }

        const char* version_str = version_fn();
        int major = parse_major_version(version_str);
        if (major != API_VERSION_MAJOR) {
            Base::Console().warning(
                "KCSolve: plugin '%s' has incompatible API version '%s' "
                "(expected major %d)\n",
                path_str.c_str(),
                version_str ? version_str : "(null)",
                API_VERSION_MAJOR);
            close_handle(handle);
            continue;
        }

        // Get the factory symbol.
        auto create_fn = reinterpret_cast<CreateFn>(
            get_symbol(handle, "kcsolve_create"));
        if (!create_fn) {
            Base::Console().warning(
                "KCSolve: plugin '%s' missing kcsolve_create() symbol\n",
                path_str.c_str());
            close_handle(handle);
            continue;
        }

        // Create a temporary instance to get the solver name.
        std::unique_ptr<IKCSolver> probe(create_fn());
        if (!probe) {
            Base::Console().warning(
                "KCSolve: plugin '%s' kcsolve_create() returned null\n",
                path_str.c_str());
            close_handle(handle);
            continue;
        }

        std::string solver_name = probe->name();
        probe.reset();

        // Wrap the C function pointer in a factory lambda.
        CreateSolverFn factory = [create_fn]() -> std::unique_ptr<IKCSolver> {
            return std::unique_ptr<IKCSolver>(create_fn());
        };

        if (register_solver(solver_name, std::move(factory))) {
            handles_.push_back(handle);
            Base::Console().log("KCSolve: loaded plugin '%s' from '%s'\n",
                                solver_name.c_str(), path_str.c_str());
        }
        else {
            // Duplicate name — close the handle.
            close_handle(handle);
        }
    }
}

void SolverRegistry::scan_default_paths()
{
    // 1. KCSOLVE_PLUGIN_PATH environment variable.
    const char* env_path = std::getenv("KCSOLVE_PLUGIN_PATH");
    if (env_path && env_path[0] != '\0') {
        std::istringstream stream(env_path);
        std::string dir;
        while (std::getline(stream, dir, PATH_SEP)) {
            if (!dir.empty()) {
                scan(dir);
            }
        }
    }

    // 2. System install path: <install_prefix>/lib/kcsolve/
    //    Derive from the executable location or use a compile-time path.
    //    For now, use a path relative to the FreeCAD lib directory.
    std::error_code ec;
    fs::path system_dir = fs::path(CMAKE_INSTALL_PREFIX) / "lib" / "kcsolve";
    if (fs::is_directory(system_dir, ec)) {
        scan(system_dir.string());
    }
}

}  // namespace KCSolve