/****************************************************************************
 *   Copyright (c) 2023 Zheng Lei (realthunder) <realthunder.dev@gmail.com> *
 *                                                                          *
 *   This file is part of the FreeCAD CAx development system.               *
 *                                                                          *
 *   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/>.                                       *
 *                                                                          *
 ***************************************************************************/

#ifndef GUI_PARAM_HANDLER_H
#define GUI_PARAM_HANDLER_H

#include <map>
#include <memory>
#include <fastsignals/signal.h>
#include <QTimer>

#include <FCGlobal.h>
#include <App/Application.h>
#include <Base/Parameter.h>

namespace Gui
{

/// Structure for storing a parameter key and its path to be used in std::map
struct GuiExport ParamKey
{
    ParameterGrp::handle hGrp;
    const char* key;

    ParamKey(const char* path, const char* key)
        : hGrp(App::GetApplication().GetUserParameter().GetGroup(path))
        , key(key)
    {}

    ParamKey(ParameterGrp* h, const char* key)
        : hGrp(h)
        , key(key)
    {}

    bool operator<(const ParamKey& other) const
    {
        if (hGrp < other.hGrp) {
            return true;
        }
        if (hGrp > other.hGrp) {
            return false;
        }
        return strcmp(key, other.key) < 0;
    }
};

/// Helper class to handle parameter change
class GuiExport ParamHandler
{
public:
    virtual ~ParamHandler()
    {}

    /** Called when the corresponding parameter key changes
     * @param key: the parameter key
     * @return Returns true if the handler needs to be delay triggered by a timer
     */
    virtual bool onChange(const ParamKey* key) = 0;
    /// Called in delay triggered
    virtual void onTimer()
    {}
};

/// Template class for a non-delayed parameter handler
template<class Func>
class ParamHandlerT: public ParamHandler
{
public:
    ParamHandlerT(Func f)
        : func(f)
    {}

    bool onChange(const ParamKey* key) override
    {
        func(key);
        return false;
    }

private:
    Func func;
};

/// Template class for a delayed parameter handler
template<class Func>
class ParamDelayedHandlerT: public ParamHandler
{
public:
    ParamDelayedHandlerT(Func f)
        : func(f)
    {}

    bool onChange(const ParamKey*) override
    {
        return true;
    }

    void onTimer() override
    {
        func();
    }

private:
    Func func;
};

// Helper class to manage handlers of a list of parameters.
//
// The handlers are stored in a map from ParamKey to shared pointer to a
// ParamHandler. The same handler can be registered with multiple keys. When
// the registered parameter key is changed, the manager will call the
// registered handler function ParamHandler::onChange(). If it returns True,
// then the handler will be appended to a queue to be invoked later by a timer
// to avoid repetitive processing on change of multiple keys.
//
// The handler manager is meant to be initiated by some static function, e.g.
// DlgSettingsGeneral::attachObserver(). It is intended to be one and only
// place of handling changes of the given set of parameters, regardless of
// whether the changes are coming from direct editing through parameter editor,
// user code changing of parameters, changing preference dialog, or loading a
// preference pack.
//
class GuiExport ParamHandlers
{
public:
    ParamHandlers();
    virtual ~ParamHandlers();

    void addHandler(const ParamKey& key, const std::shared_ptr<ParamHandler>& handler);

    void addHandler(const char* path, const char* key, const std::shared_ptr<ParamHandler>& handler)
    {
        addHandler(ParamKey(path, key), handler);
    }

    void addHandler(ParameterGrp* hGrp, const char* key, const std::shared_ptr<ParamHandler>& handler)
    {
        addHandler(ParamKey(hGrp, key), handler);
    }

    void addHandler(const std::vector<ParamKey>& keys, const std::shared_ptr<ParamHandler>& handler)
    {
        for (const auto& key : keys) {
            addHandler(key, handler);
        }
    }

    void addHandler(
        const char* path,
        const std::vector<const char*>& keys,
        const std::shared_ptr<ParamHandler>& handler
    )
    {
        for (const auto& key : keys) {
            addHandler(path, key, handler);
        }
    }

    void addHandler(
        ParameterGrp* hGrp,
        const std::vector<const char*>& keys,
        const std::shared_ptr<ParamHandler>& handler
    )
    {
        for (const auto& key : keys) {
            addHandler(hGrp, key, handler);
        }
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addHandler(const char* path, const char* key, Func func)
    {
        std::shared_ptr<ParamHandler> handler(new ParamHandlerT<Func>(func));
        addHandler(path, key, handler);
        return handler;
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addHandler(ParameterGrp* hGrp, const char* key, Func func)
    {
        std::shared_ptr<ParamHandler> handler(new ParamHandlerT<Func>(func));
        addHandler(hGrp, key, handler);
        return handler;
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addDelayedHandler(const char* path, const char* key, Func func)
    {
        auto hGrp = App::GetApplication().GetUserParameter().GetGroup(path);
        auto wrap = [hGrp, func]() {
            func(hGrp);
        };
        std::shared_ptr<ParamHandler> handler(new ParamDelayedHandlerT<decltype(wrap)>(wrap));
        addHandler(hGrp, key, handler);
        return handler;
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addDelayedHandler(ParameterGrp* hGrp, const char* key, Func func)
    {
        auto wrap = [hGrp, func]() {
            func(hGrp);
        };
        std::shared_ptr<ParamHandler> handler(new ParamDelayedHandlerT<decltype(wrap)>(wrap));
        addHandler(hGrp, key, handler);
        return handler;
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addDelayedHandler(
        const char* path,
        const std::vector<const char*>& keys,
        Func func
    )
    {
        auto hGrp = App::GetApplication().GetUserParameter().GetGroup(path);
        auto wrap = [hGrp, func]() {
            func(hGrp);
        };
        std::shared_ptr<ParamHandler> handler(new ParamDelayedHandlerT<decltype(wrap)>(wrap));
        for (const auto& key : keys) {
            addHandler(ParamKey(hGrp, key), handler);
        }
        return handler;
    }

    template<class Func>
    std::shared_ptr<ParamHandler> addDelayedHandler(
        ParameterGrp::handle hGrp,
        const std::vector<const char*>& keys,
        Func func
    )
    {
        auto wrap = [hGrp, func]() {
            func(hGrp);
        };
        std::shared_ptr<ParamHandler> handler(new ParamDelayedHandlerT<decltype(wrap)>(wrap));
        for (const auto& key : keys) {
            addHandler(ParamKey(hGrp, key), handler);
        }
        return handler;
    }

protected:
    std::map<ParamKey, std::shared_ptr<ParamHandler>> handlers;
    std::set<std::shared_ptr<ParamHandler>> pendings;
    fastsignals::scoped_connection conn;
    QTimer timer;
};

}  // namespace Gui

#endif  // GUI_PARAM_HANDLER_H