//
//  SuperTuxKart - a fun racing game with go-kart
//  Copyright (C) 2013 Joerg Henrichs
//
//  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, write to the Free Software
//  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

#ifndef HEADER_REWIND_MANAGER_HPP
#define HEADER_REWIND_MANAGER_HPP

#include "network/rewind_queue.hpp"
#include "utils/stk_process.hpp"

#include <assert.h>
#include <atomic>
#include <functional>
#include <memory>
#include <map>
#include <set>
#include <string>
#include <vector>

class Rewinder;
class RewindInfo;
class RewindInfoEventFunction;
class EventRewinder;

/** \ingroup network
 *  This class manages rewinding. It keeps track of:
 *  -  states for each rewindable object (for example a kart would have
 *     its position, rotation, linear and angular velocity etc as state)
 *     States can be confirmed (i.e. were received by the network server
 *     and are therefore confirmed to be conrrect), or not (just a snapshot
 *     on this client, which can save time in rewinding later).
 *  -  events for each rewindable object (for example any change in the kart
 *     controls, like steering, fire, ... are an event). While states can be
 *     discarded (especially unconfirmed ones), e.g. to save space, events
 *     will always be kept (in order to allow replaying).
 *  For each object that is to be rewinded an instance of Rewinder needs to be
 *  declared (usually inside of the object it can rewind). This instance
 *  is automatically registered with the RewindManager.
 *  All states and events are stored in a RewindInfo object. All RewindInfo
 *  objects are stored in a list sorted by time.
 *  When a rewind to time T is requested, the following takes place:
 *  1. Go back in time:
 *     Determine the latest time t_min < T so that each rewindable objects
 *     has at least one state before T. For each state that is skipped during
 *     this process `undoState()` is being called, and for each event
 *     `undoEvent()` of the Rewinder.
 *  2. Restore state at time `t_min`
 *     For each Rewinder the state at time t_min is restored by calling
 *     `rewindToState(char *)`.
 *     TODO: atm there is no guarantee that each object will have a state
 *     at a given time. We either need to work around that, or make sure
 *     to store at least an unconfirmed state whenever we receive a 
 *     confirmed state.
 *  3. Rerun the simulation till the current time t_current is reached:
 *     1. Determine the time `t_next` of the next frame. This is either
 *        current_time + 1/60 (physics default time step size), or less
 *        if RewindInfo at an earlier time is available).
 *        This determines the time step size for the next frame (i.e.
 *        `t_next - t_current`).
 *     2. For all RewindInfo at time t_next call:
 *        - `restoreState()` if the RewindInfo is a confirmed state
 *        - `discardState()` if the RewindInfo is an unconfirmed state
 *          TODO: still missing, and instead of discard perhaps
 *                store a new state??
 *        - `rewindToEvent()` if the RewindInfo is an event
 *     3. Do one step of world simulation, using the updated (confirmed)
 *        states and newly set events (e.g. kart input).
 */

class RewindManager
{
private:
    /** Singleton pointer. */
    static RewindManager *m_rewind_manager[PT_COUNT];

    /** En- or Disable the rewind manager. This is used to disable storing
     *  rewind data in case of local races only. */
    static std::atomic_bool m_enable_rewind_manager;

    std::map<int, std::vector<std::function<void()> > > m_local_state;

    /** A list of all objects that can be rewound. */
    std::map<std::string, std::weak_ptr<Rewinder> > m_all_rewinder;

    /** The queue that stores all rewind infos. */
    RewindQueue m_rewind_queue;

    /** Overall amount of memory allocated by states. */
    unsigned int m_overall_state_size;

    /** Indicates if currently a rewind is happening. */
    bool m_is_rewinding;

    /** How much time between consecutive state saves. */
    int m_state_frequency;

    /** This stores the original World time in ticks during a rewind. It is
     *  used to detect if a client's local time need adjustment to reduce
     *  rewinds. */
    std::atomic<int> m_not_rewound_ticks;

    std::vector<RewindInfoEventFunction*> m_pending_rief;

    bool m_schedule_reset_network_body;

    RewindManager();
   ~RewindManager();
    // ------------------------------------------------------------------------
    void clearExpiredRewinder()
    {
        for (auto it = m_all_rewinder.begin(); it != m_all_rewinder.end();)
        {
            if (it->second.expired())
            {
                it = m_all_rewinder.erase(it);
                continue;
            }
            it++;
        }
    }
    // ------------------------------------------------------------------------
    void mergeRewindInfoEventFunction();

public:
    // First static functions to manage rewinding.
    // ===========================================
    static RewindManager *create();
    static void destroy();
    // ------------------------------------------------------------------------
    /** En- or disables rewinding. */
    static void setEnable(bool m) { m_enable_rewind_manager = m; }
    // ------------------------------------------------------------------------
    /** Returns if rewinding is enabled or not. */
    static bool isEnabled() { return m_enable_rewind_manager; }
    // ------------------------------------------------------------------------
    static bool exists()
    {
        ProcessType pt = STKProcess::getType();
        return m_rewind_manager[pt] != NULL;
    }   // exists
    // ------------------------------------------------------------------------
    /** Returns the singleton. This function will not automatically create
     *  the singleton. */
    static RewindManager *get()
    {
        ProcessType pt = STKProcess::getType();
        assert(m_rewind_manager[pt]);
        return m_rewind_manager[pt];
    }   // get

    // Non-static function declarations:

    void reset();
    void update(int ticks);
    void rewindTo(int target_ticks, int ticks_now, bool fast_forward);
    void playEventsTill(int world_ticks, bool fast_forward);
    void addEvent(EventRewinder *event_rewinder, BareNetworkString *buffer,
                  bool confirmed, int ticks = -1);
    void addNetworkEvent(EventRewinder *event_rewinder,
                         BareNetworkString *buffer, int ticks);
    void addNetworkState(BareNetworkString *buffer, int ticks);
    void saveState();
    // ------------------------------------------------------------------------
    std::shared_ptr<Rewinder> getRewinder(const std::string& name)
    {
        auto it = m_all_rewinder.find(name);
        if (it != m_all_rewinder.end())
        {
            if (auto r = it->second.lock())
                return r;
        }
        return nullptr;
    }
    // ------------------------------------------------------------------------
    bool addRewinder(std::shared_ptr<Rewinder> rewinder);
    // ------------------------------------------------------------------------
    /** Returns true if currently a rewind is happening. */
    bool isRewinding() const { return m_is_rewinding; }

    // ------------------------------------------------------------------------
    int getNotRewoundWorldTicks() const
    {
        return m_not_rewound_ticks.load(std::memory_order_relaxed);
    }   // getNotRewoundWorldTicks
    // ------------------------------------------------------------------------
    /** Returns the time of the latest confirmed state. */
    int getLatestConfirmedState() const
    {
        return m_rewind_queue.getLatestConfirmedState(); 
    }   // getLatestConfirmedState
    // ------------------------------------------------------------------------
    bool useLocalEvent() const;
    // ------------------------------------------------------------------------
    void addRewindInfoEventFunction(RewindInfoEventFunction* rief)
                                            { m_pending_rief.push_back(rief); }
    // ------------------------------------------------------------------------
    void addNetworkRewindInfo(RewindInfo* ri)
                                   { m_rewind_queue.addNetworkRewindInfo(ri); }
    // ------------------------------------------------------------------------
    bool shouldSaveState(int ticks)
    {
        int a = ticks - m_state_frequency + 1;
        return ticks != 0 && a >= 0 && a % m_state_frequency == 0;
    }
    // ------------------------------------------------------------------------
    void resetSmoothNetworkBody()     { m_schedule_reset_network_body = true; }
    // ------------------------------------------------------------------------
    void handleResetSmoothNetworkBody();

};   // RewindManager


#endif