/**
 * @file llkeythrottle.h
 *
 * $LicenseInfo:firstyear=2005&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 *
 * This library 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;
 * version 2.1 of the License only.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#ifndef LL_LLKEY_THROTTLE_H
#define LL_LLKEY_THROTTLE_H

// LLKeyThrottle keeps track of the number of action occurences with a key value
// for a type over a given time period.  If the rate set in the constructor is
// exceeed, the key is considered blocked.  The transition from unblocked to
// blocked is noted so the responsible agent can be informed.  This transition
// takes twice the look back window to clear.

#include "linden_common.h"

#include "llframetimer.h"
#include <map>


// forward declaration so LLKeyThrottleImpl can befriend it
template <class T> class LLKeyThrottle;


// Implementation utility class - use LLKeyThrottle, not this
template <class T>
class LLKeyThrottleImpl
{
    friend class LLKeyThrottle<T>;
protected:
    struct Entry {
        U32     count;
        bool    blocked;

        Entry() : count(0), blocked(false) { }
    };

    typedef std::map<T, Entry> EntryMap;

    EntryMap* prevMap;
    EntryMap* currMap;

    U32 countLimit;
        // maximum number of keys allowed per interval

    U64 intervalLength;     // each map covers this time period (usec or frame number)
    U64 startTime;          // start of the time period (usec or frame number)
        // currMap started counting at this time
        // prevMap covers the previous interval

    LLKeyThrottleImpl() :
        prevMap(NULL),
        currMap(NULL),
        countLimit(0),
        intervalLength(1),
        startTime(0)
    {}

    static U64 getTime()
    {
        return LLFrameTimer::getTotalTime();
    }
    static U64 getFrame()       // Return the current frame number
    {
        return (U64) LLFrameTimer::getFrameCount();
    }
};


template< class T >
class LLKeyThrottle
{
public:
    // @param realtime = false for frame-based throttle, true for usec
    // real-time throttle
    LLKeyThrottle(U32 limit, F32 interval, bool realtime = true)
        : m(* new LLKeyThrottleImpl<T>)
    {
        setParameters( limit, interval, realtime );
    }

    ~LLKeyThrottle()
    {
        delete m.prevMap;
        delete m.currMap;
        delete &m;
    }

    enum State {
        THROTTLE_OK,            // rate not exceeded, let pass
        THROTTLE_NEWLY_BLOCKED, // rate exceed for the first time
        THROTTLE_BLOCKED,       // rate exceed, block key
    };

    F64 getActionCount(const T& id)
    {
        U64 now = 0;
        if ( mIsRealtime )
        {
            now = LLKeyThrottleImpl<T>::getTime();
        }
        else
        {
            now = LLKeyThrottleImpl<T>::getFrame();
        }

        if (now >= (m.startTime + m.intervalLength))
        {
            if (now < (m.startTime + 2 * m.intervalLength))
            {
                // prune old data
                delete m.prevMap;
                m.prevMap = m.currMap;
                m.currMap = new typename LLKeyThrottleImpl<T>::EntryMap;

                m.startTime += m.intervalLength;
            }
            else
            {
                // lots of time has passed, all data is stale
                delete m.prevMap;
                delete m.currMap;
                m.prevMap = new typename LLKeyThrottleImpl<T>::EntryMap;
                m.currMap = new typename LLKeyThrottleImpl<T>::EntryMap;

                m.startTime = now;
            }
        }

        U32 prevCount = 0;

        typename LLKeyThrottleImpl<T>::EntryMap::const_iterator prev = m.prevMap->find(id);
        if (prev != m.prevMap->end())
        {
            prevCount = prev->second.count;
        }

        typename LLKeyThrottleImpl<T>::Entry& curr = (*m.currMap)[id];

        // curr.count is the number of keys in
        // this current 'time slice' from the beginning of it until now
        // prevCount is the number of keys in the previous
        // time slice scaled to be one full time slice back from the current
        // (now) time.

        // compute current, windowed rate
        F64 timeInCurrent = ((F64)(now - m.startTime) / m.intervalLength);
        F64 averageCount = curr.count + prevCount * (1.0 - timeInCurrent);
        return averageCount;
    }

    // call each time the key wants use
    State noteAction(const T& id, S32 weight = 1)
    {
        U64 now = 0;
        if ( mIsRealtime )
        {
            now = LLKeyThrottleImpl<T>::getTime();
        }
        else
        {
            now = LLKeyThrottleImpl<T>::getFrame();
        }

        if (now >= (m.startTime + m.intervalLength))
        {
            if (now < (m.startTime + 2 * m.intervalLength))
            {
                // prune old data
                delete m.prevMap;
                m.prevMap = m.currMap;
                m.currMap = new typename LLKeyThrottleImpl<T>::EntryMap;

                m.startTime += m.intervalLength;
            }
            else
            {
                // lots of time has passed, all data is stale
                delete m.prevMap;
                delete m.currMap;
                m.prevMap = new typename LLKeyThrottleImpl<T>::EntryMap;
                m.currMap = new typename LLKeyThrottleImpl<T>::EntryMap;

                m.startTime = now;
            }
        }

        U32 prevCount = 0;
        bool prevBlocked = false;

        typename LLKeyThrottleImpl<T>::EntryMap::const_iterator prev = m.prevMap->find(id);
        if (prev != m.prevMap->end())
        {
            prevCount = prev->second.count;
            prevBlocked = prev->second.blocked;
        }

        typename LLKeyThrottleImpl<T>::Entry& curr = (*m.currMap)[id];

        bool wereBlocked = curr.blocked || prevBlocked;

        curr.count += weight;

        // curr.count is the number of keys in
        // this current 'time slice' from the beginning of it until now
        // prevCount is the number of keys in the previous
        // time slice scaled to be one full time slice back from the current
        // (now) time.

        // compute current, windowed rate
        F64 timeInCurrent = ((F64)(now - m.startTime) / m.intervalLength);
        F64 averageCount = curr.count + prevCount * (1.0 - timeInCurrent);

        curr.blocked |= averageCount > m.countLimit;

        bool nowBlocked = curr.blocked || prevBlocked;

        if (!nowBlocked)
        {
            return THROTTLE_OK;
        }
        else if (!wereBlocked)
        {
            return THROTTLE_NEWLY_BLOCKED;
        }
        else
        {
            return THROTTLE_BLOCKED;
        }
    }

    // call to force throttle conditions for id
    void throttleAction(const T& id)
    {
        noteAction(id);
        typename LLKeyThrottleImpl<T>::Entry& curr = (*m.currMap)[id];
        curr.count = llmax(m.countLimit, curr.count);
        curr.blocked = true;
    }

    // returns true if key is blocked
    bool isThrottled(const T& id) const
    {
        if (m.currMap->empty()
            && m.prevMap->empty())
        {
            // most of the time we'll fall in here
            return false;
        }

        // NOTE, we ignore the case where id is in the map but the map is stale.
        // You might think that we'd stop throttling things in such a case,
        // however it may be that a god has disabled scripts in the region or
        // estate --> we probably want to report the state of the id when the
        // scripting engine was paused.
        typename LLKeyThrottleImpl<T>::EntryMap::const_iterator entry = m.currMap->find(id);
        if (entry != m.currMap->end())
        {
            return entry->second.blocked;
        }
        entry = m.prevMap->find(id);
        if (entry != m.prevMap->end())
        {
            return entry->second.blocked;
        }
        return false;
    }

    // Get the throttling parameters
    void getParameters( U32 & out_limit, F32 & out_interval, bool & out_realtime )
    {
        out_limit = m.countLimit;
        out_interval = m.intervalLength;
        out_realtime = mIsRealtime;
    }

    // Set the throttling behavior
    void setParameters( U32 limit, F32 interval, bool realtime = true )
    {
        // limit is the maximum number of keys
        // allowed per interval (in seconds or frames)
        mIsRealtime = realtime;
        m.countLimit = limit;
        if ( mIsRealtime )
        {
            m.intervalLength = (U64)(interval * USEC_PER_SEC);
            m.startTime = LLKeyThrottleImpl<T>::getTime();
        }
        else
        {
            m.intervalLength = (U64)interval;
            m.startTime = LLKeyThrottleImpl<T>::getFrame();
        }

        if ( m.intervalLength == 0 )
        {   // Don't allow zero intervals
            m.intervalLength = 1;
        }

        delete m.prevMap;
        m.prevMap = new typename LLKeyThrottleImpl<T>::EntryMap;
        delete m.currMap;
        m.currMap = new typename LLKeyThrottleImpl<T>::EntryMap;
    }

protected:
    LLKeyThrottleImpl<T>& m;
    bool    mIsRealtime;    // true to be time based (default), false for frame based
};

#endif