/**
 * @file   llevents.cpp
 * @author Nat Goodspeed
 * @date   2008-09-12
 * @brief  Implementation for llevents.
 * 
 * $LicenseInfo:firstyear=2008&license=viewergpl$
 * Copyright (c) 2008, Linden Research, Inc.
 * $/LicenseInfo$
 */

// Precompiled header
#include "linden_common.h"

#if LL_WINDOWS
#pragma warning (disable : 4675) // "resolved by ADL" -- just as I want!
#endif

// associated header
#include "llevents.h"
// STL headers
#include <set>
#include <sstream>
#include <algorithm>
// std headers
#include <typeinfo>
#include <cassert>
#include <cmath>
#include <cctype>
// external library headers
#include <boost/range/iterator_range.hpp>
#if LL_WINDOWS
#pragma warning (push)
#pragma warning (disable : 4701) // compiler thinks might use uninitialized var, but no
#endif
#include <boost/lexical_cast.hpp>
#if LL_WINDOWS
#pragma warning (pop)
#endif
// other Linden headers
#include "stringize.h"
#include "llerror.h"
#include "llsdutil.h"

/*****************************************************************************
*   queue_names: specify LLEventPump names that should be instantiated as
*   LLEventQueue
*****************************************************************************/
/**
 * At present, we recognize particular requested LLEventPump names as needing
 * LLEventQueues. Later on we'll migrate this information to an external
 * configuration file.
 */
const char* queue_names[] =
{
    "placeholder - replace with first real name string"
};

/*****************************************************************************
*   If there's a "mainloop" pump, listen on that to flush all LLEventQueues
*****************************************************************************/
struct RegisterFlush
{
    RegisterFlush():
        pumps(LLEventPumps::instance()),
        mainloop(pumps.obtain("mainloop")),
        name("flushLLEventQueues")
    {
        mainloop.listen(name, boost::bind(&RegisterFlush::flush, this, _1));
    }
    bool flush(const LLSD&)
    {
        pumps.flush();
        return false;
    }
    ~RegisterFlush()
    {
        mainloop.stopListening(name);
    }
    LLEventPumps& pumps;
    LLEventPump& mainloop;
    const std::string name;
};
static RegisterFlush registerFlush;

/*****************************************************************************
*   LLEventPumps
*****************************************************************************/
LLEventPumps::LLEventPumps():
    // Until we migrate this information to an external config file,
    // initialize mQueueNames from the static queue_names array.
    mQueueNames(boost::begin(queue_names), boost::end(queue_names))
{
}

LLEventPump& LLEventPumps::obtain(const std::string& name)
{
    PumpMap::iterator found = mPumpMap.find(name);
    if (found != mPumpMap.end())
    {
        // Here we already have an LLEventPump instance with the requested
        // name.
        return *found->second;
    }
    // Here we must instantiate an LLEventPump subclass. 
    LLEventPump* newInstance;
    // Should this name be an LLEventQueue?
    PumpNames::const_iterator nfound = mQueueNames.find(name);
    if (nfound != mQueueNames.end())
        newInstance = new LLEventQueue(name);
    else
        newInstance = new LLEventStream(name);
    // LLEventPump's constructor implicitly registers each new instance in
    // mPumpMap. But remember that we instantiated it (in mOurPumps) so we'll
    // delete it later.
    mOurPumps.insert(newInstance);
    return *newInstance;
}

void LLEventPumps::flush()
{
    // Flush every known LLEventPump instance. Leave it up to each instance to
    // decide what to do with the flush() call.
    for (PumpMap::iterator pmi = mPumpMap.begin(), pmend = mPumpMap.end(); pmi != pmend; ++pmi)
    {
        pmi->second->flush();
    }
}

std::string LLEventPumps::registerNew(const LLEventPump& pump, const std::string& name, bool tweak)
{
    std::pair<PumpMap::iterator, bool> inserted =
        mPumpMap.insert(PumpMap::value_type(name, const_cast<LLEventPump*>(&pump)));
    // If the insert worked, then the name is unique; return that.
    if (inserted.second)
        return name;
    // Here the new entry was NOT inserted, and therefore name isn't unique.
    // Unless we're permitted to tweak it, that's Bad.
    if (! tweak)
    {
        throw LLEventPump::DupPumpName(std::string("Duplicate LLEventPump name '") + name + "'");
    }
    // The passed name isn't unique, but we're permitted to tweak it. Find the
    // first decimal-integer suffix not already taken. The insert() attempt
    // above will have set inserted.first to the iterator of the existing
    // entry by that name. Starting there, walk forward until we reach an
    // entry that doesn't start with 'name'. For each entry consisting of name
    // + integer suffix, capture the integer suffix in a set. Use a set
    // because we're going to encounter string suffixes in the order: name1,
    // name10, name11, name2, ... Walking those possibilities in that order
    // isn't convenient to detect the first available "hole."
    std::set<int> suffixes;
    PumpMap::iterator pmi(inserted.first), pmend(mPumpMap.end());
    // We already know inserted.first references the existing entry with
    // 'name' as the key; skip that one and start with the next.
    while (++pmi != pmend)
    {
        if (pmi->first.substr(0, name.length()) != name)
        {
            // Found the first entry beyond the entries starting with 'name':
            // stop looping.
            break;
        }
        // Here we're looking at an entry that starts with 'name'. Is the rest
        // of it an integer?
        // Dubious (?) assumption: in the local character set, decimal digits
        // are in increasing order such that '9' is the last of them. This
        // test deals with 'name' values such as 'a', where there might be a
        // very large number of entries starting with 'a' whose suffixes
        // aren't integers. A secondary assumption is that digit characters
        // precede most common name characters (true in ASCII, false in
        // EBCDIC). The test below is correct either way, but it's worth more
        // if the assumption holds.
        if (pmi->first[name.length()] > '9')
            break;
        // It should be cheaper to detect that we're not looking at a digit
        // character -- and therefore the suffix can't possibly be an integer
        // -- than to attempt the lexical_cast and catch the exception.
        if (! std::isdigit(pmi->first[name.length()]))
            continue;
        // Okay, the first character of the suffix is a digit, it's worth at
        // least attempting to convert to int.
        try
        {
            suffixes.insert(boost::lexical_cast<int>(pmi->first.substr(name.length())));
        }
        catch (const boost::bad_lexical_cast&)
        {
            // If the rest of pmi->first isn't an int, just ignore it.
        }
    }
    // Here we've accumulated in 'suffixes' all existing int suffixes of the
    // entries starting with 'name'. Find the first unused one.
    int suffix = 1;
    for ( ; suffixes.find(suffix) != suffixes.end(); ++suffix)
        ;
    // Here 'suffix' is not in 'suffixes'. Construct a new name based on that
    // suffix, insert it and return it.
    std::ostringstream out;
    out << name << suffix;
    return registerNew(pump, out.str(), tweak);
}

void LLEventPumps::unregister(const LLEventPump& pump)
{
    // Remove this instance from mPumpMap
    PumpMap::iterator found = mPumpMap.find(pump.getName());
    if (found != mPumpMap.end())
    {
        mPumpMap.erase(found);
    }
    // If this instance is one we created, also remove it from mOurPumps so we
    // won't try again to delete it later!
    PumpSet::iterator psfound = mOurPumps.find(const_cast<LLEventPump*>(&pump));
    if (psfound != mOurPumps.end())
    {
        mOurPumps.erase(psfound);
    }
}

LLEventPumps::~LLEventPumps()
{
    // On destruction, delete every LLEventPump we instantiated (via
    // obtain()). CAREFUL: deleting an LLEventPump calls its destructor, which
    // calls unregister(), which removes that LLEventPump instance from
    // mOurPumps. So an iterator loop over mOurPumps to delete contained
    // LLEventPump instances is dangerous! Instead, delete them one at a time
    // until mOurPumps is empty.
    while (! mOurPumps.empty())
    {
        delete *mOurPumps.begin();
    }
}

/*****************************************************************************
*   LLEventPump
*****************************************************************************/
#if LL_WINDOWS
#pragma warning (push)
#pragma warning (disable : 4355) // 'this' used in initializer list: yes, intentionally
#endif

LLEventPump::LLEventPump(const std::string& name, bool tweak):
    // Register every new instance with LLEventPumps
    mName(LLEventPumps::instance().registerNew(*this, name, tweak)),
    mEnabled(true)
{}

#if LL_WINDOWS
#pragma warning (pop)
#endif

LLEventPump::~LLEventPump()
{
    // Unregister this doomed instance from LLEventPumps
    LLEventPumps::instance().unregister(*this);
}

// static data member
const LLEventPump::NameList LLEventPump::empty;

std::string LLEventPump::inventName(const std::string& pfx)
{
    static long suffix = 0;
    return STRINGIZE(pfx << suffix++);
}

LLBoundListener LLEventPump::listen_impl(const std::string& name, const LLEventListener& listener,
                                         const NameList& after,
                                         const NameList& before)
{
    // Check for duplicate name before connecting listener to mSignal
    ConnectionMap::const_iterator found = mConnections.find(name);
    // In some cases the user might disconnect a connection explicitly -- or
    // might use LLEventTrackable to disconnect implicitly. Either way, we can
    // end up retaining in mConnections a zombie connection object that's
    // already been disconnected. Such a connection object can't be
    // reconnected -- nor, in the case of LLEventTrackable, would we want to
    // try, since disconnection happens with the destruction of the listener
    // object. That means it's safe to overwrite a disconnected connection
    // object with the new one we're attempting. The case we want to prevent
    // is only when the existing connection object is still connected.
    if (found != mConnections.end() && found->second.connected())
    {
        throw DupListenerName(std::string("Attempt to register duplicate listener name '") + name +
                              "' on " + typeid(*this).name() + " '" + getName() + "'");
    }
    // Okay, name is unique, try to reconcile its dependencies. Specify a new
    // "node" value that we never use for an mSignal placement; we'll fix it
    // later.
    DependencyMap::node_type& newNode = mDeps.add(name, -1.0, after, before);
    // What if this listener has been added, removed and re-added? In that
    // case newNode already has a non-negative value because we never remove a
    // listener from mDeps. But keep processing uniformly anyway in case the
    // listener was added back with different dependencies. Then mDeps.sort()
    // would put it in a different position, and the old newNode placement
    // value would be wrong, so we'd have to reassign it anyway. Trust that
    // re-adding a listener with the same dependencies is the trivial case for
    // mDeps.sort(): it can just replay its cache.
    DependencyMap::sorted_range sorted_range;
    try
    {
        // Can we pick an order that works including this new entry?
        sorted_range = mDeps.sort();
    }
    catch (const DependencyMap::Cycle& e)
    {
        // No: the new node's after/before dependencies have made mDeps
        // unsortable. If we leave the new node in mDeps, it will continue
        // to screw up all future attempts to sort()! Pull it out.
        mDeps.remove(name);
        throw Cycle(std::string("New listener '") + name + "' on " + typeid(*this).name() +
                    " '" + getName() + "' would cause cycle: " + e.what());
    }
    // Walk the list to verify that we haven't changed the order.
    float previous = 0.0, myprev = 0.0;
    DependencyMap::sorted_iterator mydmi = sorted_range.end(); // need this visible after loop
    for (DependencyMap::sorted_iterator dmi = sorted_range.begin();
         dmi != sorted_range.end(); ++dmi)
    {
        // Since we've added the new entry with an invalid placement,
        // recognize it and skip it.
        if (dmi->first == name)
        {
            // Remember the iterator belonging to our new node, and which
            // placement value was 'previous' at that point.
            mydmi = dmi;
            myprev = previous;
            continue;
        }
        // If the new node has rearranged the existing nodes, we'll find
        // that their placement values are no longer in increasing order.
        if (dmi->second < previous)
        {
            // This is another scenario in which we'd better back out the
            // newly-added node from mDeps -- but don't do it yet, we want to
            // traverse the existing mDeps to report on it!
            // Describe the change to the order of our listeners. Copy
            // everything but the newest listener to a vector we can sort to
            // obtain the old order.
            typedef std::vector< std::pair<float, std::string> > SortNameList;
            SortNameList sortnames;
            for (DependencyMap::sorted_iterator cdmi(sorted_range.begin()), cdmend(sorted_range.end());
                 cdmi != cdmend; ++cdmi)
            {
                if (cdmi->first != name)
                {
                    sortnames.push_back(SortNameList::value_type(cdmi->second, cdmi->first));
                }
            }
            std::sort(sortnames.begin(), sortnames.end());
            std::ostringstream out;
            out << "New listener '" << name << "' on " << typeid(*this).name() << " '" << getName()
                << "' would move previous listener '" << dmi->first << "'\nwas: ";
            SortNameList::const_iterator sni(sortnames.begin()), snend(sortnames.end());
            if (sni != snend)
            {
                out << sni->second;
                while (++sni != snend)
                {
                    out << ", " << sni->second;
                }
            }
            out << "\nnow: ";
            DependencyMap::sorted_iterator ddmi(sorted_range.begin()), ddmend(sorted_range.end());
            if (ddmi != ddmend)
            {
                out << ddmi->first;
                while (++ddmi != ddmend)
                {
                    out << ", " << ddmi->first;
                }
            }
            // NOW remove the offending listener node.
            mDeps.remove(name);
            // Having constructed a description of the order change, inform caller.
            throw OrderChange(out.str());
        }
        // This node becomes the previous one.
        previous = dmi->second;
    }
    // We just got done with a successful mDeps.add(name, ...) call. We'd
    // better have found 'name' somewhere in that sorted list!
    assert(mydmi != sorted_range.end());
    // Four cases:
    // 0. name is the only entry: placement 1.0
    // 1. name is the first of several entries: placement (next placement)/2
    // 2. name is between two other entries: placement (myprev + (next placement))/2
    // 3. name is the last entry: placement ceil(myprev) + 1.0
    // Since we've cleverly arranged for myprev to be 0.0 if name is the
    // first entry, this folds down to two cases. Case 1 is subsumed by
    // case 2, and case 0 is subsumed by case 3. So we need only handle
    // cases 2 and 3, which means we need only detect whether name is the
    // last entry. Increment mydmi to see if there's anything beyond.
    if (++mydmi != sorted_range.end())
    {
        // The new node isn't last. Place it between the previous node and
        // the successor.
        newNode = (myprev + mydmi->second)/2.0;
    }
    else
    {
        // The new node is last. Bump myprev up to the next integer, add
        // 1.0 and use that.
        newNode = std::ceil(myprev) + 1.0;
    }
    // Now that newNode has a value that places it appropriately in mSignal,
    // connect it.
    LLBoundListener bound = mSignal.connect(newNode, listener);
    mConnections[name] = bound;
    return bound;
}

LLBoundListener LLEventPump::getListener(const std::string& name) const
{
    ConnectionMap::const_iterator found = mConnections.find(name);
    if (found != mConnections.end())
    {
        return found->second;
    }
    // not found, return dummy LLBoundListener
    return LLBoundListener();
}

void LLEventPump::stopListening(const std::string& name)
{
    ConnectionMap::iterator found = mConnections.find(name);
    if (found != mConnections.end())
    {
        found->second.disconnect();
        mConnections.erase(found);
    }
    // We intentionally do NOT remove this name from mDeps. It may happen that
    // the same listener with the same name and dependencies will jump on and
    // off this LLEventPump repeatedly. Keeping a cache of dependencies will
    // avoid a new dependency sort in such cases.
}

/*****************************************************************************
*   LLEventStream
*****************************************************************************/
bool LLEventStream::post(const LLSD& event)
{
    if (! mEnabled)
        return false;
    // Let caller know if any one listener handled the event. This is mostly
    // useful when using LLEventStream as a listener for an upstream
    // LLEventPump.
    return mSignal(event);
}

/*****************************************************************************
*   LLEventQueue
*****************************************************************************/
bool LLEventQueue::post(const LLSD& event)
{
    if (mEnabled)
    {
        // Defer sending this event by queueing it until flush()
        mEventQueue.push_back(event);
    }
    // Unconditionally return false. We won't know until flush() whether a
    // listener claims to have handled the event -- meanwhile, don't block
    // other listeners.
    return false;
}

void LLEventQueue::flush()
{
    // Consider the case when a given listener on this LLEventQueue posts yet
    // another event on the same queue. If we loop over mEventQueue directly,
    // we'll end up processing all those events during the same flush() call
    // -- rather like an EventStream. Instead, copy mEventQueue and clear it,
    // so that any new events posted to this LLEventQueue during flush() will
    // be processed in the *next* flush() call.
    EventQueue queue(mEventQueue);
    mEventQueue.clear();
    for ( ; ! queue.empty(); queue.pop_front())
    {
        mSignal(queue.front());
    }
}

/*****************************************************************************
*   LLListenerOrPumpName
*****************************************************************************/
LLListenerOrPumpName::LLListenerOrPumpName(const std::string& pumpname):
    // Look up the specified pumpname, and bind its post() method as our listener
    mListener(boost::bind(&LLEventPump::post,
                          boost::ref(LLEventPumps::instance().obtain(pumpname)),
                          _1))
{
}

LLListenerOrPumpName::LLListenerOrPumpName(const char* pumpname):
    // Look up the specified pumpname, and bind its post() method as our listener
    mListener(boost::bind(&LLEventPump::post,
                          boost::ref(LLEventPumps::instance().obtain(pumpname)),
                          _1))
{
}

bool LLListenerOrPumpName::operator()(const LLSD& event) const
{
    if (! mListener)
    {
        throw Empty("attempting to call uninitialized");
    }
    return (*mListener)(event);
}

void LLReqID::stamp(LLSD& response) const
{
    if (! (response.isUndefined() || response.isMap()))
    {
        // If 'response' was previously completely empty, it's okay to
        // turn it into a map. If it was already a map, then it should be
        // okay to add a key. But if it was anything else (e.g. a scalar),
        // assigning a ["reqid"] key will DISCARD the previous value,
        // replacing it with a map. That would be Bad.
        LL_INFOS("LLReqID") << "stamp(" << mReqid << ") leaving non-map response unmodified: "
                            << response << LL_ENDL;
        return;
    }
    LLSD oldReqid(response["reqid"]);
    if (! (oldReqid.isUndefined() || llsd_equals(oldReqid, mReqid)))
    {
        LL_INFOS("LLReqID") << "stamp(" << mReqid << ") preserving existing [\"reqid\"] value "
                            << oldReqid << " in response: " << response << LL_ENDL;
        return;
    }
    response["reqid"] = mReqid;
}