/** 
 * @file llavatarnamecache.cpp
 * @brief Provides lookup of avatar SLIDs ("bobsmith123") and display names
 * ("James Cook") from avatar UUIDs.
 *
 * $LicenseInfo:firstyear=2010&license=viewerlgpl$
 * 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
 * $/LicenseInfo$
 */
#include "linden_common.h"

#include "llavatarnamecache.h"

#include "llcachename.h"		// we wrap this system
#include "llframetimer.h"
#include "llhttpclient.h"
#include "llsd.h"
#include "llsdserialize.h"

#include <boost/tokenizer.hpp>

#include <map>
#include <set>
#include <unistd.h>

namespace LLAvatarNameCache
{
	use_display_name_signal_t mUseDisplayNamesSignal;

	// Manual override for display names - can disable even if the region
	// supports it.
	bool sUseDisplayNames = true;

	// Cache starts in a paused state until we can determine if the
	// current region supports display names.
	bool sRunning = false;
	
	// Base lookup URL for name service.
	// On simulator, loaded from indra.xml
	// On viewer, usually a simulator capability (at People API team's request)
	// Includes the trailing slash, like "http://pdp60.lindenlab.com:8000/agents/"
	std::string sNameLookupURL;

	// accumulated agent IDs for next query against service
	typedef std::set<LLUUID> ask_queue_t;
	ask_queue_t sAskQueue;

	// agent IDs that have been requested, but with no reply
	// maps agent ID to frame time request was made
	typedef std::map<LLUUID, F64> pending_queue_t;
	pending_queue_t sPendingQueue;

	// Callbacks to fire when we received a name.
	// May have multiple callbacks for a single ID, which are
	// represented as multiple slots bound to the signal.
	// Avoid copying signals via pointers.
	typedef std::map<LLUUID, callback_signal_t*> signal_map_t;
	signal_map_t sSignalMap;

	// names we know about
	typedef std::map<LLUUID, LLAvatarName> cache_t;
	cache_t sCache;

	// Send bulk lookup requests a few times a second at most
	// only need per-frame timing resolution
	LLFrameTimer sRequestTimer;

    /// Maximum time an unrefreshed cache entry is allowed
    const F64 MAX_UNREFRESHED_TIME = 20.0 * 60.0;

    /// Time when unrefreshed cached names were checked last
    static F64 sLastExpireCheck;

	//-----------------------------------------------------------------------
	// Internal methods
	//-----------------------------------------------------------------------

	// Handle name response off network.
	// Optionally skip adding to cache, used when this is a fallback to the
	// legacy name system.
	void processName(const LLUUID& agent_id,
					 const LLAvatarName& av_name,
					 bool add_to_cache);

	void requestNamesViaCapability();

	// Legacy name system callback
	void legacyNameCallback(const LLUUID& agent_id,
							const std::string& full_name,
							bool is_group
							);

	void requestNamesViaLegacy();

	// Fill in an LLAvatarName with the legacy name data
	void buildLegacyName(const std::string& full_name,
						 LLAvatarName* av_name);

	// Do a single callback to a given slot
	void fireSignal(const LLUUID& agent_id,
					const callback_slot_t& slot,
					const LLAvatarName& av_name);
	
	// Is a request in-flight over the network?
	bool isRequestPending(const LLUUID& agent_id);

	// Erase expired names from cache
	void eraseUnrefreshed();

	bool expirationFromCacheControl(LLSD headers, F64 *expires);
}

/* Sample response:
<?xml version="1.0"?>
<llsd>
  <map>
    <key>agents</key>
    <array>
      <map>
        <key>display_name_next_update</key>
        <date>2010-04-16T21:34:02+00:00Z</date>
        <key>display_name_expires</key>
        <date>2010-04-16T21:32:26.142178+00:00Z</date>
        <key>display_name</key>
        <string>MickBot390 LLQABot</string>
        <key>sl_id</key>
        <string>mickbot390.llqabot</string>
        <key>id</key>
        <string>0012809d-7d2d-4c24-9609-af1230a37715</string>
        <key>is_display_name_default</key>
        <boolean>false</boolean>
      </map>
      <map>
        <key>display_name_next_update</key>
        <date>2010-04-16T21:34:02+00:00Z</date>
        <key>display_name_expires</key>
        <date>2010-04-16T21:32:26.142178+00:00Z</date>
        <key>display_name</key>
        <string>Bjork Gudmundsdottir</string>
        <key>sl_id</key>
        <string>sardonyx.linden</string>
        <key>id</key>
        <string>3941037e-78ab-45f0-b421-bd6e77c1804d</string>
        <key>is_display_name_default</key>
        <boolean>true</boolean>
      </map>
    </array>
  </map>
</llsd>
*/

class LLAvatarNameResponder : public LLHTTPClient::Responder
{
private:
	// need to store agent ids that are part of this request in case of
	// an error, so we can flag them as unavailable
	std::vector<LLUUID> mAgentIDs;

	// Need the headers to look up Expires: and Retry-After:
	LLSD mHeaders;
	
public:
	LLAvatarNameResponder(const std::vector<LLUUID>& agent_ids)
	:	mAgentIDs(agent_ids),
		mHeaders()
	{ }
	
	/*virtual*/ void completedHeader(U32 status, const std::string& reason, 
		const LLSD& headers)
	{
		mHeaders = headers;
	}

	/*virtual*/ void result(const LLSD& content)
	{
		// Pull expiration out of headers if available
		F64 expires = LLAvatarNameCache::nameExpirationFromHeaders(mHeaders);
		F64 now = LLFrameTimer::getTotalSeconds();

		LLSD agents = content["agents"];
		LLSD::array_const_iterator it = agents.beginArray();
		for ( ; it != agents.endArray(); ++it)
		{
			const LLSD& row = *it;
			LLUUID agent_id = row["id"].asUUID();

			LLAvatarName av_name;
			av_name.fromLLSD(row);

			// Use expiration time from header
			av_name.mExpires = expires;

			// Some avatars don't have explicit display names set
			if (av_name.mDisplayName.empty())
			{
				av_name.mDisplayName = av_name.mUsername;
			}

			LL_DEBUGS("AvNameCache") << "LLAvatarNameResponder::result for " << agent_id << " "
									 << "user '" << av_name.mUsername << "' "
									 << "display '" << av_name.mDisplayName << "' "
									 << "expires in " << expires - now << " seconds"
									 << LL_ENDL;
			
			// cache it and fire signals
			LLAvatarNameCache::processName(agent_id, av_name, true);
		}

		// Same logic as error response case
		LLSD unresolved_agents = content["bad_ids"];
		S32  num_unresolved = unresolved_agents.size();
		if (num_unresolved > 0)
		{
            LL_WARNS("AvNameCache") << "LLAvatarNameResponder::result " << num_unresolved << " unresolved ids; "
                                    << "expires in " << expires - now << " seconds"
                                    << LL_ENDL;
			it = unresolved_agents.beginArray();
			for ( ; it != unresolved_agents.endArray(); ++it)
			{
				const LLUUID& agent_id = *it;

				LL_WARNS("AvNameCache") << "LLAvatarNameResponder::result "
                                        << "failed id " << agent_id
                                        << LL_ENDL;

                LLAvatarNameCache::handleAgentError(agent_id);
			}
		}
        LL_DEBUGS("AvNameCache") << "LLAvatarNameResponder::result " 
                                 << LLAvatarNameCache::sCache.size() << " cached names"
                                 << LL_ENDL;
    }

	/*virtual*/ void error(U32 status, const std::string& reason)
	{
		// If there's an error, it might be caused by PeopleApi,
		// or when loading textures on startup and using a very slow 
		// network, this query may time out.
		// What we should do depends on whether or not we have a cached name
		LL_WARNS("AvNameCache") << "LLAvatarNameResponder::error " << status << " " << reason
								<< LL_ENDL;

		// Add dummy records for any agent IDs in this request that we do not have cached already
		std::vector<LLUUID>::const_iterator it = mAgentIDs.begin();
		for ( ; it != mAgentIDs.end(); ++it)
		{
			const LLUUID& agent_id = *it;
			LLAvatarNameCache::handleAgentError(agent_id);
		}
	}
};

// Provide some fallback for agents that return errors
void LLAvatarNameCache::handleAgentError(const LLUUID& agent_id)
{
	std::map<LLUUID,LLAvatarName>::iterator existing = sCache.find(agent_id);
	if (existing == sCache.end())
    {
        // there is no existing cache entry, so make a temporary name from legacy
        LL_WARNS("AvNameCache") << "LLAvatarNameCache get legacy for agent "
                                << agent_id << LL_ENDL;
        gCacheName->get(agent_id, false,  // legacy compatibility
                        boost::bind(&LLAvatarNameCache::legacyNameCallback,
                                    _1, _2, _3));
    }
	else
    {
        // we have a chached (but probably expired) entry - since that would have
        // been returned by the get method, there is no need to signal anyone

        // Clear this agent from the pending list
        LLAvatarNameCache::sPendingQueue.erase(agent_id);

        const LLAvatarName& av_name = existing->second;
        LL_DEBUGS("AvNameCache") << "LLAvatarNameCache use cache for agent "
                                 << agent_id 
                                 << "user '" << av_name.mUsername << "' "
                                 << "display '" << av_name.mDisplayName << "' "
                                 << "expires in " << av_name.mExpires - LLFrameTimer::getTotalSeconds() << " seconds"
                                 << LL_ENDL;
    }
}

void LLAvatarNameCache::processName(const LLUUID& agent_id,
									const LLAvatarName& av_name,
									bool add_to_cache)
{
	if (add_to_cache)
	{
		sCache[agent_id] = av_name;
	}

	sPendingQueue.erase(agent_id);

	// signal everyone waiting on this name
	signal_map_t::iterator sig_it =	sSignalMap.find(agent_id);
	if (sig_it != sSignalMap.end())
	{
		callback_signal_t* signal = sig_it->second;
		(*signal)(agent_id, av_name);

		sSignalMap.erase(agent_id);

		delete signal;
		signal = NULL;
	}
}

void LLAvatarNameCache::requestNamesViaCapability()
{
	F64 now = LLFrameTimer::getTotalSeconds();

	// URL format is like:
	// http://pdp60.lindenlab.com:8000/agents/?ids=3941037e-78ab-45f0-b421-bd6e77c1804d&ids=0012809d-7d2d-4c24-9609-af1230a37715&ids=0019aaba-24af-4f0a-aa72-6457953cf7f0
	//
	// Apache can handle URLs of 4096 chars, but let's be conservative
	const U32 NAME_URL_MAX = 4096;
	const U32 NAME_URL_SEND_THRESHOLD = 3000;
	std::string url;
	url.reserve(NAME_URL_MAX);

	std::vector<LLUUID> agent_ids;
	agent_ids.reserve(128);
	
	U32 ids = 0;
	ask_queue_t::const_iterator it = sAskQueue.begin();
	for ( ; it != sAskQueue.end(); ++it)
	{
		const LLUUID& agent_id = *it;

		if (url.empty())
		{
			// ...starting new request
			url += sNameLookupURL;
			url += "?ids=";
			ids = 1;
		}
		else
		{
			// ...continuing existing request
			url += "&ids=";
			ids++;
		}
		url += agent_id.asString();
		agent_ids.push_back(agent_id);

		// mark request as pending
		sPendingQueue[agent_id] = now;

		if (url.size() > NAME_URL_SEND_THRESHOLD)
		{
			LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::requestNamesViaCapability first "
									 << ids << " ids"
									 << LL_ENDL;
			LLHTTPClient::get(url, new LLAvatarNameResponder(agent_ids));
			url.clear();
			agent_ids.clear();
		}
	}

	if (!url.empty())
	{
		LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::requestNamesViaCapability all "
								 << ids << " ids"
								 << LL_ENDL;
		LLHTTPClient::get(url, new LLAvatarNameResponder(agent_ids));
		url.clear();
		agent_ids.clear();
	}

	// We've moved all asks to the pending request queue
	sAskQueue.clear();
}

void LLAvatarNameCache::legacyNameCallback(const LLUUID& agent_id,
										   const std::string& full_name,
										   bool is_group)
{
	// Construct a dummy record for this name.  By convention, SLID is blank
	// Never expires, but not written to disk, so lasts until end of session.
	LLAvatarName av_name;
	LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::legacyNameCallback "
							 << "agent " << agent_id << " "
							 << "full name '" << full_name << "'"
							 << ( is_group ? " [group]" : "" )
							 << LL_ENDL;
	buildLegacyName(full_name, &av_name);

	// Don't add to cache, the data already exists in the legacy name system
	// cache and we don't want or need duplicate storage, because keeping the
	// two copies in sync is complex.
	processName(agent_id, av_name, false);
}

void LLAvatarNameCache::requestNamesViaLegacy()
{
	F64 now = LLFrameTimer::getTotalSeconds();
	std::string full_name;
	ask_queue_t::const_iterator it = sAskQueue.begin();
	for (; it != sAskQueue.end(); ++it)
	{
		const LLUUID& agent_id = *it;

		// Mark as pending first, just in case the callback is immediately
		// invoked below.  This should never happen in practice.
		sPendingQueue[agent_id] = now;

		LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::requestNamesViaLegacy agent " << agent_id << LL_ENDL;

		gCacheName->get(agent_id, false,  // legacy compatibility
			boost::bind(&LLAvatarNameCache::legacyNameCallback,
				_1, _2, _3));
	}

	// We've either answered immediately or moved all asks to the
	// pending queue
	sAskQueue.clear();
}

void LLAvatarNameCache::initClass(bool running)
{
	sRunning = running;
}

void LLAvatarNameCache::cleanupClass()
{
}

void LLAvatarNameCache::importFile(std::istream& istr)
{
	LLSD data;
	S32 parse_count = LLSDSerialize::fromXMLDocument(data, istr);
	if (parse_count < 1) return;

	// by convention LLSD storage is a map
	// we only store one entry in the map
	LLSD agents = data["agents"];

	LLUUID agent_id;
	LLAvatarName av_name;
	LLSD::map_const_iterator it = agents.beginMap();
	for ( ; it != agents.endMap(); ++it)
	{
		agent_id.set(it->first);
		av_name.fromLLSD( it->second );
		sCache[agent_id] = av_name;
	}
    LL_INFOS("AvNameCache") << "loaded " << sCache.size() << LL_ENDL;

	// Some entries may have expired since the cache was stored,
    // but they will be flushed in the first call to eraseUnrefreshed
    // from LLAvatarNameResponder::idle
}

void LLAvatarNameCache::exportFile(std::ostream& ostr)
{
	LLSD agents;
	F64 max_unrefreshed = LLFrameTimer::getTotalSeconds() - MAX_UNREFRESHED_TIME;
	cache_t::const_iterator it = sCache.begin();
	for ( ; it != sCache.end(); ++it)
	{
		const LLUUID& agent_id = it->first;
		const LLAvatarName& av_name = it->second;
		// Do not write temporary or expired entries to the stored cache
		if (!av_name.mIsTemporaryName && av_name.mExpires >= max_unrefreshed)
		{
			// key must be a string
			agents[agent_id.asString()] = av_name.asLLSD();
		}
	}
	LLSD data;
	data["agents"] = agents;
	LLSDSerialize::toPrettyXML(data, ostr);
}

void LLAvatarNameCache::setNameLookupURL(const std::string& name_lookup_url)
{
	sNameLookupURL = name_lookup_url;
}

bool LLAvatarNameCache::hasNameLookupURL()
{
	return !sNameLookupURL.empty();
}

void LLAvatarNameCache::idle()
{
	// By convention, start running at first idle() call
	sRunning = true;

	// *TODO: Possibly re-enabled this based on People API load measurements
	// 100 ms is the threshold for "user speed" operations, so we can
	// stall for about that long to batch up requests.
	//const F32 SECS_BETWEEN_REQUESTS = 0.1f;
	//if (!sRequestTimer.checkExpirationAndReset(SECS_BETWEEN_REQUESTS))
	//{
	//	return;
	//}

	if (!sAskQueue.empty())
	{
        if (useDisplayNames())
        {
            requestNamesViaCapability();
        }
        else
        {
            // ...fall back to legacy name cache system
            requestNamesViaLegacy();
        }
	}

    // erase anything that has not been refreshed for more than MAX_UNREFRESHED_TIME
    eraseUnrefreshed();
}

bool LLAvatarNameCache::isRequestPending(const LLUUID& agent_id)
{
	bool isPending = false;
	const F64 PENDING_TIMEOUT_SECS = 5.0 * 60.0;

	pending_queue_t::const_iterator it = sPendingQueue.find(agent_id);
	if (it != sPendingQueue.end())
	{
		// in the list of requests in flight, retry if too old
		F64 expire_time = LLFrameTimer::getTotalSeconds() - PENDING_TIMEOUT_SECS;
		isPending = (it->second > expire_time);
	}
	return isPending;
}

void LLAvatarNameCache::eraseUnrefreshed()
{
	F64 now = LLFrameTimer::getTotalSeconds();
	F64 max_unrefreshed = now - MAX_UNREFRESHED_TIME;

    if (!sLastExpireCheck || sLastExpireCheck < max_unrefreshed)
    {
        sLastExpireCheck = now;
        cache_t::iterator it = sCache.begin();
        while (it != sCache.end())
        {
            cache_t::iterator cur = it;
            ++it;
            const LLAvatarName& av_name = cur->second;
            if (av_name.mExpires < max_unrefreshed)
            {
                const LLUUID& agent_id = it->first;
                LL_DEBUGS("AvNameCache") << agent_id 
                                         << " user '" << av_name.mUsername << "' "
                                         << "expired " << now - av_name.mExpires << " secs ago"
                                         << LL_ENDL;
                sCache.erase(cur);
            }
        }
        LL_INFOS("AvNameCache") << sCache.size() << " cached avatar names" << LL_ENDL;
	}
}

void LLAvatarNameCache::buildLegacyName(const std::string& full_name,
										LLAvatarName* av_name)
{
	llassert(av_name);
	av_name->mUsername = "";
	av_name->mDisplayName = full_name;
	av_name->mIsDisplayNameDefault = true;
	av_name->mIsTemporaryName = true;
	av_name->mExpires = F64_MAX; // not used because these are not cached
	LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::buildLegacyName "
							 << full_name
							 << LL_ENDL;
}

// fills in av_name if it has it in the cache, even if expired (can check expiry time)
// returns bool specifying  if av_name was filled, false otherwise
bool LLAvatarNameCache::get(const LLUUID& agent_id, LLAvatarName *av_name)
{
	if (sRunning)
	{
		// ...only do immediate lookups when cache is running
		if (useDisplayNames())
		{
			// ...use display names cache
			std::map<LLUUID,LLAvatarName>::iterator it = sCache.find(agent_id);
			if (it != sCache.end())
			{
				*av_name = it->second;

				// re-request name if entry is expired
				if (av_name->mExpires < LLFrameTimer::getTotalSeconds())
				{
					if (!isRequestPending(agent_id))
					{
						LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::get "
												 << "refresh agent " << agent_id
												 << LL_ENDL;
						sAskQueue.insert(agent_id);
					}
				}
				
				return true;
			}
		}
		else
		{
			// ...use legacy names cache
			std::string full_name;
			if (gCacheName->getFullName(agent_id, full_name))
			{
				buildLegacyName(full_name, av_name);
				return true;
			}
		}
	}

	if (!isRequestPending(agent_id))
	{
		LL_DEBUGS("AvNameCache") << "LLAvatarNameCache::get "
								 << "queue request for agent " << agent_id
								 << LL_ENDL;
		sAskQueue.insert(agent_id);
	}

	return false;
}

void LLAvatarNameCache::fireSignal(const LLUUID& agent_id,
								   const callback_slot_t& slot,
								   const LLAvatarName& av_name)
{
	callback_signal_t signal;
	signal.connect(slot);
	signal(agent_id, av_name);
}

void LLAvatarNameCache::get(const LLUUID& agent_id, callback_slot_t slot)
{
	if (sRunning)
	{
		// ...only do immediate lookups when cache is running
		if (useDisplayNames())
		{
			// ...use new cache
			std::map<LLUUID,LLAvatarName>::iterator it = sCache.find(agent_id);
			if (it != sCache.end())
			{
				const LLAvatarName& av_name = it->second;
				
				if (av_name.mExpires > LLFrameTimer::getTotalSeconds())
				{
					// ...name already exists in cache, fire callback now
					fireSignal(agent_id, slot, av_name);
					return;
				}
			}
		}
		else
		{
			// ...use old name system
			std::string full_name;
			if (gCacheName->getFullName(agent_id, full_name))
			{
				LLAvatarName av_name;
				buildLegacyName(full_name, &av_name);
				fireSignal(agent_id, slot, av_name);
				return;
			}
		}
	}

	// schedule a request
	if (!isRequestPending(agent_id))
	{
		sAskQueue.insert(agent_id);
	}

	// always store additional callback, even if request is pending
	signal_map_t::iterator sig_it = sSignalMap.find(agent_id);
	if (sig_it == sSignalMap.end())
	{
		// ...new callback for this id
		callback_signal_t* signal = new callback_signal_t();
		signal->connect(slot);
		sSignalMap[agent_id] = signal;
	}
	else
	{
		// ...existing callback, bind additional slot
		callback_signal_t* signal = sig_it->second;
		signal->connect(slot);
	}
}


void LLAvatarNameCache::setUseDisplayNames(bool use)
{
	if (use != sUseDisplayNames)
	{
		sUseDisplayNames = use;
		// flush our cache
		sCache.clear();

		mUseDisplayNamesSignal();
	}
}

bool LLAvatarNameCache::useDisplayNames()
{
	// Must be both manually set on and able to look up names.
	return sUseDisplayNames && !sNameLookupURL.empty();
}

void LLAvatarNameCache::erase(const LLUUID& agent_id)
{
	sCache.erase(agent_id);
}

void LLAvatarNameCache::fetch(const LLUUID& agent_id)
{
	// re-request, even if request is already pending
	sAskQueue.insert(agent_id);
}

void LLAvatarNameCache::insert(const LLUUID& agent_id, const LLAvatarName& av_name)
{
	// *TODO: update timestamp if zero?
	sCache[agent_id] = av_name;
}

F64 LLAvatarNameCache::nameExpirationFromHeaders(LLSD headers)
{
	F64 expires = 0.0;
	if (expirationFromCacheControl(headers, &expires))
	{
		return expires;
	}
	else
	{
		// With no expiration info, default to an hour
		const F64 DEFAULT_EXPIRES = 60.0 * 60.0;
		F64 now = LLFrameTimer::getTotalSeconds();
		return now + DEFAULT_EXPIRES;
	}
}

bool LLAvatarNameCache::expirationFromCacheControl(LLSD headers, F64 *expires)
{
	bool fromCacheControl = false;
	F64 now = LLFrameTimer::getTotalSeconds();

	// Allow the header to override the default
	LLSD cache_control_header = headers["cache-control"];
	if (cache_control_header.isDefined())
	{
		S32 max_age = 0;
		std::string cache_control = cache_control_header.asString();
		if (max_age_from_cache_control(cache_control, &max_age))
		{
			*expires = now + (F64)max_age;
			fromCacheControl = true;
		}
	}
	LL_DEBUGS("AvNameCache")
		<< ( fromCacheControl ? "expires based on cache control " : "default expiration " )
		<< "in " << *expires - now << " seconds"
		<< LL_ENDL;
	
	return fromCacheControl;
}


void LLAvatarNameCache::addUseDisplayNamesCallback(const use_display_name_signal_t::slot_type& cb) 
{ 
	mUseDisplayNamesSignal.connect(cb); 
}


static const std::string MAX_AGE("max-age");
static const boost::char_separator<char> EQUALS_SEPARATOR("=");
static const boost::char_separator<char> COMMA_SEPARATOR(",");

bool max_age_from_cache_control(const std::string& cache_control, S32 *max_age)
{
	// Split the string on "," to get a list of directives
	typedef boost::tokenizer<boost::char_separator<char> > tokenizer;
	tokenizer directives(cache_control, COMMA_SEPARATOR);

	tokenizer::iterator token_it = directives.begin();
	for ( ; token_it != directives.end(); ++token_it)
	{
		// Tokens may have leading or trailing whitespace
		std::string token = *token_it;
		LLStringUtil::trim(token);

		if (token.compare(0, MAX_AGE.size(), MAX_AGE) == 0)
		{
			// ...this token starts with max-age, so let's chop it up by "="
			tokenizer subtokens(token, EQUALS_SEPARATOR);
			tokenizer::iterator subtoken_it = subtokens.begin();

			// Must have a token
			if (subtoken_it == subtokens.end()) return false;
			std::string subtoken = *subtoken_it;

			// Must exactly equal "max-age"
			LLStringUtil::trim(subtoken);
			if (subtoken != MAX_AGE) return false;

			// Must have another token
			++subtoken_it;
			if (subtoken_it == subtokens.end()) return false;
			subtoken = *subtoken_it;

			// Must be a valid integer
			// *NOTE: atoi() returns 0 for invalid values, so we have to
			// check the string first.
			// *TODO: Do servers ever send "0000" for zero?  We don't handle it
			LLStringUtil::trim(subtoken);
			if (subtoken == "0")
			{
				*max_age = 0;
				return true;
			}
			S32 val = atoi( subtoken.c_str() );
			if (val > 0 && val < S32_MAX)
			{
				*max_age = val;
				return true;
			}
			return false;
		}
	}
	return false;
}