/*
    PowerDNS Versatile Database Driven Nameserver
    Copyright (C) 2002 - 2008  PowerDNS.COM BV

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 2 as 
    published by the Free Software Foundation

    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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
#include "utility.hh"
#include "packetcache.hh"
#include "logger.hh"
#include "arguments.hh"
#include "statbag.hh"
#include <map>
#include <boost/algorithm/string.hpp>

extern StatBag S;

PacketCache::PacketCache()
{
  pthread_rwlock_init(&d_mut,0);
  d_hit=d_miss=0;

  d_ttl=-1;
  d_recursivettl=-1;

  S.declare("packetcache-hit");
  S.declare("packetcache-miss");
  S.declare("packetcache-size");

  d_statnumhit=S.getPointer("packetcache-hit");
  d_statnummiss=S.getPointer("packetcache-miss");
  d_statnumentries=S.getPointer("packetcache-size");
}

int PacketCache::get(DNSPacket *p, DNSPacket *cached)
{
  extern StatBag S;
  if(!((d_hit+d_miss)%150000)) {
    cleanup();
  }

  if(d_ttl<0) 
    getTTLS();

  if(d_doRecursion && p->d.rd) { // wants recursion
    if(!d_recursivettl) {
      (*d_statnummiss)++;
      d_miss++;
      return 0;
    }
  }
  else { // does not
    if(!d_ttl) {
      (*d_statnummiss)++;
      d_miss++;
      return 0;
    }
  }
    
  bool packetMeritsRecursion=d_doRecursion && p->d.rd;
  if(ntohs(p->d.qdcount)!=1) // we get confused by packets with more than one question
    return 0;

  {
    TryReadLock l(&d_mut); // take a readlock here
    if(!l.gotIt()) {
      S.inc("deferred-cache-lookup");
      return 0;
    }

    if(!((d_hit+d_miss)%30000)) {
      *d_statnumentries=d_map.size(); // needs lock
    }
    string value;

    if(getEntry(p->qdomain, p->qtype, PacketCache::PACKETCACHE, value, -1, packetMeritsRecursion)) {
      //      cerr<<"Packet cache hit for '"<<p->qdomain<<"', merits: "<<packetMeritsRecursion<<endl;
      (*d_statnumhit)++;
      d_hit++;
      if(cached->parse(value.c_str(), value.size()) < 0) {
	return -1;
      }
      cached->spoofQuestion(p->qdomain); // for correct case
      return 1;
    }
  }
  //  cerr<<"Packet cache miss for '"<<p->qdomain<<"', merits: "<<packetMeritsRecursion<<endl;
  (*d_statnummiss)++;
  d_miss++;
  return 0; // bummer
}

void PacketCache::getTTLS()
{
  d_ttl=::arg().asNum("cache-ttl");
  d_recursivettl=::arg().asNum("recursive-cache-ttl");

  d_doRecursion=::arg().mustDo("recursor"); 
}


void PacketCache::insert(DNSPacket *q, DNSPacket *r)
{
  if(d_ttl < 0)
    getTTLS();
  
  if(ntohs(q->d.qdcount)!=1) {
    return; // do not try to cache packets with multiple questions
  }

  bool packetMeritsRecursion=d_doRecursion && q->d.rd;

  insert(q->qdomain, q->qtype, PacketCache::PACKETCACHE, r->getString(), packetMeritsRecursion ? d_recursivettl : d_ttl, -1, packetMeritsRecursion);
}

// universal key appears to be: qname, qtype, kind (packet, query cache), optionally zoneid, meritsRecursion
void PacketCache::insert(const string &qname, const QType& qtype, CacheEntryType cet, const string& value, unsigned int ttl, int zoneID, bool meritsRecursion)
{
  if(!ttl)
    return;
  
  //  cerr<<"Inserting qname '"<<qname<<"', cet: "<<(int)cet<<", value: '"<< (cet ? value : "PACKET") <<"', qtype: "<<qtype.getName()<<", ttl: "<<ttl<<endl;
  CacheEntry val;
  val.ttd=time(0)+ttl;
  val.qname=qname;
  val.qtype=qtype.getCode();
  val.value=value;
  val.ctype=cet;
  val.meritsRecursion=meritsRecursion;

  TryWriteLock l(&d_mut);
  if(l.gotIt()) { 
    bool success;
    cmap_t::iterator place;
    tie(place, success)=d_map.insert(val);
    //    cerr<<"Insert succeeded: "<<success<<endl;
    if(!success)
      d_map.replace(place, val);
    
  }
  else 
    S.inc("deferred-cache-inserts"); 
}

/** purges entries from the packetcache. If match ends on a $, it is treated as a suffix */
int PacketCache::purge(const vector<string> &matches)
{
  WriteLock l(&d_mut);
  int delcount=0;
  
  if(matches.empty()) {
    delcount = d_map.size();
    d_map.clear();
    *d_statnumentries=0;
    return delcount;
  }

  /* ok, the suffix delete plan. We want to be able to delete everything that 
     pertains 'www.powerdns.com' but we also want to be able to delete everything
     in the powerdns.com zone, so: 'powerdns.com' and '*.powerdns.com'.

     However, we do NOT want to delete 'usepowerdns.com!, nor 'powerdnsiscool.com'

     So, at first shot, store in reverse label order:

     'be.someotherdomain'
     'com.powerdns'
     'com.powerdns.images'
     'com.powerdns.www'
     'com.powerdnsiscool'
     'com.usepowerdns.www'

     If we get a request to remove 'everything above powerdns.com', we do a search for 'com.powerdns' which is guaranteed to come first (it is shortest!)
     Then we delete everything that is either equal to 'com.powerdns' or begins with 'com.powerdns.' This trailing dot saves us 
     from deleting 'com.powerdnsiscool'.

     We can stop the process once we reach something that doesn't match.

     Ok - fine so far, except it doesn't work! Let's say there *is* no 'com.powerdns' in cache!

     In that case our request doesn't find anything.. now what.
     lower_bound to the rescue! It finds the place where 'com.powerdns' *would* be.
     
     Ok - next step, can we get away with simply reversing the string?

     'moc.sndrewop'
     'moc.sndrewop.segami'
     'moc.sndrewop.www'
     'moc.loocsidnsrewop'
     'moc.dnsrewopesu.www'

     Ok - next step, can we get away with only reversing the comparison?

     'powerdns.com'
     'images.powerdns.com'
     '   www.powerdns.com'
     'powerdnsiscool.com'
     'www.userpowerdns.com'

  */
  for(vector<string>::const_iterator match = ++matches.begin(); match != matches.end() ; ++match) {
    if(ends_with(*match, "$")) {
      string suffix(*match);
      suffix.resize(suffix.size()-1);

      //    cerr<<"Begin dump!"<<endl;
      cmap_t::const_iterator iter = d_map.lower_bound(tie(suffix));
      cmap_t::const_iterator start=iter;
      string dotsuffix = "."+suffix;

      for(; iter != d_map.end(); ++iter) {
	if(!iequals(iter->qname, suffix) && !iends_with(iter->qname, dotsuffix)) {
	  //	cerr<<"Stopping!"<<endl;
	  break;
	}
	//	cerr<<"Will erase '"<<iter->qname<<"'\n";

	delcount++;
      }
      //    cerr<<"End dump!"<<endl;
      d_map.erase(start, iter);
    }
    else {
      delcount=d_map.count(tie(*match));
      pair<cmap_t::iterator, cmap_t::iterator> range = d_map.equal_range(tie(*match));
      d_map.erase(range.first, range.second);
    }
  }
  *d_statnumentries=d_map.size();
  return delcount;
}

bool PacketCache::getEntry(const string &qname, const QType& qtype, CacheEntryType cet, string& value, int zoneID, bool meritsRecursion)
{
  TryReadLock l(&d_mut); // take a readlock here
  if(!l.gotIt()) {
    S.inc( "deferred-cache-lookup");
    return false;
  }

  uint16_t qt = qtype.getCode();
  cmap_t::const_iterator i=d_map.find(tie(qname, qt, cet, zoneID, meritsRecursion));
  time_t now=time(0);
  bool ret=(i!=d_map.end() && i->ttd > now);
  if(ret)
    value = i->value;
  
  //  cerr<<"Cache hit: "<<(int)cet<<", "<<ret<<endl;
  
  return ret;
}

map<char,int> PacketCache::getCounts()
{
  ReadLock l(&d_mut);

  map<char,int>ret;
  int recursivePackets=0, nonRecursivePackets=0, queryCacheEntries=0, negQueryCacheEntries=0;

  enum CacheEntryType { PACKETCACHE, QUERYCACHE, NEGCACHE};
  for(cmap_t::const_iterator iter = d_map.begin() ; iter != d_map.end(); ++iter) {
    if(iter->ctype == PACKETCACHE)
      if(iter->meritsRecursion)
	recursivePackets++;
      else
	nonRecursivePackets++;
    else if(iter->ctype == QUERYCACHE)
      queryCacheEntries++;
    else if(iter->ctype == NEGCACHE)
      negQueryCacheEntries++;
  }

  ret['!']=negQueryCacheEntries;
  ret['Q']=queryCacheEntries;
  ret['n']=nonRecursivePackets;
  ret['r']=recursivePackets;
  return ret;
}

int PacketCache::size()
{
  ReadLock l(&d_mut);
  return d_map.size();
}

/** readlock for figuring out which iterators to delete, upgrade to writelock when actually cleaning */
void PacketCache::cleanup()
{
  WriteLock l(&d_mut);

  *d_statnumentries=d_map.size();

  unsigned int maxCached=::arg().asNum("max-cache-entries");
  unsigned int toTrim=0;
  
  unsigned int cacheSize=*d_statnumentries;

  if(maxCached && cacheSize > maxCached) {
    toTrim = cacheSize - maxCached;
  }

  unsigned int lookAt=0;
  // two modes - if toTrim is 0, just look through 10000 records and nuke everything that is expired
  // otherwise, scan first 5*toTrim records, and stop once we've nuked enough
  if(toTrim)
    lookAt=5*toTrim;
  else
    lookAt=cacheSize/10;

  //  cerr<<"cacheSize: "<<cacheSize<<", lookAt: "<<lookAt<<", toTrim: "<<toTrim<<endl;
  time_t now=time(0);

  DLOG(L<<"Starting cache clean"<<endl);
  if(d_map.empty())
    return; // clean

  typedef cmap_t::nth_index<1>::type sequence_t;
  sequence_t& sidx=d_map.get<1>();
  unsigned int erased=0;
  for(sequence_t::iterator i=sidx.begin(); i != sidx.end();) {
    if(i->ttd < now) {
      sidx.erase(i++);
      erased++;
    }
    else
      ++i;

    if(toTrim && erased > toTrim)
      break;

  }
  //  cerr<<"erased: "<<erased<<endl;
  *d_statnumentries=d_map.size();
  DLOG(L<<"Done with cache clean"<<endl);
}