// 
// Query.cc
//
// Query: (abstract) a parsed, 'executable' digger database query
//        a query tree is formed by leaf objects (ExactWordQuery) and
//        node objects (OperatorQuery) derived from this class.
//        Query execution results are returned as ResultList objects.
//        Query evaluation is cached. Cache policy is delegated to the
//        QueryCache class family.
// 
// Part of the ht://Dig package   <http://www.htdig.org/>
// Copyright (c) 1995-2000 The ht://Dig Group
// For copyright details, see the file COPYING in your distribution
// or the GNU Public License version 2 or later
// <http://www.gnu.org/copyleft/gpl.html>
//
// $Id: Query.cc,v 1.1.2.1 2000/09/12 14:58:55 qss Exp $
//

#include "Query.h"
#include "VolatileCache.h"

//
// the in-memory query result cache. the default instance is
// defined static so its destructor is called at program exit
//
VolatileCache theDefaultCache;

QueryCache *
Query::cache = &theDefaultCache;

extern int debug;

//
// destructor
//
Query::~Query()
{
}

//
// return a ResultList with the query results
// results are initially fetched from the cache
// if not cached, the query is evaluated
// Weight of the results is adjusted at each invocation, as
// the same result list may be shared by different queries
// but different weights may be assigned to the word
//
//
ResultList *
Query::GetResults()
{
	ResultList *result = 0;

	// try to find in cache before trying eval
	String signature;
	if(cache)
	{
		signature = GetSignature();
		result = cache->Lookup(signature);
	}

	// no cache or not in cache, evaluate
	if(!result)
	{
		if(debug) cerr << "EVAL: " << signature << endl;
		result = Evaluate();

		if(cache)
		{
			cache->Add(signature, result);
		}
	}

	// adjust if something found/returned 
	if(result)
	{
		if(result->Count())
		{
			AdjustWeight(*result);
		}
		else if(!result->IsIgnore())
		{
			result = 0;
		}
	}
	return result;
}