/*-------------------------------------------------------------------------
 *
 * giststrat.c--
 *    strategy map data for GiSTs.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    /usr/local/devel/pglite/cvs/src/backend/access/gist/giststrat.c,v 1.4 1995/06/14 00:10:05 jolly Exp
 *
 *-------------------------------------------------------------------------
 */

#include <postgres.h>
 
#include <access/gist.h>
#include <access/istrat.h>

/*
 *  Note:  negate, commute, and negatecommute all assume that operators are
 *	   ordered as follows in the strategy map:
 *
 *	contains, contained-by
 *
 *  The negate, commute, and negatecommute arrays are used by the planner
 *  to plan indexed scans over data that appears in the qualificiation in
 *  a boolean negation, or whose operands appear in the wrong order.  For
 *  example, if the operator "<%" means "contains", and the user says
 *
 *	where not rel.box <% "(10,10,20,20)"::box
 *
 *  the planner can plan an index scan by noting that GiST indices have
 *  an operator in their operator class for negating <%.
 *
 *  Similarly, if the user says something like
 *
 *	where "(10,10,20,20)"::box <% rel.box
 *
 *  the planner can see that the GiST index on rel.box has an operator in
 *  its opclass for commuting <%, and plan the scan using that operator.
 *  This added complexity in the access methods makes the planner a lot easier
 *  to write.
 */

/* if a op b, what operator tells us if (not a op b)? */
static StrategyNumber	GISTNegate[GISTNStrategies] = {
    InvalidStrategy,
    InvalidStrategy,
    InvalidStrategy
    };

/* if a op_1 b, what is the operator op_2 such that b op_2 a? */
static StrategyNumber	GISTCommute[GISTNStrategies] = {
    InvalidStrategy,
    InvalidStrategy,
    InvalidStrategy
    };

/* if a op_1 b, what is the operator op_2 such that (b !op_2 a)? */
static StrategyNumber	GISTNegateCommute[GISTNStrategies] = {
    InvalidStrategy,
    InvalidStrategy,
    InvalidStrategy
    };

/*
 * GiSTs do not currently support TermData (see rtree/rtstrat.c for 
 * discussion of
 * TermData) -- such logic must be encoded in the user's Consistent function.
 */

/*
 *  If you were sufficiently attentive to detail, you would go through
 *  the ExpressionData pain above for every one of the strategies
 *  we defined.  I am not.  Now we declare the StrategyEvaluationData
 *  structure that gets shipped around to help the planner and the access
 *  method decide what sort of scan it should do, based on (a) what the
 *  user asked for, (b) what operators are defined for a particular opclass,
 *  and (c) the reams of information we supplied above.
 *
 *  The idea of all of this initialized data is to make life easier on the
 *  user when he defines a new operator class to use this access method.
 *  By filling in all the data, we let him get away with leaving holes in his
 *  operator class, and still let him use the index.  The added complexity
 *  in the access methods just isn't worth the trouble, though.
 */

static StrategyEvaluationData GISTEvaluationData = {
    GISTNStrategies,				/* # of strategies */
    (StrategyTransformMap) GISTNegate,	/* how to do (not qual) */
    (StrategyTransformMap) GISTCommute,	/* how to swap operands */
    (StrategyTransformMap) GISTNegateCommute,	/* how to do both */
    { NULL }
};

StrategyNumber
RelationGetGISTStrategy(Relation r,
		      AttrNumber attnum,
		      RegProcedure proc)
{
    return (RelationGetStrategy(r, attnum, &GISTEvaluationData, proc));
}

#ifdef NOT_USED
bool
RelationInvokeGISTStrategy(Relation r,
			 AttrNumber attnum,
			 StrategyNumber s,
			 Datum left,
			 Datum right)
{
    return (RelationInvokeStrategy(r, &GISTEvaluationData, attnum, s,
				   left, right));
}
#endif
