/*-------------------------------------------------------------------------
 *
 * ginlogic.c
 *	  routines for performing binary- and ternary-logic consistent checks.
 *
 * A GIN operator class can provide a boolean or ternary consistent
 * function, or both.  This file provides both boolean and ternary
 * interfaces to the rest of the GIN code, even if only one of them is
 * implemented by the opclass.
 *
 * Providing a boolean interface when the opclass implements only the
 * ternary function is straightforward - just call the ternary function
 * with the check-array as is, and map the GIN_TRUE, GIN_FALSE, GIN_MAYBE
 * return codes to TRUE, FALSE and TRUE+recheck, respectively.  Providing
 * a ternary interface when the opclass only implements a boolean function
 * is implemented by calling the boolean function many times, with all the
 * MAYBE arguments set to all combinations of TRUE and FALSE (up to a
 * certain number of MAYBE arguments).
 *
 * (A boolean function is enough to determine if an item matches, but a
 * GIN scan can apply various optimizations if it can determine that an
 * item matches or doesn't match, even if it doesn't know if some of the
 * keys are present or not.  That's what the ternary consistent function
 * is used for.)
 *
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *			src/backend/access/gin/ginlogic.c
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/gin_private.h"
#include "access/reloptions.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "storage/indexfsm.h"
#include "storage/lmgr.h"


/*
 * Maximum number of MAYBE inputs that shimTriConsistentFn will try to
 * resolve by calling all combinations.
 */
#define MAX_MAYBE_ENTRIES	4

/*
 * Dummy consistent functions for an EVERYTHING key.  Just claim it matches.
 */
static bool
trueConsistentFn(GinScanKey key)
{
	key->recheckCurItem = false;
	return true;
}
static GinTernaryValue
trueTriConsistentFn(GinScanKey key)
{
	return GIN_TRUE;
}

/*
 * A helper function for calling a regular, binary logic, consistent function.
 */
static bool
directBoolConsistentFn(GinScanKey key)
{
	/*
	 * Initialize recheckCurItem in case the consistentFn doesn't know it
	 * should set it.  The safe assumption in that case is to force recheck.
	 */
	key->recheckCurItem = true;

	return DatumGetBool(FunctionCall8Coll(key->consistentFmgrInfo,
										  key->collation,
										  PointerGetDatum(key->entryRes),
										  UInt16GetDatum(key->strategy),
										  key->query,
										  UInt32GetDatum(key->nuserentries),
										  PointerGetDatum(key->extra_data),
									   PointerGetDatum(&key->recheckCurItem),
										  PointerGetDatum(key->queryValues),
									 PointerGetDatum(key->queryCategories)));
}

/*
 * A helper function for calling a native ternary logic consistent function.
 */
static GinTernaryValue
directTriConsistentFn(GinScanKey key)
{
	return DatumGetGinTernaryValue(FunctionCall7Coll(
												  key->triConsistentFmgrInfo,
													 key->collation,
											  PointerGetDatum(key->entryRes),
											   UInt16GetDatum(key->strategy),
													 key->query,
										   UInt32GetDatum(key->nuserentries),
											PointerGetDatum(key->extra_data),
										   PointerGetDatum(key->queryValues),
									 PointerGetDatum(key->queryCategories)));
}

/*
 * This function implements a binary logic consistency check, using a ternary
 * logic consistent function provided by the opclass. GIN_MAYBE return value
 * is interpreted as true with recheck flag.
 */
static bool
shimBoolConsistentFn(GinScanKey key)
{
	GinTernaryValue result;

	result = DatumGetGinTernaryValue(FunctionCall7Coll(
												  key->triConsistentFmgrInfo,
													   key->collation,
											  PointerGetDatum(key->entryRes),
											   UInt16GetDatum(key->strategy),
													   key->query,
										   UInt32GetDatum(key->nuserentries),
											PointerGetDatum(key->extra_data),
										   PointerGetDatum(key->queryValues),
									 PointerGetDatum(key->queryCategories)));
	if (result == GIN_MAYBE)
	{
		key->recheckCurItem = true;
		return true;
	}
	else
	{
		key->recheckCurItem = false;
		return result;
	}
}

/*
 * This function implements a tri-state consistency check, using a boolean
 * consistent function provided by the opclass.
 *
 * Our strategy is to call consistentFn with MAYBE inputs replaced with every
 * combination of TRUE/FALSE. If consistentFn returns the same value for every
 * combination, that's the overall result. Otherwise, return MAYBE. Testing
 * every combination is O(n^2), so this is only feasible for a small number of
 * MAYBE inputs.
 *
 * NB: This function modifies the key->entryRes array!
 */
static GinTernaryValue
shimTriConsistentFn(GinScanKey key)
{
	int			nmaybe;
	int			maybeEntries[MAX_MAYBE_ENTRIES];
	int			i;
	bool		boolResult;
	bool		recheck = false;
	GinTernaryValue curResult;

	/*
	 * Count how many MAYBE inputs there are, and store their indexes in
	 * maybeEntries. If there are too many MAYBE inputs, it's not feasible to
	 * test all combinations, so give up and return MAYBE.
	 */
	nmaybe = 0;
	for (i = 0; i < key->nentries; i++)
	{
		if (key->entryRes[i] == GIN_MAYBE)
		{
			if (nmaybe >= MAX_MAYBE_ENTRIES)
				return GIN_MAYBE;
			maybeEntries[nmaybe++] = i;
		}
	}

	/*
	 * If none of the inputs were MAYBE, so we can just call consistent
	 * function as is.
	 */
	if (nmaybe == 0)
		return directBoolConsistentFn(key);

	/* First call consistent function with all the maybe-inputs set FALSE */
	for (i = 0; i < nmaybe; i++)
		key->entryRes[maybeEntries[i]] = GIN_FALSE;
	curResult = directBoolConsistentFn(key);

	for (;;)
	{
		/* Twiddle the entries for next combination. */
		for (i = 0; i < nmaybe; i++)
		{
			if (key->entryRes[maybeEntries[i]] == GIN_FALSE)
			{
				key->entryRes[maybeEntries[i]] = GIN_TRUE;
				break;
			}
			else
				key->entryRes[maybeEntries[i]] = GIN_FALSE;
		}
		if (i == nmaybe)
			break;

		boolResult = directBoolConsistentFn(key);
		recheck |= key->recheckCurItem;

		if (curResult != boolResult)
			return GIN_MAYBE;
	}

	/* TRUE with recheck is taken to mean MAYBE */
	if (curResult == GIN_TRUE && recheck)
		curResult = GIN_MAYBE;

	return curResult;
}

/*
 * Set up the implementation of the consistent functions for a scan key.
 */
void
ginInitConsistentFunction(GinState *ginstate, GinScanKey key)
{
	if (key->searchMode == GIN_SEARCH_MODE_EVERYTHING)
	{
		key->boolConsistentFn = trueConsistentFn;
		key->triConsistentFn = trueTriConsistentFn;
	}
	else
	{
		key->consistentFmgrInfo = &ginstate->consistentFn[key->attnum - 1];
		key->triConsistentFmgrInfo = &ginstate->triConsistentFn[key->attnum - 1];
		key->collation = ginstate->supportCollation[key->attnum - 1];

		if (OidIsValid(ginstate->consistentFn[key->attnum - 1].fn_oid))
			key->boolConsistentFn = directBoolConsistentFn;
		else
			key->boolConsistentFn = shimBoolConsistentFn;

		if (OidIsValid(ginstate->triConsistentFn[key->attnum - 1].fn_oid))
			key->triConsistentFn = directTriConsistentFn;
		else
			key->triConsistentFn = shimTriConsistentFn;
	}
}
