/*-------------------------------------------------------------------------
 *
 * tlist.c
 *	  Target list manipulation routines
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.86 2009/04/19 19:46:33 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "utils/lsyscache.h"


/*****************************************************************************
 *		Target list creation and searching utilities
 *****************************************************************************/

/*
 * tlist_member
 *	  Finds the (first) member of the given tlist whose expression is
 *	  equal() to the given expression.  Result is NULL if no such member.
 */
TargetEntry *
tlist_member(Node *node, List *targetlist)
{
	ListCell   *temp;

	foreach(temp, targetlist)
	{
		TargetEntry *tlentry = (TargetEntry *) lfirst(temp);

		if (equal(node, tlentry->expr))
			return tlentry;
	}
	return NULL;
}

/*
 * tlist_member_ignore_relabel
 *	  Same as above, except that we ignore top-level RelabelType nodes
 *	  while checking for a match.  This is needed for some scenarios
 *	  involving binary-compatible sort operations.
 */
TargetEntry *
tlist_member_ignore_relabel(Node *node, List *targetlist)
{
	ListCell   *temp;

	while (node && IsA(node, RelabelType))
		node = (Node *) ((RelabelType *) node)->arg;

	foreach(temp, targetlist)
	{
		TargetEntry *tlentry = (TargetEntry *) lfirst(temp);
		Expr	   *tlexpr = tlentry->expr;

		while (tlexpr && IsA(tlexpr, RelabelType))
			tlexpr = ((RelabelType *) tlexpr)->arg;

		if (equal(node, tlexpr))
			return tlentry;
	}
	return NULL;
}

/*
 * tlist_member_match_var
 *	  Same as above, except that we match the provided Var on the basis
 *	  of varno/varattno/varlevelsup only, rather than using full equal().
 *
 * This is needed in some cases where we can't be sure of an exact typmod
 * match.  It's probably a good idea to check the vartype anyway, but
 * we leave it to the caller to apply any suitable sanity checks.
 */
TargetEntry *
tlist_member_match_var(Var *var, List *targetlist)
{
	ListCell   *temp;

	foreach(temp, targetlist)
	{
		TargetEntry *tlentry = (TargetEntry *) lfirst(temp);
		Var		   *tlvar = (Var *) tlentry->expr;

		if (!tlvar || !IsA(tlvar, Var))
			continue;
		if (var->varno == tlvar->varno &&
			var->varattno == tlvar->varattno &&
			var->varlevelsup == tlvar->varlevelsup)
			return tlentry;
	}
	return NULL;
}

/*
 * flatten_tlist
 *	  Create a target list that only contains unique variables.
 *
 * Note that Vars with varlevelsup > 0 are not included in the output
 * tlist.  We expect that those will eventually be replaced with Params,
 * but that probably has not happened at the time this routine is called.
 *
 * 'tlist' is the current target list
 *
 * Returns the "flattened" new target list.
 *
 * The result is entirely new structure sharing no nodes with the original.
 * Copying the Var nodes is probably overkill, but be safe for now.
 */
List *
flatten_tlist(List *tlist)
{
	List	   *vlist = pull_var_clause((Node *) tlist,
										PVC_INCLUDE_PLACEHOLDERS);
	List	   *new_tlist;

	new_tlist = add_to_flat_tlist(NIL, vlist);
	list_free(vlist);
	return new_tlist;
}

/*
 * add_to_flat_tlist
 *		Add more items to a flattened tlist (if they're not already in it)
 *
 * 'tlist' is the flattened tlist
 * 'exprs' is a list of expressions (usually, but not necessarily, Vars)
 *
 * Returns the extended tlist.
 */
List *
add_to_flat_tlist(List *tlist, List *exprs)
{
	int			next_resno = list_length(tlist) + 1;
	ListCell   *lc;

	foreach(lc, exprs)
	{
		Node	   *expr = (Node *) lfirst(lc);

		if (!tlist_member(expr, tlist))
		{
			TargetEntry *tle;

			tle = makeTargetEntry(copyObject(expr),		/* copy needed?? */
								  next_resno++,
								  NULL,
								  false);
			tlist = lappend(tlist, tle);
		}
	}
	return tlist;
}


/*
 * get_tlist_exprs
 *		Get just the expression subtrees of a tlist
 *
 * Resjunk columns are ignored unless includeJunk is true
 */
List *
get_tlist_exprs(List *tlist, bool includeJunk)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, tlist)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		if (tle->resjunk && !includeJunk)
			continue;

		result = lappend(result, tle->expr);
	}
	return result;
}


/*
 * Does tlist have same output datatypes as listed in colTypes?
 *
 * Resjunk columns are ignored if junkOK is true; otherwise presence of
 * a resjunk column will always cause a 'false' result.
 *
 * Note: currently no callers care about comparing typmods.
 */
bool
tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK)
{
	ListCell   *l;
	ListCell   *curColType = list_head(colTypes);

	foreach(l, tlist)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		if (tle->resjunk)
		{
			if (!junkOK)
				return false;
		}
		else
		{
			if (curColType == NULL)
				return false;	/* tlist longer than colTypes */
			if (exprType((Node *) tle->expr) != lfirst_oid(curColType))
				return false;
			curColType = lnext(curColType);
		}
	}
	if (curColType != NULL)
		return false;			/* tlist shorter than colTypes */
	return true;
}


/*
 * get_sortgroupref_tle
 *		Find the targetlist entry matching the given SortGroupRef index,
 *		and return it.
 */
TargetEntry *
get_sortgroupref_tle(Index sortref, List *targetList)
{
	ListCell   *l;

	foreach(l, targetList)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		if (tle->ressortgroupref == sortref)
			return tle;
	}

	elog(ERROR, "ORDER/GROUP BY expression not found in targetlist");
	return NULL;				/* keep compiler quiet */
}

/*
 * get_sortgroupclause_tle
 *		Find the targetlist entry matching the given SortGroupClause
 *		by ressortgroupref, and return it.
 */
TargetEntry *
get_sortgroupclause_tle(SortGroupClause *sgClause,
						List *targetList)
{
	return get_sortgroupref_tle(sgClause->tleSortGroupRef, targetList);
}

/*
 * get_sortgroupclause_expr
 *		Find the targetlist entry matching the given SortGroupClause
 *		by ressortgroupref, and return its expression.
 */
Node *
get_sortgroupclause_expr(SortGroupClause *sgClause, List *targetList)
{
	TargetEntry *tle = get_sortgroupclause_tle(sgClause, targetList);

	return (Node *) tle->expr;
}

/*
 * get_sortgrouplist_exprs
 *		Given a list of SortGroupClauses, build a list
 *		of the referenced targetlist expressions.
 */
List *
get_sortgrouplist_exprs(List *sgClauses, List *targetList)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, sgClauses)
	{
		SortGroupClause *sortcl = (SortGroupClause *) lfirst(l);
		Node	   *sortexpr;

		sortexpr = get_sortgroupclause_expr(sortcl, targetList);
		result = lappend(result, sortexpr);
	}
	return result;
}


/*****************************************************************************
 *		Functions to extract data from a list of SortGroupClauses
 *
 * These don't really belong in tlist.c, but they are sort of related to the
 * functions just above, and they don't seem to deserve their own file.
 *****************************************************************************/

/*
 * extract_grouping_ops - make an array of the equality operator OIDs
 *		for a SortGroupClause list
 */
Oid *
extract_grouping_ops(List *groupClause)
{
	int			numCols = list_length(groupClause);
	int			colno = 0;
	Oid		   *groupOperators;
	ListCell   *glitem;

	groupOperators = (Oid *) palloc(sizeof(Oid) * numCols);

	foreach(glitem, groupClause)
	{
		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);

		groupOperators[colno] = groupcl->eqop;
		Assert(OidIsValid(groupOperators[colno]));
		colno++;
	}

	return groupOperators;
}

/*
 * extract_grouping_cols - make an array of the grouping column resnos
 *		for a SortGroupClause list
 */
AttrNumber *
extract_grouping_cols(List *groupClause, List *tlist)
{
	AttrNumber *grpColIdx;
	int			numCols = list_length(groupClause);
	int			colno = 0;
	ListCell   *glitem;

	grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);

	foreach(glitem, groupClause)
	{
		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);
		TargetEntry *tle = get_sortgroupclause_tle(groupcl, tlist);

		grpColIdx[colno++] = tle->resno;
	}

	return grpColIdx;
}

/*
 * grouping_is_sortable - is it possible to implement grouping list by sorting?
 *
 * This is easy since the parser will have included a sortop if one exists.
 */
bool
grouping_is_sortable(List *groupClause)
{
	ListCell   *glitem;

	foreach(glitem, groupClause)
	{
		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);

		if (!OidIsValid(groupcl->sortop))
			return false;
	}
	return true;
}

/*
 * grouping_is_hashable - is it possible to implement grouping list by hashing?
 *
 * We assume hashing is OK if the equality operators are marked oprcanhash.
 * (If there isn't actually a supporting hash function, the executor will
 * complain at runtime; but this is a misdeclaration of the operator, not
 * a system bug.)
 */
bool
grouping_is_hashable(List *groupClause)
{
	ListCell   *glitem;

	foreach(glitem, groupClause)
	{
		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);

		if (!op_hashjoinable(groupcl->eqop))
			return false;
	}
	return true;
}
