/*-------------------------------------------------------------------------
 *
 * null.c
 *
 *
 * Copyright (c) 2008-2009, PostgreSQL Global Developent Group
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/contrib/auto_explain/auto_explain.c,v 1.4 2009/01/05 13:35:38 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "fmgr.h"

#include "parser/parse_expr.h"



PG_MODULE_MAGIC;


/* Saved hook value  */
static ParseExprTransform_hook_type	prev_transformExpr = NULL;

void	_PG_init(void);
void	_PG_fini(void);

static Node * transformEmptyStr(ParseState *pstate, Node *expr);

/*
 * Module load callback
 */
void
_PG_init(void)
{
	/* Install hooks. */
	prev_transformExpr = ParseExprTransform_hook;
	ParseExprTransform_hook = transformEmptyStr;
}

/*
 * Module unload callback
 */
void
_PG_fini(void)
{
	/* Uninstall hooks. */
	ParseExprTransform_hook = prev_transformExpr;
}


/*
 * Decode transform hook. When I diagnose decode func call, I transform it.
 */
Node *
transformEmptyStr(ParseState *pstate, Node *expr)
{
	A_Const *c = (A_Const *) expr;

	if (c->val.type == T_String && *c->val.val.str == '\0')
	{
		A_Const *n = makeNode(A_Const);
		n->val.type = T_Null;
		n->location = c->location;
		expr = (Node *) n;
	}

	if (prev_transformExpr)
		return prev_transformExpr(pstate, expr);
	else
		return standard_transformExpr(pstate, expr);
}