/*-------------------------------------------------------------------------
 *
 * rewriteRemove.c--
 *    routines for removing rewrite rules
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteRemove.c,v 1.2 1996/11/03 04:51:51 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/skey.h"
#include "catalog/pg_rewrite.h"
#include "catalog/catname.h"	/* for RewriteRelationName */
#include "utils/syscache.h"
#include "utils/elog.h"		/* for elog stuff */
#include "utils/palloc.h"
#include "utils/tqual.h"	/* 'NowTimeQual' defined here.. */
#include "access/heapam.h"	/* heap AM calls defined here */
#include "fmgr.h"		/* for CHAR_16_EQ */

#include "rewrite/rewriteRemove.h"	/* where the decls go */
#include "rewrite/rewriteSupport.h"

/*-----------------------------------------------------------------------
 * RewriteGetRuleEventRel
 *-----------------------------------------------------------------------
 */
char*
RewriteGetRuleEventRel(char *rulename)
{
    HeapTuple htp;
    Oid eventrel;
    
    htp = SearchSysCacheTuple(REWRITENAME, PointerGetDatum(rulename),
			      0,0,0);
    if (!HeapTupleIsValid(htp))
	elog(WARN, "RewriteGetRuleEventRel: rule \"%s\" not found",
	     rulename);
    eventrel = ((Form_pg_rewrite) GETSTRUCT(htp))->ev_class;
    htp = SearchSysCacheTuple(RELOID, PointerGetDatum(eventrel), 
			      0,0,0);
    if (!HeapTupleIsValid(htp))
	elog(WARN, "RewriteGetRuleEventRel: class %d not found",
	     eventrel);
    return ((Form_pg_class) GETSTRUCT(htp))->relname.data;
}

/* ----------------------------------------------------------------
 *
 * RemoveRewriteRule
 *
 * Delete a rule given its rulename.
 *
 * There are three steps.
 *   1) Find the corresponding tuple in 'pg_rewrite' relation.
 *      Find the rule Id (i.e. the Oid of the tuple) and finally delete
 *      the tuple.
 *   3) Delete the locks from the 'pg_class' relation.
 *
 *
 * ----------------------------------------------------------------
 */
void
RemoveRewriteRule(char *ruleName)
{
    Relation RewriteRelation	= NULL;
    HeapScanDesc scanDesc	= NULL;
    ScanKeyData scanKeyData;
    HeapTuple tuple		= NULL;
    Oid ruleId			= (Oid)0;
    Oid eventRelationOid	= (Oid)NULL;
    Datum eventRelationOidDatum	= (Datum)NULL;
    Buffer buffer		= (Buffer)NULL;
    bool isNull		= false;

    /*
     * Open the pg_rewrite relation. 
     */
    RewriteRelation = heap_openr(RewriteRelationName);
    
    /*
     * Scan the RuleRelation ('pg_rewrite') until we find a tuple
     */
    ScanKeyEntryInitialize(&scanKeyData, 0, Anum_pg_rewrite_rulename,
			   F_CHAR16EQ, NameGetDatum(ruleName));
    scanDesc = heap_beginscan(RewriteRelation,
			      0, NowTimeQual, 1, &scanKeyData);
    
    tuple = heap_getnext(scanDesc, 0, (Buffer *)NULL);
    
    /*
     * complain if no rule with such name existed
     */
    if (!HeapTupleIsValid(tuple)) {
	heap_close(RewriteRelation);
	elog(WARN, "No rule with name = '%s' was found.\n", ruleName);
    }
    
    /*
     * Store the OID of the rule (i.e. the tuple's OID)
     * and the event relation's OID
     */
    ruleId = tuple->t_oid;
    eventRelationOidDatum =
	PointerGetDatum(heap_getattr(tuple,
				     buffer,
				     Anum_pg_rewrite_ev_class,
		     RelationGetTupleDescriptor(RewriteRelation),
				     &isNull));
    if (isNull) {
	/* XXX strange!!! */
	elog(WARN, "RemoveRewriteRule: null event target relation!");
    }
    eventRelationOid = DatumGetObjectId(eventRelationOidDatum);
    
    /*
     * Now delete the relation level locks from the updated relation.
     * (Make sure we do this before we remove the rule from pg_rewrite.
     * Otherwise, heap_openr on eventRelationOid which reads pg_rwrite
     * for the rules will fail.)
     */
    prs2_deleteFromRelation(eventRelationOid, ruleId);

    /*
     * Now delete the tuple...
     */
    heap_delete(RewriteRelation, &(tuple->t_ctid));
    heap_close(RewriteRelation);
    heap_endscan(scanDesc);
}

/*
 * RelationRemoveRules -
 *    removes all rules associated with the relation when the relation is
 *    being removed.
 */
void
RelationRemoveRules(Oid relid)
{
    Relation RewriteRelation	= NULL;
    HeapScanDesc scanDesc	= NULL;
    ScanKeyData scanKeyData;
    HeapTuple tuple		= NULL;

    /*
     * Open the pg_rewrite relation. 
     */
    RewriteRelation = heap_openr(RewriteRelationName);
    
    /*
     * Scan the RuleRelation ('pg_rewrite') for all the tuples that
     * has the same ev_class as relid (the relation to be removed).
     */
    ScanKeyEntryInitialize(&scanKeyData,
			   0,
			   Anum_pg_rewrite_ev_class,
			   F_OIDEQ,
			   ObjectIdGetDatum(relid));
    scanDesc = heap_beginscan(RewriteRelation,
			      0, NowTimeQual, 1, &scanKeyData);

    for(;;) {
	tuple = heap_getnext(scanDesc, 0, (Buffer *)NULL);
    
	if (!HeapTupleIsValid(tuple)) {
	    break; /* we're done */
	}
    
	/*
	 * delete the tuple...
	 */
	heap_delete(RewriteRelation, &(tuple->t_ctid));
    }

    heap_endscan(scanDesc);
    heap_close(RewriteRelation);
}