/* -------------------------------------------------------------------------
 *
 * trigfuncs.c
 *	  Builtin functions for useful trigger support.
 *
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/utils/adt/trigfuncs.c
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"
#include "knl/knl_variable.h"

#include "commands/trigger.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/rel_gs.h"

/*
 * suppress_redundant_updates_trigger
 *
 * This trigger function will inhibit an update from being done
 * if the OLD and NEW records are identical.
 */
Datum suppress_redundant_updates_trigger(PG_FUNCTION_ARGS)
{
    TriggerData* trigdata = (TriggerData*)fcinfo->context;
    HeapTuple newtuple, oldtuple, rettuple;
    HeapTupleHeader newheader, oldheader;

    /* make sure it's called as a trigger */
    if (!CALLED_AS_TRIGGER(fcinfo))
        ereport(ERROR,
            (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                errmsg("suppress_redundant_updates_trigger: must be called as trigger")));

    /* and that it's called on update */
    if (!TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
        ereport(ERROR,
            (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                errmsg("suppress_redundant_updates_trigger: must be called on update")));

    /* and that it's called before update */
    if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
        ereport(ERROR,
            (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                errmsg("suppress_redundant_updates_trigger: must be called before update")));

    /* and that it's called for each row */
    if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
        ereport(ERROR,
            (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                errmsg("suppress_redundant_updates_trigger: must be called for each row")));

    /* get tuple data, set default result */
    rettuple = newtuple = trigdata->tg_newtuple;
    oldtuple = trigdata->tg_trigtuple;

    newheader = newtuple->t_data;
    oldheader = oldtuple->t_data;

    /*
     * We are called before the OID, if any, has been transcribed from the old
     * tuple to the new (in heap_update).  To avoid a bogus compare failure,
     * copy the OID now.  But check that someone didn't already put another
     * OID value into newtuple.  (That's not actually possible at present, but
     * maybe someday.)
     */
    if (trigdata->tg_relation->rd_rel->relhasoids && !OidIsValid(HeapTupleHeaderGetOid(newheader)))
        HeapTupleHeaderSetOid(newheader, HeapTupleHeaderGetOid(oldheader));

    /* if the tuple payload is the same ... */
    if (newtuple->t_len == oldtuple->t_len && newheader->t_hoff == oldheader->t_hoff &&
        (HeapTupleHeaderGetNatts(newheader, trigdata->tg_relation->rd_att) ==
            HeapTupleHeaderGetNatts(oldheader, trigdata->tg_relation->rd_att)) &&
        ((newheader->t_infomask & ~HEAP_XACT_MASK) == (oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
        memcmp(((char*)newheader) + offsetof(HeapTupleHeaderData, t_bits),
            ((char*)oldheader) + offsetof(HeapTupleHeaderData, t_bits),
            newtuple->t_len - offsetof(HeapTupleHeaderData, t_bits)) == 0) {
        /* ... then suppress the update */
        rettuple = NULL;
    }

    return PointerGetDatum(rettuple);
}