/*
 * contrib/spi/insert_username.c
 *
 * insert user name in response to a trigger
 * usage:  insert_username (column_name)
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/rel.h"

PG_MODULE_MAGIC_EXT(
     .name = "insert_username",
     .version = PG_VERSION
);

PG_FUNCTION_INFO_V1(insert_username);

Datum
insert_username(PG_FUNCTION_ARGS)
{
 TriggerData *trigdata = (TriggerData *) fcinfo->context;
 Trigger    *trigger;  /* to get trigger name */
 int   nargs;   /* # of arguments */
 Datum  newval;   /* new value of column */
 bool  newnull;  /* null flag */
 char   **args;   /* arguments */
 char    *relname;  /* triggered relation name */
 Relation rel;   /* triggered relation */
 HeapTuple rettuple = NULL;
 TupleDesc tupdesc;  /* tuple description */
 int   attnum;

 /* sanity checks from autoinc.c */
 if (!CALLED_AS_TRIGGER(fcinfo))
  /* internal error */
  elog(ERROR, "insert_username: not fired by trigger manager");
 if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
  /* internal error */
  elog(ERROR, "insert_username: must be fired for row");
 if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
  /* internal error */
  elog(ERROR, "insert_username: must be fired before event");

 if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
  rettuple = trigdata->tg_trigtuple;
 else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
  rettuple = trigdata->tg_newtuple;
 else
  /* internal error */
  elog(ERROR, "insert_username: cannot process DELETE events");

 rel = trigdata->tg_relation;
 relname = SPI_getrelname(rel);

 trigger = trigdata->tg_trigger;

 nargs = trigger->tgnargs;
 if (nargs != 1)
  /* internal error */
  elog(ERROR, "insert_username (%s): one argument was expected", relname);

 args = trigger->tgargs;
 tupdesc = rel->rd_att;

 attnum = SPI_fnumber(tupdesc, args[0]);

 if (attnum <= 0)
  ereport(ERROR,
    (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
     errmsg("\"%s\" has no attribute \"%s\"", relname, args[0])));

 if (SPI_gettypeid(tupdesc, attnum) != TEXTOID)
  ereport(ERROR,
    (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
     errmsg("attribute \"%s\" of \"%s\" must be type TEXT",
      args[0], relname)));

 /* create fields containing name */
 newval = CStringGetTextDatum(GetUserNameFromId(GetUserId(), false));
 newnull = false;

 /* construct new tuple */
 rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc,
           1, &attnum, &newval, &newnull);

 pfree(relname);

 return PointerGetDatum(rettuple);
}