I don't understand the follow red code:

static void lld_remove_lost_items(const zbx_vector_ptr_t *items, int lifetime, int lastcheck)
{
char *sql = NULL;
size_t sql_alloc = 0, sql_offset = 0;
zbx_lld_item_t *item;
zbx_vector_uint64_t del_itemids, lc_itemids, ts_itemids;
zbx_vector_uint64_pair_t discovery_itemts;
int i;

zabbix_log(LOG_LEVEL_DEBUG, "In %s()", _func_);

if (0 == items->values_num)
goto out;

zbx_vector_uint64_create(&del_itemids);
zbx_vector_uint64_create(&lc_itemids);
zbx_vector_uint64_create(&ts_itemids);
zbx_vector_uint64_pair_create(&discovery_itemts);

for (i = 0; i < items->values_num; i++)
{
item = (zbx_lld_item_t *)items->values[i];

if (0 == item->itemid)
continue;
 

###flags =0 is the plain item，ZBX_FLAG_LLD_ITEM_DISCOVERED is 1，so only when flags =0，the if condition is true and execute the if code？
if (0 == (item->flags & ZBX_FLAG_LLD_ITEM_DISCOVERED))
{
int ts_delete = lld_end_of_life(item->lastcheck, lifetime);

if (lastcheck > ts_delete)
{
zbx_vector_uint64_append(&del_itemids, item->itemid);
{color:#de350b}}*
*else if (item->ts_delete != ts_delete)
{
zbx_uint64_pair_t itemts;

itemts.first = item->itemid;
itemts.second = ts_delete;
zbx_vector_uint64_pair_append(&discovery_itemts, itemts);
{color:#de350b}}*
*}
else

{ zbx_vector_uint64_append(&lc_itemids, item->itemid); if (0 != item->ts_delete) zbx_vector_uint64_append(&ts_itemids, item->itemid); }

}

if (0 == discovery_itemts.values_num && 0 == lc_itemids.values_num && 0 == ts_itemids.values_num &&
0 == del_itemids.values_num)

{ goto clean; }

/* update item discovery table */

DBbegin();

DBbegin_multiple_update(&sql, &sql_alloc, &sql_offset);

for (i = 0; i < discovery_itemts.values_num; i++)

{ zbx_snprintf_alloc(&sql, &sql_alloc, &sql_offset, "update item_discovery" " set ts_delete=%d" " where itemid=" ZBX_FS_UI64 ";\n", (int)discovery_itemts.values[i].second, discovery_itemts.values[i].first); DBexecute_overflowed_sql(&sql, &sql_alloc, &sql_offset); }

if (0 != lc_itemids.values_num)

{ zbx_snprintf_alloc(&sql, &sql_alloc, &sql_offset, "update item_discovery set lastcheck=%d where", lastcheck); DBadd_condition_alloc(&sql, &sql_alloc, &sql_offset, "itemid", lc_itemids.values, lc_itemids.values_num); zbx_strcpy_alloc(&sql, &sql_alloc, &sql_offset, ";\n"); DBexecute_overflowed_sql(&sql, &sql_alloc, &sql_offset); }

if (0 != ts_itemids.values_num)

{ zbx_strcpy_alloc(&sql, &sql_alloc, &sql_offset, "update item_discovery set ts_delete=0 where"); DBadd_condition_alloc(&sql, &sql_alloc, &sql_offset, "itemid", ts_itemids.values, ts_itemids.values_num); zbx_strcpy_alloc(&sql, &sql_alloc, &sql_offset, ";\n"); DBexecute_overflowed_sql(&sql, &sql_alloc, &sql_offset); }

DBend_multiple_update(&sql, &sql_alloc, &sql_offset);

if (16 < sql_offset) /* in ORACLE always present begin..end; */
DBexecute("%s", sql);

zbx_free(sql);

/* remove 'lost' items */
if (0 != del_itemids.values_num)

{ zbx_vector_uint64_sort(&del_itemids, ZBX_DEFAULT_UINT64_COMPARE_FUNC); DBdelete_items(&del_itemids); }

DBcommit();
clean:
zbx_vector_uint64_pair_destroy(&discovery_itemts);
zbx_vector_uint64_destroy(&ts_itemids);
zbx_vector_uint64_destroy(&lc_itemids);
zbx_vector_uint64_destroy(&del_itemids);
out:
zabbix_log(LOG_LEVEL_DEBUG, "End of %s()", _func_);
}