Output modifier hassle

--[[+fi.category]]--
[[[[+fi.category:eq=`Day`:then=`$chunk.day`:else=`$chunk.night`]]]]

[[[[!+fi.category:eq=`Day`:then=`!$chunk.day`:else=`!$chunk.night`]]]]

--[[+fi.category]]--

[[[[!getReqParam:eq=`Day`:then=`!$chunk.day`:else=`!$chunk.night`? &name=`category`]]]]

[[!DayNight? &cat=`[[+fi.category]]`]]

<?php
/* DayNight snippet */
$cat = $modx->getOption('cat', $scriptProperties, '';
if (empty($cat)) {
   return 'Category not set';
}
$chunk = ($cat == 'Day')? 'chunk.day' : 'chunk.night;
return $modx->getChunk($chunk);

<?php
/* DayNight snippet */
return $modx->getChunk($modx->getOption('cat', $scriptProperties));