If you found the jass systems, why do you need lower quality GUI ones?
because he wants text on his screen to say "sobi mask" or "claws of attack", not 'gftg' and 'fgbg'; he wants to click on an item name and choose a new item by looking at the nice icons with nice tooltips...
jass
can do more than GUI, but not always with less effort...
---
in gui, that would look something like this:
1) you detect "Unit aquires an item" generic event
2) you check for multipart And-condition:
- triggering unit has item of type water
- triggering unit has item of type lemon
- triggering unit has item of type sugar
- triggering unit has item of type lemonade receipe
3) if he has all, remove components and create a new item for him
- item - remove (item of type water) carried by triggering unit
- ...
- hero - create lemonade and give it to triggering unit
4) copy and paste that and edit it to take care of other items...