Automating server sided GUI-s with packets

[Reun]

Hello guys!
My question is quite complicated and can only be answered with a bit of back story:
I have spent the last months making PLUGINS for minecraft and now I want to move on to mod creation, and first I want to actually break or rather automate one of my plugins purpose.
The plugin is like a villager trading menu, which opens a gui (with a heigth of 6) and if you put 2 iron ingot into the 12th slot, in the 14th slot 1 gold ingot will appear and you can choose either to drag into your inventory. And if you put 64 iron ingots into the 12th slot and you shift click the gold in the 14th slot, 32 gold ingots will be put into your inventory.

What I want is that when I open this gui, the mod (with listener) detects it, sees that the gui's name matches ("trading") and then somehow converts all of the iron in my inventory to gold.

 

Now my questions are:

- (ANSWERED) Can anyone send me a great client sided 1.8.9(or any version) documentation as I first only want to focus on client sided info?

- Is this even possible with mods? From my research I have figured out that this is not achievable in a traditional sense, as moving items in inventories requires mouse inputs that mods cannot create. But anything can be done with controlling the packets that my client sends to the server as those could inform the server that I want to move a stack from slot a->b.

- Have I gone overboard with such a hard task?

Edited December 20, 2020 by Reun

[Reun]

Well then I will use the latest version, with the mod and the plugin.