minecraft-kajetans-core-mod/src/main/resources/class_transformer/container.js

var transformerName = "Dedicated Server Transformer";
var ASMAPI = Java.type('net.minecraftforge.coremod.api.ASMAPI');
var Opcodes = Java.type('org.objectweb.asm.Opcodes');
var VarInsnNode = Java.type("org.objectweb.asm.tree.VarInsnNode");
var MethodInsnNode = Java.type("org.objectweb.asm.tree.MethodInsnNode");
var LineNumberNode = Java.type("org.objectweb.asm.tree.LineNumberNode");
var FieldInsnNode = Java.type("org.objectweb.asm.tree.FieldInsnNode");
var JumpInsnNode = Java.type("org.objectweb.asm.tree.JumpInsnNode");
var LabelNode = Java.type("org.objectweb.asm.tree.LabelNode");
var InsnNode = Java.type("org.objectweb.asm.tree.InsnNode");

function initializeCoreMod() {
    return {
        transformerName: {
            'target': {
                'type': 'CLASS',
                'name': 'net.minecraft.inventory.container.Container'
            },
            'transformer': function (classNode) {
                var methods = classNode.methods;

                var targetMethodName = ASMAPI.mapMethod("func_184996_a"); // slotClick
                var targetMethodDesc = "(IILnet/minecraft/inventory/container/ClickType;Lnet/minecraft/entity/player/PlayerEntity;)Lnet/minecraft/item/ItemStack;";

                for (var i in methods) {
                    var method = methods[i];
                    if (method.name.equals(targetMethodName) && method.desc.equals(targetMethodDesc)) {
                        transform(method);
                        break;
                    }
                }
                return classNode;
            }
        }
    };
}

function transform(method) {
    var instrList = method.instructions;
    instrList.insert(instrList.get(0), new VarInsnNode(Opcodes.ALOAD, 0));
    instrList.insert(instrList.get(1), new VarInsnNode(Opcodes.ILOAD, 1));
    instrList.insert(instrList.get(2), new VarInsnNode(Opcodes.ILOAD, 2));
    instrList.insert(instrList.get(3), new VarInsnNode(Opcodes.ALOAD, 3));
    instrList.insert(instrList.get(4), new VarInsnNode(Opcodes.ALOAD, 4));
    instrList.insert(instrList.get(5), new MethodInsnNode(Opcodes.INVOKESTATIC, "me/kcm/Hooks",
        "onSlotClick",
        "(Lnet/minecraft/inventory/container/Container;IILnet/minecraft/inventory/container/ClickType;Lnet/minecraft/entity/player/PlayerEntity;)Z", false));
    var label = new LabelNode();
    instrList.insert(instrList.get(6), new JumpInsnNode(Opcodes.IFEQ, label));
    instrList.insert(instrList.get(7), new FieldInsnNode(Opcodes.GETSTATIC, "net/minecraft/item/ItemStack",
        "EMPTY",
        "Lnet/minecraft/item/ItemStack;"));
    instrList.insert(instrList.get(8), new InsnNode(Opcodes.ARETURN));
    instrList.insert(instrList.get(9), label);
}