Logic to make MC creative inv function correctly

        if (k == 0 || k == 1) { //if left or right click

            int stackSize = 64;
            if (k == 1) { //if right click
                stackSize = 1;
            }

            Slot cslot = super.getSlotAtCoords(i, j);
            if (cslot!=null) { //if they actually clicked a slot

                ItemStack slotstack = cslot.getStack();
                ItemStack pstack = mc.thePlayer.inventory.getItemStack();

                if (slotstack!=null) { //if there is an item in that slot

                    if(pstack==null) { //if the player is not holding an item with the cursor

                        if (cslot.slotNumber>=72&&cslot.slotNumber<=80) { //hotbar slots
                            stackSize = slotstack.stackSize;
                        }
                        ItemStack newstack = new ItemStack(slotstack.itemID, stackSize, slotstack.getItemDamage());
                    mc.thePlayer.inventory.setItemStack(newstack);

                    if (cslot.slotNumber>=72&&cslot.slotNumber<=80) { //hotbar slots
                            cslot.putStack(null);
                        }

                    } else { //if the player is holding an item with the cursor

                        if (cslot.slotNumber>=72&&cslot.slotNumber<=80) { //hotbar slots

                            mc.thePlayer.inventory.setItemStack(slotstack); //switch the held item with the slot item
                            cslot.putStack(pstack);

                            //if they're the same item type and they're stackable and the slot stack isn't already full
                            if (pstack.isItemEqual(cslot.getStack())&&pstack.isStackable()&&cslot.getStack().stackSize<64) {
                                ItemStack cstack = cslot.getStack();

                                if (k == 0) { //if left click
                                    while (cslot.getStack().stackSize<64&&pstack.stackSize>=1) {
                                        pstack.stackSize-=1;
                                        cslot.putStack(new ItemStack(cstack.itemID, cstack.stackSize+1, cstack.getItemDamage()));
                                    }
                                } else { //if right click
                                    pstack.stackSize-=1;
                                    cslot.putStack(new ItemStack(cstack.itemID, cstack.stackSize+1, cstack.getItemDamage()));
                                }
                                if (pstack.stackSize==0) {
                                    mc.thePlayer.inventory.setItemStack(null);
                                }
                            }

                        } else {
                            mc.thePlayer.inventory.setItemStack(null);
                        }
                    }

                } else { //if there is not an item in that slot

                    if (pstack!=null) { //if the player is holding an item with the cursor

                        if (cslot.slotNumber>=72&&cslot.slotNumber<=80) { //if clicked in hotbar slots

                            if (k == 0) { //if left click
                                cslot.putStack(pstack);
                                mc.thePlayer.inventory.setItemStack(null);

                            } else { //if right click
                                cslot.putStack(new ItemStack(pstack.itemID, 1, pstack.getItemDamage()));
                                mc.thePlayer.inventory.setItemStack(new ItemStack(pstack.itemID, pstack.stackSize-1, pstack.getItemDamage()));
                            }

                        } else { //if clicked in item selection area
                            mc.thePlayer.inventory.setItemStack(null);

                        }

                    }
                }
            }
        }