[Garkin]

You can use a few different way how to detect change in equiped items. First is event EVENT_INVENTORY_SINGLE_SLOT_UPDATE, second is registering for callback "WornSlotUpdate" - CALLBACK_MANAGER:RegisterCallback("WornSlotUpdate", function(slotControl) end), third is hooking EquipItem(...) function and maybe you can find some other ways.

I'd try to use event first:

local function OnSlotUpdate(eventCode, bagId, slotId, isNewItem, itemSoundCategory, updateReason)
    if bagId == BAG_WORN and updateReason == INVENTORY_UPDATE_REASON_DEFAULT then
        d("Equipped item changed.")
    end
end
EVENT_MANAGER:RegisterForEvent("MyAddon", EVENT_INVENTORY_SINGLE_SLOT_UPDATE, OnSlotUpdate)

I'm not really sure if the code above will work, I have typed it off the top of my head. What I'm not sure about is if this will be enough or if you will have to store item instance IDs first - GetItemInstanceId(bagId, slotIndex) - and then compare if the item was actually changed.

If you want to use callback, it will look like this:

local slotNames = {
    [EQUIP_SLOT_HEAD] = "Head",
    [EQUIP_SLOT_NECK] = "Neck",
    [EQUIP_SLOT_CHEST]= "Chest",
    [EQUIP_SLOT_SHOULDERS] = "Shoulders",
    [EQUIP_SLOT_MAIN_HAND] = "Main Hand",
    [EQUIP_SLOT_OFF_HAND] = "Off Hand",
    [EQUIP_SLOT_WAIST] = "Waist",
    [EQUIP_SLOT_LEGS] = "Legs",
    [EQUIP_SLOT_FEET]= "Feet",
    [EQUIP_SLOT_COSTUME] = "Costume",
    [EQUIP_SLOT_RING1] = "Ring 1",
    [EQUIP_SLOT_RING2] = "Ring 2",
    [EQUIP_SLOT_HAND] = "Gloves",
    [EQUIP_SLOT_BACKUP_MAIN] = "Backup Main Hand",
    [EQUIP_SLOT_BACKUP_OFF] = "Backup Off Hand",
}
 
 
local function WornSlotUpdate(slotControl)
    d("Equip slot changed: " .. slotNames[slotControl.slotIndex])
end
 
CALLBACK_MANAGER:RegisterCallback("WornSlotUpdate", WornSlotUpdate)