[Example] Eluna Item Upgrader

--[[
Config table. Set your UpgradeSpell if this will be used, your token ID,
and what items should be upgradeable and what said item upgrades to.
]]

local ItemUpgrade = {
    UpgradeSpell = 61335, -- Temp spell to test OnCast
    UpgradeToken = 6948, -- Hearthstone, use dummy token
    Upgradeable_Items = {
        -- {OldItemEntry, NewItemEntry},
        {2092, 3296}, -- Worn Dagger, Deadman Dagger
        {3296, 4565}, -- Deadman Dagger, Simple Dagger
    };
};
-- End config table. Do not touch anything below unless you know what you're doing.

function ItemUpgrade.GetUpgradeEntry(original_entry)
    for i = 1, #ItemUpgrade.Upgradeable_Items do
        if ItemUpgrade.Upgradeable_Items[i][1] == original_entry then
            return ItemUpgrade.Upgradeable_Items[i][2];
        end
    end
end

function ItemUpgrade.OnCast(event, player, spell, skipCheck)
    if spell:GetEntry() == ItemUpgrade.UpgradeSpell then
        for i = 1, #ItemUpgrade.Upgradeable_Items do
            if player:HasItem(ItemUpgrade.Upgradeable_Items[i][1]) then
                ItemUpgrade.OnHello(event, player, original_item)
            end
        end
    end
end

function ItemUpgrade.OnHello(event, player, original_item)
    player:GossipClearMenu()

    for i = 1, #ItemUpgrade.Upgradeable_Items do
        if player:HasItem(ItemUpgrade.Upgradeable_Items[i][1]) then
            player:GossipMenuAddItem(0, "Upgrade "..GetItemLink(ItemUpgrade.Upgradeable_Items[i][1]), 0, ItemUpgrade.Upgradeable_Items[i][1], false, "Are you sure you want to upgrade "..GetItemLink(ItemUpgrade.Upgradeable_Items[i][1]).." to "..GetItemLink(ItemUpgrade.Upgradeable_Items[i][2]).."?")
        end
    end

    player:GossipSendMenu(1, player, 100)
end

function ItemUpgrade.OnSelect(event, player, original_item, sender, intid, code)
    local old_entry = intid
    local new_entry = ItemUpgrade.GetUpgradeEntry(old_entry)

    player:GossipComplete()
    -- This automatically removes the old item and adds the new item. This could be replaced
    player:RemoveItem(ItemUpgrade.UpgradeToken, 1)
    player:RemoveItem(old_entry, 1)
    player:AddItem(new_entry, 1)
    -- ie. with player:SendQuestTemplate(questId, activeAccept) -- Sends quest template to player
end

RegisterPlayerEvent(5, ItemUpgrade.OnCast)
RegisterItemGossipEvent(ItemUpgrade.UpgradeToken, 1, ItemUpgrade.OnHello)
RegisterPlayerGossipEvent(100, 2, ItemUpgrade.OnSelect)