Modifier Tracker

Tracks enemy purchases and detects debuffs landing on you with caster attribution. Demonstrates on_modifier_added, on_ability_cast, on_item_used, and a per-tick item-purchase diff.

-- Track enemy purchases and detect debuffs with caster attribution

local prev = {}

function on_modifier_added(player, modifier)
    if not player:is_local() then return end
    if not modifier.caster or not modifier.caster:is_enemy() then return end
    local who = modifier.caster:hero_name()
    local name = modifier.name or ""

    if name:find("glitch") then
        toast("CURSED by " .. who .. "!")
    elseif name:find("stunned") then
        toast("STUNNED by " .. who .. "!")
    elseif name:find("sleep") then
        toast("SLEEP by " .. who .. "!")
    end
end

function on_ability_cast(player, ability)
    if player:is_enemy() then
        toast(player:hero_name() .. " cast " .. ability.name
              .. " (" .. string.format("%.0f", ability.cooldown) .. "s)")
    end
end

function on_item_used(player, item)
    if item.name:find("metal_skin") and player:is_enemy() then
        toast(player:hero_name() .. " popped Metal Skin!")
    end
end

function on_tick()
    for _, p in ipairs(get_players()) do
        if not p:is_enemy() then goto next end
        local hero = p:hero_name()
        local cur = {}
        for _, it in ipairs(p:get_items()) do
            cur[it.token] = it.name or "?"
        end
        if prev[hero] then
            for tok, name in pairs(cur) do
                if not prev[hero][tok] then
                    toast(hero .. " bought " .. name)
                end
            end
        end
        prev[hero] = cur
        ::next::
    end
end

What this teaches

• on_modifier_added with caster attribution: modifier.caster is a player object you can call methods on. Always check is_enemy() before reacting to incoming debuffs, otherwise teammates' debuffs to you will trigger your warnings too.
• Substring matching modifier names: engine RTTI strings have prefixes like modifier_glitch_root. string.find matches anywhere in the string.
• on_ability_cast includes cooldown: useful for predicting when an ability is about to come back up.
• on_item_used for self-cast items: Metal Skin's player argument is the user, since the item targets the user themselves.
• Item purchase diff: comparing prev[hero] against the current items each tick catches new buys. Token-keyed so duplicate-name items still register.