LibClassicDurations

Tracks all whitelisted aura applications and then returns UnitAura-friendly duration, expirationTime pair.

Also can show enemy buff info. That's a completely optional feature with no impact on performance if it's not being used

Usage example 1:

-- Simply get the expiration time and duration

local LibClassicDurations = LibStub("LibClassicDurations")
LibClassicDurations:Register("YourAddon") -- tell library it's being used and should start working

hooksecurefunc("CompactUnitFrame_UtilSetBuff", function(buffFrame, unit, index, filter)
    local name, _, _, _, duration, expirationTime, unitCaster, _, _, spellId = UnitBuff(unit, index, filter);

    local durationNew, expirationTimeNew = LibClassicDurations:GetAuraDurationByUnit(unit, spellId, unitCaster, name)
    if duration == 0 and durationNew then
        duration = durationNew
        expirationTime = expirationTimeNew
    end

    local enabled = expirationTime and expirationTime ~= 0;
    if enabled then
        local startTime = expirationTime - duration;
        CooldownFrame_Set(buffFrame.cooldown, startTime, duration, true);
    else
        CooldownFrame_Clear(buffFrame.cooldown);
    end
end)

Embedding in .pkgmeta

externals:
  Libs/LibClassicDurations: https://repos.curseforge.com/wow/libclassicdurations