Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
If this card attacks an opponent's monster, this card gains 400 ATK during the Damage Step only. If this card is attacked by an opponent's monster, this card loses 400 ATK during the Damage Step only.
--暗黒ヴェロキ
--Black Veloci
local s,id=GetID()
function s.initial_effect(c)
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
	e1:SetRange(LOCATION_MZONE)
	e1:SetCode(EFFECT_UPDATE_ATTACK)
	e1:SetCondition(s.condtion)
	e1:SetValue(s.val)
	c:RegisterEffect(e1)
end
function s.condtion(e)
	local ph=Duel.GetCurrentPhase()
	return ph==PHASE_DAMAGE or ph==PHASE_DAMAGE_CAL
end
function s.val(e,c)
	if Duel.GetAttacker()==e:GetHandler() and Duel.GetAttackTarget()~=nil then return 400
	elseif e:GetHandler()==Duel.GetAttackTarget() then return -400
	else return 0 end
end