Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
When an attack is declared involving a Fusion Monster you control and an opponent's monster: That monster you control gains ATK equal to the ATK of the opponent's monster, until the end of the Damage Step. You can only activate 1 "Battle Fusion" per turn.
--決闘融合－バトル・フュージョン
--Battle Fusion
local s,id=GetID()
function s.initial_effect(c)
	--Activate
	local e1=Effect.CreateEffect(c)
	e1:SetCategory(CATEGORY_ATKCHANGE)
	e1:SetType(EFFECT_TYPE_ACTIVATE)
	e1:SetCode(EVENT_ATTACK_ANNOUNCE)
	e1:SetCountLimit(1,id,EFFECT_COUNT_CODE_OATH)
	e1:SetCondition(s.condition)
	e1:SetOperation(s.activate)
	c:RegisterEffect(e1)
end
function s.condition(e,tp,eg,ep,ev,re,r,rp)
	local a=Duel.GetAttacker()
	local at=Duel.GetAttackTarget()
	return at and ((a:IsControler(tp) and a:IsType(TYPE_FUSION))
		or (at:IsControler(tp) and at:IsFaceup() and at:IsType(TYPE_FUSION)))
end
function s.activate(e,tp,eg,ep,ev,re,r,rp)
	local a=Duel.GetAttacker()
	local at=Duel.GetAttackTarget()
	if a:IsControler(1-tp) then a,at=at,a end
	if not a:IsRelateToBattle() or a:IsFacedown() or not at:IsRelateToBattle() or at:IsFacedown() then return end
	local e1=Effect.CreateEffect(e:GetHandler())
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_UPDATE_ATTACK)
	e1:SetReset(RESET_EVENT|RESETS_STANDARD|RESET_PHASE|PHASE_DAMAGE)
	e1:SetValue(at:GetAttack())
	a:RegisterEffect(e1)
end