Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
If you control only 1 face-up monster: Target that monster; until the end of this turn, it gains ATK equal to the ATK of the monster your opponent currently controls with the lowest ATK (your choice, if tied).
--不屈の闘志
--Unbreakable Spirit
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:SetProperty(EFFECT_FLAG_CARD_TARGET+EFFECT_FLAG_DAMAGE_STEP)
	e1:SetCode(EVENT_FREE_CHAIN)
	e1:SetHintTiming(TIMING_DAMAGE_STEP)
	e1:SetCondition(s.condition)
	e1:SetTarget(s.target)
	e1:SetOperation(s.activate)
	c:RegisterEffect(e1)
end
function s.condition(e,tp,eg,ep,ev,re,r,rp)
	return aux.StatChangeDamageStepCondition()
		and Duel.GetMatchingGroupCount(Card.IsFaceup,tp,LOCATION_MZONE,0,nil)==1
end
function s.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return chkc:IsLocation(LOCATION_MZONE) and chkc:IsControler(tp) and chkc:IsFaceup() end
	if chk==0 then
		local g=Duel.GetMatchingGroup(Card.IsFaceup,tp,0,LOCATION_MZONE,nil)
		if #g==0 then return false end
		local mg,atk=g:GetMinGroup(Card.GetAttack)
		return atk>0 and Duel.IsExistingTarget(Card.IsFaceup,tp,LOCATION_MZONE,0,1,nil)
	end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_FACEUP)
	Duel.SelectTarget(tp,Card.IsFaceup,tp,LOCATION_MZONE,0,1,1,nil)
end
function s.activate(e,tp,eg,ep,ev,re,r,rp)
	local tc=Duel.GetFirstTarget()
	if tc:IsRelateToEffect(e) and tc:IsFaceup() then
		local g=Duel.GetMatchingGroup(Card.IsFaceup,tp,0,LOCATION_MZONE,nil)
		if #g==0 then return end
		local mg,atk=g:GetMinGroup(Card.GetAttack)
		local e1=Effect.CreateEffect(e:GetHandler())
		e1:SetType(EFFECT_TYPE_SINGLE)
		e1:SetCode(EFFECT_UPDATE_ATTACK)
		e1:SetReset(RESETS_STANDARD_PHASE_END)
		e1:SetValue(atk)
		tc:RegisterEffect(e1)
	end
end