Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
When a Spell Card is activated that targets this face-down card (and no other cards) (Quick Effect): Change this card to face-up Defense Position, and if you do, negate the activation. If this card is attacked, change it to Attack Position at the end of the Damage Step.
--ビッグ・シールド・ガードナー
--Big Shield Gardna
local s,id=GetID()
function s.initial_effect(c)
	--Change this card to face-up Defense Position, and if you do, negate the activation
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetCategory(CATEGORY_POSITION+CATEGORY_NEGATE)
	e1:SetType(EFFECT_TYPE_QUICK_F)
	e1:SetProperty(EFFECT_FLAG_DAMAGE_STEP+EFFECT_FLAG_DAMAGE_CAL+EFFECT_FLAG_SET_AVAILABLE)
	e1:SetCode(EVENT_CHAINING)
	e1:SetRange(LOCATION_MZONE)
	e1:SetCondition(s.negcon)
	e1:SetTarget(s.negtg)
	e1:SetOperation(s.negop)
	c:RegisterEffect(e1)
	--If this card is attacked, change it to Attack Position at the end End of the Damage Step
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_CONTINUOUS)
	e2:SetCode(EVENT_DAMAGE_STEP_END)
	e2:SetOperation(s.posop)
	c:RegisterEffect(e2)
end
function s.negcon(e,tp,eg,ep,ev,re,r,rp)
	if not (re:IsSpellEffect() and re:IsHasType(EFFECT_TYPE_ACTIVATE) and re:IsHasProperty(EFFECT_FLAG_CARD_TARGET)) then return false end
	local c=e:GetHandler()
	local tg=Duel.GetChainInfo(ev,CHAININFO_TARGET_CARDS)
	return tg and #tg==1 and tg:GetFirst()==c and c:IsFacedown()
end
function s.negtg(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return true end
	Duel.SetOperationInfo(0,CATEGORY_POSITION,e:GetHandler(),1,tp,POS_FACEUP_DEFENSE)
	Duel.SetOperationInfo(0,CATEGORY_NEGATE,eg,1,tp,0)
end
function s.negop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsRelateToEffect(e) and Duel.ChangePosition(c,POS_FACEUP_DEFENSE) then
		Duel.NegateActivation(ev)
	end
end
function s.posop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c==Duel.GetAttackTarget() and c:IsDefensePos() and c:IsRelateToBattle() then
		Duel.ChangePosition(c,POS_FACEUP_ATTACK)
	end
end