Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
When this card is Normal Summoned, put 3 counters on it. This card cannot be destroyed by battle. If this card attacks or is attacked, remove 1 counter from this card at the end of the Damage Step. If you cannot, destroy it. Once per turn, during your Main Phase, you can change 1 face-up Attack Position monster your opponent controls to face-up Defense Position.
--巨大戦艦 クリスタル・コア
--B.E.S. Crystal Core
local s,id=GetID()
function s.initial_effect(c)
	c:EnableCounterPermit(0x1f)
	--summon success
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetCategory(CATEGORY_COUNTER)
	e1:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F)
	e1:SetCode(EVENT_SUMMON_SUCCESS)
	e1:SetTarget(s.addct)
	e1:SetOperation(s.addc)
	c:RegisterEffect(e1)
	--battle indestructable
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_SINGLE)
	e2:SetCode(EFFECT_INDESTRUCTABLE_BATTLE)
	e2:SetValue(1)
	c:RegisterEffect(e2)
	--remove counter
	local e3=Effect.CreateEffect(c)
	e3:SetDescription(aux.Stringid(id,1))
	e3:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F)
	e3:SetCode(EVENT_DAMAGE_STEP_END)
	e3:SetCondition(s.rctcon)
	e3:SetOperation(s.rctop)
	c:RegisterEffect(e3)
	--destroy
	local e4=Effect.CreateEffect(c)
	e4:SetDescription(aux.Stringid(id,2))
	e4:SetCategory(CATEGORY_DESTROY)
	e4:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F)
	e4:SetCode(EVENT_DAMAGE_STEP_END)
	e4:SetCondition(s.descon)
	e4:SetTarget(s.destg)
	e4:SetOperation(s.desop)
	c:RegisterEffect(e4)
	--pos
	local e5=Effect.CreateEffect(c)
	e5:SetDescription(aux.Stringid(id,3))
	e5:SetCategory(CATEGORY_POSITION)
	e5:SetProperty(EFFECT_FLAG_CARD_TARGET)
	e5:SetType(EFFECT_TYPE_IGNITION)
	e5:SetRange(LOCATION_MZONE)
	e5:SetCountLimit(1)
	e5:SetTarget(s.postg)
	e5:SetOperation(s.posop)
	c:RegisterEffect(e5)
end
function s.addct(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return true end
	Duel.SetOperationInfo(0,CATEGORY_COUNTER,nil,3,0,0x1f)
end
function s.addc(e,tp,eg,ep,ev,re,r,rp)
	if e:GetHandler():IsRelateToEffect(e) then
		e:GetHandler():AddCounter(0x1f,3)
	end
end
function s.rctcon(e,tp,eg,ep,ev,re,r,rp)
	return e:GetHandler():GetCounter(0x1f)~=0
end
function s.rctop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsFaceup() and c:IsRelateToEffect(e) then
		c:RemoveCounter(tp,0x1f,1,REASON_EFFECT)
	end
end
function s.descon(e,tp,eg,ep,ev,re,r,rp)
	return e:GetHandler():GetCounter(0x1f)==0
end
function s.destg(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return true end
	Duel.SetOperationInfo(0,CATEGORY_DESTROY,e:GetHandler(),1,0,0)
end
function s.desop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsFaceup() and c:IsRelateToEffect(e) then
		Duel.Destroy(c,REASON_EFFECT)
	end
end
function s.filter(c)
	return c:IsPosition(POS_FACEUP_ATTACK) and c:IsCanChangePosition()
end
function s.postg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return chkc:IsLocation(LOCATION_MZONE) and chkc:IsControler(1-tp) and s.filter(chkc) end
	if chk==0 then return Duel.IsExistingTarget(s.filter,tp,0,LOCATION_MZONE,1,nil) end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_POSCHANGE)
	local g=Duel.SelectTarget(tp,s.filter,tp,0,LOCATION_MZONE,1,1,nil)
	Duel.SetOperationInfo(0,CATEGORY_POSITION,g,1,0,0)
end
function s.posop(e,tp,eg,ep,ev,re,r,rp)
	local tc=Duel.GetFirstTarget()
	if tc and tc:IsPosition(POS_FACEUP_ATTACK) and tc:IsRelateToEffect(e) then
		Duel.ChangePosition(tc,POS_FACEUP_DEFENSE)
	end
end