Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
If you control no monsters: You can reveal this card in your hand, then target 1 "Gouki" Link Monster in your GY; Special Summon this card from your hand, then, Special Summon the target, but it loses 500 ATK. You can only use this effect of "Gouki Ringtrainer" once per turn. While you control a "Gouki" Link Monster, this card cannot be destroyed by battle.
--剛鬼ヘルトレーナー
--Gouki Ringtrainer
--
local s,id=GetID()
function s.initial_effect(c)
	--special summon
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetCategory(CATEGORY_SPECIAL_SUMMON)
	e1:SetType(EFFECT_TYPE_IGNITION)
	e1:SetRange(LOCATION_HAND)
	e1:SetCountLimit(1,id)
	e1:SetCondition(s.spcon)
	e1:SetCost(s.spcost)
	e1:SetTarget(s.sptg)
	e1:SetOperation(s.spop)
	c:RegisterEffect(e1)
	--indestructable
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_SINGLE)
	e2:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
	e2:SetRange(LOCATION_MZONE)
	e2:SetCode(EFFECT_INDESTRUCTABLE_BATTLE)
	e2:SetCondition(s.indcon)
	e2:SetValue(1)
	c:RegisterEffect(e2)
end
s.listed_series={SET_GOUKI}
function s.spcon(e,tp,eg,ep,ev,re,r,rp)
	return Duel.GetFieldGroupCount(tp,LOCATION_MZONE,0)==0
end
function s.spcost(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return not e:GetHandler():IsPublic() end
end
function s.spfilter(c,e,tp)
	return c:IsSetCard(SET_GOUKI) and c:IsLinkMonster() and c:IsCanBeSpecialSummoned(e,0,tp,false,false)
end
function s.sptg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	local c=e:GetHandler()
	if chkc then return chkc:IsLocation(LOCATION_GRAVE) and chkc:IsControler(tp) and s.spfilter(chkc,e,tp) end
	if chk==0 then return Duel.GetLocationCount(tp,LOCATION_MZONE)>1
		and c:IsCanBeSpecialSummoned(e,0,tp,false,false)
		and Duel.IsExistingTarget(s.spfilter,tp,LOCATION_GRAVE,0,1,nil,e,tp) end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_SPSUMMON)
	local g=Duel.SelectTarget(tp,s.spfilter,tp,LOCATION_GRAVE,0,1,1,nil,e,tp)
	g:AddCard(c)
	Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,g,2,0,0)
end
function s.spop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if not c:IsRelateToEffect(e) then return end
	if Duel.SpecialSummon(c,0,tp,tp,false,false,POS_FACEUP)~=0 then
		local tc=Duel.GetFirstTarget()
		if tc:IsRelateToEffect(e) then
			Duel.BreakEffect()
			Duel.SpecialSummonStep(tc,0,tp,tp,false,false,POS_FACEUP)
			local e1=Effect.CreateEffect(c)
			e1:SetType(EFFECT_TYPE_SINGLE)
			e1:SetCode(EFFECT_UPDATE_ATTACK)
			e1:SetValue(-500)
			e1:SetReset(RESET_EVENT|RESETS_STANDARD)
			tc:RegisterEffect(e1)
			Duel.SpecialSummonComplete()
		end
	end
end
function s.indfilter(c)
	return c:IsFaceup() and c:IsLinkMonster() and c:IsSetCard(SET_GOUKI)
end
function s.indcon(e)
	return Duel.IsExistingMatchingCard(s.indfilter,e:GetHandlerPlayer(),LOCATION_MZONE,0,1,nil)
end