Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
If your opponent controls a monster and you control no monsters, you can Special Summon this card (from your hand). You can only Special Summon "Kaiser Sea Snake" once per turn this way. When Summoned this way: You can Special Summon 1 Level 8 Sea Serpent monster from your hand or GY, but its ATK/DEF become 0. If this card is Special Summoned, its Level becomes 4 and original ATK becomes 0.
--カイザー・シースネーク
--Kaiser Sea Snake
local s,id=GetID()
function s.initial_effect(c)
	--special summon
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_FIELD)
	e1:SetCode(EFFECT_SPSUMMON_PROC)
	e1:SetProperty(EFFECT_FLAG_UNCOPYABLE)
	e1:SetRange(LOCATION_HAND)
	e1:SetValue(1)
	e1:SetCountLimit(1,id,EFFECT_COUNT_CODE_OATH)
	e1:SetCondition(s.hspcon)
	c:RegisterEffect(e1)
	--special summon
	local e2=Effect.CreateEffect(c)
	e2:SetDescription(aux.Stringid(id,0))
	e2:SetCategory(CATEGORY_SPECIAL_SUMMON)
	e2:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_O)
	e2:SetCode(EVENT_SPSUMMON_SUCCESS)
	e2:SetCondition(s.spcon)
	e2:SetTarget(s.sptg)
	e2:SetOperation(s.spop)
	c:RegisterEffect(e2)
	--change level
	local e3=Effect.CreateEffect(c)
	e3:SetType(EFFECT_TYPE_SINGLE)
	e3:SetCode(EFFECT_SPSUMMON_COST)
	e3:SetOperation(s.lvop)
	c:RegisterEffect(e3)
end
function s.hspcon(e,c)
	if c==nil then return true end
	return Duel.GetFieldGroupCount(c:GetControler(),LOCATION_MZONE,0)==0
		and Duel.GetFieldGroupCount(c:GetControler(),0,LOCATION_MZONE)>0
		and Duel.GetLocationCount(c:GetControler(),LOCATION_MZONE)>0
end
function s.spcon(e,tp,eg,ep,ev,re,r,rp)
	return e:GetHandler():GetSummonType()==SUMMON_TYPE_SPECIAL+1
end
function s.spfilter(c,e,tp)
	return c:IsRace(RACE_SEASERPENT) and c:GetLevel()==8 and c:IsCanBeSpecialSummoned(e,0,tp,false,false)
end
function s.sptg(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.GetLocationCount(tp,LOCATION_MZONE)>0
		and Duel.IsExistingMatchingCard(s.spfilter,tp,LOCATION_HAND|LOCATION_GRAVE,0,1,nil,e,tp) end
	Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,nil,1,tp,LOCATION_HAND|LOCATION_GRAVE)
end
function s.spop(e,tp,eg,ep,ev,re,r,rp)
	if Duel.GetLocationCount(tp,LOCATION_MZONE)<=0 then return end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_SPSUMMON)
	local g=Duel.SelectMatchingCard(tp,aux.NecroValleyFilter(s.spfilter),tp,LOCATION_HAND|LOCATION_GRAVE,0,1,1,nil,e,tp)
	local tc=g:GetFirst()
	if tc and Duel.SpecialSummonStep(tc,0,tp,tp,false,false,POS_FACEUP) then
		local e1=Effect.CreateEffect(e:GetHandler())
		e1:SetType(EFFECT_TYPE_SINGLE)
		e1:SetCode(EFFECT_SET_ATTACK_FINAL)
		e1:SetValue(0)
		e1:SetReset(RESET_EVENT|RESETS_STANDARD)
		tc:RegisterEffect(e1,true)
		local e2=e1:Clone()
		e2:SetCode(EFFECT_SET_DEFENSE_FINAL)
		tc:RegisterEffect(e2,true)
	end
	Duel.SpecialSummonComplete()
end
function s.lvop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_CHANGE_LEVEL)
	e1:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
	e1:SetRange(LOCATION_MZONE)
	e1:SetValue(4)
	e1:SetReset(RESET_EVENT|(RESETS_STANDARD_DISABLE&~RESET_TOFIELD))
	c:RegisterEffect(e1)
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_SINGLE)
	e2:SetCode(EFFECT_SET_BASE_ATTACK)
	e2:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
	e2:SetRange(LOCATION_MZONE)
	e2:SetValue(0)
	e2:SetReset(RESET_EVENT|(RESETS_STANDARD_DISABLE&~RESET_TOFIELD))
	c:RegisterEffect(e2)
end