Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
When this card is flipped face-up: You can target 1 card in your opponent's GY; place that target on the bottom of their Deck. If this card is sent from the field to the GY after being flipped face-up: You can target 1 "Necrovalley" card in your GY; add that target to your hand. These effects are unaffected by "Necrovalley".
--墓守の伏兵
--Gravekeeper's Ambusher
local s,id=GetID()
function s.initial_effect(c)
	--return to deck
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetCategory(CATEGORY_TODECK)
	e1:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_O)
	e1:SetProperty(EFFECT_FLAG_CARD_TARGET+EFFECT_FLAG_DAMAGE_STEP)
	e1:SetCode(EVENT_FLIP)
	e1:SetTarget(s.tdtg)
	e1:SetOperation(s.tdop)
	c:RegisterEffect(e1)
	--salvage
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_CONTINUOUS)
	e2:SetProperty(EFFECT_FLAG_CANNOT_DISABLE)
	e2:SetCode(EVENT_FLIP)
	e2:SetOperation(s.flipop)
	c:RegisterEffect(e2)
	local e3=Effect.CreateEffect(c)
	e3:SetDescription(aux.Stringid(id,1))
	e3:SetCategory(CATEGORY_TOHAND)
	e3:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_O)
	e3:SetCode(EVENT_TO_GRAVE)
	e3:SetProperty(EFFECT_FLAG_CARD_TARGET+EFFECT_FLAG_DAMAGE_STEP+EFFECT_FLAG_DELAY)
	e3:SetCondition(s.thcon)
	e3:SetTarget(s.thtg)
	e3:SetOperation(s.thop)
	c:RegisterEffect(e3)
	--immune to necro valley
	local e4=Effect.CreateEffect(c)
	e4:SetType(EFFECT_TYPE_SINGLE)
	e4:SetCode(EFFECT_NECRO_VALLEY_IM)
	c:RegisterEffect(e4)
end
s.listed_series={SET_NECROVALLEY}
function s.tdtg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return chkc:IsControler(1-tp) and chkc:IsLocation(LOCATION_GRAVE) and chkc:IsAbleToDeck() end
	if chk==0 then return Duel.IsExistingTarget(Card.IsAbleToDeck,tp,0,LOCATION_GRAVE,1,nil) end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_TODECK)
	local g=Duel.SelectTarget(tp,Card.IsAbleToDeck,tp,0,LOCATION_GRAVE,1,1,nil)
	Duel.SetOperationInfo(0,CATEGORY_TODECK,g,1,0,0)
end
function s.tdop(e,tp,eg,ep,ev,re,r,rp)
	local tc=Duel.GetFirstTarget()
	if tc:IsRelateToEffect(e) then
		Duel.SendtoDeck(tc,nil,SEQ_DECKBOTTOM,REASON_EFFECT)
	end
end
function s.flipop(e,tp,eg,ep,ev,re,r,rp)
	e:GetHandler():RegisterFlagEffect(id,RESET_EVENT|(RESETS_STANDARD|RESET_OVERLAY)&~(RESET_LEAVE|RESET_TOGRAVE),0,0)
end
function s.thcon(e,tp,eg,ep,ev,re,r,rp)
	return e:GetHandler():GetFlagEffect(id)~=0
end
function s.filter(c)
	return c:IsSetCard(SET_NECROVALLEY) and c:IsAbleToHand()
end
function s.thtg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return chkc:IsLocation(LOCATION_GRAVE) and chkc:IsControler(tp) and s.filter(chkc) end
	if chk==0 then return Duel.IsExistingTarget(s.filter,tp,LOCATION_GRAVE,0,1,nil) end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_ATOHAND)
	local g=Duel.SelectTarget(tp,s.filter,tp,LOCATION_GRAVE,0,1,1,nil)
	Duel.SetOperationInfo(0,CATEGORY_TOHAND,g,1,0,0)
end
function s.thop(e,tp,eg,ep,ev,re,r,rp)
	local tc=Duel.GetFirstTarget()
	if tc:IsRelateToEffect(e) then
		Duel.SendtoHand(tc,nil,REASON_EFFECT)
		Duel.ConfirmCards(1-tp,tc)
	end
end