Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
FLIP: When this card is sent to the Graveyard after being flipped, each player selects 1 monster from their Graveyard, and Special Summons it in face-up Attack Position or face-down Defense Position.
--ダークファミリア
--Spear Cretin
local s,id=GetID()
function s.initial_effect(c)
	--flip effect
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_CONTINUOUS)
	e1:SetCode(EVENT_FLIP)
	e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE)
	e1:SetOperation(s.flipop)
	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_F)
	e2:SetProperty(EFFECT_FLAG_CARD_TARGET)
	e2:SetCode(EVENT_TO_GRAVE)
	e2:SetTarget(s.sptg)
	e2:SetOperation(s.spop)
	c:RegisterEffect(e2)
end
function s.flipop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsLocation(LOCATION_MZONE|LOCATION_GRAVE) then
		c:RegisterFlagEffect(id,RESET_EVENT|(RESETS_STANDARD|RESET_OVERLAY)&~(RESET_LEAVE|RESET_TOGRAVE),0,1)
	end
end
function s.filter(c,e,tp)
	return c:IsCanBeSpecialSummoned(e,0,tp,false,false,POS_FACEUP_ATTACK|POS_FACEDOWN_DEFENSE)
end
function s.sptg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return false end
	if chk==0 then return e:GetHandler():GetFlagEffect(id)~=0 end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_SPSUMMON)
	local g1=Duel.SelectTarget(tp,s.filter,tp,LOCATION_GRAVE,0,1,1,e:GetHandler(),e,tp)
	Duel.Hint(HINT_SELECTMSG,1-tp,HINTMSG_SPSUMMON)
	local g2=Duel.SelectTarget(1-tp,s.filter,1-tp,LOCATION_GRAVE,0,1,1,e:GetHandler(),e,1-tp)
	if #g1>0 and #g2>0 then
		g1:Merge(g2)
		Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,g1,2,PLAYER_ALL,g1:GetFirst():GetOwner())
	elseif #g1>0 then
		Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,g1,1,0,0)
	elseif #g2>0 then
		Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,g2,1,1,0)
	end
end
function s.spop(e,tp,eg,ep,ev,re,r,rp)
	local sg=Duel.GetTargetCards(e)
	if #sg==0 then return end
	for tc in sg:Iter() do
		if Duel.GetLocationCount(tc:GetControler(),LOCATION_MZONE)>0 then
			local sp=tc:GetControler()
			Duel.SpecialSummonStep(tc,0,sp,sp,false,false,POS_FACEUP_ATTACK|POS_FACEDOWN_DEFENSE)
		end
	end
	Duel.SpecialSummonComplete()
end