Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
You can discard 1 monster; Special Summon 1 Level 4 or lower Wyrm-Type monster from your Deck. You can only use this effect of "Giant Pairfish" once per turn.
--竜宮のツガイ
--Giant Pairfish
local s,id=GetID()
function s.initial_effect(c)
	--spsummon
	local e3=Effect.CreateEffect(c)
	e3:SetCategory(CATEGORY_SPECIAL_SUMMON)
	e3:SetType(EFFECT_TYPE_IGNITION)
	e3:SetRange(LOCATION_MZONE)
	e3:SetCountLimit(1,id)
	e3:SetCost(s.spcost)
	e3:SetTarget(s.sptg)
	e3:SetOperation(s.spop)
	c:RegisterEffect(e3)
end
function s.costfilter(c)
	return c:IsMonster() and c:IsDiscardable()
end
function s.spcost(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.IsExistingMatchingCard(s.costfilter,tp,LOCATION_HAND,0,1,nil) end
	Duel.DiscardHand(tp,s.costfilter,1,1,REASON_COST|REASON_DISCARD)
end
function s.filter(c,e,tp)
	return c:IsLevelBelow(4) and c:IsRace(RACE_WYRM) 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.filter,tp,LOCATION_DECK,0,1,nil,e,tp) end
	Duel.SetOperationInfo(0,CATEGORY_SPECIAL_SUMMON,nil,1,tp,LOCATION_DECK)
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,s.filter,tp,LOCATION_DECK,0,1,1,nil,e,tp)
	if #g>0 then
		Duel.SpecialSummon(g,0,tp,tp,false,false,POS_FACEUP)
	end
end