Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
Discard 1 card from your hand during your Main Phase 1. This monster can attack twice during the Battle Phase of this turn.
--グレイ・ウイング
--Gray Wing
local s,id=GetID()
function s.initial_effect(c)
	--multiatk
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetType(EFFECT_TYPE_IGNITION)
	e1:SetRange(LOCATION_MZONE)
	e1:SetCondition(s.atkcon)
	e1:SetCost(s.atkcost)
	e1:SetTarget(s.atktg)
	e1:SetOperation(s.atkop)
	c:RegisterEffect(e1)
end
function s.atkcon(e,tp,eg,ep,ev,re,r,rp)
	return Duel.IsAbleToEnterBP()
end
function s.atkcost(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.IsExistingMatchingCard(Card.IsDiscardable,tp,LOCATION_HAND,0,1,nil) end
	Duel.DiscardHand(tp,Card.IsDiscardable,1,1,REASON_COST|REASON_DISCARD)
end
function s.atktg(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return e:GetHandler():GetEffectCount(EFFECT_EXTRA_ATTACK)==0 end
end
function s.atkop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsRelateToEffect(e) and c:IsFaceup() then
		local e1=Effect.CreateEffect(c)
		e1:SetType(EFFECT_TYPE_SINGLE)
		e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE)
		e1:SetCode(EFFECT_EXTRA_ATTACK)
		e1:SetValue(1)
		e1:SetReset(RESETS_STANDARD_PHASE_END)
		c:RegisterEffect(e1)
	end
end