Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
Flip all face-down monsters on your opponent's side of the field face-up.
--闇をかき消す光
--Dark-Piercing Light
local s,id=GetID()
function s.initial_effect(c)
	--Activate
	local e1=Effect.CreateEffect(c)
	e1:SetCategory(CATEGORY_POSITION)
	e1:SetType(EFFECT_TYPE_ACTIVATE)
	e1:SetCode(EVENT_FREE_CHAIN)
	e1:SetTarget(s.target)
	e1:SetOperation(s.activate)
	c:RegisterEffect(e1)
end
function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.IsExistingMatchingCard(Card.IsFacedown,tp,0,LOCATION_MZONE,1,nil) end
	local g=Duel.GetMatchingGroup(Card.IsFacedown,tp,0,LOCATION_MZONE,nil)
	Duel.SetOperationInfo(0,CATEGORY_POSITION,g,#g,0,0)
end
function s.activate(e,tp,eg,ep,ev,re,r,rp)
	local g=Duel.GetMatchingGroup(Card.IsFacedown,tp,0,LOCATION_MZONE,nil)
	if #g>0 then
		Duel.ChangePosition(g,POS_FACEUP_ATTACK,POS_FACEUP_ATTACK,POS_FACEUP_DEFENSE,POS_FACEUP_DEFENSE)
	end
end