Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
All Tokens in Attack Position gain 1000 ATK, also they cannot be destroyed by battle.
--暴走闘君
--Token Stampede
local s,id=GetID()
function s.initial_effect(c)
	--Activate
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_ACTIVATE)
	e1:SetProperty(EFFECT_FLAG_DAMAGE_STEP)
	e1:SetHintTiming(TIMING_DAMAGE_STEP)
	e1:SetCode(EVENT_FREE_CHAIN)
	c:RegisterEffect(e1)
	--atk up
	local e2=Effect.CreateEffect(c)
	e2:SetType(EFFECT_TYPE_FIELD)
	e2:SetCode(EFFECT_UPDATE_ATTACK)
	e2:SetRange(LOCATION_SZONE)
	e2:SetTargetRange(LOCATION_MZONE,LOCATION_MZONE)
	e2:SetTarget(s.tg)
	e2:SetValue(1000)
	c:RegisterEffect(e2)
	--indes
	local e3=Effect.CreateEffect(c)
	e3:SetType(EFFECT_TYPE_FIELD)
	e3:SetCode(EFFECT_INDESTRUCTABLE_BATTLE)
	e3:SetRange(LOCATION_SZONE)
	e3:SetTargetRange(LOCATION_MZONE,LOCATION_MZONE)
	e3:SetTarget(s.tg)
	e3:SetValue(1)
	c:RegisterEffect(e3)
end
function s.tg(e,c)
	return c:IsType(TYPE_TOKEN) and c:IsAttackPos()
end