Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
During the Main Phase, if a face-up "War Rock" monster(s) you control leaves the field by an opponent's card effect: Destroy up to 2 cards your opponent controls. You can only activate 1 "War Rock Big Blow" per turn.
--ウォークライ・ビッグブロウ
--War Rock Big Blow
local s,id=GetID()
function s.initial_effect(c)
	--Destroy up to 2 cards your opponent controls
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetCategory(CATEGORY_DESTROY)
	e1:SetType(EFFECT_TYPE_ACTIVATE)
	e1:SetCode(EVENT_LEAVE_FIELD)
	e1:SetProperty(EFFECT_FLAG_DELAY)
	e1:SetCountLimit(1,id,EFFECT_COUNT_CODE_OATH)
	e1:SetCondition(s.condition)
	e1:SetTarget(s.target)
	e1:SetOperation(s.activate)
	c:RegisterEffect(e1)
end
function s.cfilter(c,tp)
	return c:IsPreviousSetCard(SET_WAR_ROCK) and c:GetReasonPlayer()==1-tp
		and c:IsReason(REASON_EFFECT) and c:IsPreviousControler(tp)
		and c:IsPreviousLocation(LOCATION_MZONE) and c:IsPreviousPosition(POS_FACEUP)
end
function s.condition(e,tp,eg,ep,ev,re,r,rp)
	return Duel.IsMainPhase() and eg:IsExists(s.cfilter,1,nil,tp)
end
function s.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chk==0 then return Duel.IsExistingMatchingCard(nil,tp,0,LOCATION_ONFIELD,1,nil) end
	local g=Duel.GetMatchingGroup(nil,tp,0,LOCATION_ONFIELD,nil)
	Duel.SetOperationInfo(0,CATEGORY_DESTROY,g,1,1-tp,0)
end
function s.activate(e,tp,eg,ep,ev,re,r,rp)
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_DESTROY)
	local g=Duel.SelectMatchingCard(tp,nil,tp,0,LOCATION_ONFIELD,1,2,nil)
	if #g>0 then
		Duel.HintSelection(g)
		Duel.Destroy(g,REASON_EFFECT)
	end
end