local Observable = require "rx.observable"
local Subscription = require "rx.subscription"

--- Given an Observable that produces Observables, returns an Observable that produces the values
-- produced by the most recently produced Observable.
-- @returns {Observable}
function Observable:switch()
    return Observable.create(function(observer)
        local innerSubscription

        local function onNext(...)
            return observer:onNext(...)
        end

        local function onError(message)
            return observer:onError(message)
        end

        local function onCompleted()
            return observer:onCompleted()
        end

        local function switch(source)
            if innerSubscription then
                innerSubscription:unsubscribe()
            end

            innerSubscription = source:subscribe(onNext, onError, nil)
        end

        local subscription = self:subscribe(switch, onError, onCompleted)
        return Subscription.create(function()
            if innerSubscription then
                innerSubscription:unsubscribe()
            end

            if subscription then
                subscription:unsubscribe()
            end
        end)
    end)
end