local Observable = require "rx.observable"
local util = require "rx.util"

--- Returns a new Observable that produces a default set of items if the source Observable produces
-- no values.
-- @arg {*...} values - Zero or more values to produce if the source completes without emitting
--                      anything.
-- @returns {Observable}
function Observable:defaultIfEmpty(...)
    local defaults = util.pack(...)

    return Observable.create(function(observer)
        local hasValue = false

        local function onNext(...)
            hasValue = true
            observer:onNext(...)
        end

        local function onError(e)
            observer:onError(e)
        end

        local function onCompleted()
            if not hasValue then
                observer:onNext(util.unpack(defaults))
            end

            observer:onCompleted()
        end

        return self:subscribe(onNext, onError, onCompleted)
    end)
end