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

--- Returns a new Observable that produces elements until the predicate returns falsy.
-- @arg {function} predicate - The predicate used to continue production of values.
-- @returns {Observable}
function Observable:takeWhile(predicate)
    predicate = predicate or util.identity

    return Observable.create(function(observer)
        local taking = true
        local subscription

        local function onNext(...)
            if taking then
                util.tryWithObserver(observer, function(...)
                    taking = predicate(...)
                end, ...)

                if taking then
                    return observer:onNext(...)
                else
                    if subscription then
                        subscription:unsubscribe()
                    end
                    return observer:onCompleted()
                end
            end
        end

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

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

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