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

--- Returns a new Observable that produces the first value of the original that satisfies a
-- predicate.
-- @arg {function} predicate - The predicate used to find a value.
function Observable:find(predicate)
    predicate = predicate or util.identity

    return Observable.create(function(observer)
        local subscription

        local function onNext(...)
            util.tryWithObserver(observer, function(...)
                if predicate(...) then
                    observer:onNext(...)
                    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