ActivityIndicator.swift

ActivityIndicator.swift

/**
 Enables monitoring of sequence computation.
 If there is at least one sequence computation in progress, `true` will be sent.
 When all activities complete `false` will be sent.
 */
class ActivityIndicator : DriverConvertibleType {
    typealias E = Bool
    
    fileprivate let _lock = NSRecursiveLock()
    fileprivate let _variable = Variable(0)
    fileprivate let _loading: Driver<Bool>
    
    init() {
        _loading = _variable.asObservable()
            .map { $0 > 0 }
            .distinctUntilChanged()
            .asDriver { (error: Error) -> Driver<Bool> in
                _ = fatalError("Loader can't fail")
                return Driver.empty()
        }
    }
    
    func trackActivity<O: ObservableConvertibleType>(_ source: O) -> Observable<O.E> {
        ObservableConvertibleType
        return Observable.using({ () -> ActivityToken<O.E> in
            self.increment()
            return ActivityToken(source: source.asObservable(), disposeAction: self.decrement)
            }) { t in
                return t.asObservable()
        }
    }
    
    fileprivate func increment() {
        _lock.lock()
        _variable.value = _variable.value + 1
        _lock.unlock()
    }
    
    fileprivate func decrement() {
        _lock.lock()
        _variable.value = _variable.value - 1
        _lock.unlock()
    }
    
    func asDriver() -> Driver<E> {
        return _loading
    }
}

extension ObservableConvertibleType {
    func trackActivity(_ activityIndicator: ActivityIndicator) -> Observable<E> {
        return activityIndicator.trackActivity(self)
    }
}