//
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// SingleAsync.swift
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// RxSwift
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//
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// Created by Junior B. on 09/11/15.
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// Copyright © 2015 Krunoslav Zaher. All rights reserved.
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//
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extension ObservableType {
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/**
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The single operator is similar to first, but throws a `RxError.noElements` or `RxError.moreThanOneElement`
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if the source Observable does not emit exactly one element before successfully completing.
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- seealso: [single operator on reactivex.io](http://reactivex.io/documentation/operators/first.html)
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- returns: An observable sequence that emits a single element or throws an exception if more (or none) of them are emitted.
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*/
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public func single()
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-> Observable<Element> {
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SingleAsync(source: self.asObservable())
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}
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/**
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The single operator is similar to first, but throws a `RxError.NoElements` or `RxError.MoreThanOneElement`
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if the source Observable does not emit exactly one element before successfully completing.
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- seealso: [single operator on reactivex.io](http://reactivex.io/documentation/operators/first.html)
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- parameter predicate: A function to test each source element for a condition.
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- returns: An observable sequence that emits a single element or throws an exception if more (or none) of them are emitted.
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*/
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public func single(_ predicate: @escaping (Element) throws -> Bool)
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-> Observable<Element> {
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SingleAsync(source: self.asObservable(), predicate: predicate)
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}
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}
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private final class SingleAsyncSink<Observer: ObserverType> : Sink<Observer>, ObserverType {
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typealias Element = Observer.Element
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typealias Parent = SingleAsync<Element>
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private let parent: Parent
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private var seenValue: Bool = false
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init(parent: Parent, observer: Observer, cancel: Cancelable) {
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self.parent = parent
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super.init(observer: observer, cancel: cancel)
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}
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func on(_ event: Event<Element>) {
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switch event {
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case .next(let value):
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do {
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let forward = try self.parent.predicate?(value) ?? true
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if !forward {
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return
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}
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}
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catch let error {
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self.forwardOn(.error(error as Swift.Error))
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self.dispose()
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return
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}
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if self.seenValue {
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self.forwardOn(.error(RxError.moreThanOneElement))
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self.dispose()
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return
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}
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self.seenValue = true
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self.forwardOn(.next(value))
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case .error:
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self.forwardOn(event)
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self.dispose()
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case .completed:
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if self.seenValue {
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self.forwardOn(.completed)
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} else {
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self.forwardOn(.error(RxError.noElements))
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}
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self.dispose()
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}
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}
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}
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final class SingleAsync<Element>: Producer<Element> {
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typealias Predicate = (Element) throws -> Bool
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private let source: Observable<Element>
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fileprivate let predicate: Predicate?
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init(source: Observable<Element>, predicate: Predicate? = nil) {
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self.source = source
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self.predicate = predicate
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}
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override func run<Observer: ObserverType>(_ observer: Observer, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where Observer.Element == Element {
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let sink = SingleAsyncSink(parent: self, observer: observer, cancel: cancel)
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let subscription = self.source.subscribe(sink)
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return (sink: sink, subscription: subscription)
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}
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}
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