combine3.swift

import Cocoa
import Combine
import ObjectiveC
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

enum Action {
    static func run(after delay: Double, action: @escaping () -> Void) {
        let delayTime = UInt64(delay * Double(NSEC_PER_SEC))
        let dispatchTime = DispatchTime(uptimeNanoseconds: DispatchTime.now().rawValue + delayTime)
        DispatchQueue.global(qos: .background)
            .asyncAfter(deadline: dispatchTime, execute: action)
    }
}

class AsyncRandomNumberSource {
    var number: Int
    var subject: PassthroughSubject<Int, Never>
    func action() {
        Action.run(after: Double.random(in: 0.1 ... 3.0)) { [weak self] in
            if let self = self {
                // send a number or end
                switch Int.random(in: 1 ... 20) {
                case 20:
                    self.subject.send(completion: .finished)
                default:
                    self.number = Int.random(in: 1 ..< 1000)
                    self.subject.send(self.number)
                    self.roll()
                }
            }
        }
    }
    
    func roll() {
        action()
    }
    
    init(_ subject: PassthroughSubject<Int, Never>) {
        self.subject = subject
        number = 0
        action()
    }
}

let passthroughSubject = PassthroughSubject<Int,Never>()
let cancellableSubscriber = passthroughSubject.sink { completionInfo in
    switch completionInfo {
    case .finished: print("Done!!")
    case .failure(let error): print("Error: \(error)")
    }
} receiveValue: { stringElement in
    print(stringElement, "received")
}

let source = AsyncRandomNumberSource(passthroughSubject)