AwaitPublisher.swift

import Combine

struct AwaitPublisher<Value>: Publisher {
	typealias Output = Value
	typealias Failure = Never

	private let block: () async -> Value

	init(block: @escaping () async -> Value) {
		self.block = block
	}

	func receive<S>(subscriber: S) where S : Subscriber, Never == S.Failure, Value == S.Input {
		subscriber.receive(subscription: Subscription(downstream: subscriber, block: block))
	}
}

extension AwaitPublisher {
	final class Subscription<Downstream: Subscriber>: Combine.Subscription
	where Output == Downstream.Input, Failure == Downstream.Failure {

		private let downstream: Downstream
		private let block: () async -> Value
		private var currentTask: Task<Void, Never>?

		init(downstream: Downstream, block: @escaping () async -> Value) {
			self.downstream = downstream
			self.block = block
		}

		func request(_ demand: Subscribers.Demand) {
			guard demand > .none, currentTask == nil else { return }
			currentTask = Task { [weak self] in
				let value = await block()
				_ = self?.downstream.receive(value)
				self?.downstream.receive(completion: .finished)
			}
		}

		func cancel() {
			guard let task = currentTask, !task.isCancelled else { return }
			currentTask = nil
			task.cancel()
		}
	}
}