SerialTaskQueue

SerialTaskQueue.swift

mport Foundation

public typealias TaskClosure = (_ completion: @escaping () -> Void) -> Void

public protocol SerialTaskQueueProtocol {
    func addTask(_ task: @escaping TaskClosure)
    func start()
    func stop()
    func flushQueue()
    var isEmpty: Bool { get }
    var isStopped: Bool { get }
}

public final class SerialTaskQueue: SerialTaskQueueProtocol {
    public private(set) var isBusy = false
    public private(set) var isStopped = true

    private var tasksQueue = [TaskClosure]()

    public init() {}

    public func addTask(_ task: @escaping TaskClosure) {
        self.tasksQueue.append(task)
        self.maybeExecuteNextTask()
    }

    public func start() {
        self.isStopped = false
        self.maybeExecuteNextTask()
    }

    public func stop() {
        self.isStopped = true
    }

    public func flushQueue() {
        self.tasksQueue.removeAll()
    }

    public var isEmpty: Bool {
        return self.tasksQueue.isEmpty
    }

    private func maybeExecuteNextTask() {
        if !self.isStopped && !self.isBusy {
            if !self.isEmpty {
                let firstTask = self.tasksQueue.removeFirst()
                self.isBusy = true
                firstTask({ [weak self] () -> Void in
                    self?.isBusy = false
                    self?.maybeExecuteNextTask()
                })
            }
        }
    }
}