CompositeTask.swift

class CompositeTask: Task {
    
    let tasks: [Task]
    
    init(_ tasks: [Task]) {
        self.tasks = tasks
    }
    
    func run(_ completion: @escaping (Task) -> Void) {
        let group = DispatchGroup()
        
        for task in tasks {
            group.enter()
            
            task.run({ task in
                group.leave()
            })
        }
        
        group.notify(queue: DispatchQueue.main) {
            completion(self)
        }
    }
}