Mobius2017.Sampler.swift

// https://github.com/avito-tech
//
// Sampler is like a baby of Debouncer and Throttler.
//
// Unlike Debouncer, sampler executes action immediately (if there are no actions before, for time > delay)
// Unlike Throttler it guarantees that last action in sequence will be executed (see last error in example)

/// CAUTION: This class isn't thread-safe
public final class Sampler {
    // MARK: - Public properite
    public let delay: TimeInterval

    // MARK: - Private properite
    private let queue: DispatchQueue
    private var closure: (() -> ())?
    private var isDelaying = false

    // MARK: - Init
    public init(delay: TimeInterval, queue: DispatchQueue = DispatchQueue.main) {
        avitoAssert(delay >= 0, "Sampler can't have negative delay")
        
        self.delay = delay
        self.queue = queue
    }
    
    // MARK: - Public
    public func sample(_ closure: @escaping () -> ()) {
        if isDelaying {
            self.closure = closure
        } else {
            queue.async {
                closure()
            }
            self.closure = nil
            isDelaying = true
            queue.asyncAfter(deadline: .now() + delay) { [weak self] in
                self?.isDelaying = false
                if let closure = self?.closure {
                    self?.sample(closure)
                }
            }
        }
    }
}