Swift GCD Based Debounce.swift

import Foundation

class Debounce {
    private let queue: DispatchQueue
    private let delay: Double
    private var workItem: DispatchWorkItem?
    private var cancelBlock: (() -> Void)?

    init(queue: DispatchQueue, delay: Double) {
        self.queue = queue
        self.delay = delay
    }

    func callAsFunction(action: @escaping () -> Void, onCancel: (() -> Void)?) {
        queue.async { [weak self] in
            guard let self = self else {
                onCancel?()
                return
            }
            if let workItem = self.workItem {
                workItem.cancel()
                self.cancelBlock?()
            }
            let workItem = DispatchWorkItem {
                self.cancelBlock = nil
                action()
            }
            self.workItem = workItem
            self.cancelBlock = onCancel
            self.queue.asyncAfter(deadline: .now() + self.delay, execute: workItem)
        }
    }
}

// MARK: - Tests -
let queue = DispatchQueue(label: "DebounceQueue")
let debounce: Debounce = Debounce(queue: queue, delay: 0.2)

debounce {
    print("action1 done")
} onCancel: {
    print("action1 cancelled")
}

DispatchQueue.global().async {
    debounce {
        print("action2 done")
    } onCancel: {
        print("action2 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.2) {
    debounce {
        print("action3 done")
    } onCancel: {
        print("action3 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.3) {
    debounce {
        print("action33 done")
    } onCancel: {
        print("action33 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.4) {
    debounce {
        print("action34 done")
    } onCancel: {
        print("action34 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.5) {
    debounce {
        print("action35 done")
    } onCancel: {
        print("action35 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.6) {
    debounce {
        print("action36 done")
    } onCancel: {
        print("action36 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.7) {
    debounce {
        print("action37 done")
    } onCancel: {
        print("action37 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.8) {
    debounce {
        print("action38 done")
    } onCancel: {
        print("action38 cancelled")
    }
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.9) {
    debounce {
        print("action39 done")
    } onCancel: {
        print("action39 cancelled")
    }
}

queue.async {
    debounce {
        print("action4 done")
    } onCancel: {
        print("action4 cancelled")
    }
}

queue.asyncAfter(deadline: DispatchTime.now() + 0.5) {
    debounce {
        print("action5 done")
    } onCancel: {
        print("action5 cancelled")
    }
}

queue.asyncAfter(deadline: DispatchTime.now() + 1.5) {
    debounce {
        print("action6 done")
    } onCancel: {
        print("action6 cancelled")
    }
}

queue.asyncAfter(deadline: DispatchTime.now() + 1.6) {
    debounce {
        print("action7 done")
    } onCancel: {
        print("action7 cancelled")
    }
}