InteractivePanGesture.swift

@objc
private func panGesture(_ sender: UIPanGestureRecognizer) {
    let percentThreshold: CGFloat = 0.3
    let translation = sender.translation(in: sender.view)
    let verticalMovement = translation.y / sender.view!.bounds.height
    let downwardMovement = fmaxf(Float(verticalMovement), 0.0)
    let downwardMovementPercent = fminf(downwardMovement, 1.0)
    let progress = CGFloat(downwardMovementPercent)

    guard let interactor = interactor else { return }

    switch sender.state {
    case .began:
        interactor.hasStarted = true
    case .changed:
        let velocity = sender.velocity(in: sender.view?.superview)
        let maxOffset = containerView!.bounds.height - presentedView!.frame.height
        presentedView!.frame.origin.y = max(maxOffset, maxOffset + translation.y)
        interactor.shouldFinish = progress > percentThreshold
        interactor.update(progress)
        direction = velocity.y
    case .cancelled:
        interactor.hasStarted = false
        interactor.cancel()
    case .ended:
        interactor.hasStarted = false
        if direction < 0 {
            presentedView!.frame.origin.y = containerView!.bounds.height - self.presentedView!.frame.height
            interactor.cancel()
        } else {
            presentedViewController.dismiss(animated: true, completion: nil)
            interactor.shouldFinish ? interactor.finish() : interactor.cancel()
        }
    default:
        break
    }
}