public class NKSkeleton {

  public init(configuration: NKSkeletonConfiguration, sourceView: UIView? = nil) 

  /**
    Show skeleton on `sourceView`
  */
  public func show(on sourceView: UIView? = nil) 

  /**
    Hide skeleton on `sourceView`
  */
  public func remove() 

}

public struct NKSkeletonConfiguration {

  /// The parameter indicates the need to play animation
  public var isAnimatable = false

  /// Sequence of colors to display the gradient
  public var colors = [UIColor.white.cgColor, UIColor.lightGray.cgColor]

  /// Gradient display type
  public var type: NKType = .axial

  /// The position of the beginning of the gradient vector
  public var initialPosition: NKInitialPosition = .topLeft

  /// The duration of one pass animation
  public var duration: CFTimeInterval = 0

  /// The level of subviews to be hidden by the skeleton, relative to the parent view
  public var subviewsLevel = 0

  public init()

}

public extension NKSkeletonConfiguration {

  /// Skeleton gradient type
  public enum NKType: Equatable {

    /**
      Using the parameter `.axial` gradient will be formed as a linear transition between the colors along the gradient vector
    */
    case axial

    /**
      Using the parameter `.radial(Bool)` gradient will be formed as a radial transition between the colors from the starting point in all directions

      The passed `Bool` parameter is responsible for the direction of the animation.
      If `NKSkeletonConfiguration().isAnimatable = false` passed `Bool` parameter value will be ignored.

      If passed `Bool` parameter is `true` animation will move from `NKSkeletonConfiguration().initialPosition' in all directions, else - from all directions to `NKSkeletonConfiguration().initialPosition'
    */
    case radial(Bool)

  }


  /**
  Starting (initial) point of the gradient on the `NKSkeleton().sourceView'

  In case `NKSkeletonConfiguration().type = .axial' gradient vector will be directed from the selected starting point to the opposite side/corner

  In case `NKSkeletonConfiguration().type = .radial(bool)' will be formed as a radial transition between the colors from the starting point in all directions
  */
  public enum NKInitialPosition {

    /// <if `NKSkeletonConfiguration().type = .axial'> from left side to right side
    case left

    /// <if `NKSkeletonConfiguration().type = .axial'> from right side to left side
    case right

    /// <if `NKSkeletonConfiguration().type = .axial'> from top side to bottom side
    case top

    /// <if `NKSkeletonConfiguration().type = .axial'> from bottom side to top side
    case bottom

    /// <if `NKSkeletonConfiguration().type = .axial'> from top left corner to bottom right corner
    case topLeft

    /// <if `NKSkeletonConfiguration().type = .axial'> from top right corner to bottom left corner
    case topRight

    /// <if `NKSkeletonConfiguration().type = .axial'> from bottom left corner to top right corner
    case bottomLeft

    /// <if `NKSkeletonConfiguration().type = .axial'> from bottom right corner to top left corner
    case bottomRight

    /// <if `NKSkeletonConfiguration().type = .axial'> from center to left and right sides
    case center
  }

}