SeparatorView.swift

import UIKit

enum SeparatorType {
    case Horisontal
    case Vertical
}

let kTotalSize: CGFloat = 44;    // the total height of the separator (including parts that are not visible
let kVisibleSize: CGFloat = 10;   // the height of the visible portion of the separator
let kMargin: CGFloat = (kTotalSize - kVisibleSize) / 2.0;   // the height of the non-visible portions of the separator (i.e. above and below the visible portion)
let kMinSize: CGFloat = 10;       // the minimum height allowed for views above and below the separator

protocol OnConstraintsUpdateProtocol {
    func updateConstraintOnBasisOfTouch(touch: UITouch)
}

class SeparatorView: UIView {

    var startConstraint: NSLayoutConstraint?      // the constraint that dictates the vertical position of the separator
    var primaryView: UIView                        // the view above the separator
    var secondaryView: UIView                     // the view below the separator
    
    // some properties used for handling the touches
    
    var oldPosition: CGFloat = 0.0            // the position of the separator before the gesture started
    var firstTouch: CGPoint?            // the position where the drag gesture started
    
    var updateListener: OnConstraintsUpdateProtocol?

    internal static func addSeparatorBetweenViews(separatorType: SeparatorType,  primaryView: UIView, secondaryView: UIView, parentView: UIView) -> SeparatorView {
        
        var separator: SeparatorView
        
        if (separatorType == .Horisontal) {
            separator = HorizontalSeparatorView(primaryView: primaryView, secondaryView: secondaryView)
        } else {
            separator = VerticalSeparatorView(primaryView: primaryView, secondaryView: secondaryView)
        }
        separator.setupParentViewConstraints(parentView)
        parentView.addSubview(separator)
        separator.setupSeparatorConstraints()
        
        return separator
    }
    
    init(primaryView: UIView, secondaryView: UIView){
        self.primaryView = primaryView
        self.secondaryView = secondaryView
        super.init(frame: CGRectZero)
        self.translatesAutoresizingMaskIntoConstraints = false
        self.userInteractionEnabled = true
        self.backgroundColor = UIColor.clearColor()
    }
    
    func setupParentViewConstraints(parentView: UIView){}
    
    func setupSeparatorConstraints(){}
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        self.firstTouch = touches.first?.locationInView(self.superview)
        self.startConstraint!.constant = self.oldPosition;
        self.startConstraint!.active = true;
    }
    
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        
        guard let touch = touches.first, event = event else { return }
        
        // for more responsive UX, use predicted touches, if possible
        let predictedTouch = event.predictedTouchesForTouch(touch)?.last
        if ((predictedTouch) != nil) {
            updateListener?.updateConstraintOnBasisOfTouch(predictedTouch!)
            return;
        }
        // if no predicted touch found, just use the touch provided
        updateListener?.updateConstraintOnBasisOfTouch(touch)
    }
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        guard let touch = touches.first else { return }
        updateListener?.updateConstraintOnBasisOfTouch(touch)
    }
    
    override func drawRect(rect: CGRect) {
        let path = UIBezierPath(rect: rect)
        UIColor.blackColor().set()
        path.stroke()
        path.fill()
    }
}

class HorizontalSeparatorView: SeparatorView, OnConstraintsUpdateProtocol {
    
    override init(primaryView: UIView, secondaryView: UIView) {
        super.init(primaryView: primaryView, secondaryView: secondaryView)
        updateListener = self
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func setupParentViewConstraints(parentView: UIView) {
        parentView.leadingAnchor.constraintEqualToAnchor(primaryView.leadingAnchor).active = true
        parentView.trailingAnchor.constraintEqualToAnchor(primaryView.trailingAnchor).active = true
        parentView.leadingAnchor.constraintEqualToAnchor(secondaryView.leadingAnchor).active = true
        parentView.trailingAnchor.constraintEqualToAnchor(secondaryView.trailingAnchor).active = true
        parentView.topAnchor.constraintEqualToAnchor(primaryView.topAnchor).active = true
        let height = secondaryView.heightAnchor.constraintEqualToAnchor(primaryView.heightAnchor)
        height.priority = 250
        height.active = true
        parentView.bottomAnchor.constraintEqualToAnchor(secondaryView.bottomAnchor).active = true
    }
    
    override func setupSeparatorConstraints() {
        self.heightAnchor.constraintEqualToConstant(kTotalSize).active = true
        self.superview?.leadingAnchor.constraintEqualToAnchor(self.leadingAnchor).active = true
        self.superview?.trailingAnchor.constraintEqualToAnchor(self.trailingAnchor).active = true
        primaryView.bottomAnchor.constraintEqualToAnchor(self.topAnchor, constant:  kMargin).active = true
        secondaryView.topAnchor.constraintEqualToAnchor(self.bottomAnchor, constant: -kMargin).active = true
        
        startConstraint = self.topAnchor.constraintEqualToAnchor(self.superview?.topAnchor, constant: 0)
    }
    
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        self.oldPosition = self.frame.origin.y;
        super.touchesBegan(touches, withEvent: event)
    }
    
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesMoved(touches, withEvent: event)
    }
    
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesEnded(touches, withEvent: event)
    }
    
    func updateConstraintOnBasisOfTouch(touch: UITouch) {
        // calculate where separator should be moved to
        var y: CGFloat = self.oldPosition + touch.locationInView(self.superview).y - self.firstTouch!.y
    
        // make sure the views above and below are not too small
        y = max(y, self.primaryView.frame.origin.y + kMinSize - kMargin)
        y = min(y, self.secondaryView.frame.origin.y + self.secondaryView.frame.size.height - (kMargin + kMinSize))
    
        // set constraint
        self.startConstraint!.constant = y
    }
    
    override func drawRect(rect: CGRect) {
        let separatorRect = CGRectMake(0, kMargin, self.bounds.size.width, kVisibleSize)
        super.drawRect(separatorRect)
    }

}

class VerticalSeparatorView: SeparatorView, OnConstraintsUpdateProtocol {
    
    override init(primaryView: UIView, secondaryView: UIView) {
        super.init(primaryView: primaryView, secondaryView: secondaryView)
        updateListener = self
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func setupParentViewConstraints(parentView: UIView) {
        parentView.topAnchor.constraintEqualToAnchor(primaryView.topAnchor).active = true
        parentView.topAnchor.constraintEqualToAnchor(secondaryView.topAnchor).active = true
        parentView.bottomAnchor.constraintEqualToAnchor(primaryView.bottomAnchor).active = true
        parentView.leadingAnchor.constraintEqualToAnchor(secondaryView.topAnchor).active = true
        parentView.bottomAnchor.constraintEqualToAnchor(secondaryView.bottomAnchor).active = true
        parentView.leadingAnchor.constraintEqualToAnchor(primaryView.leadingAnchor).active = true
        let width = secondaryView.widthAnchor.constraintEqualToAnchor(primaryView.widthAnchor)
        width.priority = 250
        width.active = true
        parentView.trailingAnchor.constraintEqualToAnchor(secondaryView.trailingAnchor).active = true
    }
    
    override func setupSeparatorConstraints() {
        self.widthAnchor.constraintEqualToConstant(kTotalSize).active = true
        self.superview?.topAnchor.constraintEqualToAnchor(self.topAnchor).active = true
        self.superview?.bottomAnchor.constraintEqualToAnchor(self.bottomAnchor).active = true
        primaryView.trailingAnchor.constraintEqualToAnchor(self.leadingAnchor, constant:  kMargin).active = true
        secondaryView.leadingAnchor.constraintEqualToAnchor(self.trailingAnchor, constant: -kMargin).active = true
        
        startConstraint = self.leadingAnchor.constraintEqualToAnchor(self.superview?.leadingAnchor, constant: 0)
    }
    
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        self.oldPosition = self.frame.origin.x;
        super.touchesBegan(touches, withEvent: event)
    }
    
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesMoved(touches, withEvent: event)
    }
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesEnded(touches, withEvent: event)
    }
    
    func updateConstraintOnBasisOfTouch(touch: UITouch) {
        // calculate where separator should be moved to
        var x: CGFloat = self.oldPosition + touch.locationInView(self.superview).x - self.firstTouch!.x
        
        // make sure the views above and below are not too small
        x = max(x, self.primaryView.frame.origin.x + kMinSize - kMargin)
        x = min(x, self.secondaryView.frame.origin.x + self.secondaryView.frame.size.width - (kMargin + kMinSize))
        
        // set constraint
        self.startConstraint!.constant = x
    }
    
    override func drawRect(rect: CGRect) {
        let separatorRect = CGRectMake(kMargin, 0, kVisibleSize, self.bounds.size.height)
        super.drawRect(separatorRect)
    }

}