Resizable view implementation like rectangles in the markup feature of iOS Photo app

ResizableView.swift

import UIKit

class ResizableRectangle: UIView {
    private let borderWidth: CGFloat = 10
    private var halfOfBorderWidth: CGFloat { return borderWidth / 2 }

    private let topControl = Control(position: .top)
    private let upperRightControl = Control(position: .upperRight)
    private let rightControl = Control(position: .right)
    private let lowerRightControl = Control(position: .lowerRight)
    private let bottomControl = Control(position: .bottom)
    private let lowerLeftControl = Control(position: .lowerLeft)
    private let leftControl = Control(position: .left)
    private let upperLeftControl = Control(position: .upperLeft)

    private let borderView = UIView()

    private var frameAtTouchesBegan: CGRect?

    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }

    private func setup() {
        borderView.backgroundColor = .black

        addSubview(borderView)
        addSubview(topControl)
        addSubview(upperRightControl)
        addSubview(rightControl)
        addSubview(lowerRightControl)
        addSubview(bottomControl)
        addSubview(lowerLeftControl)
        addSubview(leftControl)
        addSubview(upperLeftControl)

        relocateControls()
    }

    private func relocateControls() {
        topControl.center = CGPoint(x: frame.width / 2, y: halfOfBorderWidth)
        upperRightControl.center = CGPoint(x: frame.width - halfOfBorderWidth, y: halfOfBorderWidth)
        rightControl.center = CGPoint(x: frame.width - halfOfBorderWidth, y: frame.height / 2)
        lowerRightControl.center = CGPoint(x: frame.width - halfOfBorderWidth, y: frame.height - halfOfBorderWidth)
        bottomControl.center = CGPoint(x: frame.width / 2, y: frame.height - halfOfBorderWidth)
        lowerLeftControl.center = CGPoint(x: halfOfBorderWidth, y: frame.height - halfOfBorderWidth)
        leftControl.center = CGPoint(x: halfOfBorderWidth, y: frame.height / 2)
        upperLeftControl.center = CGPoint(x: halfOfBorderWidth, y: halfOfBorderWidth)
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        borderView.frame = CGRect(x: 0, y: 0, width: frame.width, height: frame.height)
        maskCenter()
        relocateControls()
    }

    private func maskCenter() {
        let path = UIBezierPath()
        path.move(to: CGPoint(x: halfOfBorderWidth, y: halfOfBorderWidth))
        path.addLine(to: CGPoint(x: frame.width - halfOfBorderWidth, y: halfOfBorderWidth))
        path.addLine(to: CGPoint(x: frame.width - halfOfBorderWidth, y: frame.height - halfOfBorderWidth))
        path.addLine(to: CGPoint(x: halfOfBorderWidth, y: frame.height - halfOfBorderWidth))
        path.close()

        let maskLayer = CAShapeLayer()
        maskLayer.path = path.cgPath
        maskLayer.strokeColor = UIColor.black.cgColor
        maskLayer.lineWidth = borderWidth
        maskLayer.fillColor = nil

        borderView.layer.mask = maskLayer
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first,
            touch.view != nil else { return }

        frameAtTouchesBegan = frame
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first,
            let view = touch.view else { return }


        if let control = view as? Control {
            let location = touch.location(in: superview)
            resize(control: control, locationInParentCoordinate: location)
        } else if view == borderView {
            let location = touch.location(in: self)
            let previousLocation = touch.previousLocation(in: self)
            move(currentLocation: location, previousLocation: previousLocation)
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        frameAtTouchesBegan = nil
    }

    private func resize(control: Control, locationInParentCoordinate: CGPoint) {
        guard let frameAtTouchesBegan = frameAtTouchesBegan else { return }

        let isLocationUpperSide = locationInParentCoordinate.y < frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height
        let isLocationLeftSide = locationInParentCoordinate.x < frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width

        switch control.position {

        case .top:
            frame = CGRect(
                x: frameAtTouchesBegan.origin.x,
                y: isLocationUpperSide ? locationInParentCoordinate.y : frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height,
                width: frameAtTouchesBegan.size.width,
                height: isLocationUpperSide
                    ? frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height - locationInParentCoordinate.y
                    : locationInParentCoordinate.y - frameAtTouchesBegan.origin.y - frameAtTouchesBegan.height)
        case .bottom:
            frame = CGRect(
                x: frameAtTouchesBegan.origin.x,
                y: !isLocationUpperSide ? frameAtTouchesBegan.origin.y : locationInParentCoordinate.y,
                width: frameAtTouchesBegan.size.width,
                height: !isLocationUpperSide
                    ? locationInParentCoordinate.y - frameAtTouchesBegan.origin.y
                    : frameAtTouchesBegan.origin.y - locationInParentCoordinate.y)
        case .right:
            frame = CGRect(
                x: !isLocationLeftSide ? frameAtTouchesBegan.origin.x : locationInParentCoordinate.x,
                y: frameAtTouchesBegan.origin.y,
                width: !isLocationLeftSide
                    ? locationInParentCoordinate.x - frameAtTouchesBegan.origin.x
                    : frameAtTouchesBegan.origin.x - locationInParentCoordinate.x,
                height: frameAtTouchesBegan.size.height)
        case .left:
            frame = CGRect(
                x: isLocationLeftSide ? locationInParentCoordinate.x : frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width,
                y: frameAtTouchesBegan.origin.y,
                width: isLocationLeftSide
                    ? frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width - locationInParentCoordinate.x
                    : locationInParentCoordinate.x - frameAtTouchesBegan.origin.x - frameAtTouchesBegan.width,
                height: frameAtTouchesBegan.size.height)
        case .lowerRight:
            frame = CGRect(
                x: !isLocationLeftSide ? frameAtTouchesBegan.origin.x : locationInParentCoordinate.x,
                y: !isLocationUpperSide ? frameAtTouchesBegan.origin.y : locationInParentCoordinate.y,
                width: !isLocationLeftSide
                    ? locationInParentCoordinate.x - frameAtTouchesBegan.origin.x
                    : frameAtTouchesBegan.origin.x - locationInParentCoordinate.x,
                height: !isLocationUpperSide
                    ? locationInParentCoordinate.y - frameAtTouchesBegan.origin.y
                    : frameAtTouchesBegan.origin.y - locationInParentCoordinate.y)
        case .lowerLeft:
            frame = CGRect(
                x: isLocationLeftSide ? locationInParentCoordinate.x : frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width,
                y: !isLocationUpperSide ? frameAtTouchesBegan.origin.y : locationInParentCoordinate.y,
                width: isLocationLeftSide
                    ? frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width - locationInParentCoordinate.x
                    : locationInParentCoordinate.x - frameAtTouchesBegan.origin.x - frameAtTouchesBegan.width,
                height: !isLocationUpperSide
                    ? locationInParentCoordinate.y - frameAtTouchesBegan.origin.y
                    : frameAtTouchesBegan.origin.y - locationInParentCoordinate.y)
        case .upperLeft:
            frame = CGRect(
                x: isLocationLeftSide ? locationInParentCoordinate.x : frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width,
                y: isLocationUpperSide ? locationInParentCoordinate.y : frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height,
                width: isLocationLeftSide
                    ? frameAtTouchesBegan.origin.x + frameAtTouchesBegan.width - locationInParentCoordinate.x
                    : locationInParentCoordinate.x - frameAtTouchesBegan.origin.x - frameAtTouchesBegan.width,
                height: isLocationUpperSide
                    ? frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height - locationInParentCoordinate.y
                    : locationInParentCoordinate.y - frameAtTouchesBegan.origin.y - frameAtTouchesBegan.height)
        case .upperRight:
            frame = CGRect(
                x: !isLocationLeftSide ? frameAtTouchesBegan.origin.x : locationInParentCoordinate.x,
                y: isLocationUpperSide ? locationInParentCoordinate.y : frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height,
                width: !isLocationLeftSide
                    ? locationInParentCoordinate.x - frameAtTouchesBegan.origin.x
                    : frameAtTouchesBegan.origin.x - locationInParentCoordinate.x,
                height: isLocationUpperSide
                    ? frameAtTouchesBegan.origin.y + frameAtTouchesBegan.height - locationInParentCoordinate.y
                    : locationInParentCoordinate.y - frameAtTouchesBegan.origin.y - frameAtTouchesBegan.height)
        }
    }

    private func move(currentLocation: CGPoint, previousLocation: CGPoint) {
        let distanceX = currentLocation.x - previousLocation.x
        let distanceY = currentLocation.y - previousLocation.y
        center = CGPoint(x: center.x + distanceX, y: center.y + distanceY)
    }
}

extension ResizableRectangle {
    private enum Position {
        case top, upperRight, right, lowerRight, bottom, lowerLeft, left, upperLeft
    }

    private class Control: UIView {
        private let radius: CGFloat = 8
        private let borderWidth: CGFloat = 2

        let position: Position

        init(position: Position) {
            self.position = position
            super.init(frame: CGRect(x: 0, y: 0, width: radius * 2, height: radius * 2))
            setup()
        }

        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }

        private func setup() {
            layer.borderWidth = borderWidth
            layer.borderColor = UIColor.white.cgColor
            layer.cornerRadius = radius
            backgroundColor = .blue
        }
    }
}

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