SegmentView.swift

//
//  SegmentView.swift
//  CustomUIView
//
//  Created by Maksim Vialykh on 08.06.2018.
//  Copyright © 2018 Vialyx. All rights reserved.
//

import UIKit

@IBDesignable
final class SegmentView: UIView {
    
    // MARK: - Properties
    
    @IBInspectable
    var cornerRadius: CGFloat {
        set {
            layer.cornerRadius = newValue
        }
        get {
            return layer.cornerRadius
        }
    }
    
    @IBInspectable
    var segments: [String] = ["One", "Two", "..."]
    
    @IBInspectable
    var segmentColor: UIColor = .lightGray
    
    @IBInspectable
    var activeSegmentColor: UIColor = .darkGray
    
    @IBInspectable
    var textColor: UIColor = .black
    
    @IBInspectable
    var activeTextColor: UIColor = .white
    
    @IBInspectable
    var font: UIFont = .systemFont(ofSize: 18.0, weight: .medium)
    
    @IBInspectable
    var activeFont: UIFont = .systemFont(ofSize: 18.0, weight: .medium)
    
    @IBInspectable
    var activeIndex: Int = 0 {
        didSet {
            setNeedsDisplay()
        }
    }
    
    // MARK: - Private properties
    
    private lazy var paragraphStyle: NSParagraphStyle = {
        let paragraph = NSParagraphStyle.default.mutableCopy() as! NSMutableParagraphStyle
        paragraph.alignment = .center
        return paragraph.copy() as! NSParagraphStyle
    }()
    private var segmentSize: CGFloat {
        return frame.width / CGFloat(segments.count)
    }
    
    // MARK: - Initializers
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        configure()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        configure()
    }
    
    private func configure() {
        addGestureRecognizer(
            UITapGestureRecognizer(target: self, action: #selector(didTap(recognizer:)))
        )
    }
    
    // MARK: - Actions
    
    @objc
    private func didTap(recognizer: UITapGestureRecognizer) {
        let location = recognizer.location(in: self)
        activeIndex = Int(location.x / segmentSize)
    }
    
    // MARK: - Drawing
    
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        guard let context = UIGraphicsGetCurrentContext() else { return }
        
        /*
         Draw background
        */
        context.setFillColor(segmentColor.cgColor)
        let backgroundPath = UIBezierPath(roundedRect: rect, cornerRadius: cornerRadius)
        backgroundPath.fill()
        
        /*
         Enumerate segments property and call drawing function for each item
         */
        segments.enumerated().forEach { index, title in
            let rect = CGRect(x: CGFloat(index) * segmentSize, y: 0, width: segmentSize, height: frame.height)
            
            if activeIndex == index {
                /*
                 Draw background for active index
                 */
                context.setFillColor(activeSegmentColor.cgColor)
                let path = UIBezierPath(roundedRect: rect, cornerRadius: cornerRadius)
                path.fill()
                
                draw(text: title, in: rect, with: activeTextColor, and: activeFont)
            } else {
                draw(text: title, in: rect, with: textColor, and: font)
            }
        }
    }
    
    private func draw(text: String, in rect: CGRect, with color: UIColor, and font: UIFont) {
        /*
         Draw text with incomming parameters
         */
        var rect = rect
        let attributes: [NSAttributedStringKey: Any] = [.font: font,
                                                        .foregroundColor: color,
                                                        .paragraphStyle: paragraphStyle]
        let string = NSAttributedString(string: text, attributes: attributes)
        let size = string.size()
        rect.origin.y = (frame.height - size.height) / 2
        rect.size.height = size.height
        string.draw(in: rect)
    }
    
}