SlideToActionView.swift

import UIKit

struct Colors {
	static let background = #colorLiteral(red: 0.657153666, green: 0.8692060113, blue: 0.6173200011, alpha: 1)
	static let draggedBackground = #colorLiteral(red: 0.462745098, green: 0.7843137255, blue: 0.5764705882, alpha: 1)
	static let tint = #colorLiteral(red: 0.1019607843, green: 0.4588235294, blue: 0.6235294118, alpha: 1)
}

protocol SlideToActionButtonDelegate: AnyObject {
	func didFinish()
}

class SlideToActionButton: UIView {
	
	let handleView: UIView = {
		let view = UIView()
		view.translatesAutoresizingMaskIntoConstraints = false
		view.backgroundColor = Colors.draggedBackground
		view.layer.cornerRadius = 12
		view.layer.masksToBounds = true
		view.layer.borderWidth = 3
		view.layer.borderColor = Colors.tint.cgColor
		return view
	}()
	
	let handleViewImage: UIImageView = {
		let view = UIImageView()
		view.translatesAutoresizingMaskIntoConstraints = false
		view.image = UIImage(systemName: "chevron.right.2", withConfiguration: UIImage.SymbolConfiguration(font: .systemFont(ofSize: 40, weight: .bold)))?.withRenderingMode(.alwaysTemplate)
		view.contentMode = .scaleAspectFit
		view.tintColor = Colors.tint
		return view
	}()
	
	let draggedView: UIView = {
		let view = UIView()
		view.translatesAutoresizingMaskIntoConstraints = false
		view.backgroundColor = Colors.draggedBackground
		view.layer.cornerRadius = 12
		return view
	}()

	let titleLabel: UILabel = {
		let label = UILabel()
		label.translatesAutoresizingMaskIntoConstraints = false
		label.textAlignment = .center
		label.textColor = Colors.tint
		label.font = .systemFont(ofSize: 24, weight: .semibold)
		label.text = "Slide me!"
		return label
	}()
	
	private var leadingThumbnailViewConstraint: NSLayoutConstraint?
	private var panGestureRecognizer: UIPanGestureRecognizer!

	weak var delegate: SlideToActionButtonDelegate?
	
	private var xEndingPoint: CGFloat {
		return (bounds.width - handleView.bounds.width)
	}
	
	private var isFinished = false
	
	init() {
		super.init(frame: .zero)
		setup()
	}
	
	required init?(coder: NSCoder) {
		super.init(coder: coder)
		setup()
	}
	
	func setup() {
		backgroundColor = Colors.background
		layer.cornerRadius = 12
		addSubview(titleLabel)
		addSubview(draggedView)
		addSubview(handleView)
		handleView.addSubview(handleViewImage)
		
		//MARK: - Constraints
		
		leadingThumbnailViewConstraint = handleView.leadingAnchor.constraint(equalTo: leadingAnchor)
		
		NSLayoutConstraint.activate([
			leadingThumbnailViewConstraint!,
			handleView.topAnchor.constraint(equalTo: topAnchor),
			handleView.bottomAnchor.constraint(equalTo: bottomAnchor),
			handleView.widthAnchor.constraint(equalToConstant: 80),
			draggedView.topAnchor.constraint(equalTo: topAnchor),
			draggedView.bottomAnchor.constraint(equalTo: bottomAnchor),
			draggedView.leadingAnchor.constraint(equalTo: leadingAnchor),
			draggedView.trailingAnchor.constraint(equalTo: handleView.trailingAnchor),
			handleViewImage.topAnchor.constraint(equalTo: handleView.topAnchor, constant: 10),
			handleViewImage.bottomAnchor.constraint(equalTo: handleView.bottomAnchor, constant: -10),
			handleViewImage.centerXAnchor.constraint(equalTo: handleView.centerXAnchor),
			titleLabel.leadingAnchor.constraint(equalTo: leadingAnchor),
			titleLabel.trailingAnchor.constraint(equalTo: trailingAnchor),
			titleLabel.centerYAnchor.constraint(equalTo: centerYAnchor)
		])
		
		panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(self.handlePanGesture(_:)))
		panGestureRecognizer.minimumNumberOfTouches = 1
		handleView.addGestureRecognizer(panGestureRecognizer)
	}
	
	@objc private func handlePanGesture(_ sender: UIPanGestureRecognizer) {
		if isFinished { return }
		let translatedPoint = sender.translation(in: self).x

		switch sender.state {
		case .changed:
			if translatedPoint <= 0 {
				updateHandleXPosition(0)
			} else if translatedPoint >= xEndingPoint {
				updateHandleXPosition(xEndingPoint)
			} else {
				updateHandleXPosition(translatedPoint)
			}
		case .ended:
			if translatedPoint >= xEndingPoint {
				self.updateHandleXPosition(xEndingPoint)
				isFinished = true
				delegate?.didFinish()
			} else {
				UIView.animate(withDuration: 1) {
					self.reset()
				}
			}
		default:
			break
		}
	}
	
	private func updateHandleXPosition(_ x: CGFloat) {
		leadingThumbnailViewConstraint?.constant = x
	}

	func reset() {
		isFinished = false
		updateHandleXPosition(0)
	}
}