custompagecontrol.swift

import UIKit

final class ScrollingPageControl: UIView {

	//	The number of dots
	var pages: Int = 0 {
		didSet {
			guard pages != oldValue else { return }
			pages = max(0, pages)
			invalidateIntrinsicContentSize()
			makeDotViews()
		}
	}

	private func makeDotViews() {
		dotViews = (0..<pages).map { index in
			Circle(frame: CGRect(origin: .zero, size: CGSize(width: dotSize, height: dotSize)))
		}
	}

	//	The index of the currently selected page
	var currentPage: Int = 0 {
		didSet {
			guard currentPage != oldValue else { return }
			currentPage = max(0, min (currentPage, pages - 1))
			updateColors()
			if (0..<centerDots).contains(currentPage - pageOffset) {
				centerOffset = currentPage - pageOffset
			} else {
				pageOffset = currentPage - centerOffset
			}
		}
	}

	//	The maximum number of dots that will show in the control
	var maxDots = 7 {
		didSet {
			maxDots = max(3, maxDots)
			if maxDots % 2 == 0 {
				maxDots += 1
				print("maxPages has to be an odd number")
			}
			invalidateIntrinsicContentSize()
			updatePositions()
		}
	}

	//	The number of dots that will be centered and full-sized
	var centerDots = 3 {
		didSet {
			centerDots = max(1, centerDots)
			if centerDots % 2 == 0 {
				centerDots += 1
				print("centerDots has to be an odd number")
			}
			updatePositions()
		}
	}

	//	The duration, in seconds, of the dot slide animation
	var slideDuration: TimeInterval = 0.15
	private var centerOffset = 0
	private var pageOffset = 0 {
		didSet {
			UIView.animate(
				withDuration: slideDuration,
				delay: 0.15,
				options: [.curveEaseInOut],
				animations: { [weak self] in
					self?.updatePositions()
			})
		}
	}

	private var dotViews: [UIView] = [] {
		didSet {
			oldValue.forEach { $0.removeFromSuperview() }
			dotViews.forEach(addSubview)
			updateColors()
			updatePositions()
		}
	}

	//	The color of all the unselected dots
	var dotColor = UIColor(white: 224 / 255, alpha: 1)
	//	The color of the currently selected dot
	var selectedColor = UIColor(red: 4 / 255, green: 166 / 255, blue: 225 / 255, alpha: 1)
	//	The size of the dots
	var dotSize: CGFloat = 6
	//	The space between dots
	var spacing: CGFloat = 6

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

	override init(frame: CGRect) {
		super.init(frame: frame)
		isOpaque = false
	}

	private var lastSize = CGSize.zero
	override func layoutSubviews() {
		super.layoutSubviews()
		guard bounds.size != lastSize else { return }
		lastSize = bounds.size
		updatePositions()
	}

	private func updateColors() {
		dotViews.enumerated().forEach { page, dot in
			dot.tintColor = page == currentPage ? selectedColor : dotColor
		}
	}

	private func updatePositions() {
		if pages > 5 {
			let sidePages = (maxDots - centerDots) / 2
			let horizontalOffset = CGFloat(-pageOffset + sidePages) * (dotSize + spacing) + (bounds.width - intrinsicContentSize.width) / 2
			let centerPage = centerDots / 2 + pageOffset

			dotViews.enumerated().forEach { page, dot in
				let center = CGPoint(x: horizontalOffset + bounds.minX + dotSize / 2 + (dotSize + spacing) * CGFloat(page), y: bounds.midY)

				let scale: CGFloat = {
					let distance = abs(page - centerPage)

					if distance > (maxDots / 2) { return 0 }
					return [1, 0.66, 0.33, 0.16][max(0, min(3, distance - centerDots / 2))]
				}()

				dot.frame = CGRect(origin: .zero, size: CGSize(width: dotSize * scale, height: dotSize * scale))
				dot.center = center
			}
		} else {
			dotViews.enumerated().forEach { page, dot in
				dot.frame = CGRect(origin: .zero, size: CGSize(width: dotSize, height: dotSize))
				let center = CGPoint(x: bounds.minX + dotSize / 2 + (dotSize + spacing) * CGFloat(page), y: bounds.midY)
				dot.center = center
			}
		}
	}

	override var intrinsicContentSize: CGSize {
		let pages = min(maxDots, self.pages)
		let width = CGFloat(pages) * dotSize + CGFloat(pages - 1) * spacing
		let height = dotSize
		return CGSize(width: width, height: height)
	}

	class Circle: UIView {
		override func tintColorDidChange() {
			self.backgroundColor = tintColor
		}

		override func layoutSubviews() {
			super.layoutSubviews()
			layer.cornerRadius = min(bounds.width, bounds.height) / 2
		}

		override var frame: CGRect {
			didSet {
				layer.cornerRadius = min(bounds.width, bounds.height) / 2
			}
		}
	}
}