UIView+RSKeyboardLayoutGuide.swift

//
//  UIView+RSKeyboardLayoutGuide.swift
//  RSTouchUIKit
//
//  Created by Daniel Jalkut on 12/23/18.
//

import UIKit

// Extends UIView to expose a keyboardLayoutGuide property that can be used to tie a view controller's content
// to so that it will automatically move out of the way when the keyboard appears.

extension UIView {

	func layoutGuide(withIdentifier identifier: String) -> UILayoutGuide? {
		// Should only ever be one with a matching identifier
		return self.layoutGuides.filter { $0.identifier == identifier }.first
	}

	@objc(rsKeyboardLayoutGuide)
	public var keyboardLayoutGuide: UILayoutGuide {
		get {

			let keyboardGuideIdentifier = "com.red-sweater.layoutguide.keyboard"
			if let existingGuide = self.layoutGuide(withIdentifier: keyboardGuideIdentifier) {
				return existingGuide
			}
			else {
				let newGuide = UILayoutGuide()
				newGuide.identifier = keyboardGuideIdentifier

				self.addLayoutGuide(newGuide)

				let heightConstraint = newGuide.heightAnchor.constraint(equalToConstant: 0)
				heightConstraint.isActive = true
				newGuide.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true

				// Subscribe to notifications of keyboard size change, so we can adapt our
				// guide to match.
				NotificationCenter.default.addObserver(forName: UIResponder.keyboardWillChangeFrameNotification, object: nil, queue: nil) { [weak self] note in
					guard
						let existingSelf = self,
						let noteInfo = note.userInfo,
						let keyboardFrame = noteInfo[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect,
						let superview = existingSelf.superview
					else {
						return
					}

					let keyboardFrameInSuperview = superview.convert(keyboardFrame, from: nil)
					let ourFrameInSuperview = superview.convert(existingSelf.frame, from: existingSelf)

					// Special case - if the keyboard is floating we disregard its height. I don't know how
					// to strictly tell if it's floating but when it is floating it seems to represent sometimes
					// as having a 0 width or awkward 36 height. Let's just assume a keyboard width less than
					// half the main screen width is floating.
					let screenWidth = UIScreen.main.bounds.size.width
					let isFloatingKeyboard = keyboardFrameInSuperview.width < (screenWidth / 2)

					// The height anchor constant should be our view's max Y minus the keyboad frame's
					// min Y, which is effectively the top edge of the keyboard.
					let newKeyboardHeight = isFloatingKeyboard ? 0 : max(0.0, ourFrameInSuperview.maxY - keyboardFrameInSuperview.minY)

					// Animate if we have pertinent animation info
					if let animationDuration = noteInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? TimeInterval {
						let animationCurve: UIView.AnimationCurve
						if
							let curveValue = noteInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? Int,
							let validCurve = UIView.AnimationCurve(rawValue: curveValue)
						{
							animationCurve = validCurve
						}
						else {
							 animationCurve = .easeInOut
						}

						// Map from curve value to animation options
						let animationOptions: UIView.AnimationOptions
						switch animationCurve {
						case .easeInOut:
							animationOptions = .curveEaseInOut
						case .easeIn:
							animationOptions = .curveEaseIn
						case .easeOut:
							animationOptions = .curveEaseOut
						case .linear:
							animationOptions = .curveLinear
						default:
							animationOptions = .curveEaseInOut
						}

						UIView.animate(withDuration: animationDuration, delay: 0, options: animationOptions, animations: {
							heightConstraint.constant = newKeyboardHeight
						}, completion: nil)
					}
					else {
						heightConstraint.constant = newKeyboardHeight
					}
				}
				return newGuide
			}
		}
	}
}