vds_ios/VDS/Components/Loader/Loader.swift

//
//  Loader.swift
//  VDS
//
//  Created by Matt Bruce on 7/5/23.
//

import Foundation
import UIKit
import VDSCoreTokens


/// A loader is an indicator that uses animation to show customers that there is an indefinite amount of wait time while a task is ongoing, e.g. a page is loading, a form is being submitted. The component disappears when the task is complete.
@objc(VDSLoader)
open class Loader: View {
    
    //--------------------------------------------------
    // MARK: - Initializers
    //--------------------------------------------------
    required public init() {
        super.init(frame: .zero)
    }
    
    public override init(frame: CGRect) {
        super.init(frame: .zero)
    }
    
    public required init?(coder: NSCoder) {
        super.init(coder: coder)
    }
    
    //--------------------------------------------------
    // MARK: - Private Properties
    //--------------------------------------------------
    private var icon = Icon().with { $0.name = .loader }
    private var opacity: CGFloat = 0.8
    private var iconColorConfiguration = SurfaceColorConfiguration(VDSColor.elementsPrimaryOnlight, VDSColor.elementsPrimaryOndark)
    private var loadingTimer: Timer?
    
    //--------------------------------------------------
    // MARK: - Public Properties
    //--------------------------------------------------    
    /// Loader will be active if 'active' prop is passed.
    open var isActive: Bool = true { didSet { setNeedsUpdate() } }
    
    /// The Int used to determine the height and width of the Loader
    open var size: Int = 40 {
        didSet {
            setNeedsUpdate();
            invalidateIntrinsicContentSize()
        }
    }
    
    /// The natural size for the receiving view, considering only properties of the view itself.
    open override var intrinsicContentSize: CGSize { isActive ? .init(width: size, height: size) : .zero }
    
    //--------------------------------------------------
    // MARK: - Overrides
    //--------------------------------------------------
    /// Called once when a view is initialized and is used to Setup additional UI or other constants and configurations.
    open override func setup() {
        super.setup()
        addSubview(icon)  
        isAccessibilityElement = true
        icon.isAccessibilityElement = false
        icon
            .pinTopGreaterThanOrEqualTo()
            .pinLeadingGreaterThanOrEqualTo()
            .pinTrailingLessThanOrEqualTo()
            .pinBottomLessThanOrEqualTo()
        
        NSLayoutConstraint.activate([
            icon.centerXAnchor.constraint(equalTo: centerXAnchor),
            icon.centerYAnchor.constraint(equalTo: centerYAnchor)
        ])
    }
    
    /// Used to make changes to the View based off a change events or from local properties.
    open override func updateView() {
        super.updateView()
        icon.color = iconColorConfiguration.getColor(self)
        icon.customSize = size
        if isActive && isVisibleOnScreen {
            startAnimating()
        } else {
            stopAnimating()
        }
        invalidateIntrinsicContentSize()
    }
    
    open override func updateAccessibility() {
        super.updateAccessibility()
        
        // check to make sure VoiceOver is running
        guard UIAccessibility.isVoiceOverRunning, isActive else {
            loadingTimer?.invalidate()
            loadingTimer = nil
            return
        }
        
        // Focus VoiceOver on this view
        UIAccessibility.post(notification: .layoutChanged, argument: self)
        
        // setup timer for post
        loadingTimer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true) { [weak self] _ in
            guard let self, self.isActive, self.isVisibleOnScreen else { return }
            self.accessibilityLabel = "Still Loading"
            UIAccessibility.post(notification: .announcement, argument: "Still Loading")
        }
    }
    
    //--------------------------------------------------
    // MARK: - Private Methods
    //--------------------------------------------------
    private let rotationLayerName = "rotationAnimation"
    private func startAnimating() {
        accessibilityLabel = "Loading"
        isAccessibilityElement = true
        icon.isHidden = false
        
        icon.layer.remove(layerName: rotationLayerName)
        let rotation : CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
        rotation.fromValue = 0
        rotation.toValue = Double.pi * 2
        rotation.duration = 0.5
        rotation.repeatCount = .infinity
        icon.layer.add(rotation, forKey: rotationLayerName)
    }
    
    private func stopAnimating() {
        isAccessibilityElement = false
        icon.isHidden = true
        icon.layer.removeAnimation(forKey: rotationLayerName)
        loadingTimer?.invalidate()
        loadingTimer = nil
    }
        
    deinit {
        stopAnimating()
    }
}

extension Icon.Name {
    static let loader = Icon.Name(name: "loader")
}