metatext/Views/VisualEffectBlur.swift

// Copyright © 2020 Metabolist. All rights reserved.

// Taken from Apple's Fruta example code

import SwiftUI

struct VisualEffectBlur<Content: View>: View {
    var blurStyle: UIBlurEffect.Style
    var vibrancyStyle: UIVibrancyEffectStyle?
    var content: Content

    init(blurStyle: UIBlurEffect.Style = .systemMaterial,
         vibrancyStyle: UIVibrancyEffectStyle? = nil,
         @ViewBuilder content: () -> Content) {
        self.blurStyle = blurStyle
        self.vibrancyStyle = vibrancyStyle
        self.content = content()
    }

    var body: some View {
        Representable(
            blurStyle: blurStyle,
            vibrancyStyle: vibrancyStyle,
            content: ZStack { content })
            .accessibility(hidden: Content.self == EmptyView.self)
    }
}

extension VisualEffectBlur {
    struct Representable<Content: View>: UIViewRepresentable {
        var blurStyle: UIBlurEffect.Style
        var vibrancyStyle: UIVibrancyEffectStyle?
        var content: Content

        func makeUIView(context: Context) -> UIVisualEffectView {
            context.coordinator.blurView
        }

        func updateUIView(_ view: UIVisualEffectView, context: Context) {
            context.coordinator.update(content: content, blurStyle: blurStyle, vibrancyStyle: vibrancyStyle)
        }

        func makeCoordinator() -> Coordinator {
            Coordinator(content: content)
        }
    }
}

extension VisualEffectBlur.Representable {
    class Coordinator {
        let blurView = UIVisualEffectView()
        let vibrancyView = UIVisualEffectView()
        let hostingController: UIHostingController<Content>

        init(content: Content) {
            hostingController = UIHostingController(rootView: content)
            hostingController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            hostingController.view.backgroundColor = nil
            blurView.contentView.addSubview(vibrancyView)
            blurView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            vibrancyView.contentView.addSubview(hostingController.view)
            vibrancyView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        }

        func update(content: Content, blurStyle: UIBlurEffect.Style, vibrancyStyle: UIVibrancyEffectStyle?) {
            hostingController.rootView = content

            let blurEffect = UIBlurEffect(style: blurStyle)

            blurView.effect = blurEffect

            if let vibrancyStyle = vibrancyStyle {
                vibrancyView.effect = UIVibrancyEffect(blurEffect: blurEffect, style: vibrancyStyle)
            } else {
                vibrancyView.effect = nil
            }

            hostingController.view.setNeedsDisplay()
        }
    }
}

extension VisualEffectBlur where Content == EmptyView {
    init(blurStyle: UIBlurEffect.Style = .systemMaterial) {
        self.init(blurStyle: blurStyle, vibrancyStyle: nil) {
            EmptyView()
        }
    }
}

struct VisualEffectBlur_Previews: PreviewProvider {
    static var previews: some View {
        ZStack {
            LinearGradient(
                gradient: Gradient(colors: [.red, .blue]),
                startPoint: .topLeading,
                endPoint: .bottomTrailing
            )

            VisualEffectBlur(blurStyle: .systemUltraThinMaterial, vibrancyStyle: .fill) {
                Text("Hello World!")
                    .frame(width: 200, height: 100)
            }
        }
        .previewLayout(.sizeThatFits)
    }
}