WidgetPreviewProviderModifier.swift

import SwiftUI
import WidgetKit

enum WidgetPreviewProviderMode: CaseIterable {
    
    /// Use for a system small widget preview.
    case small
    
    /// Use for a system medium widget preview.
    case medium
    
    /// Use for a system large widget preview.
    case large
    
    /// Use for a system extra large widget preview.
    case extraLarge
    
}

extension WidgetPreviewProviderMode {
    
    /// Provides the appropriate mode for the specified widget family.
    static func mode(for widgetFamily: WidgetFamily) -> WidgetPreviewProviderMode {
        switch widgetFamily {
        case .systemSmall:
            return .small
        case .systemMedium:
            return .medium
        case .systemLarge:
            return .large
        case .systemExtraLarge:
            return .extraLarge
        @unknown default:
            return .small
        }
    }
    
}

fileprivate struct WidgetPreviewProviderModifier: ViewModifier {
    
    /// The widget preview provider modes to display.
    let modes: [WidgetPreviewProviderMode]
    
    func body(content: Content) -> some View {
        Group {
            if modes.contains(.small) {
                content
                    .previewContext(WidgetPreviewContext(family: .systemSmall))
                    .previewDisplayName("Small")
            }
            
            if modes.contains(.medium) {
                content
                    .previewContext(WidgetPreviewContext(family: .systemMedium))
                    .previewDisplayName("Medium")
            }
            
            if modes.contains(.large) {
                content
                    .previewContext(WidgetPreviewContext(family: .systemLarge))
                    .previewDisplayName("Large")
            }
            
            if modes.contains(.extraLarge) {
                content
                    .previewContext(WidgetPreviewContext(family: .systemExtraLarge))
                    .previewDisplayName("Extra Large")
            }
        }
    }
    
}

extension View {
    
    /// Creates a group of views with various widget contexts that are useful for widget previews.
    ///
    /// - Parameters:
    ///   - modes: The widget preview provider modes to display, such as small, medium, large, and extra large.
    func makeForWidgetPreviewProvider(_ modes: [WidgetPreviewProviderMode] = WidgetPreviewProviderMode.allCases) -> some View {
        modifier(WidgetPreviewProviderModifier(modes: modes))
    }
    
    /// Creates a group of views with various widget contexts that are useful for widget previews.
    ///
    /// - Parameters:
    ///   - mode: The widget preview provider mode to display, such as small, medium, large, or extra large.
    func makeForWidgetPreviewProvider(_ mode: WidgetPreviewProviderMode) -> some View {
        modifier(WidgetPreviewProviderModifier(modes: [mode]))
    }
    
    /// Creates a group of views with various environment settings that are useful for widget previews.
    ///
    /// - Parameters:
    ///   - modes: The widget preview provider modes to be excluded from being displayed. All other modes will be displayed.
    func makeForWidgetPreviewProvider(excluding modes: [WidgetPreviewProviderMode]) -> some View {
        let included = WidgetPreviewProviderMode.allCases.filter { modes.contains($0) == false }
        return modifier(WidgetPreviewProviderModifier(modes: included))
    }
    
    /// Creates a group of views with various environment settings that are useful for widget previews.
    ///
    /// - Parameters:
    ///   - mode: The widget preview provider mode to be excluded from being displayed. All other modes will be displayed.
    func makeForWidgetPreviewProvider(excluding mode: WidgetPreviewProviderMode) -> some View {
        makeForWidgetPreviewProvider(excluding: [mode])
    }
    
}