Mockable SwiftUI.AsyncImage

AsyncImage.swift

import SwiftUI

public struct AsyncImage<Content>: View where Content: View {
  private var content: (ImageProvider) -> _ConditionalContent<
    SwiftUI.AsyncImage<Content>, Content
  >

  @Environment(\.imageProvider) var imageProvider

  public init(
    url: URL?,
    scale: CGFloat = 1
  ) where Content == Image {
    self.content = { imageProvider in
      if let uiImage = url.flatMap(imageProvider) {
        return ViewBuilder.buildEither(
          second: Image(uiImage: uiImage)
        )
      } else {
        return ViewBuilder.buildEither(
          first: SwiftUI.AsyncImage(
            url: url,
            scale: scale
          )
        )
      }
    }
  }

  public init<I, P>(
    url: URL?,
    scale: CGFloat = 1,
    @ViewBuilder content: @escaping (Image) -> I,
    @ViewBuilder placeholder: @escaping () -> P
  ) where Content == _ConditionalContent<I, P>, I: View, P: View {
    self.content = { imageProvider in
      if let uiImage = url.flatMap(imageProvider) {
        return ViewBuilder.buildEither(
          second: ViewBuilder.buildEither(
            first: content(Image(uiImage: uiImage))
          )
        )
      } else {
        return ViewBuilder.buildEither(
          first: SwiftUI.AsyncImage(
            url: url,
            scale: scale,
            content: content,
            placeholder: placeholder
          )
        )
      }
    }
  }

  public init(
    url: URL?,
    scale: CGFloat = 1,
    transaction: Transaction = Transaction(),
    @ViewBuilder content: @escaping (AsyncImagePhase) -> Content
  ) {
    self.content = { imageProvider in
      if let uiImage = url.flatMap(imageProvider) {
        return ViewBuilder.buildEither(
          second: content(.success(Image(uiImage: uiImage)))
        )
      } else {
        return ViewBuilder.buildEither(
          first: SwiftUI.AsyncImage(
            url: url,
            scale: scale,
            transaction: transaction,
            content: content
          )
        )
      }
    }
  }

  public var body: some View {
    self.content(self.imageProvider)
  }
}

public typealias ImageProvider = (URL) -> UIImage?

private struct Key: EnvironmentKey {
  static var defaultValue: ImageProvider = { _ in nil }
}

extension EnvironmentValues {
  public var imageProvider: ImageProvider {
    get { self[Key.self] }
    set { self[Key.self] = newValue }
  }
}