Allow making empty and single image MMMPhoto

MMMCommonUI.podspec

@@ -6,7 +6,7 @@
 Pod::Spec.new do |s|
 
 	s.name = "MMMCommonUI"
-	s.version = "3.10.0"
+	s.version = "3.11.0"
 	s.summary = "Small UI-related pieces reused in many components from MMMTemple"
 	s.description =	"#{s.summary}."
 	s.homepage = "https://github.com/mediamonks/#{s.name}"

Sources/MMMCommonUI/MMMPhoto.swift

@@ -0,0 +1,38 @@
+//
+// MMMCommonUI. Part of MMMTemple.
+// Copyright (C) 2016-2023 MediaMonks. All rights reserved.
+//
+
+import Foundation
+
+/// A photo that vends the same image regardless of the requested size.
+///
+/// This can be handy when implementing APIs involving `MMMPhoto` while having only a single image.
+/// (It could be useful to proxy it and do downscaling, but that could only help with rendering
+/// and would not improve overall memory usage as we would be still holding the original image.)
+public final class MMMPhotoFromLoadableImage: NSObject, MMMPhoto {
+
+	public let image: MMMLoadableImage
+
+	public init(_ image: MMMLoadableImage) {
+		self.image = image
+	}
+
+	public func image(forTargetSize targetSize: CGSize, contentMode: MMMPhotoContentMode) -> MMMLoadableImage {
+		self.image
+	}
+}
+
+/// A photo that is always failing to load.
+///
+/// Sometimes we need to implement a non-optional `MMMPhoto` without having an image. Returning an always failing
+/// to load image is better in this case as it would allow to fall back to a placeholder of the corresponding image view.
+public final class MMMEmptyPhoto: NSObject, MMMPhoto {
+
+	// Using the property of `MMMPublicLoadableImage` to quickly fail for `nil` images.
+	private lazy var image = MMMPublicLoadableImage(url: nil)
+
+	public func image(forTargetSize targetSize: CGSize, contentMode: MMMPhotoContentMode) -> MMMLoadableImage {
+		self.image
+	}
+}