[Issue-47] Add SystemImage protocol

Author: Mark Pospesel

Sources/YCoreUI/Protocols/ImageAsset.swift

@@ -6,7 +6,6 @@
 //  Copyright © 2022 Y Media Labs. All rights reserved.
 //
 
-import Foundation
 import UIKit
 
 /// Any named image asset can be loaded from an asset catalog.

Sources/YCoreUI/Protocols/SystemImage.swift

@@ -0,0 +1,54 @@
+//
+//  SystemImage.swift
+//  YCoreUI
+//
+//  Created by Mark Pospesel on 3/8/23.
+//  Copyright © 2023 Y Media Labs. All rights reserved.
+//
+
+import UIKit
+
+/// Any string corresponding to a system image (SF Symbols).
+///
+/// All properties and functions have default implementations. At a minimum just have your string-based enum conform
+///  to `SystemImage`.  The raw value of the enum should match a sytem image name (e.g. `checkmark.seal`).
+public protocol SystemImage: RawRepresentable where RawValue == String {
+    /// Fallback image to use in case a system image cannot be loaded.
+    /// (default is a 16 x 16 square filled with `.systemPink`)
+    static var fallbackImage: UIImage { get }
+
+    /// A system image for this name value.
+    ///
+    /// Default implementation calls `loadImage` and nil-coalesces to `fallbackImage`.
+    var image: UIImage { get }
+
+    /// Loads the named system image.
+    /// - Returns: The named system image or else `nil` if the system image cannot be loaded.
+    func loadImage() -> UIImage?
+}
+
+extension SystemImage {
+    /// Fallback image to use in case a system image cannot be loaded.
+    /// (default is a 16 x 16 square filled with `.systemPink`)
+    public static var fallbackImage: UIImage {
+        let renderer = UIGraphicsImageRenderer(size: CGSize(width: 16, height: 16))
+        let image = renderer.image { ctx in
+            UIColor.systemPink.setFill()
+            ctx.fill(CGRect(origin: .zero, size: renderer.format.bounds.size))
+        }
+        return image
+    }
+
+    /// Loads the named system image.
+    ///
+    /// Default implementation uses `UIImage(systemName:)` passing in the associated `rawValue`.
+    /// - Returns: The named system image or else `nil` if the system image cannot be loaded.
+    public func loadImage() -> UIImage? {
+        UIImage(systemName: rawValue)
+    }
+
+    /// A system image for this name value.
+    ///
+    /// Default implementation calls `loadImage` and nil-coalesces to `fallbackImage`.
+    public var image: UIImage { loadImage() ?? Self.fallbackImage }
+}

Tests/YCoreUITests/Protocols/SystemImageTests.swift

@@ -0,0 +1,57 @@
+//
+//  SystemImageTests.swift
+//  YCoreUI
+//
+//  Created by Mark Pospesel on 3/8/23.
+//  Copyright © 2023 Y Media Labs. All rights reserved.
+//
+
+import XCTest
+import YCoreUI
+
+final class SystemImageTests: XCTestCase {
+    func test_fallbackImage_deliversImage() {
+        XCTAssertNotNil(Symbols.fallbackImage)
+        XCTAssertEqual(MissingSymbols.fallbackImage, UIImage(systemName: "x.squareroot"))
+    }
+
+    func test_loadImage_deliversImage() {
+        Symbols.allCases.forEach {
+            XCTAssertNotNil($0.loadImage())
+        }
+    }
+
+    func test_missingImage_deliversCustomFallback() {
+        MissingSymbols.allCases.forEach {
+            XCTAssertNil($0.loadImage())
+            XCTAssertEqual($0.image, UIImage(systemName: "x.squareroot"))
+        }
+    }
+
+    func test_systemImage_deliversDefaultFallback() {
+        XCTAssertEqual(DefaultSymbols.defaultCase.image.pngData(), DefaultSymbols.fallbackImage.pngData())
+    }
+}
+
+extension SystemImageTests {
+    enum Symbols: String, CaseIterable, SystemImage {
+        case checked = "checkmark.square"
+        case unchecked = "square"
+        case warning = "exclamationmark.triangle.fill"
+        case error = "exclamationmark.octagon"
+    }
+
+    enum MissingSymbols: String, CaseIterable, SystemImage {
+        case notHere
+        case gone
+
+        static var fallbackImage: UIImage {
+            let image: UIImage! = UIImage(systemName: "x.squareroot")
+            return image
+        }
+    }
+
+    enum DefaultSymbols: String, CaseIterable, SystemImage {
+        case defaultCase
+    }
+}