[AltStoreCore] Adds AppScreenshot to support dynamically-sized screenshots

Preserves StoreApp.imageURL field in database model for backwards compatibility.

AltStoreCore/Model/AppScreenshot.swift

@@ -0,0 +1,85 @@
+//
+//  AppScreenshot.swift
+//  AltStoreCore
+//
+//  Created by Riley Testut on 9/18/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+import CoreData
+
+@objc(AppScreenshot)
+public class AppScreenshot: NSManagedObject, Fetchable, Decodable
+{
+    /* Properties */
+    @NSManaged public private(set) var imageURL: URL
+    
+    public private(set) var size: CGSize? {
+        get {
+            guard let width = self.width?.doubleValue, let height = self.height?.doubleValue else { return nil }
+            return CGSize(width: width, height: height)
+        }
+        set {
+            if let newValue
+            {
+                self.width = NSNumber(value: newValue.width)
+                self.height = NSNumber(value: newValue.height)
+            }
+            else
+            {
+                self.width = nil
+                self.height = nil
+            }
+        }
+    }
+    @NSManaged private var width: NSNumber?
+    @NSManaged private var height: NSNumber?
+    
+    @NSManaged public internal(set) var appBundleID: String
+    @NSManaged public internal(set) var sourceID: String
+    
+    /* Relationships */
+    @NSManaged public internal(set) var app: StoreApp?
+    
+    private enum CodingKeys: String, CodingKey
+    {
+        case imageURL
+        case width
+        case height
+    }
+    
+    private override init(entity: NSEntityDescription, insertInto context: NSManagedObjectContext?)
+    {
+        super.init(entity: entity, insertInto: context)
+    }
+    
+    internal init(imageURL: URL, size: CGSize?, context: NSManagedObjectContext)
+    {
+        super.init(entity: AppScreenshot.entity(), insertInto: context)
+        
+        self.imageURL = imageURL
+        self.size = size
+    }
+    
+    public required init(from decoder: Decoder) throws
+    {
+        guard let context = decoder.managedObjectContext else { preconditionFailure("Decoder must have non-nil NSManagedObjectContext.") }
+        
+        super.init(entity: AppScreenshot.entity(), insertInto: context)
+        
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        
+        self.imageURL = try container.decode(URL.self, forKey: .imageURL)
+        
+        self.width = try container.decodeIfPresent(Int16.self, forKey: .width).map { NSNumber(value: $0) }
+        self.height = try container.decodeIfPresent(Int16.self, forKey: .height).map { NSNumber(value: $0) }
+    }
+}
+
+public extension AppScreenshot
+{
+    @nonobjc class func fetchRequest() -> NSFetchRequest<AppScreenshot>
+    {
+        return NSFetchRequest<AppScreenshot>(entityName: "AppScreenshot")
+    }
+}