[AltStoreCore] Refactors core AltStore logic into AltStoreCore framework

AltStoreCore will contain all shared AltStore code between AltStore and any app extensions. Initially, it includes all AltStore model logic.

AltStoreCore/Model/MergePolicy.swift

@@ -0,0 +1,88 @@
+//
+//  MergePolicy.swift
+//  AltStore
+//
+//  Created by Riley Testut on 7/23/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import CoreData
+
+import Roxas
+
+open class MergePolicy: RSTRelationshipPreservingMergePolicy
+{
+    open override func resolve(constraintConflicts conflicts: [NSConstraintConflict]) throws
+    {
+        guard conflicts.allSatisfy({ $0.databaseObject != nil }) else {
+            for conflict in conflicts
+            {
+                switch conflict.conflictingObjects.first
+                {
+                case is StoreApp where conflict.conflictingObjects.count == 2:
+                    // Modified cached StoreApp while replacing it with new one, causing context-level conflict.
+                    // Most likely, we set up a relationship between the new StoreApp and a NewsItem,
+                    // causing cached StoreApp to delete it's NewsItem relationship, resulting in (resolvable) conflict.
+                    
+                    if let previousApp = conflict.conflictingObjects.first(where: { !$0.isInserted }) as? StoreApp
+                    {
+                        // Delete previous permissions (same as below).
+                        for permission in previousApp.permissions
+                        {
+                            permission.managedObjectContext?.delete(permission)
+                        }
+                    }
+                    
+                default:
+                    // Unknown context-level conflict.
+                    assertionFailure("MergePolicy is only intended to work with database-level conflicts.")
+                }
+            }
+            
+            try super.resolve(constraintConflicts: conflicts)
+                        
+            return
+        }
+        
+        for conflict in conflicts
+        {
+            switch conflict.databaseObject
+            {
+            case let databaseObject as StoreApp:
+                // Delete previous permissions
+                for permission in databaseObject.permissions
+                {
+                    permission.managedObjectContext?.delete(permission)
+                }
+                
+            case let databaseObject as Source:
+                guard let conflictedObject = conflict.conflictingObjects.first as? Source else { break }
+
+                let bundleIdentifiers = Set(conflictedObject.apps.map { $0.bundleIdentifier })
+                let newsItemIdentifiers = Set(conflictedObject.newsItems.map { $0.identifier })
+
+                for app in databaseObject.apps
+                {
+                    if !bundleIdentifiers.contains(app.bundleIdentifier)
+                    {
+                        // No longer listed in Source, so remove it from database.
+                        app.managedObjectContext?.delete(app)
+                    }
+                }
+                
+                for newsItem in databaseObject.newsItems
+                {
+                    if !newsItemIdentifiers.contains(newsItem.identifier)
+                    {
+                        // No longer listed in Source, so remove it from database.
+                        newsItem.managedObjectContext?.delete(newsItem)
+                    }
+                }
+                
+            default: break
+            }
+        }
+        
+        try super.resolve(constraintConflicts: conflicts)
+    }
+}